Artificial Lift TECHNOLOGY FOCUS Artificial Lift There is by fdh56iuoui

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Artificial Lift

There is nothing wrong with change, if it is in the right direction.                        Shauna Noonan, SPE, is a Staff
—Winston Churchill                                                                          Production Engineer for ConocoPhillips
In the artificial-lift community, do we understand the current technology well              where she works as an artificial-lift
enough to know what improvements are needed? Are we advancing technology or                 specialist in the Completions and
just providing “band-aid” solutions because the root cause of failure is not under-         Production Technology group. Noonan’s
stood? Where does the industry need to focus effort—technology development or               responsibilities include development and
reduction of failures caused by poor design, installation, and operating practices?         validation of artificial-lift and comple-
  Questions such as these were the driving force behind two industry consortiums
to develop databases to collect thousands of electrical-submersible-pump (ESP) and          tion systems for thermal applications
progressing-cavity-pump (PCP) installation and failure records for performance              and improving artificial-lift reliability.
analysis and benchmarking (www.esprifts.com and www.pcprifts.com, respec-                   She has worked on artificial-lift proj-
tively). Data collection and its analysis from the databases have become very valu-         ects worldwide at ConocoPhillips, and
able in understanding the performance and reliability of these lift systems. Some           previously at Chevron, for more than
of the lessons learned from the PCP consortium will be presented at the 2010 SPE
                                                                                            17 years. Noonan has chaired industry
Progressing Cavity Pumps Conference (PCPC) to be held in Edmonton, Alberta,
Canada, in September.                                                                       forums and committees and authored
  Both the PCP and ESP industries have been impaired by a lack of standardiza-              or coauthored numerous papers on
tion, especially in the areas of equipment rating, testing, and nomenclature. In            artificial lift. She serves as a member
2009, the International Organization for Standardization (ISO) published a revised          of the SPE Production and Operations
ISO 15136-1 as an international standard for PCP equipment, and a session on                Advisory Committee, as an Associate
its use will be presented at the 2010 SPE PCPC. Currently ISO 15551-1, which is
expected to be the new international standard for ESP systems, is in development            Editor for SPE Prod & Oper, a mem-
and will, undoubtedly, be a hot topic for discussion at the 2011 SPE ESP Workshop           ber of the JPT Editorial Committee,
in Texas in April.                                                                          and she will cochair the 2010 SPE
  The reliability-improvement consortiums and the development of new interna-               PCPC. Noonan began her career with
tional standards are helping to define where we are today as an industry and provide        Chevron Canada Resources and holds a
clear direction for technology advancement.
                                                                                            BS degree in petroleum engineering from
  The three artificial-lift papers featured in this section contain unique solutions that
may become starting points from which other developments may evolve: The geared             the University of Alberta.
centrifugal pump has a distinctive downhole-transmission assembly that offers an
opportunity for other pump configurations to be driven by a rod string, a method to
use gas lift above and below a packer in a single completion with long perforation
intervals might expand to areas other than unloading tight gas wells, and the use of
hybrid data-evaluation models to visualize and analyze production information better
may become an essential tool for artificial-lift selection and optimization. The papers
selected for additional reading also contain innovative artificial-lift solutions. JPT

                      Artificial Lift additional reading
                available at OnePetro: www.onepetro.org
SPE 124926 • “Real-Time Diagnostics of Gas Lift Systems Using Intelligent
Agents: A Case Study” by G. Stephenson, SPE, Occidental Petroleum, et al. (See
JPT, May 2010, page 55, and SPE Prod & Oper, February 2010, page 111.)
SPE 124646 • “Application of Beam-Pumping Wells’ Energy-Saving Rebuilding
Techniques in Daqing Oil Field” by Wang Fengshan, SPE, Daqing Oilfield Co., et al.
SPE 124515 • “Plunger-Lift Modeling Toward Efficient Liquid Unloading in Gas
Wells” by G. Chava, SPE, Texas A&M University (now at Chevron), et al. (See SPE
Proj Fac & Const, March 2010, page 38.)

