Get documents about "Untitled - repository
Shared by: yaofenji
-
Stats
- views:
- 1
- posted:
- 9/4/2011
- language:
- English
- pages:
- 95
Document Sample
DISCLAIMER
This report was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor any agency Thereof, nor any of their employees,
makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or any
agency thereof. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States
Government or any agency thereof.
DISCLAIMER
Portions of this document may be illegible in
electronic image products. Images are produced
from the best available original document.
FE-2346-20 (APP.)
(SSS-R-78-3442)
Distribution Category UC-91
DON SHALE SITE
TRACER GAS PRESSURIZATIOl STUDY
E , W , PETERSON
P,' L', LAGUS NOTICE
sponsored by the United Stater Government. Netther the
United Stater nor the United Stater Department or
Energy, nor any o f their employees. nor any of their
contractors. subcontractors, or their employees, maker
any warranty. express or tmplled, or assumes any legal
liability or responsibllily for the accuracy, completeness
or usefulness of any information, apparatus, product or
proeess dscloscd, or represenrs that its use would not
F i n a l Report
3
S P r o j e c t No. 32021
OCTOBER 1977
Submitted to
Dow Chemical Co.
SYSTEMS, S C I E N C E A N D S O F T W A R E
TABLE OF CONTENTS
Section Page
1. INTRODUCTION 1
2. RESULTS
3
2.1 Flow through the Antrim Formation 6
2.2 Permeability and Porosity of the Retort 11
Volume
2.2.1 Injection Well Characteristics 12
2.2.2 Cross-Hole Permeabilities 13
2.2.3 Two-Dimensional Analyses of Retort 22
Region
2.2.4 Summary of Pzrneability and Porosity 31
Analysis
2.3 Characterization of the Fracturing 32
3. CONCLUSIONS 35
4 -. RECOMMENDAT IONS 37
APPENDIX A - Data Summary 41
APPENDIX B - Experimental Techniques 71
APPENDIX C - Analytical Model 79
APPENDIX D - Wellbore Effects 85
ii
1. INTRODUCTION
3
Systems, Science and Software (S 1 has developed tracer-
gas/pressurization techniques necessary to determine critical
media properties of undergrcund regions. .Application of this
technology is especially relevant to analysis of an oil shale
retort volume. During the period 7 July to 14 July 1977, a
series of tracer g a s pressurization experiments were undertaken
at the Dow shale site at Peck, Michigan. General objectives of
this study were to:
0 Evaluate flow communication between boreholes open to
both the Antrim and False Antrim layers of the retort
volume.
e Determine permeability and porosity distributions within
the retort volume.
0 Assess qualitatively the uniformity of the fracturing
or rubblization within the retort volume.
This report summarizes the results of the tracer gas pressur-
ization study. The system cross-hole flow communication, per-
meability and porosity distributions, and fracturing uniformity
are discussed in detail. The influence of these individual
characteristics on the total system response is also presented.
Conclusions and recommendations are made.
A'set of appendices is also included. The first presents
graphical displays of all data, together with brief interpretive
narratives. Experimental techniques are described in the second
appendix. Descriptions of the analytical and numerical models
used for data interpretation are presented in the final two
appendices.
Theresults given here represent our best effort to char-
acterize the Dow shale site. Conclusions presented are based
on the interpretation of the tracer gas pressurization data
only. Our knowledge of the Dow shale site is therefore some-
what limited. We recognize that the tracer gas pressurization
data taken in conjunction with additional data obtained using
1
other diagnostic methods may lead t o somewhat different con-
clusions as to the characteristics of the Dow s i t e .
c
2
2. RESULTS
The objective of the study was to determine the char-
acteristics of the retort volume, shown in Figure 1, in terms of
the tracer gas pressurization data. Experimental tests were
designed to provide answers to the following questions:
e Is there flow through the Antrim formation in the
region of Well # 4 ?
What is the dist.ribution of permeability and porosity
throughout the retort volume?
If the volume is fractured or rubblized, is this
fracturing uniform or is there excessive flow channeling?
How does the permeability and porosity of the forgation
surrounding Well # 4 compare to that in the vicinity of
Well # 3 ?
These questions will be specifically addressed in the following
sections.
The tracer gas pressurization data serve as the basis
for evaluation of the Dow retort volume. Data available from
these tests include injection well measurements of air flow
rates, tracer gas concentrations and pressures. In addition,
pressures, flow rates, and tracer gas arrival times and con-
centrations are measured at the production wells. A summary
of the data obtained during the 7 July through 14 July test is
presented in Appendix A.
The test proceeded as follows. Well # 4 had been de-
signated by Dow as the next "burn" well and was therefore the
primary subject of this investigation. Prior to pressurizing
this well, tracer gases were injected into Wells # 7 and # 3 .
The intent of this preinjection was to introduce tracer gas at
some outlying areas to provide better flow definition throughout
the system. Primary injection occurred in Well # 4 . Approximately
240,000 standard cubic feet (scf) of air were injected into
3
n
m
c:
11)
3
0
a
a,
0 c
u
8
t h i s w e l l o v e r a 96 h o u r t i m e p e r i o d d u r i n g w h i c h i t s p r e s s u r e
increased t o approximately 850 psi. During t h e p r e s s u r i z a t i o n
p h a s e , four p u l s e s of v a r i o u s t r a c e r g a s e s were i n j e c t e d i n t o
Well # 4 . P r e s s u r e s and tracer g a s a r r i v a l s and c o n c e n t r a t i o n s
were c o n s t a n t l y m o n i t o r e d a t t h e p r o d u c t i o n w e l l s t h r o u g h o u t
t h e d u r a t i o n of t h e t e s t .
A d d i t i o n a l t e s t s were p e r f o r m e d , a t t h e r e q u e s t of DOW,
u s i n g Well # 3 a s t h e i n j e c t i o n w e l l i n o r d e r t o o b t a i n d e t a i l e d
i n f o r m a t i o n on t h e f o r m a t i o n p r o p e r t i e s i n t h e v i c i n i t y of t h i s
well. A p p r o x i m a t e l y 1 1 0 , 0 0 0 scf of a i r were i n j e c t e d i n t o t h i s
w e l l o v e r a 24 h o u r t i m e p e r i o d d u r i n g w h i c h i t s pressure i n -
c r e a s e d t o a p p r o x i m a t e l y 775 p s i . Two d i s t i n c t t r a c e r g a s p u l -
ses were i n j e c t e d i n t o Well # 3 d u r i n g t h i s t i m e . Again, a l l
p r o d u c t i o n w e l l s were m o n i t o r e d d u r i n g t h e t e s t .
I n p e r f o r m i n g t h e s e v a r i o u s t r a c e r tests, it w a s nec-
e s s a r y , i n o r d e r t o unambiguously i n t e r p r e t tracer g a s a r r i v a l
a n d c o n c e n t r a t i o n d a t a f r o m t h e many b o r e h o l e s , t o u s e n u m b e r s
of t r a c e r g a s e s . The r e s u l t s d e s c r i b e d h e r e were o b t a i n e d
u s i n g s u l f u r h e x a f l u o r i d e ( S F 6 ) a n d t h e F r e o n s 13B1, C318 a n d
12B2 a s t r a c e r s . I n a d d i t i o n , i n j e c t i o n p u l s e d u r a t i o n s and
c o n c e n t r a t i o n s were v a r i e d a s was n e c e s s a r y t o i d e n t i f y mul-
t i p l e i n j e c t i o n s of a p a r t i c u l a r t r a c e r g a s . A summary of t h e
e x p e r i m e n t a l t e c h n i q u e s is g i v e n i n A p p e n d i x B.
Under c o n d i t i o n s w h e r e t h e r e t o r t volume i s a c t u a l l y
r u b b l i z e d , d a t a r e d u c t i o n i s accomplished u s i n g a two-dimensional
h y d r o d y n a m i c code w h i c h d e s c r i b e s t h e d i f f u s i v e f l o w of t h e
i n j e c t e d a i r p l u s t r a c e r g a s t h r o u g h o u t t h e r e t o r t volume.
T h i s h y d r o d y n a m i c m o d e l i s d e s c r i b e d i n A p p e n d i x C. Also i n -
c l u d e d i n A p p e n d i x C a r e d e t a i l e d d e s c r i p t i o n s of m e t h o d s u s e d
t o d e t e r m i n e c r o s s - h o l e p e r m e a b i l i t i e s based o n m e a s u r e d t r a c e r
g a s i n j e c t i o n and a r r i v a l times. A m o d e l w h i c h c a n be u s e d
t o a p p r o x i m a t e f r a c t u r e d i m e n s i o n s , s h o u l d i t be deemed t h a t cross-
h o l e f l o w o c c u r s a l o n g a --- i t e number of f r a c t u r e p a t h s r a t h e r
fin
t h a n t h r o u g h a permeable f o r m a t i o n , i s a l s o i n c l u d e d .
5
B e c a u s e t h e Dow r e t o r t volume h a s a l o w p o r o s i t y , w e l l -
@
bore e f f e c t s a r e s i g n i f i c a n t . The w e l l volume p l a y s a n i m p o r -
t a n t role i n i n t e r p r e t i n g p r e s s u r e , f l o w r a t e s , and tracer gas
c o n c e n t r a t i o n measurements. The i n f l u e n c e of wellbore e f f e c t s
on i n t e r p r e t a t i o n of t h e s e d a t a a r e d i s c u s s e d i n A p p e n d i x D.
2.1 FLOW THROUGH THE A N T R I M FORMATION
The m u l t i p l e t r a c e r g a s i n j e c t i o n t e c h n i q u e d e s c r i b e d
i n F i g u r e 2 was u s e d t o d e t e r m i n e i f f l o w o c c u r s t h r o u g h t h e
A n t r i m f o r m a t i o n i n t h e v i c i n i t y of W e l l # 4 . During p r e s s u r -
i z a t i o n of Well # 4 , a i r w a s i n j e c t e d i n t o t h e a n n u l u s r e g i o n a t
t h e wellhead. A t r a c e r g a s was t h e n i n j e c t e d t h r o u g h t h e c a p -
i l l a r y t u b e w h i c h e x t e n d e d i n t o t h e A n t r i m t o a d e p t h of 1 2 6 5
ft. S m a l l a m o u n t s of t r a c e r g a s ( % l o 0 s c f ) w e r e i n j e c t e d
t h r o u g h t h e c a p i l l a r y t u b e once t h e w e l l p r e s s u r e had approached
i t s maximum v a l u e of a b o u t 8 0 0 p s i . A t these pressures the
wellbore c o n t a i n s more t h a n 1 4 0 0 scf of a i r b e t w e e n t h e e n d of
t h e c a p i l l a r y t u b e a n d t h e t o p of t h e A n t r i m f o r m a t i o n . There-
f o r e , t h e s m a l l v o l u m e of i n j e c t e d t r a c e r c a n n o t d i s p l a c e
s u f f i c i e n t a i r i n t h e wellbore t o r e a c h t h e F a l s e A n t r i m l a y e r .
I f air i n j e c t e d i n t o W e l l # 4 travels t o t h e o u t l y i n g w e l l s
t h r o u g h t h e F a l s e A n t r i m l a y e r , t h i s a i r s h o u l d be f r e e of
tracer gas upon a r r i v a l a t t h e o u t l y i n g w e l l s . However, if t h e
f l o w f r o m W e l l 84 o c c u r s through t h e Antrim l a y e r , tracer g a s
i n j e c t e d t h r o u g h t h e c a p i l l a r y s h o u l d be d e t e c t e d a t t h e p r o d u c -
tion wells.
F l o w from W e l l # 4 t h r o u g h t h e A n t r i m formation is
i l l u s t r a t e d schematically i n F i g u r e 3 . T h e C318 i n j e c t e d
t h r o u g h t h e c a p i l l a r y a t 0330 o n 1 0 J u l y was f o u n d t o h a v e
p e n e t r a t e d t o Wells # 3 , # 6 , # 8 , #lo and #12. The 13B1 i n j e c t e d
t h r o u g h t h e c a p i l l a r y a t 0930 o n 11 J u l y was fbund o n l y a t Wells
113 a n d #12. Two s i g n i f i c a n t c h a n g e s o c c u r r e d w i t h i n t h e s y s -
t e m b e t w e e n t h e i n i t i a l C318 i n j e c t i o n a n d t h e l a t t e r 13B1 i n j e c t i o n .
There e x i s t e d c o n s i d e r a b l e b r i n e f l o w i n t o W e l l # 6 . A t 1 7 0 0 o n
6
' . I n j e c t t r a c e r g a s 8 1 at b o t t o m
I n j e c t a i r plus of retort r e g i o n ( a b o v e b r i n e l e v e l )
tracer gas I 2 u s i n g s m a l l diameter t u b e
rface
F i g u r e 2. Schematic i l l u s t r a t i n g m u l t i p l e tracer-gas i n j e c t i o n
i n t o a s i n g l e b o r e h o l e i n o r d e r t o e v a l u a t e f l o w through
0 the A n t r i m and F a l s e A n t r i m l a y e r s .
7
C318 i n j e c t e d t h r o u g h
W e l l r(4 c a p i l l a r y b e g i n -
n i n g 0330 o n 1 0 J u l y .
---- 13B1 i n j e c t e d t h r o u g h
W e l l # 4 c a p i l l a r y begin-
n i n g 0930 o n 1 J u l y1
( c o n f i r m a t i o n of a r r i v a l
o f t h i s tracer a t W e l l
1 1 2 is u n c e r t a i n ) .
Note: T h e l i n e s shown are o n l y
intended to illcstrate t h e
cross-hole comunication
a n d are n o t i n t e n d e d t o
i l l u s t r a t e t h e p a t h traveled
by t h e g a s .
Figure 3. Schematic i l l u s t r a t i n g cross-hole tracer gas flow o r i g i n a t i n g
in Antrim f o r m a t i o n a t Well # 4 .
1 0 J u l y t h e c a p i l l a r y l i n e i n Well # 6 became b l o c k e d w i t h
b r i n e thereby preventing f u r t h e r tracer d e t e c t i o n a t t h i s w e l l .
A t 1 0 0 0 on 11 J u l y Well # 3 was v e n t e d to a b a c k p r e s s u r e of
8 0 p s i g f r o m i t s m a x i m u m p r e s s u r e of 3 0 0 p s i g . Subsequent t o
v e n t i n g # 3 , t h e r e was n o a d d i t i o n a l f l o w i n t o Wells 118 o r #lo.
Even t h o u g h p r e s s u r i z a t i o n c o n t i n u e d o n Well # 4 , t h e p r e s s u r e a t
Wells # 8 a n d # 1 0 r e m a i n e d c o n s t a n t f o r t h e d u r a t i o n of t h e t e s t .
Flow i n t o t h e s e wells a p p e a r s t o d e p e n d o n t h e pressure f i e l d i n
t h e v i c i n i t y of Well # 3 .
Cross-hole communication through t h e Antrim f o r m a t i o n
b e t w e e n \ < e l l s # 4 a n d # 7 may e x i s t . However, C318 w a s n o t
d e t e c t e d a t Well # 7 , p o s s i b l y b e c a u s e t h e h i g h p r e s s u r e i n t h e
r e g i o n or t h i s w e l l e f f e c t i v e l y b l o c k e d t h e f l o w . Even a t l a t e r
t i m e s , a 13B1 a r r i v a l i s n o t a p p a r e n t , h o w e v e r , t h i s a r r i v a l may
be masked b y t h e r e s i d u a l 13B1 r e m a i n i n g from t h e p r e i n j e c t i o n
of t r a c e r i n t o Well # 7 .
S u l f u r h e x a f l u o r i d e was i n j e c t e d w i t h t h e m a i n a i r f l o w
i n t o Well # 4 o n t w o o c c a s i o n s . Any t r a c e r i n j e c t e d a t t h e
w e l l h e a d becomes t h o r o u g h l y m i x e d w i t h a i r p r i o r t o r e a c h i n g
t h e F a l s e Antrim or Antrim l a y e r s . S i n c e t h i s t r a c e r may l e a v e
W e l l # 4 t h r o u g h e i t h e r l a y e r , i t i s of i n t e r e s t t o compare t h e
r e s u l t i n g c r o s s - h o l e communication w i t h t h a t determined u s i n g
c a p i l l a r y i n j e c t e d tracer g a s e s which must f l o w through t h e
Antrim layer.
