SPE 87235

3D geological model to reservoir simulation of the Lower Arab Formation –Abu Al Bukhoosh (ABK) field, offshore Abu DhabiC. Javaux, F. Cochet, B. Gauthier, C. Prinet, L. Ten haven, TOTALFINAELF & M. Herriou, TOTAL ABK

Copyright 2000, Society of Petroleum Engineers, Inc.

This paper was selected for presentation at the 9th Abu Dhabi International PetroleumExhibition and Conference held in Abu Dhabi, U.A.E., 15-18 October 2000.This paper was selected for presentation by the ADIPEC Program Committee followingreview of information contained in an abstract submitted by the author(s). Contents of thepaper as presented, have not been reviewed by the ADIPEC and are subject to correctionby author(s). The material, as presented, does not necessarily reflect any position of theADIPEC or its members. Permission to copy is restricted to an abstract of not more than300 words. Illustrations may not be copied. The abstract should contain conspicuousacknowledgment of where and by whom the paper was presented. Write ADIPECCoordinator, GEC, P.O. Box 5546, Abu Dhabi, U.A.E. – Fax 009712-4446135.

Summary

The Abu Al Bukhoosh (ABK) field is already in productionsince 1974. At this stage, the distribution of the remainingreserves and further development programme, including gasinjection, become highly sensitive to a better understandingof the reservoir. The present paper focuses on the detailed3D geological model of the ABK Lower Arab Formationconducted through an integrated study. In particular, itincorporates an original methodology to determine rocktypes from cores and extend them to wireline logs, build asequence stratigraphy-related reservoir layering, populatethe 3D model for rock types and introduce the effects offracturing. Emphasis is also placed upon the input of the 3Dgeological model in the reservoir simulation model.

Introduction

The offshore Abu Al Bukhoosh (ABK) – Salman field isstraddling the Abu Dhabi – Iran border some 30 km NNWof the Umm Shaif field. One third of the structure fallswithin the territorial waters of Abu Dhabi.The oil from the ABK field is produced since 1974, mainlyfrom the reservoirs of the Thamama, Upper Arab and LowerArab Formations. Around 45% of the oil initially in placeare concentrated in the Lower Arab reservoirs. A significantpart of the Lower Arab initial reserves have already beenproduced by end 1997.At this stage, the distribution of the remaining reserves andfurther development programme, including gas injection,become highly sensitive to a better understanding ofreservoir behaviour which can only be achieved through thebuilding of a detailed 3D geological model.

The integrated study of the Lower Arab Formation wascarried out in 1998 with the following objectives:

(1) to develop an updated geological model, (2) to modify /refine the layering using the sequence stratigraphy concept,(3) to understand the impact of diagenetic processes on thereservoir properties, (4) to perform the reservoircharacterisation through a rock typing approach, (5) toextend this rock type identification to non cored wells, (6) toidentify, emphasise and predict the impact of fracturing atthe field scale, (7) to incorporate all available data and builda detailed 3D geological model which reflects the reservoirheterogeneities.

Detailed sedimentological and petrophysical core studieswere carried out on cores from a recently drilled well, usedas reference, and previously cored wells have beenreviewed/studied to be integrated in the present study to geta better understanding of the geological model and rocktypes distribution in cored wells. At this stage the log typingmethodology was performed on 28 wells and allowed toextend, with a rather good confidence, the rock type schemeto the non-cored wells. In the 3D model additional non-cored wells were also used to improve the structuralconfiguration. Fracture study started with cores, followed byimaging and wireline logs, yielding a statistical distributionof fractures at field scale. This integrated study took apluridisciplinary approach to establish a detailed 3Dgeological model of the Lower Arab Formation which maybe used for reservoir simulation studies.

Geological Model

Objectives The sedimentological, petrographical andreservoir characterisation based on ten cored wells aims atrevising and building a reliable model for the Lower ArabFormation reservoirs. Detailed sedimentology andpetrography studies combined with a sequence stratigraphicframework are the basic requirements for establishing the3D geological model supporting the reservoir simulation.Diagenetic processes and diagenetic history provide a basisfor understanding the reservoir characteristics.

