The Role of Reservoir Simulation in Optimal Reservoir Management

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    SPE 14129

    The Role of Reservoir Simulation in Optimal

    Reservoir Management

    by G.W. Thomas, Scientific Software-intercomp

    SPE Member

    Copyright

    1X, Sockty of

    PetroleumEnginaara

    This paperwas proaantd at theSPE 19SSInternationalMeeting

    on petroleumEngineeringheld in Beijing,CMa

    March

    17-20,

    19SS.The materialis

    subjecttocorrectionbythe author.PermissiontoCOPYsrestrictedto an ab.str~ OfMt morethan300 words,WriteSPE. P.O. SoxS33S3S,Richardson.

    Taxas 7SCSMS3S. Telex 730SS9 SPE DAL.

    SIMULATIONANDVIRGINRESERVOIR DEVELOPMENT

    When a reservoir simulator is employed to assist in

    ABSTRACT

    ptenning the development of a virgin reservoir, the

    reservoir description is typically limited. Consequ@ly,

    This paper discusses the role reservoir simulators only a minimal degree

    of

    optimisat ion is poa%ible.

    play in formulating initial development plans, history

    Nevertheless, some useful insights can be cbtained with

    matching and optimizing future production and in planning

    the aid of a simulator that can minimise the number of

    and designing enhanced oil recovery projects. The Hibernia

    decisions one must make in planning field development.

    Field in Canada and the Hassi R’Mel in AIgeria illustrate how

    In perticuter, the simulator can end should be used to

    simulation can be used to asdst in initial reservoir

    a$sesa sensitivity in computed results to uncertainties in

    development. The Lookout Butte F.undle (Alberta) and others

    the reservoir description and rock-fluid data.

    It is

    are cited to exemplify Optimhsl,fon of future production

    surprising how often variations

     

    input data over

    plans with the aid of simutetion. Finally, applications to

    reasonable ranges of uncertainty, for some reservoirs,

    several reported EOR projects are briefly discussed with

    yield modest changes in the computed results. On the

    major emptux~is concentrating on the Bati Raman Field in

    Turkey.

    other hand, it is useful to know, in the early stages of

    development, where the greatest effort should be

    concentrated to obtain those data that affect calculated

    INTRODUCTION

    performance the most.

    ‘he purpose of this paper is to provide an overview

    Simulation studies at the development stage

    on the role of reservoir simulation in managing hydrocarbon

    because of the uncertainties involved, are regarded as

    reservoirs. As pointed out by Coatsl , reservoir simulation, in

    the broad sense, has been practiced since the 1930%, when

    preliminary. Npically, they are periodically updated as

    more information becomes available; This means that

    some

    of

    the first calculetionaI procedures were deveIoped to

    early development plans arising from the first sim’? ation

    predict reservoir performance. Here, however, we take a

    studies should be sufficiently flexible to accom mudate

    narrower view, and restrict our discussion to applications of

    future contingencies as one learns more about the

    numerical reservoir simulation. ‘his involves solving targe reservoir. This presents a severe challenge where the

    s~ algebraic equations on digitaI computers to

    reservoir in question is highIy complex, large in extent or

    approximate transient, multiphaee

    or

    muIticomponent flow in in a hostiIe environment - all of which may require large

    heterogeneous media. ‘I?tis technoIgy started in the mid to

    investments to put it on production.

    late 1950%and, within the last twenty years, has played an

    increasingly important-role in the development, planning and

    In cases where the reservoir description and roek-

    management of gas and oiI reservoirs.

    fluid properties are reasonably defined, one can we a

    simutetor to plan well locations and densities aswtming

    In the folluwing, we first discus~ the role of

    voidege replacement by injection to maintain pres..ure.

    reservoir simulation as a tool in planning the initia 1 Such strategies can be compared to primary depletion

    development of a reservoir. The discussion then turns to through the same number of wells to arrive at the best

    their uses as predictive tools when investigating various

    development policy for the reservoir.

    future operating strategies.

    Finally, some attention is

    devoted to their utility in planning and executing enhanced Arwlication to the Hibcrnia FieId

    oil recovery schemes. Illustrations in the form of case

    histories are provided, albeit these are necessarily not

    To illustrate, we cite the Hibernia Field off the

    detailed because of space limitations.

    Neverthele$w,

     3fIStePn Ccest of Canada2. me fjeId lies abut 32tI km

    sufficient references to recent literature on the subject are

    southeast of St. John%, Newfoundland in a water depth of

    given for the interested reader.