50                                                                                                                JPT • JULY 2010
ARTIFICIAL LIFT




The Geared Centrifugal Pump:
A New High-Volume Lift System

The geared centrifugal pump (GCP) is          of the special controls or transformers     mize the lift merely by changing the
a high-volume artificial-lift system con-     necessary for high-voltage ESP motors.      size of the motor sheave on the drive
sisting of a progressing-cavity-pump          The rotating rod string transmits power     head. This capability allows the use of
(PCP) -style rotating rod string driving a    downhole with low power losses. This        a portable VSD to determine the opti-
bottom-intake electrical-submersible-         system combines the highly efficient        mum pump speed on the basis of the
pump (ESP) -style multistage centrifugal      GCP transmission assembly with a            productivity of the well, and then size
pump by use of a downhole speed-              modern ESP pump. This combination           the motor sheave to give that optimum
increasing transmission. The heart of         results in a system with lift efficiency    speed. This capability gives the opera-
the system is the unique transmission         greater than 50%. Because all of the        tional flexibility of having a permanent
that uses a novel gearing configuration       downhole components of the GCP are          VSD without the associated cost.
that allows high torque and power. The        mechanical, the design is adaptable            If, however, the sizing of an ESP is
GCP provides the high-volume lift of an       to very-high-temperature applications       found to be less than perfect, optimiz-
ESP but with better gas handling, sim-        such as steam-assisted gravity-drainage     ing lift by changing the pump speed
pler operation, and lower capital and         (SAGD) projects.                            requires a permanent-VSD installation,
operating costs.                                                                          and it also may require changing the
                                              GCP Components                              downhole motor voltage to optimize
Introduction                                  Drive Head. The GCP uses the same           the power requirement. Optimizing a
The GCP is an artificial-lift system con-     drive system as a PCP system. A surface     GCP to maximize the productivity of a
sisting of the rotating-rod-string drive of   drive head turns a rotating rod string      well should be simpler and less expen-
a PCP, driving the multistage centrifugal     that drives the downhole assembly.          sive than for an ESP.
pump of an ESP by a downhole speed-           The only difference between a PCP
increasing transmission. The transmis-        drive head and one built for the GCP        GCP Transmission. The heart of the
sion is required to increase the relatively   is the load-capacity requirements of the    GCP is the speed-increasing transmis-
slow rotational speed of the PCP rod          thrust bearing carrying the rod load. In    sion. Transmissions that have con-
string, typically less than 500 rev/min,      a PCP drive head, the thrust bearing        straints on the size of the gears because
up to the 3,500-rev/min operational           must carry the weight of the rod string     of space limitations, such as the inside
speed of the centrifugal pump.                as well as the fluid load. Because the      diameter of oilfield casing, but are
   The GCP was developed as an artifi-        rod string of the GCP does not carry        nonetheless required to transmit signif-
cial-lift system to provide the high-vol-     any fluid load, the thrust bearing in       icant power present a difficult problem.
ume lift of an ESP without the expen-         the GCP drive head can have a cor-          The most obvious potential solution is
sive and troublesome downhole electric        respondingly lower capacity. Another        to use a planetary or related epicyclic
motor and cable of the ESP system. The        characteristic of both PCP and GCP          configuration, which has a high power
GCP uses efficient and relatively inex-       drive heads is prime-mover flexibility.     density and concentric input and out-
pensive industrial electric motors in         Although the majority of well locations     put. However, the small diameters of
the surface drive head, requiring none        have electric power, the GCP can be         oilfield casing severely limit even the
                                              powered by an internal-combustion           power of a planetary transmission—a
This article, written by Assistant Tech-      engine, a hydraulic motor, or an elec-      situation worsened by the fact that
nology Editor Karen Bybee, contains           tric motor.                                 significant annular space must be pro-
highlights of paper SPE 123938, “The             One of the features of the GCP           vided between the transmission case
Geared Centrifugal Pump: A New High-          drive head is the ability to change the     and the outer pressure housing as a
Volume Lift System,” by J.C. Patterson,       pump rotational speed without having        produced-fluid flow channel, further
SPE, ConocoPhillips; W.B. Morrow, SPE,        to install a permanent variable-speed       reducing the already small gearbox
Harrier Technologies.; and M.R. Berry,        drive (VSD). The typical drive head         diameter. The problem is that an epicy-
SPE, Mike Berry Consulting, originally        uses a belt-drive speed reducer between     clic transmission has only one gear set
prepared for the 2009 SPE Annual              the prime mover and the rod string. If      to handle all the input, and there just
Technical Conference and Exhibition,          the sizing of the GCP installed in a well   is not sufficient steel in the single gear
New Orleans, 4–7 October. The paper           turns out to be less than optimum, the      set in these small diameters to handle
has not been peer reviewed.                   pump speed can be adjusted to opti-         significant torque and power.

