Advanced technology makes new use of age-old drilling fluid agent by oym20829

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									DOWNHOLE FLUIDS




                       Barite reserves from mines like this one in Battle Mountain, Nev., which produced its 8 millionth ton in
                       2003, could be extended significantly with a switch to the alternate 4.1 sg grade.


           Advanced technology makes
        new use of age-old drilling fluid agent
     Days of using drilling-grade barite just to increase fluid density is changing

     THOUGH ALWAYS FRAUGHT                              By Doug Oakley, Daryl Cullum, M-I SWACO       sure spikes, while possibly improving
     with limitations, barite remains the time-                                                       data transmission for downhole tools.
     honored weighting agent of choice for              ing agents with the base oils comprising      Improved hole cleaning combined with
     drilling fluids. However, highly complex           non-aqueous drilling fluids have again        their ability to bridge and plug fractures
     well geometries, tightening supplies and           challenged long-held conventional wis-        and permeable formations and reduce
     soaring commodity prices are driving               dom on the rheology of weighted fluid         barite sag significantly make these fluids
     modifications to a product that has been           systems.                                      well-suited for technically demanding
     a staple of the oilfield for 8 decades.                                                          applications such as the deepwater,
                                                        And, in a related development, a varia-       ultra-extended reach wells and the
     Since the petroleum industry’s pioneer-            tion of long-standing density specifica-      advancing development of mature reser-
     ing days, barium sulfate essentially had           tions for drilling-grade barite promises      voirs.
     been used with no adjustments to its               to extend dramatically the worldwide
     natural density or particle size. However,         supply of accessible and economical           Today, approximately 45% of the world’s
     the recent development of micronized               reserves.                                     oil production comes from reservoirs
     barite for oil- and water-based drill-                                                           that have passed their peak production,
     ing and completion fluids has opened               The most recent technical advancement         thus generating increased interest in
     the door for expanded applications of              in hydraulic modeling cleared the way         ERD, horizontal, through tubing and
     a material that has been the industry              for the development of ultra-thin weight-     slim-hole drilling techniques to access
     standard for some 85 years. Even more              ed fluids that, in the field, have proven     reserves at the extremities of existing
     recently, breakthroughs in the ability to          their capacity for lowering equivalent        production zones.
     model and manage the physio-chemical               circulating densities (ECD) significantly,
                                                        reducing surge and swab pressures,            Fluids with flat, low rheological values
     interactions of extremely small weight-
                                                        increasing flow rates and reducing pres-      over extremes of temperature and pres-

96     May/June 2007                                 D R I L L I N G CONTRACTOR
                                                                                                                                                        DOWNHOLE FLUIDS

sure are engineered to deliver perfor-
mance in an optimized operating win-
                                                                         Property                    Procedure                   Spec                             Test Result
dow, which is constructed from hydraulic        Density                                              Sec. 7.3        4.20 s.g. min                     4.12 s.g.              Fail
modeling of the specific details of each
                                                Water-Soluble
project using fluid parameters estab-
lished in the lab and offset field data.
                                                Alkaline Earth                                       Sec. 7.6        250 mg/kg max                     26 mg/kg               Pass
                                                Metals, as Calcium
CHALLENGING LONG-HELD                           Residue >75 µm                                       Sec. 7.9        3.0 wt% max                       1.76 wt%               Pass
CONVENTION
The first attempts at well control with         Particles <6 µm
drilling fluids came in the early 1920s         in equivalent                                        Sec. 7.12       30 wt% max                        24.95%                 Pass
during the wildcatting days in Texas.           spherical diameter
With the shallow and vertical wells being
drilled at the time, drilling fluids com-      Above: Properties of 4.1-sg barite compared with the API-specified 4.2 sg grade.
prised no more than simple mixtures of         Below: Rheological comparison of conventionally weighted drilling fluids with systems
water and clay. It was inevitable that as      incorporating the new micronized weighting technology.
wells were drilled deeper, well control
problems would became more and more                            100
                                                                         MUD WEIGHT: 12.8 to 13.0 lb/gal
prevalent.                                                      90
                                                                         OWR 80:20