Data Base Ten cored wells (Fig. 1) have been usedfor this study, corresponding to 365 m of cores. Theirdistribution provides a good coverage for the south-easternpart of the field, but a poorer one for the north-western part(two wells only). Two other cored wells have not been

2 3D GEOLOGICAL MODEL TO RESERVOIR SIMULATION OF THE LOWER ARAB FORMATION – ABK FIELD, OFFSHORE ABU DHABI SPE 87235

considered in this study due to the discontinuous recovery ofcores. Only three wells cored almost the entire Lower ArabFormation.About 1200 thin sections were examined, including thinsections made from preserved samples for special coreanalysis (SCAL). Cathodoluminescence and SEM analyseshave been also performed to improve the diageneticanalysis.A full set of logs was used. In addition, 5 available FullboreFormation MicroImager logs (FMI) were studied.

Depositional Model The Lower Arab Formation (Fig.2) corresponds to the D2 reservoir. It is most probablyKimmeridgian in age according to regional data1-2-3 and asconfirmed by biostratigraphic analysis performed for threewells. It mainly consists of limestones below the D2ainterval and of an alternation of dolomite and limestone inthe D2a interval. Nodular anhydrite beds separate the LowerArab from the Upper Arab.

A geological model (Fig.3) combining an open marine shelfwith prograding sand-waves which evolves laterally to aconfined inner shelf (lagoonal environment) and tosupratidal environment, as emerged shoal, is proposed toexplain the depositional system of the Lower ArabFormation.The ABK area appears as a gentle carbonate ramp with lowangle. There is an abrupt transition from an open seadepositional system to a temporarily confined depositionalsystem, which appears in the D2a interval. Confinedconditions seem to result from the insulation by a belt of anintra-shelf basin, from open sea influences.

Sequence stratigraphy (Fig. 4) Sequence stratigraphyof the Lower Arab was already tackled by several authors4-

5-6. A sequence stratigraphy framework is provided for theLower Arab in the ABK area. In particular, layersD2d+D2c+D2b on one hand and layer D2a on the otherhand correspond to two sequences of 3rd order, in turn madeof several parasequences.The sequence boundary between D2a and D2b isunderlined by a complete or partial emergence phase of thearea, which is highlighted by karstic processes. Thissequence boundary appears as a good candidate for regionalcorrelation. A similar interpretation was done for the ArabFormation in Qatar7. The sea level fall probablycorresponds to a forced regression in the terminology of theliterature8-9.These changes in sedimentation patterns are more readilyrelated to the pattern of eustatic sea-level changes than totectonic events.

Diagenetic Model Diagenetic processes have moreinfluences in the D2a interval than in the other D2 layers.The main diagenetic processes are related to dolomitisationwith a minor impact due to incipient cement precipitation.

This ubiquitous dolomitisation is responsible for the mainenhancement of the reservoir properties. Chemicalovergrowth of dolomite acts as a late factor for minordecrease of the reservoir properties. Three different steps ofdolomite crystallisation are identified, being (1) primaryeuhedral dolomite, (2) pervasive subhedral mosaic dolomite

(creation of secondary porosity), (3) late saddle dolomite.Similar stages are observed in different places in the Ghawarfield10-11 and in the Arab Formation of Qatar7.A mixing zone model is seen as the main process of earlydolomitisation in the Lower Arab of ABK field. This modelcould be applied for the emerged shoal where meteoricwater can percolate and create lenses as well as thetemporarily emerged shoal following a relative sea level fall.In these conditions, the dolomitisation could be intense.

Cementation has a minor impact on the reservoir propertiesof the Lower Arab Formation except for the first layer D2a1that is locally cemented by anhydrite.

The intergranular primary porosity is well preserved inlimestone deposits, associated with vugs and molds resultingfrom bioclasts leaching. In dolomites, porosity is mainly ofthe intercrystalline type. This latter is associated with vugsin dolomitic limestones.The fracture porosity is preferentially observed in dolomites,but some exists in limestones.

Fracturing In the ABK field, fracture systems have amajor influence upon the Lower Arab reservoir behaviour.These fracture systems have therefore been intensely studiedfrom core and image log data. Two sets of fractures, arerecognised in terms of orientation, typology, density andrelation with lithology and major structures such as faults ordoming (Fig. 5A):- In unfaulted zones only open NE-SW fractures develop in

less porous thin layers. Two types of such fractures can bedefined. Short, bedded constrained fractures are more orless uniformly distributed. Long, vertically extensivefractures develop as corridors.