         For a limited time, the full-length paper is available free to SPE members at www.spe.org/jpt.

JPT • JULY 2010                                                                                                                 51
                                                                                          the D-tubes filled with the relative
                                                                                          cool produced well fluid. This close
                                                                                          proximity allows rapid and effective
                                                                                          dissipation of the heat generated in the
                                                                                          gear meshes and bearings. Keeping the
                                                                                          gear train, and hence the lubricating
                                                                                          oil, cool is critical to transmission life.
Fig. 1—Schematic of PHG gear train after load balance is achieved.
                                                                                          Field Trial
                                                                                          The first field trial of a GCP was per-
   One potential way to obtain more          ing but varying tooth loads, depending       formed in a west Texas well former-
gear sets and hence more steel in the        upon the relative and uneven timing          ly equipped with an ESP. The well
gear train is to use a parallel-shaft        of each gear. The gears that bear the        had been producing approximately
configuration, with multiple gears on        higher loads push axially more strongly      1,300 BFPD with a 98% water cut and a
a common shaft. Although this option         than their neighbor gear, moving away        very low gas rate from 4,600 ft when it
is appealing in concept, it has proved,      from engagement, while at the same           was converted to GCP lift. The princi-
in the past, to be impractical because       time pushing those neighbor gears into       pal purposes of the conversion were to
of the difficulty in achieving load shar-    more engagement. This process contin-        understand the installation and opera-
ing among the multiple gears. That is,       ues among all the gear pairs until the       tional issues of a GCP in an actual oil
because of manufacturing tolerances,         axial forces are opposite and equal, and     well, determine the “real-world” effi-
the multiple gears are not likely to be      no further lateral movement occurs.          ciency of this new artificial-lift system,
aligned perfectly and do not all engage      Because the axial force of a helical gear    and test some of the features unique to
simultaneously. The misalignment             is proportional to the torque load on        the high-temperature GCP.
causes the gears to engage unevenly,         the gear, when axial forces among the           The well, a producer in a carbonate
resulting in some of them being loaded       gears are balanced, gear torsional load-     waterflood, was chosen because it has
more heavily than they are designed          ing also is balanced.                        7-in. casing through the productive
for, causing premature failure as a             Because multiple gears can be mount-      interval and it has sufficient total-fluid
result of excessive load or wear.            ed on a common shaft, and load sharing       productivity to test the operational lift
                                             ensured, the capacity of a PHG transmis-     capacity of the GCP. The GCP installed
Paired Helical Gearing (PHG). The            sion is not limited by gear strength or      in the well is a normal-temperature
solution to this problem is a new gear-      wear issues but by the ultimate strength     version of the 100-hp high-tempera-
ing configuration termed PHG. A PHG          of the input shaft—a much less restric-      ture model being planned for use in a
gear train consists of pairs of heli-        tive criterion. If a more powerful trans-    SAGD project in Alberta and, hence, is
cally cut gears arranged along common        mission is desired, all that is required     designed for the 7-in. or larger casing
shafts. Each half of the pair is cut in      is the addition of more pairs of gears       used in that project.
the opposite sense, so they look like        until the input-shaft strength is reached.      The unit ran for 4 weeks before fail-
herringbone gears, except that the two       Little additional design work is needed      ing as a result of rod-coupling fatigue
halves are not attached and are free to      to increase the capacity of the transmis-    at the top of the stab-in connector.
move axially relative to one another.        sions significantly, and the incremental     The rod-connector coupling was rede-
The shaft is splined, as are the gears, so   manufacturing costs are minimal.             signed, and the well was put back on
that the gears are free to move laterally       The ability to add pairs of gears as      production but went down after 2 more
along the shaft, but can drive the shaft     needed also has profound effects on          weeks because of a faulty weld in one
or be driven by it. The basic principle      bearing issues. Bearing life and capacity    of the D-tubes. The bad weld allowed
that results in load sharing in a PHG        frequently are the limitation of conven-     water into the transmission, resulting
gear train is that helical gears exert an    tional transmissions, particularly epicy-    in multiple bearing failures. Tear down
axial force that is proportional to their    clic gear trains where the heavily load-     of the entire assembly showed that
radial, or torque, load. This axial force    ed planet gear bearings are the Achilles     the seals and compensator operated as
is in a direction that would move the        heel of the designs. The PHG allows          designed, and that the transmission was
gear away from engagement were the           the addition of pairs of gears solely to     showing normal wear when the water
gear free to move axially on its shaft.      increase bearing capacity and life.          contamination caused bearing failure.
Conversely, if the gear were pushed axi-        The PHG layout allows easy cooling           During the 6 weeks of operation, the
ally in the opposite direction, the gear     of the gear train. Planetary transmis-       performance of this first installation
would move into greater engagement.          sions, with the heavily loaded planet        of a GCP went as might be expected.
   If a load were imposed on such            gears “buried” deep inside the gearbox       The construction flaw in the D-tube
a gear train, the first thing to hap-        and shrouded by the planet carrier and       was disappointing, but no fundamen-
pen, before any significant rotation         annulus gear, have problems with cool-       tal design problems were discovered.
occurred in either shaft, would be the       ing. With the parallel-shaft configura-      Modifications to the prototype D-tube
gears reacting to the tooth loads and        tion of the PHG transmissions, all the       construction have been made, which
immediately moving axially along their       gears and bearings are in close proxim-      should minimize this problem with
respective shafts until they bumped          ity to the external cooling medium—in        future prototypes. Production GCP
into one another (Fig. 1). At this point,    the case of the GCP, the lubricating         transmissions will most likely use
the gears would begin to bear increas-       oil the gear train is immersed in and        shaped seamless tubes.               JPT