T h e f i r s t SF6 i n j e c t i o n o c c u r r e d a t t h e t i m e t h e Well # 4
pressurization was initiated. The r e t o r t v o l u m e p r e s s u r e s were
l o w a t t h i s t i m e e x c e p t i n t h e n e a r v i c i n i t y of W e l l # 7 . T h i s
SF6 p u l s e was d e t e c t e d a s shown o n F i g u r e 4 , a t Wells # 3 , #6,
a n d #12, b u t n o t a t Wells # 8 a n d #lo. A s e c o n d SF6 i n j e c t i o n
occurred b e g i n n i n g a t 0 9 0 0 o n 11 July. T h i s p u l s e was d e t e c t e d a t
Wells # 3 , 117 a n d #12. A g a i n , d e t e c t i o n a t W e l l & 6 w a s p r o h i b -
ited b y the h i g h b r i n e l e v e l . Eote t h a t b o t h SF6 i n j e c t i o n s
o c c u r r e d when t h e W e l l # 3 p r e s s u r e w a s l o w . N e i g h e r SF6 p u l s e
was d e t e c t e d a t Wells # 8 o r #lo.
9
8 SF6 i n j e c t e d t h r o u g h
Well # 4 a n n u l u s b e q i n -
i n g at 1 6 5 0 o n 9 J u l y .
- .- -- SF6 i n j e c t e d t h r o u g h
W e l l 1 4 annulus begin-
n i n g a t 0 9 0 0 o n 11 J u l y .
-- -- 13B1 i n j e c t e d i n t o Well
17 annulus beginning
0 6 5 0 o n 9 July.
- 0 -12B2 i n j e c t e d i n t o Well
1 3 at 1430 o n 8 J u l y .
Figure 4. Schematic i l l u s t r a t i n g cross-hole t r a c e r gas flow o r i g i n a t i n g
i n e i t h e r t h e A n t r i m or False Antrim f o r m a t i o n a t Well # 4 .
!id
SF detection at Well # 7 implies communication with
6
Well # 4 . Furthermore, the absence of a noticeable C318 or
13B1 arrival strongly implies little communication occurs through
the Antrim between these wells. However, interpretation of the
cross-hole communication between these wells is difficult to
assess because of the initial high pressures at the immediate vic-
inity of Well #7.
The capillary tube extended into the Antrim formation only
in Well # 4 . In most other wells, it cannot be determined
whether tracer gas flow occurred through the Antrim or False Antrim
layers. However, since the brine level in Well ti3 was always
higher than the top of the Antrim, it is known that gas flow
into Well # 3 came through the False Antrim. Obviously, the
transition area in which the flow from Well # 4 passed from
the Antrim into the False Antrim cannot be located from results
of these tests, It can only be determined that initially some
flow exits Well # 4 through the Antrim formation.
2.2 PERMEABILITY AND POROSITY OF THE RETORT VOLUME
Values for the retort volume permeability and porosity,
as determined by she tracer gas pressurization tests, will be
presented in this section. The methods of analysis used are
described in Appendix C. First, one-dimensional results
describing the permeability and porosity in the immediate
vicinities of the injection wells will be given. These results
are based on the well pressurization data. Following this,
cross-hole permeabilities, calculated assuming flow occurs through
discrete channels at speeds determined by measured tracer-gas
transit times, will be presented. Next, the results of two-
dimensional calculations describing the gas flow through the
retort volume are given. Finally, characteristics of the retort
volume such a s uniformity and flow channeling, will be discussed
i n terms of the data previously presented.
11
2.2.1 Injection W e l l Characteristics
One-dimensional axisymmetric a n a l y s e s are performed i n
order t o d e t e r m i n e t h e a v e r a g e f o r m a t i o n c h a r a c t e r i s t i c s i n t h e
i m m e d i a t e v i c i n i t y of a n i n j e c t i o n w e l l . T h e s e r e s u l t s re-
p r e s e n t s o l u t i o n s t o E q u a t i o n ( C . 5 ) a s s u m i n g c y l i n d i r c a l sym-
metry with formation p r o p e r t i e s varying o n l y i n t h e radial
direction. Wellbore e f f e c t s , d i s c u s s e d i n A p p e n d i x D , a r e
considered. Numbers o f c a l c u l a t i o n s a r e p e r f o r m e d a s s u m i n g v a r -
i o u s c o m b i n a t i o n s o f p e r m e a b i l i t y a n d p o r o s i t y u n t i l o n e is
o b t a i n e d i n which t h e measured and c a l c u l a t e d p r e s s u r e s a g r e e .
V a l u e s u s e d f o r t h a t p a r t i c u l a r c a l c u l a t i o n a r e t h e n assumed
r e p r e s e n t a t i v e of t h e f o r m a t i o n . S i n c e t h e s e r e s u l t s a r e based
on t h e e a r l y t i m e p r e s s u r i z a t i o n d a t a , f o r m a t i o n p r o p e r t i e s
so d e t e r m i n e d a r e o n l y v a l i d i n t h e immediate v i c i n i t y of t h e
injection well.
Corresponding pressure/time h i s t o r i e s a t a d j a c e n t w e l l s
are a l s o d e t e r m i n e d d u r i n g t h e s e one-dimensional c a l c u l a t i o n s .
A l t h o u g h t h e s e h i s t o r i e s may i n some cases compare w i t h t h e
m e a s u r e d d a t a , t h e c o m p a r i s o n i s somewhat f o r t u i t o u s s i n c e
wellbore e f f e c t s c a n n o t be a d e q u a t e l y i n c l u d e d i n t h e s e a x i -
symmetric c a l c u l a t i o n s f o r w e l l s o t h e r t h a n t h e i n j e c t i o n w e l l .
The i n d i c a t e d p r e s s u r e r i s e a t t h e s e o u t l y i n g w e l l s w o u l d n o t
o c c u r i f w e l l b o r e e f f e c t s were c o n s i d e r e d s i n c e t h e f o r m a t i o n
c a n n o t t r a n s m i t t h e r e q u i r e d q u a n t i t y o f f l o w g i v e n t h e permea-
. b i l i t y shown. The r e s u l t s d o , h o w e v e r , g i v e some i n d i c a t i o n of
t h e total formation porosity.
A p r i m a r y o b j e c t i v e of t h e a x i s y m n i e t r i c c a l c u l a t i o n s was
t o p r o v i d e b a s i s f o r i n i t i a t i o n o f t h e more c o m p l e x t w o -
d i m e n s i o n a l a n a l y s i s . A s e c o n d a r y o b j e c t i v e was t o p r o v i d e
a comparison of t h e a v e r a g e media p r o p e r t i e s i n t h e v i c i n i t y
of Wells # 3 and # 4 s o t h a t phenomena o b s e r v e d t o o c c u r d u r i n g
" b u r n s " i n i t i a t e d a t t h e s e w e l l s c a n be a n a l y z e d i n terms of
the formation properties.
12
d
6 R e s u l t s of t h e o n e - d i m e n s i o n a l . a x i s y m m e t r i c a n a l y s i s a r e
shown i n F i g u r e s 5-7 f o r Wells # 4 , # 3 , a n d # 7 , r e s p e c t i v e l y .
Measured a n d c a l c u l a t e d p r e s s u r e h i s t o r i e s a g r e e f o r W e l l # 4
i f t h e formation permeability is taken a s 0.045 m i l l i d a r c i e s
a n d i f t h e p o r o s i t y i s a s s u m e d t o be 0 . 1 f o r a r a d i u s l e s s t h a n
1 . 7 5 f t , a n d 0.001 f o r r a d i i g r e a t e r t h a n 1 . 7 5 f t . Since the
wellbore d i a m e t e r i n t h e A n t r i m f o r m a t i o n i s a p p r o x i m a t e l y
F 3/4 i n c h e s , t h e i n c r e a s e d p o r o s i t i e s o u t to t h e 1 . 7 5 f t r a d i i
i m p l y t h e f o r m a t i o n i n m e d i a t e l y s u r r o u n d i n g t h e w e l l was f r a c -
t u r e d or r u b b l i z e d t o some e x t e n t . C a l c u l a t e d and measured
pressure h i s t o r i e s a g r e e f o r Well P 3 i f i t i s a s s u m e d t h a t
k = 0 . 4 5 m i l l i d a r c i e s , w i t h ( = 0 . 3 o u t t o a r a d i u s of 3 . 9 f t
I
a n d t h a t 4 = 0 . 0 0 3 w i t h k = 0 . 3 5 m i l l i d a r c i e s f o r a l l r a d i i lar-
ger than this. The l a r g e r p e r m e a b i l i t y a n d p o r o s i t y v a l u e s i n
t h e v i c i n i t y o f Well #3 i n d i c a t e t h e f o r m a t i o n s u r r o u n d i n g t h i s
w e l l i s much more h i g h l y f r a c t u r e d or r u b b l i z e d t h a n i s t h e
F o r m a t i o n s u r r o u n d i n g Well t 4 .
C a l c u l a t e d and m e a s u r e d p r e s s u r e h i s t o r i e s a g r e e f o r .
Well # 7 a s shown i n F i g u r e 7 i f i t i s a s s u m e d t h e f o r m a t i o n
h a s a p e r m e a b i l i t y o f 0 . 0 2 7 m i l l i d a r c i e s a n d a p o r o s i t y of 0 . 0 0 1 .
I n t h i s c a s e , t h e r e i s n o e n h a n c e d p e r m e a b i l i t y or p o r o s i t y
region adjacent to the w e l l . Well # 7 a p p e a r s t o t e r m i n a t e i n
\
virgin material. I t i s i n t e r e s t i n g t o note t h a t t h e W e l l # 7
p r e s s u r e i n c r e a s e s v e r y r a p i d l y u n t i l s u c h t i m e a s i t ' becomes
c o n s t a n t . T h i s p r e s s u r e h i s t o r y i s t y p i c a l of t h a t o b t a i n e d
i f a i r f r a c t u r i n g of t h e m e d i a o c c u r r e d d u r i n g t h e t e s t . Note
also t h a t t h e maximum s y s t e m pressures o b t a i n e d a r e o n t h e
o r d e r o f t h e local. o v e r b u r d e n pressure.
2.2.2 Cross-Hole P e r m e a b i l i t i e s
_-.___I--
T r a c c r - g a s p r e s s u r i z a t i o n t e s t s p r o v i d e a means Of
d i r e c t l y m e a s u r i n g t h e t i m e r e q u i r e d f o r g a s t o f l o w from a n
injection to a production w e l l . Cross-hole p e r m e a b i l i t i e s d e t e r -
m i n e d a s s u m i n g t h e f l o w o c c u r s i n c h a n n e l s s u c h a s shown i n
@
13
900
0 0 0 0
Well 1 4
I
O,A Measured p r e s s u r e s
- measuredt e dflow erater eisn b o s Wde lon 1 4
Calcula pr ssu
t
a e
l
600b
I Note: Media p r o p e r t i e s u s e d i n v i c i n i t y
of Well 14
k = 0 . 0 4 5 mdarcy
4 = 0 . 1 for r 1.75 f t
@ = 0.001 f o r r > 1.75 f t
Q,
2
v)
400L
Q,
k
a 0
A A
A A
0 A
200
01
0 1
0 10 20 30 40
July 9
1700 Time (hours)
Figure 5. Comparison of measured and calculated pressures at Well # 4
during pressurization of this well.
VQ
E E
W
r(
s"
Q
Q
0
0
e4
15
,
x
V
k
m
a
E
I--4
..
N O
cc
00
u u
Y’B
..
Q,
u
0
z
0
0
0
0
0
a 0
0 0 O 0 0 0 0
0 0 0 0 0 0 0
00 I- 10 Lri cr N -
tl
(brsd) aanssaid A
16
crs F i g u r e 8 , c a n be c a l c u l a t e d u s i n g E q u a t i o n (C.6) g i v e n i n
Appendix C. If t h e c r o s s - h o l e f l o w r a t e i s known, E q u a t i o n
( C . 7 ) c a n t h e n be u s e d t o e s t i m a t e t h e c r o s s - s e c t i o n a l a r e a
of t h e c h a n n e l .
I f , as d i s c u s s e d i n t h e p r e v i o u s s e c t i o n , a n axisyinmetric
c o n f i g u r a t i o n w i t h t h e media p r o p e r t i e s d e t e r n i n e d by t h e
one-dimensional c a l c u l a t i o n s i s used, t h e flow t o t h e p r o d u c t i o n
w e l l w i l l be i n a d e q u a t e t o p r o d u c e t h e m e a s u r e d p r e s s u r e s . TO
account f o r t h e observed f l o w i n t o t h e production w e l l , t h e r e
must e x i s t a c h a n n e l or r e g i o n having an enhanced permeability.
The p e r m e a b i l i t y of t h e s e c h a n n e l s i s g i v e n i n t h i s s e c t i o n .
T h e s e c a l c u l a t i o n s a s s u m e a p l a n a r f l o w , t h u s t h e r e is
n o c y l i n d r i c a l d i v e r g e n c e a s i n t h e a x i s y m m e t r i c case n o r i s
t h e r e a n y loss t h r o u g h t h e c h a n n e l w a l l s . As a r e s u l t ,for a
g i v e n p e r m e a b i l i t y , t h e t r a c e r g a s t r a n s i t t i m e i s much lower
i n t h e p l a n a r c a s e a s c o m p a r e d t o t h e a x i s y m m e t r i c case. F o r ease
of p r e s e n t a t i o n , t h e p e r m e a b i l i t y v a l u e s shown h e r e a s s u m e a
t o t a l s y s t e m p o r o s i t y of 0 . 0 0 1 . These v a l u e s a r e c o n s i s t e n t w i t h
t h e one-dimensional r e s u l t s , w h i c h s a t i s f y c o n s e r v a t i o n of mass
p r i n c i p l e s . If t h e p o r o s i t y of t h e f l o w c h a n n e l d i f f e r s from
t h i s v a l u e , t h e p e r m e a b i l i t y i s changed a c c o r d i n g l y s i n c e
E q u a t i o n (C.6) d e f i n e s t h e r a t i o of p e r m e a b i l i t y t o p o r o s i t y
b
(i.e. , k/$).
C r o s s - h o l e p e r m e a b i l i t i e s a r e shown o n F i g u r e s 3 a n d 4
for tracer g a s e s i n j e c t e d through t h e W e l l # 4 c a p i l l a r y and
annulus, respectively. I n g e n e r a l , t h e c r o s s - h o l e permeabilities
a r e a l l o n t h e o r d e r of a few h u n d r e d t h s of a m i l l i d a r c y w i t h
t h e e x c e p t i o n of t h a t b e t w e e n Wells # 4 a n d #12. G a s i n j e c t e d
t h r o u g h t h e Well # 4 c a p i l l a r y moved toward W e l l # 1 2 a s i f t h e
p e r m e a b i l i t y were o n e - t e n t h m i l l i d a r c y ,
Note t h a t t h e i n j e c t i o n t o p r o d u c t i o n w e l l t r a c e r - g a s t r a n s i t
t i m e s d e c r e a s e ( i . e . , see A p p e n d i x A ) a s t h e s y s t e m p r e s s u r e
0
17
Figure 8 . S u r f a c e view i l l u s t r a t i o n of f l o w c h a n n e l between i n j e c t i o n
and p r o d u c t i o n wells.
c3 increases. The c h a n g e s a r e c o n s i s t e n t w i t h t h a t r e q u i r e d
for Equation ( C . 6 ) t o i n f e r p e r m e a b i l i t i e s which a r e , w i t h t h e
e x c e p t i o n of SF f l o w from Wells # 4 t o #3, p r e s s u r e i n d e p e n d e n t .
6
I n a x i s y m m e t r i c flow, a s shown i n F i g u r e s 5 a n d 9 , t h e t r a c e r
gas t r a n s i t t i m e i n c r e a s e s s i g n i f i c a n t l y a s t h e i n j e c t i o n w e l l
and s y s t e m p r e s s u r e i n c r e a s e .