- In faulted zones (seismic or subseismic faults) mineralisedNW-SE fractures cluster in the hanging wall. From imagelogs in horizontal wells, it was found that the width of themineralised fracture zone along faults could reach circa150 m. in these zones, open NE-SW fractures are alsopresent but they are short since their extension is limitedby the mineralised fractures. From these abuttingrelationships, it can be shown that the NW-SW systemdeveloped first.

- It was also found that the density of open NE-SWfractures tends to be higher in zones of high structuralcurvature. Such a relationship does not stand for the NW-SW trend.

- Furthermore, open fracture density is lithologicalycontrolled. Dolomitised units with low porosity (<16%)are always intensively fractured (spacing < 0.25 m) whilelimestone units with high porosity (>16 %) are alwayspoorly fractured (spacing > 3 m). Anhydrite streaks arealmost not fractured.

A 3D fracture model has subsequently been constructed(Fig. 5B). and the relations with production data beenanalysed. Although these relations are quite complex, itseems that the open fractures and particularly the fracturecorridors, could enhance water breakthrough. Conversely,the NW-SE mineralised fractures associated with faults canlocally hamper fluid flow.

SPE 87235 C. JAVAUX, F. COCHET, B. GAUTHIER, C. PRINET, L. TEN HAVEN, & M. HERRIOU 3

Reservoir Characterisation

Rock Type Identification The purpose of theLower Arab Formation reservoir characterisation is toprovide a better reservoir description / understanding forboth conventional and tertiary development.In order to perform the reservoir characterisation, a rocktyping approach was used. A rock type is defined as a rockwith a well identified porous network resulting from ageological history and leading to a well definedpetrophysical law at field scale. The identification of therock types has been achieved using the reference well. Itmainly consisted in linking groups of similar lithotypesdescribed from thin section analysis to specific groups ofpore size distribution obtained by mercury injection tests inliaison with poroperm characteristics.The lithotype identification took into account texture,mineralogy, pore types and interconnection quality. Theselithotypes correspond to four major categories: tight,limestone, dolomitic limestone, dolomite.Afterwards, the identification of the rock types performedon the reference well was applied to all the cored wellsthrough thin sections, additional mercury injection tests andporosity/permeability values.

From the identification of lithotypes groups and the specificgroups of pore size distribution, 9 rock type (RT) classes(Fig. 6) were defined and identified in each cored well.Below is a summary of the 9 rock types.

MineralogyL: limestone

DL:dolomiticlimestone

D: dolomite

DepositionalTexture

M: mudstoneW:wackestoneP: packstoneG: grainstone

Poro.Range

(%)

Perm.range(mD)

Av.pore

throatdiam.(μm)

RT1 L or DL or D M – W – P – G 0 – 5 0.01– 0.1 0.1RT2 D Mainly M - W 5 – 12 0.7 - 13 1.9RT3 D Mainly P - G 12 – 35 50 – 500 18RT4 DL W 7 – 25 0.1 – 10 0.8RT5 DL W – P 17 – 25 0.5 – 20 1.3RT6 L W – P 10 – 28 0.2 – 20 1.2RT7 L W – P 18 – 28 3 – 80 2.2RT8 L G 18 – 26 6 – 600 5.3RT9 L G 16 – 30 100–1600 20

Rock Type Characterisation / SCAL MeasurementsThe preserved samples have been selected such that theyare:- representative of the 9 rock types encountered in front of

the reference well (except the tight RT1),- representative of the main rock type encountered within

the layer these preserved sections come from,- and taken above the OWC to ensure their wettability state

is the same as the one of the initial reservoir oil zone.

Wettability: ABK Lower Arab D2 is a mixed-wet formation,at the location of the reference well, dolomites (RT3) beingslightly more oil-wet than rock types RT7 and RT8.

Formation factor at ambient conditions: cementation factor“m” (1.87 for RT3, 1.70 for RT5, 1.82 for RT7, 1.76 forRT9) is always lower than the standard value: m = 2previously used for log interpretation in the Middle Eastarea. The average “m” for all samples is equal to 1.78.

Capillary pressure curves in drainage and imbibition:Dolomitic rock types (RT2 and RT3) and limestones (RT5,RT7, RT8, RT9), are characterised by specific watersaturation as a function of water permeability laws. Tworegressions (n°1 for dolomites and n°2 for limestones) canbe plotted with good correlation coefficients (Fig. 7).This result is in good agreement with the pore throat sizedistribution of all of these rock types. In addition, RT2 andRT3 are characterised by a lower transition zone than RT5,RT6, RT7, RT8 and RT9.