52                                                                                                                JPT • JULY 2010
ARTIFICIAL LIFT




Annular-Velocity Enhancement With Gas
Lift as a Deliquefication Method

It is common practice in the industry         pumps, electrical submersible pumps,        the formation below the packer is up
to complete multiple reservoirs in a          and progressing-cavity pumps). Each         the tubing/casing annulus. To lift the
single wellbore to establish commercial       method has drawbacks when it comes          liquid from the wellbore effectively, the
production rates from tight gas comple-       to deliquefying wells with long comple-     tubing must be sized such that criti-
tions. In some cases, these zones are         tion intervals. Effective liquid removal    cal velocity in the annulus is approxi-
separated vertically by several hundred       can improve overall well performance        mately the same as the critical velocity
to more than 1,000 ft. The deliquefica-       significantly. However, an effective sys-   in the tubing above the packer. This is
tion of these completions is one of the       tem cannot ignore the potential pres-       accomplished either by running larger
most challenging problems facing our          ence of a static liquid column. Current     tubing below the packer or by wrapping
industry. Many of the deliquefication         completion technology has been found        the tubing below the packer externally
methods currently being used are effec-       to have limited effectiveness when          with fiberglass to the desired outside
tive over only a portion of the wellbore.     long productive intervals are involved.     diameter (OD). To obtain maximum
                                              Therefore, a modified continuous-flow       lift, the tubing below the packer is run
Introduction                                  gas lift system is proposed that includes   to a point below the lowermost perfora-
It is common practice to complete             a packer and crossover system and that      tion in the well. A gas lift orifice with a
tight gas wells with the tubing tail          allows for gas lifting the well below the   back check is installed at the bottom of
above the bottom perforation. This            bottom perforation. The details of this     the string as the planned operating gas-
completion practice allows static liquid      completion process and its field appli-     injection point.
to stand across the lower set of perfo-       cations are discussed in the body of the       The critical velocity for the casing/
rations. Static liquid standing across        full-length paper.                          tubing annulus cross-sectional area was
the perforations promotes increased                                                       assumed to be 30 to 50% less than the
near-well liquid saturations through a        New Artificial-Lift System                  critical velocity in tubing with the same
process of spontaneous imbibition. The        An alternative type of lift system has      cross-sectional area. On the basis of this
imbibition process is a damage mecha-         been deployed to effectively deliquefy      assumption the recommended tubing
nism that can be present upon initial         wells completed over long intervals.        installation inside of 51/2-in., 17-lbm/
completion and can continue through-          The system is a modified continuous-        ft casing is 31/2-in. flush-joint tubing or
out the productive life of the well if        flow gas lift system that allows for        27/8-in. tubing externally wrapped with
allowed to form through ineffective           lifting intervals below a packer using      fiberglass to an OD of 4 in.
liquid-removal/completion practices.          side-pocket mandrels and wireline-
   There are a number of different meth-      retrievable gas lift valves both above      Below-Packer Annular Gas Lift With
ods currently in use for the deliquefi-       and below the packer. Lifting below the     Velocity Enhancement. Fig. 1 shows a
cation of gas wells. Some of the more         production packer allows the well to be     a normal annulus gas lift system above
common are plunger lift, chemical-foam        gas lifted below the bottom perforation,    the packer, where gas is injected down
lift, and conventional pumps (i.e., rod       which effectively addresses the static-     the annulus and then the gas crosses
                                              liquid-column issue. This is accom-         over and is injected below the packer
This article, written by Assistant Technol-   plished by installing a bypass access       through the tubing. This allows the
ogy Editor Karen Bybee, contains high-        mandrel immediately above the pack-         well to be lifted from the bottom of the
lights of paper SPE 130256, “Annular          er in the well. A wireline-retrievable      perforated interval. The increased OD
Velocity Enhancement With Gas Lift as a       crossover assembly is inserted into the     of the tubing increases fluid velocity in
Deliquification Method for Tight Gas          bypass access mandrel. This assembly        the annular area below the packer by
Wells With Long Completion Intervals,”        extends through the packer into a lower     reducing the cross-sectional flow area.
by S.A. Pohler, SPE, W.D. Holmes,             seal receptacle that is located below a
SPE, and S.A. Cox, SPE, Marathon Oil          slotted nipple. Side-pocket mandrels are    Crossover System. Fig. 2 shows how
Corporation, originally prepared for the      installed above and below the packer.       the gas is injected through the cross-
2010 SPE Unconventional Gas Con-              The gas lift valves installed above the     over system and then is injected down
ference, Pittsburgh, Pennsylvania, 23–25      packer are standard tubing-flow valves,     the inside of the larger tubing below
February. The paper has not been peer         while the gas lift valves below the pack-   the packer. Below the packer, pro-
reviewed.                                     er are casing-flow valves. The flow from    duction flows up the annulus, crosses