R e c a l l t h a t 13B1 a n d 1 2 B 2 were i n i t i a l l y i n j e c t e d i n t o
Wells # 7 a n d # 3 , r e s p e c t i v e l y , p r i o r t o i n i t i a t i o n of p r e s s u r i z a t i o n
of Well # 4 . The 13B1 a n d 1 2 B 2 were e v e n t u a l l y d e t e c t e d i n Wells
R12 a n d 115, r e s p e c t i v e l y . T h e s e t r a c e r g a s i n j e c t i o n s o c c u r r e d
t h r o u g h t h e a n n u l u s a n d t h e r e f o r e i t c a n n o t be d e t e r m i n e d w h e t h e r
t h e f l o w , i n t h e c a s e of W e l l #7, i n i t i a t e d i n t h e A n t r i m o r F a l s e
Antrim layers. The Well # 7 t o $ 1 2 c r o s s - h o l e p e r m e a b i l i t y is
shown i n F i g u r e 4 . Cross-hole p e r m e a b i l i t i e s corresponding t o
t h e 12B2 i n j e c t i o n c o u l d n o t be d e t e r m i n e d s i n c e t h e Well # 5
c a p i l l a r y was b l o c k e d t h u s p r e v e n t i n g g a s s a m p l i n g .
D u r i n g a s e c o n d t e s t c a r r i e d out t o a n a l y z e t h e c h a r -
a c t e r i s t i c s of t h e r e t o r t r e g i o n i n t h e v i c i n i t y of W e l l # 3 ,
1 2 B 2 a n d C318 were i n j e c t e d i n t o t h i s well t h r o u g h t h e a n n u l u s .
1 2 B 2 i n j e c t i o n o e c u r r e d when t h e w e l l h e a d p r e s s u r e was 8 0
psi. T h i s t r a c e r g a s t r a v e l e d t o Well # 6 . The W e l l # 3 p r e s s u r e
was a p p r o x i m a t e l y 3 0 0 p s i g d u r i n g t h e C318 i n j e c t i o n a n d t h i s
t r a c e r g a s t r a v e l e d t o both W e l l s # 5 a n d # 6 . I n o r d e r to pre-
v e n t b r i n e movement away f r o m W e l l # 3 t o w a r d Well # 4 a n d t h e
r e m a i n d e r of t h e r e t o r t r e g i o n , p r e s s u r i z a t i o n of Well # 3 was
c a r r i e d o u t o n l y l o n g enough t o e v a l u a t e comrnunication between
Well # 3 a n d Wells # 5 a n d # 6 . T h i s was n o t s u f f i c i e n t t i m e to
e v a l u a t e c o m m u n i c a t i o n b e t w e e n Wells # 3 a n d Wells # 8 , #9, # l o ,
and # 1 2 . Cross-hole p e r m e a b i l i t i e s d e t e r m i n e d from t h e s e i n -
j e c t i o n s a r e shown i n F i g u r e 1 0 . I n t h i s case g a s s a m p l e s
were t a k e n f r o m t h e v e n t l i n e s a n d c o u l d o n l y be o b t a i n e d once
outflow o c c u r r e d from Wells # 5 a n d # 6 . The p e r m e a b i l i t y v a l u e s
shown t h e r e f o r e r e p r e s e n t a m i n i m u m v a l u e s i n c e t h e e x a c t t i m e
of t r a c e r g a s a r r i v a l a t t h e s e w e l l s c o u l d n o t be d e t e r m i n e d .
19
h,
0
July 9 T i m e (hours)
1700
F i g u r e 9. P o s i t i o n of tracer gas f r o n t as a f u n c t i o n of t i m e d u r i n g
p r e s s u r i z a t i o n of Well # 4 .
c
8
- Well injected into
1282
13 through annulus
beginning at 0650 on
.Ol md 13 July.
1 .01 md e--- C318 i n j e c t e d into
Well 1 3 through annulus
beginning at 0900 on
13 July.
Figure 10. Schematic illustrating cross-hole tracer gas flow originating
in False Antrim formation at Well #3.
The c r o s s - s e c t i o n a l a r e a of t h e f l o w c h a n n e l shown i n
F i g u r e 8 may be d e t e r m i n e d a s d e s c r i b e d i n A p p e n d i x C. If
these channels occur t h e i r porosity i s necessarily l a r g e r than
t h e a v e r a g e system p o r o s i t y of 0.001 determined from t h e one-
dimensional axisymmetric analyses. I t i s of i n t e r e s t t o c a l -
c u l a t e a p o s s i b l e c h a n n e l s i z e s u c h a s miry a c c o u n t f o r t h e
7 . 1 s c f m f l o w f r o m Wells # 4 t o # 3 . I f t h e a c t u a l c h a n n e l por-
o s i t y i s t a k e n a s 0 . 0 5 t h i s i m p ] - i e s a p e r m e a b i l i t y o f 1 md a n d
a channel cross-sectional a r e a o f 20 f t
2
.
E q u a t i o n s g i v e n i n A p p e n d i x C c a n a l s o be u s e d t o e s t i m -
ate f l o w along f r a c t u r e paths. I f i t i s a s s u m e d t h a t Wells # 4
a n d # 3 a r e connected b y , s a y 1@ f r a c t u r e s h a v i n g a d e p t h of 1 0
f t , t h e n i t follows f r o m E q u a t i o n ( C . 8 ) t h a t t h e crack w i d t h
m u s t be a p p r o x i m a t e l y 0 . 0 0 1 c m . Given t h i s c r a c k w i d t h t h e
W e l l # 4 t o # 3 t r a c e r g a s t r a n s i t t i m e w o u l d b e , from E q u a t i o n
(C.9), o n t h e o r d e r of m i n u t e s r a t h e r t h a n h o u r s a s d e t e r m i n e d
experimentally. The a s s u m p t i o n t h a t f l o w o c c u r s t h r o u g h a
f i n i t e number o f f r a c t u r e s i s i n c o n s i s t e n t w i t h t h e e x p e r i m e n t a l
d a t a s i n c e it i n p l i e s t r a n s i t t i m e s and porosities t h a t are
s m a l l compared t o t h o s e measured.
2.2.3 -
Two-Dimensional A n a l y s e s o f R e t o r t R e g i o n
The r e t o r t v o l u m e r e s p o n s e t o a n i m p o s e d g a s f l o w w a s s i m -
u l a t e d u s i n g a two-dimensional model. D e t a i l s o f t h i s model-
i n g a r e p r e s e n t e d i n A p p e n d i x C. The o b j e c t i v e o f t h e t w o -
dimensional a n a l y s i s w a s t o obtain f u r t h e r d e f i n i t i o n of t h e
p e r m e a b i l i t y a n d p o r o s i t y d i s t r i b u t i o n s w i t h i n t h e r e t o r t vol-
ume s o t h a t g a s f l o w t h r o u g h t h e v o l u m e c o u l d be d e f i n e d .
I t i s a p p a r e n t from t h e r e s u l t s g i v e n i n S e c t i o n s 2 . 2 . 1 and
2.2.2 t h a t t h e r e t o r t r e g i o n c a n n o t be m o d e l e d a s a u n i f o r m v o l -
ume. To p r o v i d e t h e measured f l o w t o p r o d u c t i o n w e l l s such
a s #3 and # 1 2 r e q u i r e s t h e e x i s t e n c e o f flow c h a n n e l s h a v i n g an
22
0
enhanced p e r m e a b i l i t y . A somewhat a r b i t r a r y r e p r e s e n t a t i o n of
our e s t i m a t e s of t h e s e c h a n n e l s i s g i v e n i n F i g u r e 11, w h i c h
shows t h e n u m e r i c a l g r i d u s e d f o r t h e t w o - d i m e n s i o n a l a n a l y s e s .
The t w o - d i m e n s i o n a l a n a l y s e s a r e c a r r i e d o u t i n t h e same
manner a s d e s c r i b e d f o r t h e o n e - d i m e n s i o n a l c a l c u l a t i o n s .
A i r is forced i n t o the injection w e l l a t t h e experimentally
determined r a t e . N u m b e r s o f c a l c u l a t i o n s a r e p e r f o r m e d assum-
ing v a r i o u s combinations of permeability and p o r o s i t y u n t i l one
i s o b t a i n e d i n w h i c h t h e m e a s u r e d a n d c a l c u l a t e d pressures
( i . e . , t h e r e f o r e flow r a t e s ) a g r e e a t t h e p r o d u c t i o n a n d i n j e c -
tion wells. O n c e a g r e e m e n t i s o b t a i n e d , t h e s e v a l u e s of m a t e r -
i a l p r o p e r t i e s a r e a s s u m e d r e p r e s e n t a t i v e of t h e f o r m a t i o r . .
V a l u e s of p e r m e a b i l i t y a n d p o r o s i t y u s e d f o r t h e t w o -
d i m e n s i o n a l a n a l y s e s a r e shown i n T a b l e 1. T h e p e r m e a b i l i t y is
a s s u m e d p r e s s u r e d e p e n d e n t i n o r d e r to b e t t e r s i m u l a t e t h e ex-
perimental data. R e s u l t s f r o m Run V , d e f i n e d b y T a b l e 1 a n d
F i g u r e 11, w i l l be d i s c u s s e d i n t h e f o l l o w i n g p a r a g r a p h s .
M e a s u r e d a n d c a l c u l a t e d p r e s s u r e h i s t o r i e s a r e shown
i n F i g u r e 1 2 f o r yells # 7 , # 4 , a n d # 3 f o r t h e f i r s t 5 0 h o u r s of
t h e test, The p r e s s u r e d i s t r i b u t i o n w i t h i n t h e r e t o r t v o l u m e
a t t h e e n d of t h i s p e r i o d i s shown i n F i g u r e 1 3 . A h i s t o r y of
t h e tracer g a s m o t i o n i s g i v e n i n F i g u r e 14.
During t h e p r e s s u r i z a t i o n phase t h e W e l l #7 c a l c u l a t e d
a n d m e a s u r e d r e s p o n s e s a g r e e c l o s e l y a s shown i n F i g u r e 12.
Once t h e Well # 7 i n j e c t i o n i s t e r m i n a t e d t h e r e follows a r a p i d
d e c a y i n c a l c u l a t e d p r e s s u r e t y p i c a l of t h a t o c c u r r i n g in
any porous formation. However, d u r i n g t h e t e s t , when t h e i n -
j e c t i o n stopped, t h e p r e s s u r e dropped s l i g h t l y and t h e r e a f t e r
remained constant'. T h i s b e h a v i o r i s . t y p i c a l of t h a t e x p e c t e d
t o o c c u r i f t h e f o r m a t i o n were f r a c t u r e d (i.e., s e p a r a t e d a l o n g
t h e bedding p l a n e s ) by t h e a i r i n j e c t i o n . I n t h a t case, p r o v i d e d
@ t h e " c r a c k " p r o p a g a t i o n i s s t a b l e , o n c e t h e d r i v i n g pressure i s
23
I
a
.-
L' -
CC
0 0
e
e
CJ ln 0
(u 4
c
24
c
Table 1.
V a l u e s of p e r m e a b i l i t y a n d p o r o s i t y u s e d i n t h e t w o - d i m e n s i o n a l
a n a l y s e s f o r t h e r e g i o n s shown i n F i g u r e 11.
r
1
' I
1" i
II
I
R e g i o n A6 8ame,as Region 13
Q = 0.004
k = 9 u d
65 u d
0.001
30 ud
60 pd I
0.0005
1 8 ud
180 p d
0.004
12s ud
1.2 ud I
0.001
200 ud
0.001
10 ud
75 ud
4 = 0.004
k - 9ud
I
I
0.001
30 ud
I 0.0005
1 8 ud
0.004
125 ud
0.001
100 vd I
S i z e of Region C0 a n d 010 i n c r e a s e d t o i n c l u d e e n t i r e d o t t e d r e g i o n shown i n F i g u r e 11.
0.001
10 ud
j. NOTE: I t W A S assumed t h a t Q = 0 . 0 0 3 a n d k = 1 u d a r c y i n all r e g i o n s
of t h e g r i d shown i n F i g u r e 11 w h i c h a r e n o t d e f i n e d a b o v e . w h e r e
K v a l u e s a r e shown in p a r e n t h e s e s , i t was assumed t h a t k was
p r e s s u r e d e p e n d e n t . The p e r m e a b i l i t y was t a k e n c o n s t a n t , a t t h e
lower v a l u e , u p t o a p r e s s u r e o f SO0 psi a n d t h e n i n c r e a s e d l i n e a r l y
a t 8 0 0 psi.
PRESSURE V S T I M E
**O i X
@
Well 1 7
Well 1 4
v well 113
6.0
--- P r ea s u ri set ai n c the ' f ofroma tti h n
s n rm o
-
n
v,
at d e 7
c e n t e r l i n e of W e l l 1 3
measured toward W e l l 1 4
e
a
N
0
4
U
4.0
2.0
0.0
0.0 1.0 2.0 3.0 4.0
-
TIME c IO'MIN I
Figure 12. Comparison of measured and c a l c u l a t e d pressure h i s t o r i e s
at Wells # 7 , # 4 and # 3 a s determined from two-dimensional
arralvses.
c
20.
15.
10.
5.
0.
0
F i g u r e 13. Calculated pressure d i s t r i b u t i o n w i t h i n r e t o r t volume 50
h o u r s a f t e r i n i t i a t i o n of Well # 7 p r e s s u r i z a t i o n .
20.0 I
15.0
I
0.0
0.0 5.0 10.0 15.0
20.0 25.0 30.0
X AXIS (IO'FT 3
Note : These r e s u l t s a r e i n c l u d e d f o r c o m p l e t e n e s s o n l y .
Because of t h e requirement to assume d i s c r e t e f l o w
c h a n n e l s t h e t r a c e r - g a s motion i s n o t a d e q u a t e l y r e p r e -
s e n t e d s i n c e t h e t r a c e r p a r t i c l e s d o n o t n e c e s s a r i l y stay
i n t h e c h a n n e l s . Thus, f o r example, t h e r e appeer to
be no t r a c e r p a r t i c l e s moving toward W e l l R12.
Figure 1 4 . H i s t o r y of t r a c e r gas motion during the 5 0 hour period
f o l l o w i n g i n i t i a t i o n of Well #7 p r e s s u r i z a t i o n .
G3
s l i g h t l y relaxed, t h e t i p p r e s s u r e d r o p s and c r a c k growth stops.
Since a i r i n t h e crack is a t very high pressure, unlike t h a t i n
a p o r o u s m e d i a where t h e p r e s s u r e d r o p s r a p i d l y a s o n e moves
r a d i a l l y from t h e w e l l , t h e r e i s l i t t l e p r e s s u r e d e c a y once t h e
system i s shut-in. I t i s of importance t o note t h a t t h e system
shut-in pressure i s approximately equal t o t h e overburden
pressure.
A c o m p a r i s o n of t h e c a l c u l a t e d a n d measured. W e l l X 4 p r e s -
s u r e s a r e a l s o shown i n F i g u r e 1 2 . T h e c o m p a r i s o n i s n o t a s good
a s t h a t shown f o r W e l l # 7 , p r i m a r i l y a s a r e s u l t o f t h e l a r g e
wellbore v o l u m e a n d c o a ' r s e z o n i n g . M a t e r i a l s p r o p e r t i e s c o u l d
be s l i g h t l y a d j u s t e d s o t h a t t h e c u r v e s m a t c h d u r i n g t h e
p r e s s u r i z a t i o n p h a s e , h o w e v e r , t h e e f f o r t d o e s n o t seem w a r r a n t e d .
The mass f l o w r a t e i n t o Well # 4 i s e x a c t l y t h e e x p e r i m e n t a l f l o w
r a t e t h u s mass i s c o n s e r v e d p r o p e r l y and t h e f i n a l p r e s s u r e i s
approaching t h e measured p r e s s u r e . Therefore, t h e flow rate
away from t h e v i c i n i t y of Well # 4 i n t o t h e r e t o r t v o l u m e is
r e p r e s e n t a t i v e of t h a t a c t u a l l y o c c u r r i n g .
The p r e s s u r e b u i l d - u p a t Well # 3 i s s e e n i n F i g u r e 12 t o
be much t o o s l o w . Even t h e f l o w c h a n n e l a s s u m e d i n t h i s a n -
a l y s i s i s i n a d e q u a t e and c a n n o t p r o v i d e t h e o b s e r v e d flow.