Log Typing For a consistent reservoir model, the rocktype identification needs to be extended to wells where nocores are available, i.e. where the only information availableare the electric logs. So far, attempts carried out to extendthe RT approach to non-cored wells, using various statisticaltechniques, cannot be considered to have been successful.The present “Log Types” study provides an alternativesolution to solve this problem.The log typing approach uses the electric logs as a startingpoint and statistical techniques to recognise and grouphomogeneous electro-facies (“Log Types”). This study hasbeen carried out for twenty-eight wells penetrating theLower Arab Formation. To this end, the fuzzy c-meansclustering program12 was used, after data preparation andnew log interpretation.

Despite shoulder effects and non assigned data points orintermediate log types, a relatively coherent set of log typesis obtained, which can be correlated from well to well.However the success of this method can only been verifiedafter integration of geologic and petrophysical data. Thus aconfrontation between log types and rock types (Fig. 8) forthe reference well has been made. A model includingmatrix density, permeability (derived via regression linesfrom porosity), and volumes of anhydrite, calcite, dolomite,effective porosity as variables was adopted as a workingmodel. In addition to afore mentioned variables the six logtypes are further characterised by specific petrophysicalparameters as derived from the rock type study, and theirspatial distribution can be extended to non-cored wells.

3D Geological Model And ReservoirCharacterisation

General The reservoir characterisation of theLower Arab D2 carbonate reservoirs in the ABK field wascompleted using a 3D geological model. This incorporatesthe detailed sedimentological, log typing and SCAL dataand takes into account the high degree of vertical and lateralheterogeneity of these reservoirs. Additionally the 3Dvisualisation represents an incomparable data quality andcoherence control.

4 3D GEOLOGICAL MODEL TO RESERVOIR SIMULATION OF THE LOWER ARAB FORMATION – ABK FIELD, OFFSHORE ABU DHABI SPE 87235

A log and core database was created. A total of 69 wellswere used for correlations. Among them, 28 key wells,populated with log types and rock types, were selected forthe 3D reservoir characterisation.The number of wells usable for this study decreases fromthe upper reservoir layers (28 key wells in D2a1) to thelowest one (3 key wells in the top of D2h).

Layering And Structural Mapping The initial reservoirlayering of ABK was modified to take into account thesequence stratigraphy surfaces defined from cored wells.This refined layering was extended to non-cored wells usinglog signature. The new layering in 23 “reservoir units” leadsto more homogeneous units regarding the reservoirproperties.A single 3D seismic derived depth structure map, at top D2level, was available at the beginning of the study. The topD2 grid includes the fault pattern and structural maps usedin the 3D model thus account for the fault throw. Thicknessmaps of the individual reservoir units were created using anauto-gridding technique and back interpolated to well data.The depth structure maps of each reservoir unit below thetop D2 were generated by addition of the thickness maps ofthe individual reservoir units.

Rock Type Scheme And Mapping At this stage of thestudy a set of rock type schemes was available for the coredsections in 10 wells and a set of log types was available inthe 28 key wells. In order to use the rock typing approach inthe 3D model, the log types calibrated on cores and thenextended to the non-cored wells were interpreted in terms ofrock types. The procedure of log type to rock typereattribution was done through correspondence analysis andaccording to laws of stratigraphic occurrence.To guide the lateral distribution and to predict the continuityof a given rock type in a particular reservoir unit, piediagrams were used. They show the percentages of the rocktypes (reattributed from log types) present in each key wellfor a given reservoir unit.A geostatistical study was then run to model the rock typetrends suitable for input as templates in the 3D model. Theproportions of rock types were modelled by kriging withexternal drift on a set of 2D grids corresponding to each ofthe 23 main reservoir units. This procedure resulted in 23 *9 = 207 rock type grids. Combining the RT proportion mapsand the isochore maps allows to build thickness maps for agiven rock type in a given layer. This can be a tool tooptimise the field development plan by locating the best andthe worst zones, from a reservoir point of view.Improvement reached: rock type mapping of the LowerArab reservoirs, through the pie diagrams or through themore elaborated kriging method, illustrates that, behind thelarge variety of reservoir properties in space-and-time(which can be disheartening for the first time!), the RTdistribution is organised. The key factors explaining thevertical and lateral changes are of course deposition anddiagenesis. This means that the distribution, theinterpolation and extrapolation of rock types at the wholefield scale is meaningful.The log typing approach has allowed to extend the initial 10control points (i.e. 10 cored wells with rock types) to 28control points covering the whole field. By mapping therock type proportions per reservoir unit in these 28 key

points, according to a proper method (kriging withgeologically meaningful external drift) one gets reliabletrend maps for 3D modelling and particularly forpetrophysical attributes (porosity and permeability)modelling.