    80 m. Five welts were drilIed to confirm the existence of

    substantial hydrocarbon reserves

    in at least two

    reservoirs, the Avalon and the Hibernia sendstones. The

    .

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    THEROLEOF RZSEPSfOIR SIMULATIONN OPTIMALRSSERVOIRNANAGENENT

    SPE 14129

    Avalon reservoir appears to be heterogeneous with wide

    Applications to Gas Condensate Systems

    variations in the porosity and permeability, whereas the

    deeper Hibernia is more homogeneous. Correlations of the

    In the Hibernia Field, a black-oil reservoir simulator

    limited porosity - permeabili ty data were used to extrapolate

    was employed to arrive at preliminary development

    into areas where data were lacking.

    Correlations of decisions.

    This 1s frequently done even though the

    verticaI/horizontal permeability ratios were used in a similar

    reservoir may contain fluids that undergo substantial

    manner. A porosity cutoff of 13% was used to define the net

    compositional changes during production. The motivation

    pay in the Avalon while 10% was employed in the Hibernia.

    for doing so is most often due to lack of data precisely

    Average connate and residual oil saturations in the Avalon

    defining the compositional behaviour of the fluids in the

    were estimated at 25%.

    For the Hibernia, connate water

    early development stages. Moreover, black-il simulators

    varied from 11 to 15% while 30% average residual oil

    can still provide usefuI information in such systems at

    saturation was assumed.

    substantially lea.. cost than a compositional simuIator5.

    EventuaNy, however, resources must be devoted early on

    AH evidence indicates that the two reservoirs are

    to the correct characterisation of the fluids and definition

    non-cornmunicating.

    The Avalon ccntains an apparent

    of their phase behaviour.

    undersaturated crude oil with a relative density of 0.873. PVT

    properties for the hydrocarbon were obtained from a drill stem

    As exampIes, we cite two large gas condensate

    test fluid sample.

    The Hibernia reservoir has more

    reservoirs.

    The first, the Has..i R’Mel is located in

    complicated fluid propties in two separate fault blocks. In

    Algeria6. The field was discovered in 1953 and contained

    one, a saturated crude, probably a volatile oil, of relative

    about 1.7 x 1012 mS

    of

    retrograde condensate gas at

    density, 0.825, is apparently overlain by what appears to be a

    32x10S kPa.

    The reservoir has a surface area of 4800

    gas condensate with a liquid gas content of 0.001 m /m*. For

    km’.

    Because of its vast reserves and closeness to ports,

    this block the fluid properties

    were generated using an ambitious development plan was executed in the earIy

    correlations assuming an initial seturat ion pressure of 40x10

    1970%baaed on a bleck-oit simulation study. At the time,

    end a sclut ion gasail ratio of 356 m ‘/m’. In the other fault

    only 20 wells had been drilIed and the geological

    block, the oil appears to be undersaturated having a relative description was limited. Consequently, full continuity of

    density of 0.850, there again, a drill stem test fluid was

    the reservoir was assumed. The objective was to produce

    analysed to determine the PVTproperties.

    a fixed daily rate of rich gas, extract the condensate,

    market scma of the- dry gas end reinject the rest to

    The first simulation runs involved 2-dimensional

    recover any condensate dropout that might occur.

    For

    cross-sect ions to generate pseudo functions3~4 for subsequent

    this purpose, a line drive gas injection scheme was

    use in 3+3imensional model% For the Avalon and Hibernia, 21-

    implemented.

    and 5-layer models, respectively, were used to generate

    pseudo relative permeabiIities.

    These subsequently were

    Haaei R’Mel now has about 200 welLs and giant

    employed in a 28 x 23 x 2 AvaIon model and a 24 x 20 x 2

    plants for ga? treatment and gas injection. production to-

    Hibernia model. h each case, square grid blocks 569 m on a

    date is 5 to 6% of the initial gas reserves. During the

    side were employed. Well locations were originally selected to development drilling, en oil ring of 0.82 relative density

    give reasonable pettern coverage over thoseregions where the and 15.2 m thickness was discovered - hence Haasi RIMel

    oil accumulations were considered to be greatest . Completion

    can be regarded as a volatile oil reservoir with a huge rich

    intervals for producers and injectors were selected such that

    gas cap. A fault system was also discovered that was

    oil production would be favoured while production of gas and subsequently better defined by seismic investigation.

    water, where pert inent, was minimised.