The p r e s s u r e o u t s i d e t h e h i g h p o r o s i t y r e g i o n s u r r o u n d i n g
W e l l # 3 , a s d e t e r m i n e d by t h i s t w o - d i m e n s i o n a l a n a l y s i s , is
s e e n t o be r e p r e s e n t a t i v e of t h e m e a s u r e d W e l l # 3 p r e s s u r e .
C l e a r l y , b e c a u s e of t h e l a r g e w e l l b o r e v o l u m e , p r e s s u r e s
m e a s u r e d i n Well # 3 a r e n o t r e p r e s e n t a t i v e of t h e p r e s s u r e i n
t h e f o r m a t i o n s u r r o u n d i n g t h i s well.
The t w o - d i m e n s i o n a l a n a l y s e s were o n l y c o m p l e t e d t o a
t i m e of 5 0 h o u r s f o l l o w i n g t h e i n i t i a l i n j e c t i o n i n t o W e l l # 7 .
B e c a u s e o f t h e f a i l u r e of t h e m e a s u r e d W e l l s # 7 a n d # 4 , pres-
s u r e s t o d e c a y a Z t e r c o m p l e t i o n of p r e s s u r i - z a t i o n (see F i g u r e
1 5 ) no a d d i t i o n a l i n f o r m a t i o n c o n c e r n i n g t h e system c h a r a c t e r i s t i c s
@
29
n
I .-
0 0 b
tn
0
O
bD
-
0
Y
a
b,
0 0 0
b o t
0
0 0
D 0
0 O Q O
0 ' 0
D
b
B
b m
0
c z
d m t c O N
LI d d
b
0 P
0,
O b E
-4
0 0 cl
o
0 O
0
0 0
0 0
b
0
0
I O b I
0 0 0 0 0 0 0 0 0
a
0 0 0 0 0 0 0 0
k
oo r- W Y) * rl ( Y d 5
tr,
4
E
30
Grs
c o u l d be o b t a i n e d b y c o n t i n u i n g t h e s e r u n s t o l a t e r t i m e s .
I f t h e a n a l y s i s were c o n t i n u e d , once t h e o u t l y i n g Wells # 6 a n d
# l O b e g a n t o p r e s s u r i z e , t h e y would c o n t i n u e t o d o s o b e c a u s e
of t h e d i f f u s i o n c h a r a c t e r i s t i c s r e p r e s e n t a t i v e of f l o w t h r o u g h
a porous f o r m a t i o n e v e n i f t h e p r e s s u r e i n W e l l # 3 were r e l i e v e d .
I t i s c o n c e i v a b l e t h a t a m o d e l of t h e r e t o r t r e g i o n c o u l d be
d e v e l o p e d s h o w i n g s p e c i f i c c h a n n e l s t o v a r i o u s wells s u c h
t h a t t h e p r e s s u r e r i s e o n a l l w e l l s were m o d e l e d . However,
t h e model d e v e l o p e d i s so non-unique as t o h a v e l i t t l e v a l u e .
2.2.4 Summarv o f P e r m c a b i l i t v a n d P o r o s i t v A n a l v s i s
T o s u m m a r i z e , t h e r e s u l t s of t h e p l a n a r , a x i s y m m e t r i c a n d
two-dimensional a n a l y s e s i n d i c a t e f r a c t u r i n g occurs or t h a t
e x i s t i n g fractures open (i.e., separation along bedding planes
a t h i g h p r e s s u r e s ) o n c e p r e s s u r e s r e a c h t h e n e i g h b o r h o o d of t h e
overburden. As a r e s u l t , t h e s y s t e m r e s p o n s e c a n n o t be d e s c r i b e d
u s i n g a p o r o u s f l o w model.
T h e s t r o n g e s t e v i d e n c e s u p p o r t i n g t h e a b o v e p r e m i s e is
t h e m a i n t e n a n c e of h i g h p r e s s u r e s once wells a r e s h u t - i n . In
addition, the f l o w rate i n t o W e l l # 3 (note the constant f l o w
r a t e i n t o t h i s w e l l a s e v i d e n c e d by t h e c o n s t a n t p r e s s u r e r i s e
shown i n F i g u r e 4 ) i s i n d e p e n d e n t of t h e W e l l # 3 p r e s s u r e . This
i n d i c a t e s t h a t t h e pressure i n t h e f o r m a t i o n surrounding t h i s
w e l l i s , even a t e a r l y t i m e s , a t l e a s t 300 p s i . T h i s would
o c c u r o n l y i f t h e c r a c k s o r f r a c t u r e s were b e i n g f o r c e d o p e n a t
t h e h i g h p r e s s u r e s . T r a c e r g a s t r a n s i t t i m e s a r e a l s o s e e n to
e i t h e r s l i g h t l y i n c r e a s e or r e m a i n t h e same o n c e t h e s y s t e m
p r e s s u r e becomes e l e v a t e d . I n a uniformly porous media, t h e s e
t r a n s i t t i m e s would d e c r e a s e a s t h e s y s t e m p r e s s u r e i n c r e a s e d .
Fiow c h a n n e l i n g i s a l s o s t r o n g l y i n d i c a t e d cxperimen-
t a l l y by t h e p o r t i o n o f t h e f l o w w h i c h a r r i v e s a t W e l l # 3 a n d
#12, a n d a n a l y t i c a l l y b y t h e r e s u l t s of t h e t w o - d i m e n s i o n a l
0
31
analyses. Based o n s o l i d a n g l e a r g u m e n t s , t h e s e w e l l s s h o u l d
r e c e i v e less t h a n 2 p e r c e n t and 0.3 p e r c e n t o f t h e t o t a l f l o w
i f t h e s y s t e m were u n i f o r m , w h e r e a s t h e y r e c e i v e 1 8 p e r c e n t
and 4 p e r c e n t , r e s p e c t i v e l y .
2.3 CHARACTERIZATION OF THE FRACTURING
The u n i f o r m i t y o f t h e m b b l i z a t i o n , f r a c t u r i n g , or bed-
d i n g p l a n e s e p a r a t i o n can be d e t e r m i n e d from t r a c e r g a s c o n c e n -
t r a t i o n measurements a t t h e p r o d u c t i o n w e l l s . I f t h e formation
i s u n i f o r m t o t h e e x t e n t t h a t a l l g a s f l o w i n g from t h e i n j e c t i o n
w e l l to a production w e l l t r a v e l s along geometrically iden-
t i c a l f i v w p a t h s t h e n g a s motion occurs a s s l u g f l o w . In that
case, t h e t r a c e r g a s p u l s e w i d t h a n d c o n c e n t r a t i o n m e a s u r e d a t
the production w e l l is i d e n t i c a l t o t h a t occurring a t t h e in-
jection well. I f t h e i n j e c t i o n t o p r o d u c t i o n well f l o w p a t h s
are not uniform, then t h e first t r a c e r gas a r r i v a l s a t t h e
p r o d u c t i o n w e l l s w i l l be o f l o w c o n c e n t r a t i o n , a n d t h e t i m e re-
quired for t h e concentration t o i n c r e a s e t o t h e i n j e c t i o n level
will be l o n g c o m p a r e d t o t h e i n j e c t i o n p u l s e l e n g t h .
I n t e r p r e t a t i o n of t r a c e r g a s C o n c e n t r a t i o n m e a s u r e m e n t s
made i n t h e p r o d u c t i o n w e l l s i s c o m p l i c a t e d by t h e l a r g e w e l l -
bore v o l u m e a n d l o w s y s t e m p o r o s i t y . E x p e c t e d maximum p r o d u c t i o n
w e l l t r a c e r g a s c o n c e n t r a t i o n s c a n be e s t i m a t e d u s i n g A p p e n d i x
D. The u n i f o r m i t y of t h e c r o s s - h o l e f l o w p a t h s c a n be q u a l i -
t a t i v e l y e v a l u a t e d b y c o m p a r i s o r , of t h e m e a s u r e d c o n c e n t r a t i o n s
and r i s e t i m e s w i t h t h o s e e s t i m a t e d a s s u m i n g no d i s p e r s i o n .
The r a t i o s g i v e n by t h e maximum d e t e c t e d p r o d u c t i o n w e l l
t r a c e r g a s c o n c e n t r a t i o n s d i v i d e d b y t h e maximum e x p e c t e d
c o n c e n t r a t i o n s , determined a c c o r d i n g t o t h e f o r m u l i g i v e n i n
A p p e n d i x D , a r e shown i n p a r e n t h e s i s i n F i g u r e s 3 a n d 4 .
T h e tracer g a s i n j e c t i o n p u l s e l e n g t h ( u s u a l l y approx-
i m a t e l y 3 - 4 h o u r s ) a n d the time r e q u i r e d f o r t h e maximum c o n c e n -
t r a t i o n I.cvels t o o c c u r i n t h e p r o d u c t i o n w e l l s c a n be s e e n i n
@
32
G t h e d a t a summary g i v e n i n A p p e n d i x A . D a t a shown i n F i g u r e s 3
and 4 a r e f o r t r a c e r g a s e s i n j e c t e d i n t o W e l l # 4 . T h e r e i s i n s u f -
f i c i e n t d a t a t o make a c c u r a t e i n t e r p r e t a t i o n s from t r a c e r g a s
i n j e c t i o n s i n W e l l s f13 a n d # 7 .
Gas f l o w from Well # 4 t o # 3 i s e s s e n t i a l l y s l u g f l o w .
The r a t i o o f m e a s u r e d t o a n t i c i p a t e d maxiinum c o n c e n t r a t i o n i s
shown t o be 0 . 3 f o r t h e C318, 13B1 a n d s e c o n d SF6 p u l s e s .
A s shown in F i g u r e A . 2 of A p p e n d i x A , t h e r i s e t i m e , m e a s u r e d
f r o m t h e t i m e of t h e f i r s t a r r i v a l of t h e t r a c e r t o t h e t i m e a t
w h i c h t h e p e a k c o n c e n t r a t i o n i s o b t a i n e d , i s o n t h e same o r d e r
as the injection pulse t i m e . One e x c e p t i o n t o t h e s l u g f l o w is
t h e f i r s i SF6 a r r i v a l o c c u r r i n g a t l o w p r e s s u r e . I t i s much
more d i s p e r s i v e , a s i n d i c a t e d b o t h by i t s lower peak r e l a t i v e
c o n c e n t r a t i o n a n d by t h e f a c t a p p r o x i m a t e l y 30 h o u r s o c c u r r e d
b e t w e e n t h e t i m e o f f i r s t a r r i v a l a n d t h e a t t a i n m e n t of t h e
peak c o n c e n t r a t i o n .
Tracer g a s i n j e c t e d t h r o u g h t h e Well # 4 c a p i l l a r y was
d e t e c t e d a t Wells # 8 a n d #10 a t low c o n c e n t r a t i o n s . T h e detec-
t i o n t i m e was s h o r t ( a p p r o x i m a t e l y 1 0 h o u r s a n d 3 h o u r s a t
Wells # 8 a n d # l o , r e s p e c t i v e l y ) s i n c e f l o w i n t o t h e s e w e l l s
s t o p p e d o n c e Well if3 w a s v e n t e d . The p e a k c o n c e n t r a t i o n s w h i c h
may h a v e eventually occurred at t h e s e wells i s therefore i n -
determinant. However, d u r i n g t h e m e a s u r e m e n t t h e c o n c e n t r a t i o n
l e v e l s i n c r e a s e d v e r y s l o w l y if a t a l l . T h e l o w i n i t i a l c o n -
c e n t r a t i o n l e v e l s t o g e t h e r w i t h t h e s l o w i n c r e a s e i n concen-
t r a t i o n i n d i c a t e f l o w c h a n n e l s from K e l l # 4 t o Wells # 8 a n d #10
are h i g h l y n o n - u n i f o r m .
For t h e f i r s t 8 0 t o 1 0 0 h o u r s of t h e t e s t (see F i g u r e s 3
a n d 4 and A . 1 7 ) g a s f l o w i n t o W e l l #12 i s predominantly t h a t
o r i g i n a l l y i n j e c t e d i n t o W e l l # 7 a s i n d i c a t e d by t h e h i g h 1 3 B l
concentration. A t later t i m e s (100 h o u r s ) t h e s e c o n d SF6 p u l s e
i n j e c t e d i r . t o \ J e l l 114 b e g i n s t o a r r i v e a t Well # 1 2 . AS
33
i n d i c a t e d by t h e c o n c e n t r a t i o n l e v e l a n d a p p a r e n t r i s e t i m e ,
t h i s flow i s approaching s l u g f l o w .
T h e r e was i n s u f f i c i e n t d a t a t o e v a l u a t e t h e u n i f o r m i t y
of t h e f o r m a t i o n b e t w e e n W e l l # 3 a n d Wells # 5 a n d # 6 . The l a c k
of d a t a r e s u l t s p r i m a r i l y from t h e f a c t t h a t t h e c a p i l l a r y t u b e s
o n W e l l s # 5 a n d # 6 were p l u g g e d or c l o s e d , t h u s d a t a c o u l d n o t
be o b t a i n e d f r o m t h e s e w e l l s w h i l e t h e y were s h u t - i n . When
Well # 3 was p r e s s u r i z e d , b o t h Wells # S a n d # 6 were r e g u l a t e d
a t 4 0 p s i g . Once p r e s s u r e s i n t h e s e w e l l s e x c e e d e d t h i s v a l u e
o u t f l o w occurred a n d s a m p l e s were o b t a i n e d f r o m t h e f l o w i n g g a s .
The t i m e a t w h i c h t r a c e r g a s f i r s t e n t e r e d t h e s e w e l l s c a n n o t
be a c c u r a t e l y d e t e r m i n e d . However, a s shown i n F i g u r e s A . 6 a n d
A.8 once t h e outflow had been established, the C318 (C318 and
12B2) l e v e l s a t Wells # 5 ( # 6 ) were on t h e o r d e r of t h e i r i n -
j e c t i o n concentrations. T h i s evidence strongly suggests slug
f l o w o c c u r s b e t w e e n Wells # 3 a n d Wells # 5 a n d # 6 .
34
3, CONCLUSIONS
An e x t e n s i v e a m o u n t of d a t a w a s o b t a i n e d f r o m t h e D o w
s h a l e s i t e during t h e tracer g a s p r e s s u r i z a t i o n study. From
t h i s d a t a , a number o f s i g n i f i c a n t c o n c l u s i o n s c a n be d e t e r m i n e d .
T h e s e a r e p r e s e n t e d below.
0 The s y s t e m i s n o n - u n i f o r m . F l o w from W e l l # 4 t o t h e
o t h e r w e l l s o c c u r s p r i m a r i l y t h r o u g h v a r i o u s f l o w chan-
nels. T h e s e c h a n n e l s o p e n when t h e w e l l h e a d p r e s s u r e
approaches t h e overburden pressure and appear closed a t
lower p r e s s u r e s . C o n s e q u e n t l y , t h e s y s t e m i s p r e s s u r e
s e n s i t i v e and t h e f l o w i s enhanced a t e l e v a t e d system
pressures. Flow t o o u t l y i n g w e l l s , s u c h a s f18 a n d #lo,
o c c u r o n l y when Well # 3 w a s a t a n e l e v a t e d p r e s s u r e .
When t h e s y s t e m a p p r o a c h e d s t e a d y s t a t e , a s i n d i c a t e d
b y a n absence of p r e s s u r e c h a n g e s , t h e p r o d a c t i o n
r a t e was a b o u t 1 / 3 t h e i n j e c t i o n r a t e , The a d d i t i o n a l
i n j e c t e d g a s m u s t be c o n t a i n e d i n e v e r - i n c r e a s i n g p o r -
t i o n s of t h e r e t o r t v o l u m e . B e c a u s e of t h e low s y s t e m
p e r m e a b i l i t i e s t h i s flow p r o b a b l y c a n n o t be t a p p e d , e v e n
w i t h i n t r o d u c t i o n of a d d i t i o n a l p r o d u c t i o n wells.