Obviously, many drillers of that era                            80
                                                                                                                                         CONVENTIONAL
                                                                                                                                         OIL-BASE DRILLING
thought that increasing the weight of the                                                                                                FLUIDS
drilling fluid would help counter down-                         70

hole pressures, but at the time the only
                                                                60
way to increase density was to rely on
                                                Fann Reading




                                                                                                                                       Plastic Viscosity=35 cps
the accumulation of drilled solids. The                         50
problem was, doing so often made the                                                                                                                          Micronized Weighting
fluid too thick for drilling purposes.                          40                                                                                            Agent Technology
                                                                                                                                         Plastic Viscosity=25 cps
The original patent for barite as a weight                      30

control agent for drilling fluid was filed                                Yield Point = 17 lb/100sq.ft
                                                                20
in 1924, but it was believed to have been
first used around 1922, and it did not                          10
take long for its benefits to be realized.                                   Yield Point = 7 lb/100sq.ft
This is a material that is chemically                            0
                                                                     0                   100               200             300               400                    500              600
inert, has a naturally high density of 4.2                                                                       Fann 35 Rheometer Speed (rpm)
specific gravity (sg), is non-abrasive, soft
and easily ground, accessible and rela-
tively inexpensive.                            Since the early days, API drilling-grade                                      and there is growing concern that the
                                               barite with the adopted density and par-                                      quality, economic viability and acces-
As early as 1939, specifications for           ticle size specifications has always been                                     sible supplies of ore are depleting rap-
drilling-grade barite were already in          the preferred product for adjusting the                                       idly. This is particularly true in North
place both for density (>4.25 g/cm3)           weight of drilling fluids.                                                    America, where significant imports from
and particle size, which stipulated that                                                                                     China and other global producers are
98.75% should pass through a 300-mesh          Arguably, for the horizontal, small bore,                                     required to meet high demands. With
(45-micron equivalent) shaker screen.          extended long-reach, and other chal-                                          increasing demand and smaller reserves,
Since then, several refinements to the         lenging drilling techniques employed                                          the price of 4.2 sg barite produced out-
specification have been made through           routinely today, many consider API spec-                                      side the US, particularly those from
the American Petroleum Institute (API)         ification barite a troublesome product                                        perennial exporter China — where use
to the point that today, >4.20 g/cm3 has       that oftentimes is viewed as a necessary                                      internally is crimping reserves further
been adopted as the specified density.         evil. Other than the density require-                                         — has doubled over the last couple of
Moreover, API specifications provide that      ments, API specification barite provides                                      years. China currently produces between
the maximum size particle retained on          little value to a drilling fluid. On the                                      45% and 48% of the worldwide total of
a 75-micron screen should be 3%, and           contrary, barite always has been prone                                        available barite.
particles less than 6 micron equivalent        to sag, thereby requiring the addition of
spherical diameter should be no more           viscosifiers and other gellants to keep it                                    Clearly, without significant worldwide
than 30%. The upper and lower particle         suspended. In addition, the drilled solids                                    investment to locate and produce mate-
sizes largely reflect the performance in       that are inevitably incorporated into a                                       rial to meet the API 4.2 sg and con-
a drilling fluid. Should the particle size     drilling fluid quickly assume the particle                                    taminant specifications, it is likely that
be too coarse, barite is likely to segre-      size of API specification barite, resulting                                   producers of drilling grade barite will be
gate from the fluid in the surface mixing      in reduced, or poor, solids separation                                        unable to supply the industry with low-
tanks and from the fluid in the wellbore.      efficiency by the shakers and centri-                                         cost product in just a few years.
                                               fuges.
Of the 7.6 million tons of barite currently                                                                                  The complex geometries being drilled
produced annually, approximately 6.7           Furthermore, supplies of 4.2 sg barite                                        today and the likely future shortages
million tons are used in drilling fluids.      are not as plentiful as they once were,                                       of barite have caused many to question

                                              D R I L L I N G CONTRACTOR                                                                                                  May/June 2007    97
DOWNHOLE FLUIDS

     whether strict adherence to the API
     specification for particle size and density
     is necessary in today’s drilling climate.