    Some revisions were made in the geological description of

    the field when 100 weUa were in place. The subsequent

    Four production/injection

    scenarios were

    need is to @rform a major update using information from

    investigated in the Avalon while four and five were considered

    all welt., the production history, the seismic surveys and

    for each of the fault blocks in the Hibernia reservoir. Some of

    state-of-the-art simulation tooLs.

    In particular, the

    the results of the study are shown in Figs. 1-3. In the~

    effects of the faults and retrograde condensation and

    figures W.I. and G.I. refer to flank water and crestal gas

    revapourisation need to be examined in detail. The

    injection, respectively.

    It is seen that in the AvaIon,

    appropriatenes~ of the line drive is aLscin question.

    differences in the water and gas injection cases were

    insignificant with the present geological description of the In such an update, one first determines to what

    reservoir. In the Hibernia, it was found that an ultimate

    extent, if any, he can use previous seismic, geological and

    recovery level of 50% of the original oil-in-place may be

    petrophysical interpretations.

    With regard to a

    achieved through an optimised production/injection strategy.

    retrograde condensate, the effect of liquid dropout on

    The uncertainties in these reauIts are linked to the geological well deliverability is also an important issue. Moreover,

    model. As”the latter is improved in the early development

    where cycling is performed, one would like to know what

    planning process, optimum recovery schemes can be desigiwd the .~timum is to maximise Iiquid revapouriaation.

    to account for the reservoir complexities.

    Again, in reservoirs with thin oil zones overlain by

    massive gas reserves - and possibly underlying water - the

    probebitity of coning can be high should producing weila

    be completed in the oil zone. The question arises, can the

    oil be recovered through displacement or vapouriaat ion by

    selective completion of dry gas injection welLs, as an

    alternative to producing directly from the oil zone?

    14

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    SPE 14129

    G.w. Thomas

    Finally, given a certain well pattern - like the line drive in

    development. Here we’ve just conveyed the flavour for

    the Has$i R’Mel -

    is it the optimum in view of possible

    some particular cases. The approach one takes is of

    geological discontinu{ties such as faults, pinchouts etc?

    course problem+ependent and may be unique for a given

    These and similar issues constitute the natural province for

    reservoir. (2) The devebpment plan, even though aided by

    reservoir simulators and sometimes definitive answers can

    sophisticated tools, should be regarded as tentative.

    emerge from carefully constructed models.

    Effort should be made, during the early stages, to endow

    it with maximum flexibility and continually upd&te it with

    The issues of lSquid dropout, revapourisation, etc.

    additional simulation studies as new data are obtained.

    may at some point require application of a compositional

    wimulator. Such simulators internaUy generate the PVT SIMULATORS AS PREDICTIVE TOOLS IN DEVELOPED

    characteristics of the hydrocarbon fluids using a “tuned”

    RESERVOIRS.

    phase behaviour package. me ‘tuning” as performed prior to

    the simulations by adjusting certain coefficients and/or

    In a sense, development of a reservoir is an on-going

    parameters in the phase behaviour package such that it

    process that continues over its productive life. However,

    reproduces, within acceptable limits? the results of a

    one can divide reservoirs into two categories - those with

    particular laboratory experiment on the hydrocarbon fluid.

    little or no productive history, end those that have

    The coefficient adjustment is accomplished using regression

    produced for some period of time. ‘Ihe distinction is

    analysis5 or trial-and+rror computer runs. It is important in

    particularly clear with regard to reservoir simulation. In

    such applications that data errors (from sampling, laboratory

    the former case, the simulator is applied in a qualitative

    analysis, etc) be kept to en absolute minimum. Furthermore,

    sense, i.e., it is not a priori calibrated to a particular

    fluid samples from different wells wiU, hopeful~y, have

    reservoir% characteristics, since these are largely

    similar or neer+imilar characteristics such that a

    unknown. In the latter, the response of the reservoir to

    representative or several regional representatives can be

    some predecided development plan is presumably known,

    used to typify the whole. Unfortunately, this is not always

    and effort is first devoted to the task of calibrating the

    the case.

    simulator such that it reproduces the response i.e. the

    past production history. This history matching involves

    For

    example, h Fig. 4’we djspley plots of retrograde

    trial-end-error runs with the simulator in which input data

    liquid dropout (as percentage of hydrocarbon pore volume) as

    adjustments are made within reasonable bounds until a

    functions of pressure for several fluid samples taken from a

    satisfactory match is achieved. *

    large (2000 km*) lean gas retrograde condensate reservoir

    (the name and location are witheld for proprietary reasons).