0 M u l t i p l e t r a c e r g a s i n j e c t i o n i n t o Well # 4 a t v a r i o u s
d e p t h s d e m o n s t r a t e d c o n c l u s i v e l y t h a t f l o w d o e s occur
t h r o u g h t h e A n t r i m f o r m a t i o n i n t h e v i c i n i t y o f Well
#4. I t c a n n o t be d e t e r m i n e d t o w h a t d i s t a n c e t h i s f l o w
c o n t i n u e s t o p a s s t h r o u g h t h e Antrim l a y e r .
a T h e p e r m e a b i l i t y a n d p o r o s i t y f o u n d i n t h e v i c i n i t y of
Well # 4 was k 2, 0.045 m i l l i d a r c y and @ = 0 . 1 for a
radius <1.75 f t a n d % 0 . 0 0 1 f o r r a d i i g r e a t e r t h a n 1 . 7 5
f t . T h i s may be c o m p a r e d t o Well # 3 v a l u e s of k 0.45
Q
m i l l i d a r c y w i t h @ = 0 . 3 f o r o u t t o a r a d i u s of 3 . 9 f t
35
A
and $ = 0.003 w i t h k = 0.35 m i l l i d a r c i e s for a l l
r a d i i larger than this. In effect, the permeability i n
t h e r e g i o n o f W e l l # 3 i s a n o r d e r of m a g n i t u d e l a r g e r
I
t h a n t h a t f o u n d i n t h e v i c i n i t y of W e l l # 4 . In addi-
t i o n , t h e volume p e r f t of w e l l l e n g t h o f t h e h i g h
permeability, high p o r o s i t y region surrounding W e l l # 3
i s 5 times l a r g e r t h a n t h a t s u r r o u n d i n g W e l l # 4 .
Q The major f l o w f r o m W e l l # 4 i s t o w a r d Well 13, w h i c h i n
t u r n c o m m u n i c a t e s r e a d i l y w i t h Wells # S a n d # 6 . This
f l o w occurs as a slug flow. Decreasingly smaller por-
t i o n s o f t h e f l o w go t o Wells #12, # 8 , a n d #lo. Flow
t o Well # 1 2 may o c c u r a s a s l u g f l o w , h o w e v e r , f l o w t o
Wells # 8 a n d # l o i s d i s p e r s i v e .
36
4. RECOMMENDATIONS
A number of r e c o m m e n d a t i o n s a r e d i s c u s s e d i n t h e follow-
ing paragraphs. F i r s t s u g g e s t i o n s a r e g i v e n which would l e a d
t o improvements i n t h e t r a c e r g a s p r e s s u r i z a t i o n t e s t r e s u l t s .
F o l l o w i n g t h i s some comments a r e i n c l u d e d c o n c e r n i n g t h e
m o d e l i n g a n d d e s i g n of p o s s i b l e f u t u r e i n - s i t u r e t o r t volumes.
F i n a l l y , comments a r e p r o v i d e d r e l a t i n g t o d e v e l o p i n g a r e t o r t
v o l u m e so t h a t i t may p e r f o r m t o d e s i g n o b j e c t i v e s . Many o f t h e
3
t h o u g h t s p r e s e n t e d w e r e b r o u g h t t o l i g h t d u r i n g t h e j o i n t S /Dow
e f f o r t t o c h a r a c t e r i z e t h e e x i s t i n g r e t o r t volume u s i n g t r a c e r -
gas p r e s s u r i z a t i o n techniques. I n t h a t s e n s e , many of t h e i d e a s
P u t f o r t h a r e n o t u n i q u e t o S3, b u t a r e i n c l u d e d h e r e f o r
completeness.
Many c h a r a c t e r i s t i c s of t h e e x i s t i n g r e t o r t r e g i o n were
determined during t h e tracer-gas p r e s s u r i z a t i o n tests reported
here. However, t e c h n i q u e s c a n be e m p l o y e d o n f u t u r e t e s t s t o
e n s u r e b o t h t h a t better d a t a i s o b t a i n e d and t h a t t h e s e d a t a .
focus on answering specific q u e s t i o n s r e l a t i n g t o t h e retort
volume p e r f o r m a n c e . A number of s t r i c t l y t e c h n i c a l problems s h o u l d
be a d d r e s s e d . I f p o s s i b l e , i n f u t u r e t e s t s a l l h o l e s s h o u l d be
c a s e d down t o a n d p e r h a p s e v e n a f e w f e e t i n t o t h e A n t r i m forma-
t i o n . T h i s w o u l d e n s u r e t h a t a n y a n d all f l o w c h a r a c t e r i s t i c s
w e r e b e i n g measured i n t h e Antrim and n o t i n t h e False Antrim o r
some o t h e r z o n e . I t may a l s o p r e c l u d e a major s o u r c e of g r o u n d
water leakage i n t o t h e formation. Correspondingly, t h e h o l e s
should terminate w i t h i n t h e Antrim r e g i o n , i f possible. Several
d o w n h o l e m e a s u r e m e n t s t a k e n d u r i n g t h i s t e s t were compromised
b e c a u s e of b r i n e a c c u m u l a t i o n . Problems w h i c h w i l l a r i s e d u r i n g
t h e r e t o r t i n g process i f b r i n e i s p r e s e n t a r e o b v i o u s . It i s
t h e r e f o r e recommended t h a t f u t u r e i . n - s i t u r e t o r t v o l u m e s h a v e
d o w n h o l e pumps p e r m a n e n t l y i n s t a l l e d a n d operated i n a l l w e l l s
37
A
where brine accumulation is a problem. In future tests, as done
with this test, it is recommended that the specific objectives for
the tracer gas analyses be well-defined before testing commences.
To aid in this definition, it is recommended that preliminary pres-
sure test data, specifically related to the tracer gas test, be
obtained before initiation of the tracer gas tests. These tests
would utilize compressed air only. This would greatly improve the
tracer gas test design and data interpretation. Applying the usual
hindsight to the tests reported here, two changes are apparent which
could possibly have been determined with preliminary pressure
testing. First and foremost, additional shut-in pressure decay
data is required. Secondly, initial tracer gas injection into
Wells P 7 and t 3 should h a v e t a k e n p l a c e a f t e r t h e f i r s t a r r i v a l
of f l o w from Well 8 4 .
The required porosity and permeability distributions
needed for successfully retorting the Dow shale site are, from
a technology standpoint, unknown at this time. We are of the
opinion that significantly more fracturing than was in evidence
in the retort (especially around Well # 4 ) would lead to considerably
easier burning of the in-situ kerogen. Because the required
degree of rubblization is unknown, it is recommended that a
combined theoretical-experimental effort be undertaken in which
the question of required porosity and permeabilities necessary
for successful retorting be addressed. A first step in the
theoretical aspects of this program may be to develop a theoretical
model describing the in-situ burning and recovery processes.
Natural building blocks for such a model could be models pre-
viously developed by S3 to describe porous media flow and com-
bustion as related to coal gasification. T h e s e analyses could
be integrated to provide a model describing in-situ retorting.
Development of a theoretical model together with the experimental
38
@ work would eventually lead to characterizing media requirements
necessary for successful in-situ oil retorting.
In conjunction with model development, it is also re-
commended that efforts be made to rubblize future retort volumes
a s required to provide the necessary porosity and permeability
distributions. In this sense it is recommended that the explo-
sive requirements and placements such as downhole pre-hydrofrac-
turing, etc., be developed and designed so that required system
characteristics can be obtained. It is also recommended that
pressure tests, and possibly tracer gas tests, be conducted
as required during the fracturing program in order to ensure that
3
the desire6 rubblization is being accomplished. Again, S has
extensive experience in characterizing explosively fractcred
media of this type. These analytical methoc7,s may be used to
provide a theoretical prediction of the extent of fracturing and
the distribution of porosity. Again, attainment of suitable per-
meabilities and porosities are necessary ingredients for devel-
opment of a successful in-situ retort.
39
APPENDIX A
DATA SUMMARY
A summary of t h e test d a t a is included i n t h i s appendix.
Table A . l o u t l i n e s t h e t e s t s c h e d u l e a n d d e f i n e s t h e s e q u e n c e
of a l l c r i t i c a l o p e r a t i o n s . F i g u r e A . l i s a s c h e m a t i c of t h e
well l a y o u t s h o w i n g t h e w e l l n u m b e r s w h i c h w i l l be r e f e r r e d t o
in l a t e r s e c t i o n s of t h e a p p e n d i x a n d t h r o u g h o u t t h e r e p o r t .
T a b l e A . 2 p r o v i d e s a h i s t o r y of t h e s y s t e m b r i n e l e v e l s m e a s u r e d
d u r i n g t h e t e s t p e r i o d . F o l l o w i n g t h i s , t h e r e s p o n s e of e a c h
individual w e l l is discussed i n d e t a i l , Included i n t h e dis-
c u s s i o n i s a summary of s i g n i f i c a n t e v e n t s o c c u r r i n g a t t h i s
w e l l , t o g e t h e r w i t h a r e c o r d of t h e p r e s s u r e h i s t o r y a n d t r a c e r
gas c o n c e n t r a t i o n h i s t o r i e s a s measured i n t h e w e l l .
41
Table A . l
Summary of T e s t P r o g r a m
Date
AiiI-nj e c t i on Remarks
---
--- u l y l
(J Time
07 7000 All wells shut in at this time.
08 14 30 l Z B ? into Well 43 Well 4 3 fillet with 12B2 at concen-
(through capil l c r y tration of -10-5. Tracer in2ecteC into
at w b i e n t pressure) this w e l l prior to pressurization Of
Well 4 4 in order to observe flow from
Well t3.
08 1630 lZB2 injection completed
08 2200 Brine purr.pe3 Iran 2293 gallons obtained f r o = Well (3.
Uells (3 and bS Kone from 45.
09 0640 On at 47
09 0650 1381 into annulus at 13Bl tracer < a s injected into region
well 1 7 at -10-6 surrounding Hell 1 7 . Hovenent of
concentration this tracer vi11 be observed during
pressurization test from b4.
09 0850 1 3 B 1 injection completed
09 0945 Off st (7 No f l w into formation at t h f r t b e ,
air flou continued.
09 1030 On at b7
09 1630 Off at ( 7 1381 tracer gar should be in formation
at thir time.
09 1650 On at 1 4 P r h . A r y test program initiated.
09 1650 dF into annulus at b r 6 I s mixed with injection air i n
WePl 1 4 at concentra- annulur.
tion of -10-7
09 1930 SF6 injection completed
10 0330 C318 into capillary at End of capillary is 1265 ft depth.
Well 1 4 at concentration C318 will enter forration only i f
of -10-6 (if mixed v i t h there is f l o w through Antrim.
air r t r e a m )
10 0600 C318 injection completed
11 0900 SF into annulus at Repeat earlier test to observe system
wet1 1 4 at concentration response at operating prersure
of %io-7
11 0930 1381 into capillary at Repeat earlier tent to observe s y s t a
Well 4 4 at concentration response at operating pressure
of %10-6
11 1000 Initiate vent o n Well (3 outflow at B O psig back pressure.
Well (3 per Lm
h (Prevent Well 83 pressure becoming l a r g e
requeat enough to displace brine to other n l l r ) .
11 1300 SFg an8 13Bl injections
completed
13 0430 Vent terminated Prepare system for pressurization fram
o n Well 4 3 Well 43.
13 0650 Off at 0 4 Test froa Well ( 4 completed.
13 0650 On at 4 3 Determine communication from 13 to
4 5 And ( 6 per Dov requert.
13 0650 l ? B Z injection into
ar.nuIus At %io-6
concentration
13 0700 Uellr ( 5 and 16 vented t o and regulated
at 40 psig. Cas from ( 5 saturated w i t h
12B2 (sample obtained at 0600). Noter
Capillaries o n both ( 5 and (6 plugged.
13 0850 1 ? R 2 completed
13 0900 C318 injectlon into Observe system response at higher prer-
annulus at %io-6 sure and use g a r not found in Hell 8 5 .
concent ration
13 1200 C 3 1 8 injection completed
14 0700 off at e3 Test completed.
42
\
.
43
Table A . 2
History of B r i n e L e v e l in Wells
Quantity
Well Brine Date Removed
Number Level Examined -a l l o n s )
(G Remarks
3 1176f 6/2 8 3876
7/3 1097
7/7 137
7/8 2293
7/11 9
7/13 1703
4 1315 6/24
1316 7/5
1312 7/16
5 1311* 7/10 129
6 1098 6/26 Air L i f t e d
1138 7/5
1167 7/15
7 1320 6/26
1339 7/5
1330 7/15
8 1295 7/4
1283 7/6 L e v e l dropped
1323 7/14 40' during test
period.
10 1347 7/5
1330 7/6
'1315 7/15
12 1327 7/5 Level increased
1210 7/14 117 ' during
test period
+REDA pumps l o c a t e d i n t h e s e w e l l s .
n
44
FG2SPONSE O F WELL 43
(See F i g u r e s A . 2 t h r o u g h A . 4 )
Summary:
0 SFg a r r i v e d a t 5 3 a t l o w c o n c e n t r a t i o n s 1 4 h o u r s
after injection a t #4. The f l o w p a t h c o u l d be
e i t h e r t h r o u g h t h e A n t r i m or F a l s e A n t r i m l a y e r s .
.If t h e r e i s n o d i s p e r s i o n , w h i c h r e s u l t s p r i m a r i l y
from v a r i a t i o n s i n f l o w c h a n n e l d i m e n s i o n s , t h e n
t h e t r a c e r gas concentrations should reach t h e i r
maximum l e v e l s of 3 x 10-8, 2 x 10-7, 3 x 10-7 a n d
4 x 10-8 for t h e SF^, c 3 1 8 , 1 3 B 1 a n d SF^ a r r i v a l s ,
r e s p e c t i v e l y . T h e s e p e a k v a l u e s s h o u l d be o b t a i n e d
w i t h i n 1 6 0 , 1 5 0 , 2 4 5 a n d 2 l n m i n u t e s (i.e.! t h e
i n j e c t i o n p u l s e d u r a t i o n ) of t h e i r r e s p e c t i v e f i r s t
arrivals.
0 T h e i n i t i a l SF a r r i v a l o c c u r s a f t e r 14 h o u r s .
I n i t i a l c o n c e n t r a t i o n s a r e low, t h e r i s e t i m e i s
l o n g ( > 3 0 h o u r s ) a n d t h e p e a k c o n c e n t r a t i o n i s low.
A l l t h e s e f a c t o r s i n d i c a t e l a r g e dispersion.
e C 3 1 8 a r r i v e d a t P 3 , w i t h l i t t l e d i s p e r s i o n , 28 h o u r s
a f t e r i n j e c t i o n through c a p i l l a r y tube a t #4.
I n i t i a l l y , t h e C 3 1 8 f l o w m u s t be t h r o u g h t h e A n t r i m
f o r m a t i o n ( s e e F i g u r e -2 ,
t h e v o l u m e of t r a c e r g a s
i n j e c t e d t h r o u g h c a p i l l a r y i s s o s m a l l t h a t it
c a n n o t f i l l t h e w e l l v o l u m e up t o t h e F a l s e A n t r i m ,
t h u s t h e flow i n t o t h e f o r m a t i o n m u s t o c c u r t h r o u g h
the Antrim).
@ T e s t r e p e a t e d w i t h s y s t e m a t h i g h e r p r e s s u r e by
i n j e c t i o n of 1 3 B 1 i n t o c a p i l l a r y a t # 4 . Transit
t i m e through Antrim reduced t o 1 0 hours. Dispersion
of t r a c e r g a s was a g a i n s m a l l .
eSF injection i n t o annulus repeated w i t h system a t
h i t h e r p r e s s u r e . A 1 0 h o u r t r a n s i t t i m e was o b s e r v e d .
Under t h e s e c o n d i t i o n s , t h e r e was l i t t l e d i s p e r s i o n
Of the S F g .
The a p p a r e n t p e r m e a b i l i t y a n d p o r o s i t y v a l u e s f o r t h e
f o r m a t i o n i n t h e v i c i n i t y of \+e11 8 3 a r e shown i n
Figure 6.
45
n
Conclusions :
0 There is flow through Antrim formation a t l e a s t in
vicinity of 8 4 .