         For a limited time, the full-length paper is available free to SPE members at www.spe.org/jpt.

54                                                                                                                JPT • JULY 2010
                                               27/8-in. tubing




                                                                    Lift Gas                                        Production


Lift Gas                                         Production



Side pocket
gas lift                                     Larger OD tubing
mandrel




Fig. 1—Normal annular gas lift system.                             Fig. 2—Gas injected through the crossover system.

over at the packer, and flows up the         wells, the packer and the crossover are      The foam injection was unsuccessful in
tubing above the packer. The internal        set in the vertical section of the hole,     maintaining stable production from the
part of the crossover assembly is wire-      the tubing is run to the lowest point        well. The base decline for this well was
line retrievable, which allows wellbore      in the horizontal completion so that         35%/yr, established while the well was
access below the packer.                     gas can be injected to sweep the liquid      rod pumped. The gas lift installation
                                             from the horizontal section, and an          resulted in an initial rate of 500 Mscf/D
New-System Benefits                          orifice is run either at the end of the      and a stable decline of 11%/yr. The
The below-packer annular gas lift sys-       tubing or in the crossover assembly.         incremental recovery from the gas lift
tem with velocity enhancer makes             The system can be run in 41/2-in. and        system is estimated at 1.3 Bscf on the
it possible to produce zones several         larger casing sizes.                         basis of decline-curve projections.
thousand feet long. The system uses             To date, 16 systems have been run            The second example well is a hori-
standard wireline-retrievable gas lift       in east Texas; one of the systems            zontal completion producing from
valves below the packer and allows for       is in a horizontal well. The major-          the Pettet reservoir at approximately
running pressure/temperature memory          ity of the installations have been in        13,386 ft measured depth, with a hori-
tools below the packer. It also allows       wells equipped with 51/2-in. casing          zontal displacement of approximately
access to the wellbore below the perfo-      and 27/8-in. tubing above the packer.        4,400 ft. The well was completed with
rations and reduces the lift gas required    Incremental rate after the installation of   an uncemented liner and was fracture
to reach critical velocity. In addition to   the system has averaged approximately        stimulated. As a result of the lim-
deliquefying the completion effectively,     200 Mcf/D.                                   ited formation-flow capacity, the well
this system provides an excellent oppor-                                                  was unable to flow naturally at rates
tunity to chemically treat the entire        Field Application                            sufficient to unload the wellbore and
wellbore for corrosion. This can be          The first example well is producing          remained shut-in. During shut-in, the
accomplished by atomizing corrosion          from the Travis Peak reservoir from a        well would build pressure but it was
inhibitor into the gas-injection stream.     depth of approximately 9,600 ft. The         not able to be returned to production
The injected gas then will carry the         well is completed in six intervals, with     because of liquid loading. The decision
corrosion inhibitor through the entire       a vertical separation of 2,058 ft. A rod     was made to install tubing and gas lift
wellbore. The below-packer annular           pump was installed on the well at 1,600      in an attempt to return the well to pro-
gas lift system with velocity enhancer       days of production. After 2,400 days,        duction. As a result of this work, the
has minimal restrictions through the         the well was recompleted to add addi-        well currently is producing at a stable
system, and it removes more liquid and       tional zones to the well. The rod pump       rate of 180 Mscf/D.
results in increased production com-         was removed as part of this recomple-           The full-length paper contains well-
pared with conventional completions.         tion. Before the installation of the new     bore diagrams showing how the com-
   The system can be run both in verti-      gas lift system, the well was producing      pletion system works in vertical and
cal and horizontal wells. In horizontal      with foam injection down the casing.         horizontal wells.                   JPT