    TypicaUy, one seeks to reproduce the field-wide pressure,

    Such data are derived from constant volume depletion

    water-oil ratio and ges+il tatio performance and also

    experiments under controUed laboratory conditions on what

    match individual weU behaviour for the asme vnriables.

    presumably are representative fluid semples7. Obviously,

    Unfortunately, the procedure frequently involves iu-

    from Fig. 4 one cannot easily decide which well sample is conditioned systems, and unique results are not

    representative.

    The proper choke becomes even more

    guaranteed.

    As a consequence, it can be time

    cIouded given the poasibititiea for eempting errora

    consuming, coatty, and, at times, frustrating. However, a

    (contamination, fluid 10ss, long dMsnce transport, etc.).

    reaourcefuI engineer with in-depth understanding of

    However, in development planning, one frequently empIoye a

    reservoir behaviour can achieve meaningful matches.

    simulator in worst caee/beet case scenarios.

    An effort is

    then made to determine the most likely case between these

    Performing Evaluation of the

    extremes (this could be the average

    of the

    extremes), and

    Lookout Eutte RundleA Pool

    then plan the development around the latter. In this context.

    if one considers depletion without cycling, men the data from Once a satisfactory match is achieved, the

    WeUe 1 and 6 clearly define the worat and best cases,

    simutator is used in a predictive mode to investigate

    respectively, assuming retrograde liquid condensation occurs

    various production alternatives. Here again, the objective

    in the reservoir prior to fluid entry into the welLs. The phase

    is to optimise future operations of the reservoir. As an

    behaviour package is then tuned to each situation, i.e. an example of such an appUcation, we cite the Lookout Butte

    effort is made to reproduce the curves in Fig. 4 for WeUs 1

    Rundle A Pool located in Alberta, Canada~4. The

    end 6 to characterise the hydrocarbon properties for the

    reservoir is a tight, interbedded limestone having an

    worst end best case situations. Should the resuIts from the

    average porosity of 6.5% and permeabilities in the range

    subsequent simulations for each scenario not differ

    0.1 to 0.3 md. fie reservoir dips to the west end north

    subetant. ‘Jly, then one need not concern himself about and is delineated by en extensive aquifer on the west, and

    defining the most likely case since averages from the

    a fault on the east (see Fig 5). It contains a dry gas

    eXtrema would be sufficient. Otherwise, one might take

    some curve weighted in favour of the pIots that are closest

    together in Fig. 4 (shown by the dashed line), fit the phase

    beheviour package to this, end w this tuned result in the

    *Efforts have been made to deveIop software

    simulator for the moat Iikely scenario.

    ~ams that automate the history matching t-e=.

    However, these have not found Iairge scale use on a

    In concluding this section we emphasise two things: commerical basis to+ate.

    (1) ‘llIere are many different waya in which a reservoir

    simulator can play a vital role in optimum reservoir

    15

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    THEROLE  RJZSERVOIRIMULATIONN OPTIMALWSERVOIRMANAGEMENT

    SPE 141

    condensate underIain by the aquifer. GeoIogicaI and core

    northern and southern parts. Moreover, it is aIso regarded

    data indicate the reservoir is extensively fractured and that

    ashight’isk since it is near to Well 4-32 which was shut i

    vertical fractures dominate.

    In late 1963 production

    because of high water production. The 13-32 location

    commenced by depletion coupled with gaa cycling. Dry gas

    gives the highest cumulative gas production and increase

    was injected into one weU(We114-13 in Fig. 5)untiIlate 1967

    field deliverability 3.4 x 106 m:/D over the productivity

    at which time it was converted to a producer and blowdown

    in 1972 (the year the study was performed). This well

    started.

    Prior

    to this, only minor amounts of water, were

    in communication with some other wetls in the field an

    produced. However,

    thereafter four producing welL~

    was considered as a future drilling location. There wa

    experienced water production that increased steadily until

    however, some concern because of its proximity to th

    the water-gas ratio averaged 1 x 10-5 m‘/m 1 by June, 1972. fault on the east.

    The objectives of the study were to determine the

    The utility of a reservoir simulator should b

    mechanisms causing the water production, develop an

    recognised in this brief case history.