F l o w rate between 6 4 and 113 increases and dispersion
decreases as system pressure is increased.
e Immediate vicinity of 8 3 is highly fractured a n d has
a porosity r a n g i n g up to QO.3. T h e apparent perme-
ability of r e g i o n surrounding 113 is % 0 . 4 md.
A
46
c
(i) (ii) ("1 13Bl
I I C318
4
c
2Ja
L
2a
mm
I'
0
Gas injection at Well 14
(i) sF6 injection at annulus
(ii) SF6 injection at annulus
liii) C318 injection at capillary
(iv) 1381 injection at capillary
m m (VI Time at which sF6 reaches Antrim
. . t:/+lo4 ( v i ) 4 3 venting from 320 psig t o
* B B hours 80 p i g . After this period,
10-lC t 3 regulated at 8 0 psig.
-8
2 4
hours
c 1 4 4
hours
1 I I A A I 1 I
20 40 50 80 100 120 140
July 9 Time (hours)
1700
Figure A . 2 . History of t r a c e r g a s c o n c e n t r a t i o n s m e a s u r e d a t Well # 3
d u r i n g p r e s s u r i z a t i o n of Well # 4 .
400 x Annulus p r e s s u r e
Note: Reda pump down h o l e ,
t h e r e f o r e , no p r e s s u r e
i n d i c a t e d on t u b e .
30C
4
cn
20c
01 I I 1 1 I i I
0 20 40 60 80 100 120 IO
July 9 T i m e (hours)
1700
Figure A . 3 . Pressure history of Well # 3 during pressurization of Well # 4 .
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
I I I I I 1 ’ - 0 - i
0 0 0 0 0 0 0 0 I
0 0 o + 0 0 0 0 0
0) e W v1 w 0 cy 4
(67sd) a r n s s a z d
49
A
RESPONSE OF WELL # 4
(See Figure A . 5 )
Summary :
-
0 The apparent permeability and porosity values for
the formation in the vicinity of Well # 4 are shown
in Figure 5.
i
Conclusions :
0 The region surrounding # 4 has a significantly lower
permeability and porosity compared to that observed
in the region surrounding Well #3.
..
A
50
.
rl
rl
P
0 tn
-4
0 c
U
0 vc
0
0 c
0
-4
0 u
a
0 N
-4
k
0 3
v)
0 v)
al
k
0 a
tn
0 c
4
0 k
1
a
0
0
0 w
0"
r(
0:s
0
0
0
0
0
0
0
0 .
O O
0 0 0 0 0 0 0 0 0 0
0 0 0 0
m m fi * 0
VI
0
0
0
0
0
N
0
r(
51
RESPONSE OF W L L # S
(See F i g u r e s A . 6 and A.7)
Summary:
F a i l u r e of c a p i l l a r y t u b e to r e m a i n o p e n r e s u l t e d
i n n o d a t a u n t i l p r e s s u r i z a t i o n of 6 3 i n d u c e d flow
into Y5.
.Well / 5 w z s v e n t e d p r i o r to p r e s s u r i z a t i o n of 8 3 .
A t t h i s t i m e , a i r i n d5 c o n t a i n e d 12B2 a t t h e
c o n c e n t r a t i o n i n j e c t e d i n t o # 3 a t 1430 o n J u l y 8.
T h i s a i r c o n t a i n e d no o t h e r t r a c e r g a s e s .
e C318 i n j e c t e d i n t o 8 3 a r r i v e d a t 4 5 w i t h l i t t l e
d i s p e r s i o n i n less t h a n 1 0 hours.
12B2 i n j e c t e d i n t o 113 when # 3 was a t a v e r y l o w
pressure was not d e t e c t e d a t /!.(No explanation.)
O L ~ cWn c e n t r a t i o n s of 13B1 a n d SF6 o r i g i n a l l y
o
i n j e c t e d i n 114 d i d a r r i v e a t 8 5 .
Conclusion:
0 I n i t i a l l y , c o m m u n i c a t i o n o c c u r s b e t w e e n Wells 4 3
and b 5 a s if k ; .01 mdarcy.
0
NOTE: !
T h e Well b p r e s s u r e w a s r e g u l a t e d at 4 0 - 5 0 p s i g .
About 1 0 h o u r s following p r e s s u r i z a t i o n of W e l l 8 3 ,
t h e r e was s u f f i c i e n t flow t o well 8 5 t o c a u s e t h i s
well t o b e g i n v e n t i n g . A i r flowing from Well 1 5
c o n t a i n e d t r a c e r g a s e s i n t h e a m o u n t s shown i n
F i g u r e A.6. The p e r m e a b i l i t y w a s c a l c u l a t e d based
o n the 1 0 h o u r t r a n s i t t i m e using E q u a t i o n (C.6)
( w i t h 0 = 0,001) a n d t h e r e f o r e r e p r e s e n t s a lower
limit.
52
c c
1381
A C318
m SF6 * 4
..
G a s samples
-4
b
Capillary l i n e blocked
obtained
Could n o t o b t a i n gas sample
1 from v e n t lin'e
(regulated a t
4 0 - 5 0 psig)
( i ) l r i r a n d l2B2 i n j e c t i o n i n i t i a t e d a t W e l l 1 3
( 2 h o u r p u l s e of 1 2 8 2 )
( i i ) C318 i n j e c t i o n i n i t i a t e d a t W e l l 1 3
0
0
..
0 .
* '
( 3 h o u r p u l s e o f C318)
( i i i ) I n i t i a t i o n of o u t f l o w f r o m W e l l 1 5
(iv) W e l l 1 5 v e n t e d t o a r e g u l a t e d b a c k p r e s s u r e
o f 50 p s i g . Gas samples t a k e n d u r i n g v e n t
were s a t u r a t e d w i t h 12R2 o r i g i n a l l y i n j e c t e d
i n t o 83. S a m p l e c o n t a i n e d no o t h e r t r a c e r gases.
e
m
10-l1 1 1 I 1 I
20 40 60 80 100 I 10
July 9 Time (hours)
1700
Figure A . 6 . History of tracer concentration measured at Well # 5
during pressurization of Well #3.
!
4 00 x Annulus p r e s s u r e
Note: Leak on Reda pump fitting
may be c a u s e of f a i l u r e
to p r e s s u r i z e
loo
C I 1 I 1 I
20 40 60 80 100 0
July 9 Time ( h o u r s )
1700
Figure A . 7 . Pressure h i s t o r y of Well # 5 .
Q
RESPOXSE OF WELL 1 6
(See F i g u r e s A. 8 and A . 9 )
Summary :
0 SF6 a n d C318 a r r i v e d a t # 6 a t h i g h c o n c e n t r a t i o n s
( t h u s i n d i c a t i n g l i t t l e d i s p e r s i o n ) even prior t o
n o t i c e a b l e pressure a r r i v a l . These t r a c e r g a s e s
had b e e n i n j e c t e d a t 8 4 . T r a c e r a r r i v a l i n 86
s u b s t a n t i a l l y p r e c e d e d t h a t i n 113.
e Once pressure i n c r e a s e d i n $6, t h e c a p i l l a r y t u b e
a p p a r e n t l y f i l l e d w i t h b r i n e so t h a t f u r t h e r g a s
samples c o u l d not be o b t a i n e d .
~ K h e n e l l R6 v e n t e d , p r i o r t o p r e s s u r i z a t i o n f r o m
W
# 3 , t r a c e a m o u n t s of SF6 were f o u n d , h o w e v e r , t h e r e
w a s no 12B2 i n t h i s w e l l .
0 1 2 B 2 a n d C318 i n j e c t e d i n t o 1 3 a r r i v e d a t 6 5 w i t h
l i t t l e d i s p e r s i o n i n less t h a n 1 0 h o u r s . T h e 12B2,
i n j e c t e d i n t o Well t 3 when wells f 3 , d 5 and 6 6 were
at l o w pressure a p p e a r s t o have p r e f e r e n t i a l l y
t r a v e l l e d t o W e l l 116.
e w e 1 1 86 r a p i d l y f i l l e d w i t h b r i n e f o l l o w i n g pres-
s u r i z a t i o n 'of 1 3 .
Conclusions:
@ T h e e a r l y a r r i v a l of C318 a n d SFg i n a6 i n d i c a t e s
f l o w t r a v e l s from 1 4 t o # 6 t o E3 a n d t h e n t o # 5 .
S i m i l a r l y , 12B2 o r i g i n a l l y i n j e c t e d i n t o P 3 w a s
f o u n d i n 4 5 , b u t not in 86. C o m m u n i c a t i o n b e t w e e n
4'4 a n d 86 s t o p p e d once t h e p r e s s u r e in W e l l # 3 h a d
reached ~ 2 0 0 psig.
@ I n i t i a l l y , c o m m u n i c a t i o n occurs b e t w e e n Wells # 3 a n d
$6 a s i f k 2 0.01 m d a r c y ( c a l c u l a t e d a s d e s c r i b e d
for Well # 5 ) * T h e a i r flow d e g e n e r a t e s w i t h t i m e as
a p p a r e n t l y b r i n e i s p u s h e d t o w a r d #6. T h e r a p i d
i n c r e a s e i n t u b e pressure shown i n F i g u r e A . 9 r-cslulted
from b r i n e f i l l i n g the t u b e .
55
SF6 t t
4 12B2
A
10"
'7
b
.A
a
C
' 88: 1
Capillary line blocked. I. ,'.
Could not obtain gas Gas samples
sample obtained from
vent line (regu-
I, lated at 40-50
0 rn Psi91
0
510 m
(i) Air and 12B2 injection initiated at Well 13
- (2 hour pulse of 1282)
(ii) C318 injection initiated at Well 13 (3 hour pulse of C318)
(iii) 'Initiation of outflow from Well 1 5
(iv) Well t 5 vented to a regulated back pressure of ~ 5 psig.
0
Gas sample taken during vent contained a trace Of SF6, but
n o other tracer gasee.
lo-l:
I I I 1 1
0 20
July 9 Time (hour81
1700
F i g u r e A.8. H i s t o r y of tracer c o n c e n t r a t i o n measured a t Well # 6 .
c c
400 x Annulus p r e s s u r e
0 Tube p r e s s u r e
h
.
v
P
d
v)
a
P)
Ll
3
v)
9
Lc
0.
300
200
f
I
100
0
20 40 60 80 100 -
l 0
July 9 Time (bourn)
1700
Figure A.9. Pressure history of Well # 6 .
RESPONSE O F WELL # 7
(See Figures A . 1 0 through A . 1 2 )
Summary :
@The l o n g duration 13B1 pulse results from the
injection of 13B1 in Well 117 at 0 6 5 0 on July 9.
This tracer gas was initially forced into the
formation around 8 7 and is now returning as a
result of pressurization of 8 4 .
- eThe later SF6 arrival at 8 7 corresponds to a
formation permeability of %Lo. 01 mdarcy* (calculated
according to Equation !C.6)). The long time required
for the pulse to reach a maximum concentration indi-
cates much dispersion.
o C 3 1 8 injected at 8 4 did not reach # 7 .
.The apparent permeability and porosity values
for the formation in the vicinity of Well 8 7
are shown in Figure 7 .
Conclusions:
.There is no measureable flow between R4 and # 7
through kntrim formation.
.The apparent permeability and porosity in immediate
vicinity of Well 8 7 is 0.03 mdarcy and 0.001,
respectively.
It is assumed that SF6 detected at Well ill corresponds to the
first injection of SFg in W e l l # 4 . If it results from the
second SF6 injection, then k Q 0 . 0 4 mdarcy. This would a l s o
imply there is no communication between 8 4 and through the
Antrim since no C 3 1 8 was detected at 1 7 .
58
(il (ii)
1 (VI
I Gas i n j e c t i o n a t W e l l 1 4
( i ) SF6 i n j e c t i o n a t a n n u l u s
( i i ) SF6 i n j e c t i o n a t a n n u l u s
( i i i ) C318 i n j e c t i o n a t c a p i l l a r y
( i v ) 1381 i n j e c t i o n a t c a p i l l a r y
(VI T i m e a t w h i c h SF6
injection
(ii) reaches antrim.
L
, . I '
4.
: e
ul L
W AJL
co,
@a
u
cu)
o a .
v.m '
L k 13B1
U4-J . ,.*<
u
. I
Note :
1. Well 17 w a s p r e s s u r i z e d for eaB'
m .
14 h o u r s prior to a i r i n j e c t i o n
10-1
at 14.
90,
2. 1 3 8 1 was i n j e c t e d i n t o Well 117
d u r i n g f i r s t 2 h o u r s of
p r e e s u r i za t i o n .
m m
10-1 I I 1 1 I
20 40 60 till 100 I !O
Ju'ly 9 Time ( h o u r s )
1700
F i g u r e A.lO. H i s t o r y of t r a c e r g a s c o n c e n t r a t i o n s m e a s u r e d a t W e l l #7
d u r i n g p r e s s u r i z a t i o n of W e l l # 4 .
u-l
0
u-l
0
60
9 oc
0 ooo O C P 0
0 0 0 0
700 0
00
600
0 Measured pressures
500
0
400
300
0
200
100 3
I I I
OJuly 9 10 20 30
0640
T i m e (hours)
Figure A . 1 2 . Pressure measured at Well # 7 during pressurization of this
well.
I
RESPONSE OF WELLS C8 AND # l o
(See F i g u r e s A . 1 3 t h r o u g h A.16)
Summary:
8 Flow occurs t o Wells 48 a n d dl0 when Well # 3 has
a n e l e v a t e d p r e s s u r e . T h e C318 a r r i v a l t i m e s cor-
r e s p o n d t o a p e r m e a b i l i t y of 0 . 0 4 m d a r c y . It
s h o u l d be n o t e d t h a t t h i s i s a f i r s t a r r i v a l
a t a 1 o w . c o n c e n t r a t i o n . The R a v e r a g e " p e r m e a b i l i t y
f o r t h e b u l k f l o w may be f a c t o r s o f t e n l e s s t h a n
t h i s value.
0 The l o w c o n c e n t r a t i o n of C318 i n d i c a t e c o n s i d e r a b l e
d i s p e r s i o n o c c u r s b e t w e e n i n j e c t i o n a t Well 114 a n d
d e t e c t i o n a t Wells t 8 a n d 410. (If slug flow
o c c u r r e d w i t h n o d i s p e r s i o n , t h e C318 c o n c e n t r a t i o n s
a t Wells # 8 a n d $10 s h o u l d r e a c h a m a x i m u m l e v e l of
a b o u t 1 x 10-7 w i t h i n 3 h o u r s a f t e r t h e f i r s t d e t e c t i o n . )
0 Flow t o 118 a n d F10 i n i t i a l l y s t a r t s t h r o u g h A n t r i m
formation around 84.
0 Absence of SF6 a t t h e s e w e l l s i n d i c a t e s f l o w p a t h s
were n o t o p e n when S F 6 i n j e c t e d ( s y s t e m p r e s s u r e
was l o w d u r i n g SF6 i n j e c t i o n ) .
Conclusion :
Q Flow o c c u r s f r o m # 4 t h r o u g h A n t r i m f o r m a t i o n t o
# 8 a n d 810 so l o n g a s W e l l 8 3 is a t a n e l e v a t e d
pressure.
62
lo-6
(i)
(ii)
10”
1 AC318
( i ) SF6 injection into
c
&
rl
1 4 annulus
cm
0 ( i i ) C318 injection into
#4 capillary
( i i i ) Well 1 3 venting from
320 p s i g t o 8 0 p s i g .
After t h i s period, 1 3
A d regulated at 8 0 p s i g .
_. -
A
* *- .f
*- .
- .I---
rii7
1O’ll
0 20 40 60 80 100
July 9 Time (hours)
1700
63 F i g u r e A . 13. History of t r a c e r gas c o n c e n t r a t i o n s m e a s u r e d at
Well # E l .
63
4
X
I
0
-
0,
4
3
m
a
Y
0,
&
:
& 2
a
1 I Annulus p r e s s u r e
0 Tube p r e s s u r e
' I i I
20 40 60 EO 100' 10
July 9 Time (hours)
1700
F i g u r e A.14. P r e s s u r e history of Well #8.
64
I (i I SF6 injection into
1 4 annulus
(ii] C318 injection into
k 1 4 capillary
4
c a ( i i i ) Well 1 3 venting from
0
-4 4J 320 psig t o 80 psig.