JPT • JULY 2010                                                                                                                55
ARTIFICIAL LIFT




Integrating Data Mining and Expert Knowledge
for an Artificial-Lift Advisory System

The full-length paper describes a new          tion with the asset team to ensure the        Current Situation. Under the current
workflow to accelerate and improve             validity and consistency of the system        working environment, two main situa-
decisions regarding where and when             recommendations. While the iterative          tions challenge the asset team:
to apply an artificial-lift system in fields   validation is necessary for the BBN              1. Analysis of the huge amount of
with a considerable number of active           setup, it also enables the asset team         data involves a significant time delay,
wells. The workflow deploys a hybrid           to review and visualize their complex         which leads to lost production because
combination of a user-driven expert            decision-making process thoroughly            of delayed well intervention (e.g.,
system and a data-driven knowledge-            and helps to define more-efficient            installing the right artificial-lift system
capturing system calibrated with his-          decision logic.                               in time).
torical data. The two systems interact            In parallel, a data-mining analysis           2. There is insufficient processed
to determine the right point in time           on historical data is performed to find       data to make an informed decision,
to support a particular well with an           the decision logic as it was applied          which means that the asset team initi-
artificial-lift system.                        in the field. The data-mining study           ates well interventions too early and
                                               incorporates operational data (e.g., tub-     hence blocks the intervention resourc-
Introduction                                   inghead pressures, line pressures, and        es for other wells that might require the
Typically, asset expertise is stored in        calculated gas rates), well-test data,        intervention investment sooner.
spreadsheets that define the limits for        and information from well-intervention           Currently, AIB has a contractual
condition parameters within which              reports. The objectives of the data-          scheme in which several service com-
a specific artificial-lift system needs        mining analysis are:                          panies participate by measuring well
to be installed. As a first step toward           • To identify patterns in operational      parameters in the field and creating
decision automation, these limits are          and well-test data that lead to the deci-     engineering analysis of candidates to
implemented in a rule-based reason-            sion of a new artificial-lift system.         install the most appropriate artificial-
ing system deploying if-then-else logic           • To identify potential correlations       lift system. Because of the large number
to automate the knowledge. After suc-          of well-intervention activity and incre-      of wells in the asset, the associated
cessful validation of the rule-based           mental production after intervention          capture of required measurements, and
approach, the information about the            to quantify the success of a specific         the distance to the location of interest,
limits and the combination and inter-          artificial-lift installation under specific   the existing analysis process was per-
action of the parameters is fed into a         conditions.                                   formed at an average rate of only two
Bayesian belief network (BBN) capable                                                        wells per week.
of performing a more robust reasoning          Case Study                                       The current strategy focuses on
process under uncertainty or miss-             Activo Integral Burgos (AIB) is a typi-       accelerating the quantity and improv-
ing parameters. The setup process of           cal example of a large gas field where        ing the quality of the recommenda-
the BBN requires frequent interac-             production declined as a result of gas-       tions at the well level that help increase
                                               loading backpressure and reduced              or at least maintain the production of
This article, written by Assistant Tech-       permeability in the target formation.         the current asset. The asset team wants
nology Editor Karen Bybee, contains            The fast decline of the gas wells             to take advantage of its investment in
highlights of paper SPE 128636, “Inte-         during their first year of production         the automation of current processes
grating Data Mining and Expert Knowl-          drove a change from a reactive to a           related to operational data storage and
edge for an Artificial Lift Advisory           proactive management approach to              engineering workflows, such as gas-
System,” by E. De la Vega,             G.      monitor the field and select candi-           rate estimation and event detection
Sandoval, and M. Garcia, SPE, Pemex,           dates for workovers and artificial-lift       and notifications.
and G. Nunez, SPE, A. Al-Kinani, SPE,          systems. However, the large number               An investigation of current condi-
R.W. Holy, SPE, H. Escalona, SPE, and          of wells in AIB (approximately 3,500          tions also shows that while all deci-
M. Mota, Schlumberger, originally pre-         active wells) and the fact that 95%           sions are made on the basis of field
pared for the 2010 SPE Intelligent Energy      of the data is obtained by manu-              data, analysis relies heavily on an
Conference and Exhibition, Utrecht, The        al surveillance suggest the need for          engineer’s experience and judgment.
Netherlands, 23–25 March. The paper            some level of automation to aid deci-         Engineers typically move from one job
has not been peer reviewed.                    sion making.                                  position to the next, and the arrival