    It provide

    optimum depIetion plan for the reservoir, and evaIuate the

    engineering answers to certain questions that one migh

    surface facilities required to carry out the depletion plan. To

    pose regarding future exploitation of a reservoir. I

    determine if water production was caused by water coning or

    however, cannot make the decision as to which possibilit

    fingering, two types of modeI studies were executed:

    is the optimum. This remains within the realm of huma

    Individual well coning studies using a radial gas-water

    judgment (thankfully). The judgment, in this case, wa

    simulator, and crossaectional studies to evaluate fingering.

    that Well 5-21, because of Iow risk, should be drilled

    t

    Both invoked history matching the performance data. In

    recover gas from the southern portion of the reservoir

    addition, the adequacy of the reservoir description required

    Moreover, Well 14-13 shouId be drilled even though

    to match the history was evaluated. Finally, calibration of

    constitutes a high risk because of substantial water influx

    the simulator was accomplished by matching the pressure

    However, without it, gas in the North may be trapped

    history of the entire

    field and the individual well

    otherwise by the incoming water.

    FinalIy, one shouI

    performances. The results of the history match were used to

    abandon Well 15-29 as a poasibilit y and re+vaIuate

    determine the distribution of gas-in-place and the water

    drilling of Well 13-32 after more history become

    influx in the prediction and optimisation phases of the study.

    available.

    In addition the reservoir simulator, after history matching,

    was coupled with a gas gathering system simulator to

    Other interesting case histories involving histor

    optimise the surface faciUtiea15. The latter exercise

    matching and predictions have appeared in the recen

    involved examining various possible effective line diameters

    literature. One involves the Leroy Gas Storge Facility i

    and welI connections to yield a maximum in deliverability. In

    Wyoming16. A simulator wqa used to match the pressur

    Figs. 6 and 7 we show typical matches of pressure and water- history of the reservoir incIuding the effect of a time-and

    gas ratio for one of the wells in the field.

    pressure-dependent leak to the surface. The simulato

    was a useful tool in the ccmprehensi /e analysis required

    It was concluded from the history match runs that

    to understand, monitor and control the leakage. The cas

    water coning was the cause

    of

    the water production in the

    history is significant in that it documents how reIevan

    reservoir. The prediction phase

    of

    the study involved computer simulations can, with other engineering studies

    choosing one or more optimum infill drilling locations from lead to safe and economic gas storage operations. Tw

    among the four possible sites indicated by the arrows in Fig.

    other recent studies akc are of interest. One describe

    5. A base case, with no infiU drilling was also run. The total

    application of a black OK simulator to the El Gueri

    field deliverability for each case is shown in Fig. 8. For the

    reservoir in the Ashstart Field

    of offshore Tunisia17. Th

    predictions, both the reservoir and surface system were other treats the Sawtelle Field in California 18, The E

    simulated simultaneously. The field was produced at the

    Gueria is a moderately to highly fractured nummulitic

    maximum of the production facilities. Wells were shut in

    limestone originaUy containing an undersaturated oil o

    when their production declined below 0.15 x 106 m‘/D or

    0.88 relative density. The reservoir is produced wit

    when the gas-water contact reached the bottom perforations. injection of seawater to maint~in pressure above th

    bubblepoint pressure. A three+imensional model wa

    Well 14-13 initially increased the field deliverability

    constructed to perform the history match and predictions

    about 3 x 106 m ‘/D over the other cases and 5.8 x 106 ma/D ‘Ihe model was also augmented by wellbore hydraulic

    over the base case. Because the gas-water contact had been

    routines to simulate vertical

    or

    inclined flow to th

    depressed by gas-injection in the proximity of this location, surface. fie Sawtell study employed a two+imensional,

    the water influx rate was very high as the contact rebounded.

    three-phase black oil model and is of interest since

    As a result, the well watered out at Lfie end of 1978.

    involves a complex and unusually shaped reservoir

    Consequently, this is regarded as a high risk well. Well 5-21

    Finally, we cite the simulation study of the East Velm

    presents a low risk end is necessary to drain gas from the West Block Sims Sand Unit in 0klahoma19. This study

    tighter portions of the reservoir in the south. The 15-29 weIl

    of intereat since it involves a rather old reservoir fo

    is located in that part of the reservoir which is poorly

    which

    few data exists for the primary production phas

    defined.

    This region has limited communication with the

    (1949-1962). The history match of field pressures, gas

    and water+il ratios was largely for the secondary

    recovery phase (1962-1972) in which water was injected

    Predictions included the possibility of continue

    waterflood operations and inject ion of carbon dioxide.

    16

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    SPE 14129

    G.K.