U k
Q I Q After t h i s period, 1 3
ka regulated a t 80 psig.
U
C k
001
oa
c
om
om b A
D,
m
4 k
0101
o
alk
v u
4
kr,
ek
m
a
CI
July 9
1700 Time (hours)
br3 Figure A. 15. H i s t o r y of t r a c e r gas concentrations m e a s u r e d at
Well #lo.
65
50
/ 0 0 0 0 0 -
b
40
X
X
X Annulus pressure
o Tube pressure
10
0
0 20
July 9 Time (hours)
1700
Figure A.16. P r e s s u r e h i s t o r y of W e l l #lo.
66
RESPONSE OF WELL 1 9
Summary:
e Well # 9 developed a p r e s s u r e , b u t air samples
taken from t h e w e l l contained n o evidence of
tracer g a s e s . T h e v a l v e o n t h e compressed air
inlet w a s f o u n d to leak. T h e w e l l was vented
( 0 7 0 0 o n 1 2 July) and t h e air line r e m o v e d .
S u b s e < u e n t l y , t h e p r e s s u r e on \;ell 8 9 remained
con s t a n t .
Conc l u s ions :
e Subsequent t o 0700 o n 12 J u l y , t h e r e w a s no
c o m m u n i c a t i o n w i t h Well t 9 .
E a r l i e r communication w i t h W e l l %9 c o u l d
n o t be d e t e r m i n e d s i n c e # 9 w a s b e i n g
p r e s s u r i z e d from t h e s u r f a c e .
67
RESPONSE OF WELL #12
(See F i g u r e s A . 1 7 a n d A . 1 8 )
Summary:
. T h e r a p i d 13B1 a r r i v a l a t 1112 occurs a t a t i m e
e x p e c t e d i f t h e 87 t o 1112 p e r m e a b i l i t y w e r e
m
~ 0 . 1 darcy.
. F l o w from t 4 t o C12 o r i g i n a t i n g t h r o u g h t h e A n t r i m
f o r m a t i o n ( e v i d e n c e d by t h e s h a r p C318 a r r i v a l ,
t h e s u g g e s t i v e s e c o n d 13B1 a r r i v a l ) o c c u r s
a t a t i m e corresponding t o a permeability
of ~ 0 . 1m d a r c y .
.Flow a t l o w p r e s s u r e s through t h e F a l s e Antrim
o r some other p a t h d i f f e r e n t from t h a t followed
by t h e C318 ( e v i d e n c e d b y t h e f a c t t h e f i r s t
SF6 p e a k a r r i v e d 28 h o u r s a f t e r t h e C318) was
much slower t h a n t h a t o r i g i n a t i n g t h r o u g h t h e
Antrim.
.The low c o n c e n t r a t i o n s of C318 a n d SFg c o m p a r e d
t o t h a t of t h e 13B1 i n d i c a t e m o s t f l o w into .
Well e12 i s 13B1 o r i g i n a l l y i n j e c t e d i n t o W e l l 87.
(If a l l g a s e n t e r i n g W e l l # 1 2 c o n t a i n e d
t r a c e r a t t h e i n j e c t i o n c o n c e n t r a t i o n , t h e C318
a n d S F g c o n c e n t r a t i o n s i n W e l l # 1 2 w o u l d be
e x p e c t e d t o o b t a i n a peak of 7 x 10-7 a n d
7 x 10-8, r e s p e c t i v e l y . )
Conclusions :
~ C o m r n u n i c a t i o n b e t w e e n 117 a n d 8 1 2 c o r r e s p o n d s t o
a p e r m e a b i l i t y of ~ 0 . 1 d a r c y .
m
.Flow o r i g i n a t i n g t h r o u g h A n t r i m f o r m a t i o n from # 4
t o 8 1 2 i s much f a s t e r a t t h e h i g h e r pressures t h a n
is t h e f l o w a t l o w p r e s s u r e s w h i c h possibly w e n t
t h r o u g h t h e False A n t r i m f o r m a t i o n .
68
'i" (7
Gas injection at Well 1 4
(i) SF6 injection at annulus
(iii) (ii) sF6 injection at annulus
(iv)
1o - ~ I (iii)
(iv)
C318 injection at capillary
13B1 injection at capillary
( v ) Time at 'which SF6 reaches
antrim
' e . _.
.. . .* *. -- e - **. . . 4
6 A '%
a. , '
4 4
m
- --•
13Bl
A c318
SF6
0l-
1-' Note:
1. Well 17 w a s p r e s s u r i z e d for
14 hours prior to air injection
at 1 4 . 0,
2. 13B1 w a s injected into Well ( 7
during first 2 hours of a
pressurization. -'
I I -dA! I I
6d Figure A . 1 7 . H i s t o r y of t r a c e r g a s c o n c e n t r a t i o n s measured at
Well #12.
69
400 -
300
Note: Lack of s u b s t a n t i a l C 3 1 8
f o l l o w e d by l a t e r i n p u t
of SF6
0 Tube p r e s s u r e
x P.nnulus p r e s s u r e
Note: Pressure d i d not increase
a t Well ( 1 2 u n t i l 16 hour
a6 a r e s u l t of v a l v e
leaking. P r e s s u r e began
to i n c r e a s e a s soon a s
leak f i x e d .
0 20 40 60 80 100 120
July 9 Time (hours)
1700
Figure A.18. Pressure history of Well #12.
70
crs APPENDIX B
EXPERIMENTAL TECHNIQUES
The a c t u a l i m p l e m e n t a t i o n o f t h e e x p e r i m e n t a l p r o g r a m i n
t h e f i e l d was p r e d i c a t e d on d e t e r m i n i n g t h e d e g r e e a n d e x t e n t
of c o m m u n i c a t i o n b e t w e e n t h e v a r i o u s b o r e h o l e s a t t h e Dow T e s t
Site. I n o r d e r t o h a v e a r e a s o n a b l e c h a n c e a t success f o u r d i s -
t i n c t t r a c e r g a s e s were u t i l i z e d : s u l f u r h e x a f l u o r i d e (SF6) a n d
t h e F r e o n s 13B1, C-318, a n d 12B2. W h a s t e n t o p o i n t o u t t h a t
e
the use of d i s t i n c t t r a c e r gases is a necessity i n undertaking a
c h a r a c t e r i z a t i o n program u t i l i z i r . ; m u l t i p l e b o r e h o l e i n j e c t i o n ,
s i n c e i t i s iiilpossible t o u n a m b i g u o u s l y i n t e r p r e t t r a c e r g a s
a r r i v a l and c o n c e n t r a t i o n d a t a from m u l t i p l e b o r e h o l e s u s i n g o n l y
a single tracer gas.
Due t o t h e a n t i c i p a t e d e x t r e m e l y h i g h i n j e c t i o n p r e s s u r e s ,
and t h e f a c t t h a t a l l proposed tracer g a s e s l i q u e f y a t s u b s t a n t i a l l y
lower p r e s s u r e s , t h e v a r i o u s t r a c e r g a s e s were c o m m e r c i a l l y d i l u t e d
10,OOO:l i n n i t r o g e n a n d t h e n c o m p r e s s e d t o 6 , 0 0 0 p s i by t h e
Linde Corporation. I n t h i s m a n n e r , a q u a n t i t y of t r a c e r g a s w a s
a v a i l a b l e a t s u f f i c i e n t p r e s s u r e t o overcome any r e a s o n a b l e
injection pressure expected at t h e Dow Test S i t e .
T r a c e r g a s flow r a t e s a n d t h e r e f o r e i n j e c t i o n c o n c e n t r a -
t i o n s were a d j u s t e d u s i n g a v a r i a b l e o r i f i c e m e t e r i n g v a l v e
which had been p r e v i o u s l y c a l i b r a t e d . With t h i s t e c h n i q u e t h e
t r a c e r g a s c o u l d be d i l u t e d t o t h e d e s i r e d c o n c e n t r a t i o n l e v e l s
i n t h e c o m p r e s s e d a i r stream. A s a n a d d i t i o n a l d a t u m , t h e t o t a l
tracer g a s f l o w was d e t e r m i n e d b a s e d o n t h e p r e s s u r e d r o p of t h e
Compressed g a s c y l i n d e r .
P r e s s u r e a n d t r a c e r g a s h i s t o r i e s were m o n i t o r e d a t a l l
wells. I n g e n e r a l , pressures were r e a d on Dow-provided p r e s s u r e
(-, g a u g e s c o n n e c t e d t o c a p p e d m a n i f o l d s e x t e n d i n g i n t o e a c h of t h e
71
A
boreholes. I n addition, polypropylene tubing extended i n t o m o s t
of t h e b o r e h o l e s down t o t h e l e v e l of t h e A n t r i m f o r m a t i o n . Since
a l l t h e b o r e h o l e s were e x p e c t e d t o be p r e s s u r i z e d , w e u t i l i z e d
t h e s e downhole c a p i l l a r i e s i n c o n j u n c t i o n w i t h s a i n p l i n g b a g s
(i.e., l a r g e b a l l o o n s ) t o d r a w s a m p l e s f r o m d o w n h o l e w i t h o u t t h e
u s e of a s o p h i s t i c a t e d s a m p l i n g pump. T h i s t e c h n i q u e , of u s i n g
downhole p r e s s u r e t o f i l l t h e s a m p l e b a g s , w a s c o n s i d e r a b l y
s i m p l e r t h a n o t h e r a v a i l a b l e methods.
I n p r a c t i c e , a sample bag w a s p l a c e d on t h e v a l v e d c a p i l l a r y
I
l i n e . S i n c e t h e b o r e h o l e was p r e s s u r i z e d , s a m p l e s c o u l d be ob-
t a i n e d by o p e n i n g t h e v a l v e . O n e o r more b a l l o o n s were u s e d , as
r e q u i r e d t o c l e a r t h e c a p i l l a r y l i n e of t h e p r e v i o u s s a m p l e , t o
e n s u r e t h e m a j o r p o r t i o n of t h e c o n t a i n e d g a s w a s from t h e w e l l -
b o r e . A i r s a m p l e s w e r e t h e n drawn f r o m t h e b a l l o o n s u s i n g d i s -
p o s a b l e Nalgene s y r i n g e s . The g a s w i t h i n t h e s y r i n g e w a s t h e n
i n j e c t e d i n t o t h e chromatograph and a n a l y z e d . A l l a n a l y s e s w e r e
3
accomplished u s i n g a n S t r a c e r gas monitor. T h i s i n s t r u m e n t
is described i n the next section.
S y r i n g e S a m p l e s were o b t a i n e d f r o m t h e area i m m e d i a t e l y
s u r r o u n d i n g t h e i n j e c t i o n and o u t l y i n g sampling m a n i f o l d s a t
p e r i o d i c i n t e r v a l s t o i n s u r e t h e r e w a s no tracer g a s l e a k a g e
fron? e i t h e r t h e a b o v e - g r o u n d p i p i n g o r from c r a c k s e x t e n d i n g t o
t h e formation. The m e a s u r e m e n t i n t e r v a l w a s i n i t i a l l y o n t h e
o r d e r of e v e r y t w o h o u r s , d e c r e a s i n g u l t i m a t e l y t o o n c e a d a y
,during t h e f i n a l phases of t h e experiment. No l e a k s w e r e
detected.
T h r o u g h o u t t h e c o u r s e of t h e e x p e r i m e n t p o r t a b l e hand-
h e l d d i c t a t i o n - t y p e r e c o r d e r s were u t i l i z e d b y a l l f i e l d p e r -
s o n n e l t o make r e a l t i m e f i e l d n o t e s . I n t h i s manner a l l
o b s e r v a t i o n s a n d occurrences were c a p t u r e d a s t h e y a c t u a l l y
h a p p e n e d . P r e v i o u s e x p e r i e n c e h a s shown t h a t i n a p r o g r a m of
t h i s magnitude, it i s v e r y u n l i k e l y t h a t p e r s o n n e l i n v o l v e d w i l l
remember m i n o r d e t a i l s some number of d a y s a f t e r t h e y o c c u r .
Monitoring Instrumentation
The S3 tracer gas monitor is an electron capture gas
chromatograph shown schematically in Figure B.l. The electron
capture gas chromatograph utilizes the high electron affinity
of gases with halogen group elements to provide a measurable
signal. A sample to be analyzed is injected into the instrument
by means of a disposable syringe. Injection is through a rubber
septum located on the sample port. This septum prevents spur-
ious contaminants from diffusing into the chromatograph and
producing anomalous signals.
The heart of the instrument is the column. It sepzretes
the various gaseous components cf a sample by selectively slow-
ing down some gases relative to others. The column can be
thought of as a device to elute the distinct components in a
gas sample in a definite order.
When monitoring SF6 p l u s selected Freons, experience
has shown that a column (stationary phase) consisting of one
of the Porapaks provides excellent separation. This separ-
ation is illustrated in Figure B . 2 f o r the tracer gases used
in tests repeated here. Porapak is a porous polymer composed of
ethylvinylbenzene cross-linked with divinylbenzene to form a
uniform structure of distinct pore size. The columns and
detector are generally operated at elevated temperatures to
increase detector sensitivity to tracer peaks and to allow a
complete measurement to be performed in a relatively short time.
Care must be exercised in the choice of operating temperature
since the relative arrival time (elution time) is a function of
Porapak type as temperature and chemical species (see Figure
B.3). Incorrect operating temperature could provide erroneous
or confusing data output due to peak arrival overlap.
73
4
4
Figure B . l . Schematic drawing af e l e c t r o n capture gas chromatograph.
Time
Figure B . 2 . C h r o m a t o g r a p h response showing separation of v a r i o u s
t r a c e r g a s e s o n aOonc meter P o r a p a k Q c o l u m n . Column
t e m p e r a t u r e = 1 0 0 C; C a r r i e r f l o w r a t e = 5 0 cc/min.
75
1
cc
m
Q,
+,
3
c
-4
E
Y
Q)
E
.PI
4J
c
0
.ri
JJ
7
d
'W
0.2 :
10
I I
20
I i I
40
1 I
60
I T
80 100
T e m p e r a t u r e ("C)
Figure B . 3 . Elution time as a function of temperature for
selected tracers on a o n e meter Porapak Q column. @
76
6rs
The detector portion of the chromatograph consists of a
tritiated titanium foil encased within an electrically con-
ductive housing. Specific pulse-generator circuitry energizes the
detector, initiating a flow of electrons from the tritium foil.
A collector wand within the detector receives the electrons and
establishes a current flow which is amplified through an
electrometer circuit. Should an "electron-capturing gas"
(such as SF6 or one of the Freons) flow through the stream of
electrons, the current is decreased in proportion to the con-
centration of the gas.
77
n
crs APPENDIX C
ANALYTICAL MODEL
The tracer gas pressurization technique may be used to
determine many characteristics of an in situ retort region.
- c _ _
Methods of analyzing data for a homogeneous porous formation,
a F x o u s formation with channeling, or a fractured formation
are discussed in this Appendix.
Porous Flow
When the system responds as IC it were a porous media,
a two-dimc-nsional finite element time-dependent diffusion code
isused in a iterative manner to aid in determining permeabilities
and porDsities. Specifically, a set of material properties
is selected. A calculation is then made using this set of
material properties and the known injection rates. Calculated
pressures and tracer gas arrival times are then compared with
the experimentally measured pressures and tracer arrivals.
Various distributions of permeability and porosity are selected
until the calculated and measured results agree.
In a uniformly rubblized material, the calculated and
measured tracer g a s arrival times agree provided the calculated
and measured pressure and flow rate histories agree. Further-
more, tracer gas concentrations measured at sampling locations are
essentially equivalent to the injection concentration. Early
tracer gas arrivals at low concentration levels imply non-
uniformities within the formation. For example, a portion of
the tracer gas may rapidly flow through a fracture to the samp-
ling region. Under such conditions, the initially measured
tracer gas concentration at the sampling region is much lower
than the concentration at the injection region and the time required
to reach the maximum concentration is long compared to the injec-
6d tion pulse duration.
79
This a n a l y s i s d e s c r i b e s flow through a l o c a l l y uniform
media. I f t h e f o r m a t i o n i s l a c e d w i t h n u m b e r s o f f r a c t u r e s or
flow c h a n n e l s , t h i s s h o u l d be a p p a r e n t b y t h e f a i l u r e of
t h e a n a l y s i s t o simulate t h e observed response.