Permeability Computation From Phi/K Laws Regardingthe high heterogeneity of the Lower Arab reservoirs thePhi/K relationships have been investigated:- per rock type, leading to general Phi/K laws at the

whole reservoir scale,- per rock type and per layer, leading to specific Phi/K

laws for the considered reservoir unit.Most often, specific Phi/K laws for a given layer have abetter coefficient determination and thus are used in the 3Dmodel. To check the accuracy of these results, the computedpermeability was compared to the core permeability in thefew wells having both log types and rock types. The resultsare coherent and in good agreement (Fig. 9).

3D Modelling To reflect the depositional and diageneticpatterns and the resultant space-and-time variability in rocktype distribution, a stochastic approach was favoured. Thestochastic modelling was constrained, however, by the rocktype proportion maps used as an external drift.The depth structure map for each reservoir unit was loadedinto the geomodel. The structural model was built by downstacking the appropriate unit isochores from top D2 down toD2h.Within each reservoir unit, a cellular stratigraphicframework (Fig. 10) was constructed to reflect thedepositional patterns and to mirror the scale of heterogeneityobserved from well data and rock types.The log and core data at each well location were introducedinto the cellular framework. The data were up-scaled to thecell resolution according to pre-defined statisticaltechniques.A process was devised to introduce the rock type scheme inthe model. Rock types were distributed using a stochasticmethod (Fig. 11). This gives a degree of random variation tothe rock distribution, but with the control of distanceweighting and particularly with the control of templatesconstituted by the rock type proportion maps. The resultantinterpolation shows a “polka-dot” distribution where therock types become more constant with distance away fromwells, while respecting the rock types of the key wells.Log porosity (Phie) and core porosity were averagedarithmetically in the well model. Log porosity in the 28 keywells, recently reinterpreted, was considered to be morerepresentative than the core porosity in the 12 cored wells.The horizontal core permeability was both arithmeticallyand geometrically averaged at the well model scale. But toget a more representative and regional distribution,permeability was predicted from rock types and log porosityusing regression functions determined beforehand.Permeability was computed in two ways. The first optionassigned a permeability value, according to Phi/Krelationships established for each rock type in each unit, toevery cell, in the 3D model, populated with a dominant rocktype and with a Phie value ; permeability computed withoption 1 was named “modelled”. The second optioninterpolated in 3D the permeability calculated in the wells;

SPE 87235 C. JAVAUX, F. COCHET, B. GAUTHIER, C. PRINET, L. TEN HAVEN, & M. HERRIOU 5

permeability computed with option 2 was named “K fromLT-RT logs”.It is thought that the noisy permeability maps issued from“K modelled” are more representative of the reservoirheterogeneities and thus will be more appropriate formodelling the flow (water and gas). Additionally thearithmetic average appears to be in line with the productiondata and reservoir behaviour.

Barriers A detailed investigation of potentialpermeability “barriers” was done for the Lower Arabreservoirs. It includes two approaches : on one hand thefiltering of the intervals with low permeability (< 1mD)using software utilities and on the second hand the review ofRFT/MDT data.Only D2c and D2e layers can act as efficient permeability“barriers” at the field scale. But local permeability “barriers”seem, however, to exist in various places within the D2alayer, and also in D2b2 and D2g. The effects of these field-scale or local “barriers” have to be taken into account in thereservoir simulation model by imposing a reduced verticaltransmissibility.