    Thomas

    APPLICATIONS TO EOR PROJECTS

    Sometimes reservoir simulators are used to assess

    the relative merits of various enhanced oil recovery (EOR)

    schemes. In such cases, the simulator is used in a predictive

    mode both with or without prior history matching. In

    particular, Aydelotte and Pope20 and George, et a121 report

    on the novel use of reservoir simulators to validate and assist

    in the development of simplified, reliable inexpensive

    predictive- modeLs for steamfloodin

    ~ and micell

    ar~lymer

    flooding. Recently, Frazier and Todd 2 employed a simulator

    to design and evaluate an application of Iiquified petroleum

    gas (LPG) in a reservoir that had previously been

    waterflooded. The choice was to either abandon the field or

    attempt an EOR process. The simulation study indicated that

    an additional 7% of the original oil in-place could be

    recovered from a miscible LPG flood.

    me predictions

    involved use of the best available reservoir description, i.e.

    no history match runs were employed to calibrate the

    simutator. l%e project was initiated in the field with propane

    injection in three wells starting in July, 1980.

    As of

    December 1981, it appeared as though the process was

    working as predicted by the simulation study.

    Simulation has been used to design, monitor and

    evaluate several steam in”ection projects23-27. The

    A

    Georgsdorf Field in Germany 7 presents an interesting case

    history. Here, production history over 10 years, including six

    with

    steam injection,

    was

    satisfactorily

    matched.

    Considering the usual reservoir complexities and the

    difficulties associated with nonisothermaI operations, the

    matches are remarkably good. Predictions were then made

    to determine steam requirements in certain portions of the

    reservoir, to arrive at a plan for future project expansion,

    and to ascertain where new injection welLs and infill

    producers should be located.

    A very interesting application of the use of

    reservoir simulators in the management of reservoirs is

    provided by the Bati Raman Field in Turkey 28. The reservoir

    contains substantial reserves (2.9 x 108 m‘) of a heavy crude

    oil (relative density = 0.986) with a bubble point pressure of

    1103 kPa, The amount of gas in solution at the bubble point

    pressure is quite low, i.e. 3.2 m ‘/m 1. There is no natural

    water intlux into the reservoir.

    At discovery in 1961 the

    reservoir prewre was 11,032 kPa. Currently, it is 2,758 kPa.

    There are 103 wells - all pumping - with a total production

    rate of 413 m‘/D. The estimated primary recovery is 1.5%

    of the original oil in-place. A pilot waterflood indicated that

    an additional 3.5% could be recovered by this means. The

    reservoir presents an intriguing and difficult challenge for

    two reasons: (1) lt is Turkey??largest single oil reserve; (2) It

    has essentially no internal energy to as..ist production, i.e.

    recovery must  rely almost entirely on external means.

    A suite of simulation studies were executed to

    screen various EOR processes. Simulation of water flooding

    led to a prediction of 5% recovery, confirming the field pilot

    tests. ‘fhe reservoir presents other complexities in that it is

    fractured and displays dual porosity29 characteristics in .aome

    parts. Simulation of steam flooding indicates 32% recovery if

    the system behaves like a single poiosity system whereas only

    half

    this amount is recoverable by steam if it is indeed a dual

    system throughout.

    Nevertheless, this process and

    immiscibIe carbon dioxide injection appear the most

    favorable. From an economic viewpoint, the latter

    process is the most feasible because of a nearby carbon

    dioxide gas reserve and the high initiaI investment

    requirements for steam injection. Currently, a large

    reservoir simuiat ion study using a fractured reservoir

    simuIator capable of handling carbon dioxide diffusion

    into the heavy oil is being executed. At the same time a

    field pilot project is being planned to assist in optimum

    development of the reservoir. Early indications are that

    17- 32% recovery can be expected.

    CONCLUSIONS

    Reservoir simulators play an active and important

    role in the optimum management of oil and gas reservoirs.

    They prGvide insights which could not otherwise be

    obtained, especially in complex systems where simpler

    reservoir engineering methods are found wanting. We

    have seen how they can be used in the infancy, maturity

    and final days of a reservoir% life. Indeed, in some

    instances, they have indicated the existence of additional

    oil reserves which were later ‘discovered” by subsequent

    driIling30. However, we emphasise that there is no

    substitute for sound engineering judgment. Ultimately,

    the opt imisation must be done on that level. A reservoir

    simulator is just another tool in the engineer% arsenal

    that, hopefully, enables him to probe deeper, and gain a

    larger measure of “understanding.

    REFERENCES

    1.

    Coats, K.H.: “Reservoir Simulation: State~f-the-

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    Nigeria”, J. Pet. Tech. (April, 1984) 671-677.

    18

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