     An extensive analysis has uncovered an
     alternate grade of drilling-grade barite,
     which, other than its density, can be
     produced with the same quality, envi-
     ronmental and specification standards
     as 4.2 sg ore. In addition, 4.1 sg barite
     production will prevent rapid depletion
     of existing reserves and minimize ongo-
     ing and expected increases in end-user
     costs.

     One report suggests that if 4.20 sg
     remains the only acceptable grade,
     the reserve depletions of leading US
     producer Nevada alone will require an
     industrywide investment of US $100
     million to ensure 20 more years of sup-
     ply. Conversely, widespread use of the
     alternate 4.10 sg material and a modest
     industry investment in the range of US
     $7.5 million over the next 2 to 4 years              10 µm
     would allow Nevada reserves to handle
     today’s demand load into at least 2016.        How fine are micronized barite particles? About 1/8 the size of the human blood cell.
     Technically, the only property of the 4.1      material will consistently maintain this           ing the 4.1 sg barite with the current 4.2
     sg grade that does not meet the current        level of quality throughout its lifetime.          sg standard in several commonly used
     specification is density. All other proper-                                                       drilling fluid formulations at varying
     ties fall well within the current specifi-     In assessing performance, a series of              densities. The formulations included a
     cation, and investigations confirm the         laboratory tests were conducted compar-




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98     May/June 2007                               D R I L L I N G CONTRACTOR
                                                                                                             DOWNHOLE FLUIDS

weighted “pad” mud normally employed          many fines in the fluid will increase rhe-   been shown to reduce torque by as much
in deepwater surface-hole applications,       ology, which is particularly problematic     as 25%, allowing for greater horsepower
conventional clay-based lignosulfonate        when drilling complex well geometries.       at the bit, faster drilling rates and less
fluids, and invert-emulsion system and        However, extensive research and field        drag.
2 aqueous, non-dispersed polymer flu-         experience has shown that reducing
ids. The testing parameters compared          particle diameter by 100 reduces set-        The micronized barite technology has
similarly treated fluids before and after     tling, or sag, by a factor of 10,000. With   been used successfully in the North
rolling heat aging tests. The intent was      this development, barite is ground from      Sea, Gulf of Mexico and elsewhere in a
to determine the effects on viscosity by      an average of 75 to less than 5 microns,     variety of technically demanding appli-
comparing differences between plastic         with an average size of 1 to 3 microns, or   cations. In the Norwegian sector of the
viscosity and yield point. Several for-       about 1/8 the size of a human blood cell.    North Sea and the Gulf of Mexico, the
mulations were contaminated with clay                                                      technology has been employed widely for
solids to ascertain differences in proper-    In field applications worldwide, in some     the development of maturing reservoirs
ties or performance when the fluids were      of the most challenging well trajectories,   where such criteria as ECD manage-
subjected to drill solids contamination.      the technology delivers benefits never       ment, hole cleaning, sag, downhole tool
Results showed performance between            before observed with conventionally          performance, quality cement jobs and
the 2 grades were either identical or         weighted fluids. The system has been         wellbore productivity are paramount.
exhibited negligible differences.             shown to eliminate or minimize dra-
                                              matically the occurrence of sag, improve     In one Norwegian well, the system was
While wide acceptance of lower-density        wellbore hydraulics and reduce drilling      used in a 3,189-ft 5 7/8-in. TTRD reservoir
barite would go a long way to miti-           risk. Moreover, its lower rheological pro-   section drilled from 13,441 ft with a max-
gate the supply predicament, patented         file effectively reduces ECDs for drilling   imum inclination of 78° and fluid density
advancements in colloidal barite has          in narrow mud-weight windows. Owing          of 13.2 lb/gal. The original producing
been shown to alleviate settling and          to higher permissible pump rates and         well had been plugged and abandoned
other interminable problems inherent          non-laminar flow regimes, fluids for-        in the 7-in. tubing, thus requiring a new
with barite-weighted fluids.                  mulated with the micronized weighting        well to be drilled out into a new forma-
                                              agent technology enhance bit hydrau-         tion from the existing completion to
                                                                                           access known pools of hydrocarbons.
AN OLD PRODUCT                                lics, thus improving hole cleaning while
                                              increasing rates of penetration and pipe-    Drilling fluids using the micronized
Conventional wisdom holds that micron-        running and casing speeds. Compared
size particles are detrimental to drilling                                                 barite system were engineered with
                                              with offset wells drilled with convention-   characteristically low fluid rheologies (3
fluids. It has long been believed that too    al weighted fluids, the system also has      rpm reading of 2-3 Fann Units) to con-