Up-scaling Attributes were summed and vertically up-scaled per reservoir unit in order to get 2D grids of porosityand permeability as input for reservoir model. Some detailmay be lost when 126 fine cell layers are reduced to acoarser layering, in this case to 25. Nevertheless, as the 3Dstatic reservoir model cannot deal with 25 layers (too longCPU time not suitable for a history match of 30 years), itwas requested to decrease the number of reservoir units to18 layers by regrouping the closest ones. Thus additionalupscaling was performed according to rock type, porosityand permeability similarity and in order to respect thepreviously defined “barriers”. Mesh maps were thereforegenerated for the 18 layers.The reservoir simulation grid was oriented to follow themain faults and is slightly rotated compared to the 3Dgeological model grid. The values attributed to each modelcell were therefore resampled.As explained above, the lateral variations of the verticalpermeability is a key parameter for this thick Arab D2reservoir with full field gas injection. It was thereforeessential to populate the model with reliable verticalpermeability maps. The idea was to harmonically averagethe horizontal permeability in the 3D model at the stage ofupscaling.The rock type proportion maps were loaded and the mostrepresented RT was attributed to the each reservoir grid cell.Capillary pressure and relative permeability curves weredefined for each cell depending on the RT.The permeability maps loaded in the model are matrixpermeability. The simulated well productivity being farbelow the observed values in the first history match run,these maps had to be multiplied to take the fissuration intoaccount. From the production data the reservoir does notexhibit a clear dual porosity behaviour. Initially, only theD2a dolomitic layers were multiplied since more fractureswere observed in these layers. They are however very thinand did not enhance enough the global productivity, evenwith an active aquifer support. Finally all the horizontalpermeability maps were multiplied.

Concl�sions

A combined sedimentological, petrophysical and sequencestratigraphic approach enables subdivision of the LowerArab into 23 reservoir units. The proposed depositionalenvironment reflects an abrupt transition from an overallopen sea depositional system to a temporarily confineddepositional system. After deposition, during burial,diagenetic processes controlled the porous network throughenhancing / inhibiting effects. The main factor isdolomitisation ; cementation has only a minor impact.For a consistent geological/reservoir model, rock typeidentification, usually performed using core examination,thin-section petrography, conventional core analysis andmercury injection data, was extended to non-cored wells. Anew solution to solve this difficult problem was providedthrough a fuzzy logic-based log-typing approach which hasbeen carried out for 28 wells. It resulted in a coherent set oflog types that can be correlated to rock types, after someregrouping, and extended between wells. Some specificSCAL measurements were performed to fully characterisethe most representative rock types. They showed thatdolomitic rock types on one hand and limestone ones on theother, present specific fluids distribution and saturations.The refined layering defined from cored wells was extendedthrough correlations to a total of sixty nine wells. A 3Dseismic-derived depth structure map at top D2 was used andthe other maps for each reservoir unit resulted from it.The 3D geomodel incorporated the structural configuration,the sedimentological and petrographical data and took intoaccount the high degree of vertical and lateralheterogeneities of this complex lithology series (limestones,dolomites, anhydrites). Rock types calibrated on cores andthen extended to non-cored wells were distributed using astochastic method constrained by proportion maps. ThePhi/K relationships have been thoroughly investigated foreach rock type and reservoir layer. Permeability waspredicted from rock type and log porosity using variousregression functions.A detailed investigation of potential permeability barrierswas done and a tentative reservoir ranking based onpetrophysical characteristics has been proposed.The occurrence of faulting and fracturing was studied fromcores, FMI and wireline logs. Spatial distribution of thevarious fissure families was modelled.The ongoing reservoir simulation incorporates the newlayering, the rock type derived petrophysical maps and thefracture distribution maps.

Ac�no�ledge�ents

The authors would like to thanks ADNOC andTOTALFINA management for the permission to prepareand present this paper. Also, the authors wish to expresstheir thanks to Vincent Auzias and Simon Vriend for theircontributions to this subject.

Re�erences

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6 3D GEOLOGICAL MODEL TO RESERVOIR SIMULATION OF THE LOWER ARAB FORMATION – ABK FIELD, OFFSHORE ABU DHABI SPE 87235

Dhabi - in Simmons M. D. ed., Micropaleontology andhydrocarbon exploration in the Middle East, p. 81-99

2. ALSHARAN A.S. AND WHITTLE G.L. (1995) – Carbonate-evaporite sequences of the Late Jurassic, southern andsouthwestern Arabian Gulf – AAPG Bull., v. 78, p. 1075-1096

3. AL SILWADI M. S., KIRKHAM A., SIMMONS M. D. &TWOMBLEY B. N. (1996) - New insights into regionalcorrelation and sedimentology, Arab Formation (UpperJurassic), Offshore Abu Dhabi - GeoArabia, v. 1, n. 1, p. 6-27

4. AL HUSSEINI M.I. (1997) – Jurassic sequence stratigraphy ofthe western and southern Arabian Gulf – GeoArabia, vol. 2,n°4, p. 361-382