If t h e r e t o r t r e g i o n i s r u b b l i z e d s o t h a t g a s c a n s l o w l y
d i f f u s e from t h e i n j e c t i o n w e l l t o t h e p r o d u c t i o n w e l l s , t h i s
f l o w may be m o d e l e d u s i n g t h e t w o - d i m e n s i o n a l h y d r o d y n a m i c
c o d e . T h i s code d e s c r i b e s s i m p l e Darcy f l o w . Thus, t h e
area a v e r a g e f l u i d v e l o c i t y 6 is p r o p o r t i o n a l t o t h e g r a d -
i e n t pressure, p, giving
- = - - kv p
q
IJ
w h e r e k a n d p a r e t h e p e r m e a b i l i t y a n d f l u i d v i s c o s i t y , re-
spectively. The c o r r e s p o n d i n g f l u i d p a r t i c l e v e l o c i t y ( i . e . ,
tracer p a r t i c l e v e l o c i t y ) i s j u s t
where 9 i s t h e porosity. Note t h a t k a n d 41 may be f u n c t i o n s
of b o t h p o s i t i o n a n d p r e s s u r e . C o m b i n i n g E q u a t i o n ((2.2) w i t h
t h e mass c o n s e r v a t i o n e q u a t i o n a n d e q u a t i o n of s t a t e
p = cpy (C.4)
where p , y , and c r e p r e s e n t d e n s i t y , r a t i o o f s p e c i f i c h e a t s a n d
a c o n s t a n t , r e s p e c t i v e l y , y i e l d t h e d e f i n i n g e q u a t i o n for
compressible f l o w i n the porous m e d i a .
80
T h e terms o n t h e f a r r i g h t hand s i d e o f E q u a t i o n (C.4) a n d (C.6)
r e p r e s e n t a s o u r c e w i t h i n t h e m e d i a ( i . e . , a n i n j e c t i o n well).
n o l u t i o n s t o E q u a t i o n (C.5) a r e a v a i l a b l e i n b o t h one- and two-
d i m e n s i o n s ( e i t h e r a x i s y m m e t r i c or C a r t e s i a n ) b y u s i n g a f i n i t e
element numerical code. I n t h e r e t o r t r e g i o n , i t i s assumed
t h e f l o w i s i s o t h e r m a l , t h u s y = 1.
Some comments a r e n e c e s s a r y c o n c e r n i n g t h e a n a l y s e s u s e d
t o i n t e r p r e t r e s u l t s of t h i s e x p e r i m e n t . T o o b t a i n e c o n o m i c a l
c o m p u t e r c o s t s , it i s n e c e s s a r y t o h a v e t h e z o n e s i z e r e l a t i v e l y
large. The s m a l l e s t z o n e s ( s e e F i g u r e 11) i n t h e r e g i o n s of
Wells ct3, & 4 , #7, a n d P6 were t h e r e f o r e t a k e n a s 3 f t x 3 f t ,
w h i c h i s much l a r g e r t h a n t h e wellbore d i m e n s i o n s . To simulate
w e l l b o r e e f f e c t s , t h e p o r o s i t y of t h e s h a d e d z o n e s , r e p r e s e n t -
i n g t h e w e l l s , w a s i n c r e a s e d t o c o n s i d e r t h e t o t a l v o l u m e of t h e
wellbore p l u s t h e p o r o s i t y of t h e m a t e r i a l . S i n c e t h e calcu-
l a t i o n is two-dimensional and t h e r e f o r e m u s t be of constant
t h i c k n e s s , some a d j u s t m e n t s m u s t be made i n t h e a n a l y s i s t o
account for v a r i a t i o n s i n brine l e v e l t h r o u g h o u t t h e r e t o r t
region. Experimental evidence i n d i c a t e s t h a t except i n t h e
r e g i o n of Wells # l 2 a n d # 6 , t h e b r i n e l e v e l s d i d not s i g n i -
f i c a n t l y change throughout t h e test. The measured g a s f l o w
w a s t h e r e f o r e p r e d o m i n a n t l y t h r o u g h tgose r e g i o n s of t h e s y s t e m
w h i c h were f r e e of b r i n e . I n t h e r e g i o n of t h e i n j e c t i o n W e l l
# 4 , t h e d e p t h of t h i s b r i n e f r e e r e g i o n i s a b o u t 1 5 2 f t . This
d i s t a n c e was t h e n t a k e n a s t h e t h i c k n e s s of t h e s y s t e m . In
t h e r e g i o n of Well # 3 , t h e b r i n e free d e p t h i s a b o u t 36 f t .
F o r c a l c u l a t i o n p u r p o s e s t h e m e d i a p r o p e r t i e s i n t h e r e g i o n of
d
6
81
a well such as 113 would be adjusted so that this 36 ft section
is simulated by a 150 ft section. The total porosity in the
region of Well # 3 is conserved, but spread over the 150 ft section.
Correspondingly the permeability used in the numerical model was
taken as the actual permeability reduced by the ratio of the real
depth of the brine free region at Well # 3 divided by the depth
used in the analysis. Properties in regions surrounding the
other wells were changed in a similar manner to account for var-
iations in brine depth.
Channel Flow
Equation ( C . 5 ) can be solved assuming flow occurs in
one direction only (1-D plane flow). This solution can be
used to estimate the s o u r c e to production well permeability
corresponding to an observed tracer gas transit time through
a flow channel such as illustrated in Figure 8. The resulting
permeability to porosity ratio is given by
4pL2
3T
where T is the tracer gas transit time and where L is the dis-
.
tance between the injection and production wells (denoted by
subscripts I and P,* respectively) .
The mass flow rate (w)
through th.is channel is given by
PI’ - 2
Pp
(C.7)
Since the flow rate can usually be inferred from the well
pressurization data, Equation (C.7) can be used to determine
the cross-sectional area (A) of the channel.
Fracture Flow
Flow along a fracture can also be modeled by assuming
the flow occurs between two parallel flat plates. If the 69
82
CIS
cross-sectional a r e a of t h e f l o w i s t a k e n a s t h a t a r e a b e t w e e n
t h e f r a c t u r e p l a n e s , t h e n t h e m a s s flow a n d c o r r e s p o n d i n g v e l -
o c i t y a r e g i v e n by*
2 - (PI -
Hb3
p
PPI
w = F r;- L e
-
1 b2
v = - v (PI-PP )
3
(C.9)
v h e r e b i s t h e d i s t a n c e between t h e f r a c t u r e p l a n e s (i.e.8
w i d t h of t h e c r a c k ) a n d H i s t h e d r a c k d e p t h m e a s u r e d i n a d i r e c t i o n
normal t o t h e f l o w v e l o c i t y . G i v e n measured t r a n s i t t i m e s a n d
flow r a t e s , t h e c o r r e s p o n d i n g c r a c k d e p t h a n d w i d t h may be i n -
f e r r e d f r o m E q u a t i o n s (C.8) a n d & . 9 j , i f it i s a s s u m e d t h a t a l l
f l o w occurs through t h e s e fractures.
*
S c h l i c h t i n g , H., B o u n d a r y L a y e r T h e o r y , M c G r a w H i l l , 1960.
83
cps APPENDIX D
WELLBORE EFFECTS
Wellbore e f f e c t s m u s t be c o n s i d e r e d when i n t e r p r e t i n g
d a t a t a k e n d u r i n g t h e t r a c e r g a s p r e s s u r i z a t i o n t e s t s of t h e D o w
i n s i t u retort region.
7- T h e s e e f f e c t s are v e r y i m p o r t a n t b e c a u s e
t h e w e l l volume i s l a r g e c o m p a r e d t o t h e v o i d v o l u m e i n t h e
A n t r i m i n t h e n e a r r e g i o n of t h e w e l l . The w e l l v o l u m e m u s t
be c o n s i d e r e d i n a n y i n t e r p r e t a t i o n s of m e a s u r e m e n t s of pres-
s u r e , t r a c e r g a s c o n c e n t r a t i o n , tracer g a s a r r i v a l t i m e and
f l o w rate i n t o a production w e l l .
The w e l l a c t s a s a l a r g e r e s e r v o i r f o r i n c o m i n g f l o w .
S i n c e t h e incoming f l o w rates are small, i t t a k e s a c o n s i d e r -
able t i m e f o r t h e w e l l p r e s s u r e t o i n c r e a s e . As a r e s u l t ,
t h e w e l l p r e s s u r e may be s i g n i f i c a n t l y lower t h a n t h e p r e s s u r e
i n t h e formation immediately surrounding t h e w e l l . This is
p a r t i c u l a r l y t r u e i f t h e f l o w i n t o t h e w e l l i s moving t h r o u g h
f r a c t u r e s r a t h e r t h a n through a uniformly porous media. The
n e t e f f e c t i s t h a t t h e w e l l p r e s s u r e w i l l be much lower t h a n t h e
p r e s s u r e i n t h e s G r r o u n d i n g media. T h e s e w e l l p r e s s u r e s pro-
v i d e a t l e a s t a lower bound f o r t h e p r e s s u r e i n t h e s u r r o u n d i n g
media, b u t g i v e no i n d i c a t i o n w h a t t h e a c t u a l p r e s s u r e level
may be.
I n o r d e r t o q u a l i t a t i v e l y e v a l u a t e t h e u n i f o r m i t y of
t h e l o c a l i z e d f r a c t u r e s , i t i s n e c e s s a r y t o know t h e t r a c e r
c o n c e n t r a t i o n i n t h e gas a r r i v i n g a t t h e p r o d u c t i o n w e l l s .
C o n c e n t r a t i o n m e a s u r e m e n t s are c o n f u s e d by t h e l a r g e p r o d u c t i o n
w e l l volume. I n o r d e r t o i n t e r p r e t t h e measured tracer g a s
concentrations it is necessary to determine t h e concentration
w h i c h would e x i s t i n t h e p r o d u c t i o n w e l l i f a l l i n c o m i n g g a s
c o n t a i n e d tracer a t t h e i n j e c t i o n c o n c e n t r a t i o n . Measurements
a5
t a k e n f r o m c a p i l l a r y samples w i l l h a v e t r a c e r g a s c o n c e n t r a t i o n s
e q u a l t o t h a t i n t h e a i r l e a v i n g r e g i o n A shown i n F i g u r e D.l.
The r e l a t i o n s h i p b e t w e e n t h e c o n c e n t r a t i o n of t r a c e r i n t h e a i r
l e a v i n g r e g i o n A t o t h a t i n t h e a i r a r r i v i n g i n r e g i o n A is
vO + J (GI - GL) dt
0
where
-
.
C
W -
tracer g a s concentration
f l o w r a t e (scfm)
vO
- v o l u m e of g a s c o n t a i n e d i n r e g i o n " A " shown
i n F i g u r e D.l a t t i m e of f i r s t a r r i v a l of
t r a c e r (scf)
t - t irne
a n d w h e r e t h e s u b s c r i p t s a r e g i v e n by
I - f l o w i n t o r e g i o n "A"
L - f l o w l e a v i n g r e g i o n "A"
0 - i n i t i a l c o n d i t i o n s e x i s t i n g i n r e g i o n "A".
I n w r i t i n g Equation ( D . l ) , i t i s assumed t h a t t h e g a s i n r e g i o n "A"
i s c o m p l e t e l y m i x e d s o t h a t t h e t r a c e r g a s c o n c e n t r a t i o n is
uniform throughout. I f , as i n t h i s case, t h e f l o w rates are
t a k e n a s c o n s t a n t w i t h respect t o t i m e and i f it i s assumed
t h a t CI i s c o n s t a n t , t h e n t h e s o l u t i o n of E q u a t i o n (D.l) is
j u s t g i v e n by
c(t) = CI - (CI - co) { r+yqT-\ 1
_.
(D.2)
vo
86
@
.
wI
.
wI
wL
Figure D.1.
=
=
-
'
I
-I--
False A n t r i m
Antrim
A i r flow i n t o p r o d u c t i o n well f r o m a n t r i m or
false a n t r i m region
A i r flow i n t o cased p o r t i o n of well
Model u s e d f o r e v a l u a t i o n of t r a c e r conc
i n air entering p r o d u c t i o n w e l l .
87
Equation ( D . 3 ) i s v a l i d i n t h e s i t u a t i o n where t h e p r o d u c t i o n
w e l l i s o p e n so t h e r e e x i s t s n o n e t f l o w i n t o or o u t of r e g i o n
A. These e q u a t i o n s i n d i c a t e t h e e x p e c t e d tracer g a s c o n c e n t r a -
t i o n s m e a s u r e d a t t h e c a p i l l a r y t u b e i n t h e case w h e r e t h e r e is
no d i s p e r s i o n w i t h i n t h e s y s t e m .
T h e r e e x i s t s a t i m e d e l a y b e t w e e n t h e moment a t r a c e r
gas f i r s t e n t e r s a p r o d u c t i o n w e l l and t h e t i m e i t i s d e t e c t e d
a t t h e c a p i l l a r y tube. If t h e t r a c e r gas uniformly e n t e r s t h e
p r o d u c t i o n w e l l t h i s t i m e p e r i o d i s u s u a l l y small (i.e., cO.5
h o u r f o r W e l l # 3 ) . However, i f t h e t r a c e r g a s were t o e n t e r
t h e production w e l l a t t h e t o p of t h e b r i n e l e v e l only, t h e
t i m e p e r i o d b e t w e e n i t s f i r s t arrLl/..al a n d i t s d e t e c t i o n c o u l d
be s i g n i f i c a n t . The a r r i v a l to d e t e c t i o n t i m e p e r i o d i s j u s t
t h a t t i m e r e q u i r e d for t h e i n c o m i n g flow to d i s p l a c e all t h e
g a s b e t w e e n t h e t o p of t h e b r i n e a n d t h e bottom o f t h e c a p i l l a r y
tube. T h i s t i m e i s d e f i n e d by
V
t = -C
where
vc
- t h e v o l u m e ( s c f ) of g a s i n t h e w e l l b o r e b e t w e e n
t h e b r i n e and c a p i l l a r y a t t h e t i m e tracer is
first detected a t t h e capillary.
W e l l # 3 , b e k a u s e of i t s l a r g e volume a n d r e l a t i v e l y h i g h
t e s t p r e s s u r e s , p r o v i d e s a good e x a m p l e f o r e x a m i n i n g t h e s e
e f f e c t s . The maximum p o s s i b l e t r a n s i t t i m e s r e q u i r e d f o r g a s
i n j e c t e d i n t o t h i s w e l l , a t t h e t o p of t h e b r i n e l e v e l , t o
reach t h e c a p i l l a r y tube are 5.5, 7 . 7 , 3 . 6 and 5 . 2 hours for t h e
a r r i v a l of t h e f i r s t S F 6 , C318, 13B1 a n d s e c o n d SF6 p u l s e s ,
respectively. T h e s e t i m e s c a n n o t be c o n s i s t e n t l y i n t e r p r e t e d
i n terms o f t h e m e a s u r e d c r o s s - h o l e f l o w i n t e r v a l s . I t was
t h e r e f o r e assumed t h e f l o w e n t e r e d t h e w e l l u n i f o r m l y a n d t h a t
measured t i m e i n t e r v a l s r e p r e s e n t t h e t i m e r e q u i r e d f o r t h e
tracer g a s t o f l o w from t h e i n j e c t i o n w e l l t o t h e p r o d u c t i o n w e 1
88
When t h e p r o d u c t i o n w e l l is s h u t - i n , the pressure t i m e
h i s t o r y c a n be u s e d t o d e t e r m i n e e i t h e r t h e f l o w i n t o t h e w e l l ,
o u t o f t h e w e l l , or if t h e f l a w i s known, t h e a c t u a l w e l l v o l -
ume. Assuming i s o t h e r m a l c o n d i t i o n s , t h e r e l a t i o n b e t w e e n t h e
w e l l in-flow or out-flow and t h e c o r r e s p o n d i n g p r e s s u r e change
is g i v e n i n E q u a t i o n ( D . 5 )
B
' dP (D.5 )
w = p dt
where P i s t h e w e l l p r e s s u r e