                                             D R I L L I N G CONTRACTOR                                                  May/June 2007   99
DOWNHOLE FLUIDS

   trol ECD without risking barite settle-
                                                                                4,500,000
   ment at this critical mud weight and to                                                                                                                                                     1992
   deliver between 135 and 185 gal/min to                                       4,000,000
                                                                                                                                                                                               2003

   the geosteering tool. The section was                                                                                                                                                       2005

   completed trouble-free at an average                                         3,500,000

   ROP of 52.48 to 59.04 ft/hr, which was
                                                                                3,000,000
   10% above the planned program of 49.2




                                                  Million Tonnes/yr
   ft/hr. Overall fluid costs were under bud-                                   2,500,000
   get by 18%.
                                                                                2,000,000
   Following modeling with a proprietary                                                                                                                                              GERMANY
                                                                                                                                                                                       FRANCE
                                                                                                                                                                                                                BRAZIL
                                                                                                                                                                                                                RUSSIA

   hydraulic software package, an ultra-                                        1,500,000                                                                                                 UK
                                                                                                                                                                                      BULGARIA
                                                                                                                                                                                                               ALGERIA
                                                                                                                                                                                                               VIETNAM
   thin version of the micronized barite                                                                                                                                              ROMANIA
                                                                                                                                                                                         EIRE
                                                                                                                                                                                                             NORTH KOREA

                                                                                1,000,000
   technology was used in the Gulf of
   Mexico, where it has been employed                                            500,000
   successfully in ERD, depleted sand and
   managed pressure drilling ERD appli-                                                 -

   cations. In each, key properties of the




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   system were low sag tendency, ECD and




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   gel strengths.
                                                 Above: Historical production trends of 4.2 sg barite by country. Below: Percent by
   The system was introduced to the Gulf
   as an alternative to a conventional syn-      volume solids of 10.0 lb/gal fluids using 4.20, 4.10 and 4.00 sg barite.
   thetic-base system. It was first used in a
   9 ¼-in. production interval of a 31,500-ft                                    40%
   MD well with 25,000 ft of horizontal dis-                                                          Percent Solids Added 4.20 S.G. Barite
   placement. In this application, the sys-                                      35%
                                                                                                      Percent Solids Added 4.10 S.G. Barite

   tem reduced the losses that could occur                                                            Percent Solids Added 4.00 S.G. Barite


   had ECD exceeded the fracture gradient,                                       30%
   while also eliminating sag, reducing well-
                                                   Percent Solids from Barite




   control issues. The system also reduced                                       25%
   surge/swab pressures, while delivering
   lower pressure drops. The higher annu-                                        20%
   lar velocities, turbulent flow potential
   and easier cuttings bed removal charac-                                       15%
   teristic of an ultra-thin fluid effectively
   cleaned the high-angle hole.                                                  10%


   The days where drilling-grade barite is                                         5%
   just used to increase fluid density are
   changing. Technological advances and                                            0%
   world supply of this crucial mineral for                                                      11               12                13                  14          15          16                17           18
   drilling is changing the manner in which                                                                                            Final Fluid Weight in lb/gallon
   this age-old drilling fluid agent is used.




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100 May/June 2007                               D R I L L I N G CONTRACTOR

								
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