         For a limited time, the full-length paper is available free to SPE members at www.spe.org/jpt.

JPT • JULY 2010                                                                                                                     57
        Gas Rate After (MMscf/D)              Gas Rate Before (MMscf/D)                Line Pressure Before (psi)                   Type Numeric ( )




 0.1 0.3 0.6 0.8 1.1 1.3 1.6 1.8 2.1 2.3   0.1 0.4 0.7 1.0 1.3 1.6 1.9 2.2 2.5 2.8   122 294 465 636 807 978 1,149          0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
      Wellhead Pressure After (psi)        Wellhead Pressure Before (psi)                 Liquid Level Before (ft)       Last Well-Test Gas Rate (MMscf/D)




  190 487 783 1,080 1,377 1,874 1,971      178 478 778 1,078 1,378 1,678 1,978       89   503 917 1,330 1,744 2,157 2,571 0.1 0.5 0.8 1.1 1.5 1.8 2.1 2.5 2.8 3.1

Last Well-Test Water Rate (STB/D)

                                                        Type Numeric
                                                        Red: AL System A
                                                        Green: AL System B
                                                        Blue: AL System C
  1     19 38   56 74 92 111 129 147

Fig. 1—SOM to investigate historical decision making regarding artificial-lift installations.


of new engineers makes knowledge                        expert-knowledge application and                       criteria. Additionally, the user-driven
transfer to those in charge of the                      reasoning analysis, and finally report-                expert system can be revised easily and
field additionally difficult. Therefore,                ing is implemented to run once a day.                  changes can be undertaken should the
the following main questions need to                    Results are presented to the produc-                   need arise (e.g., technical or economi-
be asked:                                               tion engineer in the form of a list in                 cal limitations).
   • How to capture the knowledge of                    which candidate wells are ranked by                      During the implementation of the
experienced personnel and make it                       priority of intervention according to                  user-driven expert system, two differ-
available to the whole organization?                    their critical condition. The engineer                 ent methods have been applied: (1) a
   • How to apply this knowledge                        then is empowered to initiate the nec-                 rule-based approach that can be con-
in a general and unbiased manner                        essary engineering workflows (e.g.,                    sidered deterministic because the out-
throughout the assets of the organiza-                  nodal analysis) more effectively and                   come is either “artificial lift=true” in
tion?                                                   make the final decision on how to                      case the input conditions are favorable
   • How to keep this knowledge                         distribute resources.                                  or “artificial lift=false” in case they
updated by use of new experience?                                                                              are not and (2) a stochastic approach
   The solution presented in the full-                  User-Driven Expert System                              implemented through a BBN in which
length paper is based on an expert                      The user-driven expert system is an                    the outcome is not just true or false
system and automated reasoning tools                    automated workflow that fully relies                   but a probability distribution denot-
that are able to capture and apply                      on the knowledge and experience of                     ing the “degree of applicability of an
knowledge and make it available to                      the engineer. The asset team has the                   artificial-lift system” that takes into
the whole organization. In general,                     ability to incorporate its complex busi-               account the uncertainty of a certain
the combination of these two tech-                      ness reasoning into surveillance rules                 decision or choice.
nology-based approaches enables the                     to detect potential artificial-lift candi-
asset team to process the field data                    dates. The advantage of this system                    Rule-Based Approach. The rule-based
and apply the knowledge system-                         is the trustworthiness and, most sig-                  approach consists of implementing the
atically at the field level, obtaining                  nificantly, the traceability of decisions              engineer’s reasoning into an automated
results faster and on time for all wells                leading to the artificial-lift candidates              routine comprising a sequence of if-
in the field and independently of                       detected by the system, because the                    then-else loops. In this way, complex
asset, well, or engineer. An automat-                   inference rules have been created in                   knowledge can be captured and used
ed workflow consisting of data cap-                     close cooperation with the asset engi-                 in real-time surveillance and detection
ture, data validation and processing,                   neers and fully reflect their provided                 workflows. These workflows can be