5. MCGUIRE M.D., KOEPNICK R.B., MARKELLO J.R., STOCKTONM.L., WAITE L.E., KOMPANIK G.S., AL-SHAMMERY M.J. &AL-AMOUDI M.O. (1993) – Importance of sequencestratigraphic concepts in development of reservoirarchitecture in Upper Jurassic grainstones, Hadriya andHanifa reservoirs, Saudi Arabia – Proceedings of hte 8th

Middle East Oil Show, SPE 25578, p. 489-4996. AZER S.R. & PEEBLES R.G. (1995) – Sequence stratigraphy

of the Hith/Upper Arab Formations, Offshore Abu Dhabi,U.A.E. – Proceedings of the 9th Middle East Oil Show, SPE,29799, p. 277-292

7. BOUROULLEC J. & MEYER A. (1995) - Sedimentological anddiagenetic model of the Arab Formation (Qatar) : reservoir

implications - in Husseini M. I. ed., Middle East PetroleumGeosciences Geo’94: Gulf Petrolink, Bahrain, v. 1, p. 236-246

8. POSAMENTIER H.W., ALLEN G.P., JAMES D.P. & TESSON M.(1992) - Forced regressions in a sequence stratigraphicframework: concepts, examples and exploration significance- Bull. Amer. Assoc. Petr. Geol., 76, 1687-1709

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10. MITCHELL J. C., LEHMANN P. J., CANTRELL I. A., AL-JALLALI. A. & AL THAGAFY M. A. R. (1988) - Lithofacies,diagenesis and depositional sequence; Arab-D Member,Ghawar Field, Saudi Arabia - in Lomando A. J. & Harris P.M. eds., Soc. of Ec. Paleont. and Min. Core Workshop n°12,p. 459-514

11. BRAY R.D. (1997) – The Arab D reservoir exposed: evidencefor vadose diagenesis in Ghawar field, Saudi Arabia –GeoArabia, v. 2, n°4, Jurassic/Cretaceous Platform-Basinsystems Conference abstracts, p. 481-482

12. VRIEND S.P., VAN GAANS, P.F.M., MIDDELBURG J. AND DENIJS A. (1988) The application of fuzzy c-means clusteranalysis and non-linear mapping to geochemical data sets :examples from Portugal. Applied Geochemistry, 3, 213-224.

Catherine Javaux received her Ph. D in geology from the University of Burgundy at Dijon in 1991, where she studied the MiddleJurassic carbonate reservoirs of the Paris Basin. She joined TOTAL in 1992 and worked as a carbonate sedimentologist from 1992to 1997 in TOTAL's Scientific and Technical Center. She is presently a reservoir geologist with the Department of ReservoirGeology and Geophysics at Paris-La-Défense. Her work mainly deals with Middle East assets. Catherine is in charge of a teamconcentrated on carbonate reservoir characterisation. She co-ordinates full field geological studies, integrating core and logevaluation, sequence stratigraphy, diagenesis and 3D modelling.

Fabrice Cochet received his Ph. D in geology from the University of Lyon-I in 1995, where he studied the sequence stratigraphyof the Upper Jurassic Carbonates from South East of France. He joined TOTAL in 1996 and worked as a carbonatesedimentologist from 1996 to 1998 in TOTAL's Scientific and Technical Center. He is presently geologist within the SubsurfaceDepartment at Paris-La-Défense. His work mainly deals with Middle East, South America and Indonesia assets. Fabrice activitiesconsist in well site geologist jobs as well as in log analysis.

Bertrand Gauthier received his Ph.D at the University of Paris VI in 1986, focussing on fault and fracture numerical andgeological analyses in the Gulf of Suez and Lorraine. He joined Shell Research in Holland in 1988 as a structural geologistgeometry, working mainly on developing probabilistic models of faults below the limit of seismic resolution. He then joined ShellNetherlands in 1993 as a production seismologist working on seismic interpretation and reservoir characterisation in the DutchOffshore. In 1996, he joined Total in Paris an since then, he is in charge of fractured reservoir studies and related R&D.

Catherine Prinet is graduated from engineering of the “Ecole Nationale Supérieure de Geologie”' of Nancy (1993). She receivedher Ph. D in “Materials Physics and Chemistry” in 1997. She joined TOTAL in 1997, to be one of the responsibles of thePetrophysic laboratory of TOTAL's Scientific and Technical Center for 3 years. She is now at TOTALFINAELF's ReservoirGeology and Geophysics department at Paris-La-Défense in charge of some reservoir simulations of heavy oil thermal recovery.