58                                                                                                                                           JPT • JULY 2010
                                                                                         SPE Bookstore
scheduled to run at any time and as             It can be seen in Fig. 1 that there      www.spe.org/store
often as desired, enabling immediate         is a distinction between when to use
detection when the conditions of a well      Method A (red) and when not to
indicate need of an artificial-lift system   (green or blue). Artificial Lift Method
and enabling early notification to the       A typically is applied for low- to very-
asset team and engineers.                    low-gas-rate wells with low pressures
                                             but with a moderately high static-
Data-Driven Expert System. Data-             liquid level in the well. However, it was
driven approaches are used widely            considerably more difficult to clearly
to reveal hidden information in large        identify the conditions under which                     NEW BOOK
data sets. Typically, in a brownfield        Method C was applied in the well to
with a large number of wells and             decrease the likelihood of liquid load-
a production history spanning many           ing in the well. The operating condi-
years or decades, the amount of data         tions that lead to the choice of Method
available overwhelms the convention-         C are very much like those of Method
al approach to data screening (e.g.,         B (higher gas rates, higher pressures).
spreadsheets or production plots). A            The data that were used to calibrate
data-driven approach allows the engi-        the SOM then were clustered to find
neer to visualize data in different con-     groups of similarly behaving wells.
texts to facilitate the analysis of cor-     The wells per cluster are selected by
relations and the process of knowledge       the clustering algorithm to minimize
discovery. The presented workflow            the variation of the individual items
applied an unsupervised clustering           (wells) in each cluster. Using the clus-
algorithm and a special visualization        tering information, the problem space
technique using Kohonen’s self-orga-         could be reduced from several hun-
nizing maps (SOMs)                           dred individual wells to five clusters      Transient Well Testing
                                             of similarly behaving wells. This gen-
SOMs. SOMs display multidimension-           eralization helps the asset team (and       Monograph Series, Vol. 23
al data sets in a 2D map. The SOM uses       the surveillance engineer) to classify      Medhat M. Kamal
the Euclidian distance between two           a well immediately according to its
points in the multidimensional space         production features (which are driving
as a measure of their similarity. The        the cluster number) rather than having      Transient well testing is one of the
more similar the measurement, the            to investigate all available production     most important diagnostic tools
closer the points are placed together in     information of a well before knowing        used by petroleum engineers to
the 2D projection—the “map.”                 how to classify it.                         characterize hydrocarbon assets
   In this work, SOMs have been applied                                                  and predict future performance.
to identify a pattern in the historical      Conclusions                                 This new monograph has the latest
decision making of the asset team.           After analyzing the implemented work-       reference information on designing,
The objective is to discover the pattern     flow and the results obtained, the fol-     running, and analyzing different
under which a decision for a specific        lowing conclusions were reached:            types of transient tests in oil and
artificial-lift installation was typically      1. The main benefit from applying        gas reservoirs.
made. Ideally, this pattern corresponds      this methodology is the reduction
to the rule-based expert system as           of lost production by the ability to
discussed earlier; however, sometimes        install an artificial-lift system sooner.   Contents:
it does not as a result of exceptional          2. It is possible to capture the
issues (e.g., no infrastructure available    knowledge and field experience and
to support a certain installation).          implement them in an automated
   Fig. 1 presents the depiction of          workflow, which can be used in a
several realizations of the same SOM.        systematic way, acting as a fast field
Each realization corresponds to a            screening tool. The asset team then
parameter that has been used to cali-        can focus its attention on the candi-
brate the SOM (gas rate before and           dates identified, saving valuable time.
after artificial lift installation, line        3. As knowledge is captured—
pressure before artificial-lift installa-    including multiparameter criteria—
tion, wellhead pressures before and          and applied systematically, the meth-
after artificial-lift installation, liquid   odology can be applied in an unbi-
level in the tubing before installa-         ased way to the whole field, allowing
tion). The output can be seen in the         identification of new opportunities
top-right realization of the parameter       for artificial lift systems that could
(i.e., “type numeric”, representing the      not have been identified simply by
artificial-lift system that was chosen       selecting one parameter as the rank-
for the particular well).                    ing criterion.                      JPT

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