Monia Herriou received her MS degree in fluid mechanics in P. & M. Curie University in 1991 and was graduated in engineeringin 1993. From 1994 to 1997 she worked for TOTAL in simulation studies for Middle East zone. She joined TOTAL ABK in AbuDhabi in 1997 where she is in charge of reservoir development studies.

SPE 87235 3D GEOLOGICAL MODEL TO RESERVOIR SIMULATION OF THE LOWER ARAB FORMATION – ABK FIELD, OFFSHORE ABU DHABI 7

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Reference well

Cored well usedin this work

Wells with FMIused in this work

Cored well notused in this work

1 km

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Fig.1 - ABK field, offshore Abu Dhabi - Wells with cores and FMI

S h a l y l i m e s t o n e s

H i a t u s

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D o l o m i t e

L im e s t o n e

Fig. 2 - Lower Arab series

Fig. 3 - Depositional model of the ABK Lower Arab

Fig. 4 - Sequence stratigraphy and layeringof the ABK Lower Arab

8 C. JAVAUX, F. COCHET, B. GAUTHIER, C. PRINET, L. TEN HAVEN, & M. HERRIOU SPE 87235

Fig. 5 - Distribution of open fracturesin ABK Lower Arab

Fig. 6 - Poroperm characteristics of the ABK Lower Arab rock types

Fig. 7 - Petrophysical characteristics of the ABK Lower Arab rock types

Dolomites Limestones

�ert

ical

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ater

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istr

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0

10

20

30

40

50

60

70

80

Limestone

Anhydri teDolostone

0 31.5

FREQUENCY(fracture/m)

64.5

Thickness (m)

N

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ture

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LengthAnhydrite layers

FRACTURE STRIKE

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Continuous open

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W WP

WP

G

G

WP

RT2 RT3 RT5 RT6 RT7 RT8 RT9

Sw @ Pc = 20 psi = -5.06 log(Kw) + 22.0 R²=0.91Sw @ Pc = 20 psi = -8.84log(Kw) + 47.1 R²=0.86

0

10

20

30

40

50

60

70

80

90

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0 10 20 30 40 50 60 70 80 90 100

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1 10 100� ater �er�ea�ilit�� �D

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SPE 87235 3D GEOLOGICAL MODEL TO RESERVOIR SIMULATION OF THE LOWER ARAB FORMATION – ABK FIELD, OFFSHORE ABU DHABI 9

D�a

D��D�cD�dD�e

D��D�g

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Structural Modelling

� 3D Grid Design� �tratigra�hic �ra� e�or�

Rock type Modelling� �tochastic� �e� �lates

Petrophysical Modelling�Attri��tes���nctions��ol�� etrics

����scaled �hie � � �a�s�Grids �or si��lationOutput

Input

�De�th �tr�ct�re Ma�s� �sochores�� ell data �location� deviation� ���ogs ��hie� � �ro� ���R�����Core data ��hi� �h�� Roc� t��e �ro�ortion �a�s

Fig. 8 - Confrontation between ABK Lower Arablog types and rock types

Fig. 9 - Prediction of permeability in ABK Lower Arab reference well

Fig. 11 - 3D distribution of ABK Lower Arab rock typesFig. 10 - Process of 3D modelling

1 2 3 4 5 6 7 8 9���R�

0.00 0.01 0.10 1.00 10.00 100.00 1000.00 10000.00�� �D

2605

2610

2615

2620

2625

2630

2635

2640

2645

2650

2655

2660

2665

2670

2675

2680

2685

2690

2695

2700

2705

2710

MD��

K calculatedfrom LT-RT

LT-RT

K modeled

K core2610

2615

2620

2625

2630

2635

2640

2645

2650

2655

2660

2665

2670

2675

2680

2685

2690

2695

D2a1

D2a2

D2a3

D2a4

D2a5

D2a6

D2a7

D2b1

D2b2

D2B3

D2C

D2D

D2E

D2F

2610

2615

2620

2625

2630

2635

2640

2645

2650

2655

2660

2665

2670

2675

2680

2685

2690

2695

Depth LayeringResults 6 Clusters

Memberships Semi-hardRock Types

Original Grouped Flow Unit Type2606

2608

2614

2619

2622

2626

2630

2636

26412642

2662

2665

2673

2683

Depth

no core

no core