ACKNOWLEDGEMENTOur immense gratitude goes out to the management and staff of the Institute of Petroleum Studies especially Mr. Francis Fusier for working assiduously to ensure the smooth running of our MSc program and for putting all required logistics in place for a successful one week of STATIC RESERVOIR Simulation with PETREL software.

Our heart goes out to TOTAL Exploration and Production Nigeria Ltd for the rare opportunity granted us in funding our MSc degree program with the IPS initiative.

Finally, we thank God for His constant strength and guidance especially in this tough and mentally-challenging environment, and extend our thanks also to the entire exciting, fun-loving, intelligent and smart individuals that make up Batch Seven of IPS.

CHAPTER ONE

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1.0 Introduction

The Gulfalks field (about 61°15’N, 2°15’E) is one of the three giant oil

fields located at the edge of the North Sea Plateau, located on the

western flank of the North Viking Graben (Norwegian sector), also with

high gas accumulations. The sediments are coarse sands due to their

proximity to submerged beach zone.

Gullfaks field has no pockmark structures probably due to coarseness

of sediments. The gas found at Gullfaks, of which 98% of it is methane

can easily migrate vertically through the porous sediments. Numerous

shallow gas accumulations lie at a depth of about 300-450 m below

seafloor. The source rock of Gullfaks Oil field is from the Permian age.

These gas hydrocarbons migrated to the mean, economical, interesting

reservoirs of Jurassic age. The origin of methane is fossil (Hovland and

Judd, 1988). The temperature at the reservoir is 8°C.

The Gullfaks field (see figures 1.1 and 1.2) comprises marine and

fluvio-deltaic sandstone reservoirs of the Middle Jurassic Brent Group.

The Broom, Rannoch, Etive and lower Ness formations represent the

delta’s advance or progradation, while the upper Ness and Tarbert

formations represent its retreat or retrogradation. The intensely faulted

and compartmentalized structure contains an accommodation zones

sandwiched between a system of strongly rotated fault (domino-type)

blocks to the west and a horst complex to the east. Some of the crestal

areas have been eroded and are directly overlain in places by the

base-Cretaceous unconformity.

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3

EXECUTIVE SUMMARY

This is a project on the static reservoir modelling of the Joana field: an oilfield located inthe Paris Basin at 300km South-East of France. The field was discovered in the 1960s,drilled in the 1980s and the 1990s with one of its wells still producing at present.Data was obtained from the existing Joana field wells in the form of geological andseismic survey, sedimentology, well correlation, coring, logging, fluid properties, andproduction data. These were all quality-checked, prepared and geostatisiticallyextrapolated as inputs to be used in the characterization of the reservoirs of the field.A 3-D static model of the field was produced using the Petrel software whichencompassed the gridding, layering, facies modelling, fault modelling, zonation, etc ofthe field. This threw more light on the overall structure of the reservoir and was used inthe calculation of the Original Oil in Place (OOIP) for the two major scenarios chosen.That is, for the connected reservoirs case, a value of 1,394 MM bbls OOIP was obtainedwhile the assumption of unconnected reservoirs yielded 478 MM bbls manually and thesoftware-calculated value as 403 MM bbls.Economical analysis of the field (assuming a recovery factor of 0.25 and a price of $65per barrel of oil), a gross revenue of $22.70 billion was obtained for the connectedreservoirs, $7.77 billion for the unconnected reservoirs (manual) and the soft-warecalculated as $6.50 billion. On the basis of all of the above, a recommendation for theupscale of the model to a dynamic one was made with a view to producing the field asearly as possible.6RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

TABLE OF CONTENTSACKNOWLEDGEMENT .................................................................................................. 4EXECUTIVE SUMMARY ................................................................................................ 5TABLE OF CONTENTS .................................................................................................... 6LIST OF FIGURES ............................................................................................................ 9LIST OF TABLES ............................................................................................................ 11CHAPTER ONE: GENERAL INTRODUCTION ........................................................... 121.1 OBJECTIVES OF THE STUDY ....................................................................... 12

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1.2 SCOPE OF THE STUDY .................................................................................. 121.3 DATA USED ..................................................................................................... 131.4 METHODS ADOPTED .................................................................................... 131.5 HISTORY OF THE PARIS BASIN .................................................................. 141.6 STRUCTURE OF THE PARIS BASIN ........................................................... 151.7 STRATIGRAPHY OF THE PARIS BASIN .................................................... 161.8 THE PETROLEUM SYSTEM .......................................................................... 171.8.1 Source Rock ................................................................................................ 201.8.2 Reservoir Rock ............................................................................................ 201.8.3 Traps ........................................................................................................... 211.8.4 Migration .................................................................................................... 211.8.5 Seals ............................................................................................................ 211.8.6 Time............................................................................................................. 22CHAPTER TWO: SEISMIC INTERPRETATION AND ANALYSIS ........................... 232.1 PICKING OF TOPS ........................................................................................... 232.2 TIME DEPTH CONVERSION ......................................................................... 232.3 FAULT PATTERNS .......................................................................................... 24CHAPTER THREE: SEDIMENTOLOGY OF JOANA FIELD...................................... 273.2 STRATIGRAPHY OF JOANA FIELD.................................................................. 303.3 CORRELATION ............................................................................................... 327RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER FOUR: PETROPHYSICS ............................................................................. 364.1 LOGS AND INTERPRETATION ..................................................................... 364.1.1 Identification of the Reservoir zones........................................................... 384.1.2 Identification of Non-reservoir areas (shale zones) ................................... 394.1.3 Summary of the Petrophysical Analysis of the Logs ................................... 39CHAPTER FIVE: STATIC RESERVOIR MODELING ................................................. 415.1 DATA QC/QA AND ANALYSIS ..................................................................... 415.2 STRUCTURAL MODELING ........................................................................... 415.3 COMPARISON OF THE GEOSTATIC MODELLING METHODS .............. 415.1 DATA QC/QA AND ANALYSIS ..................................................................... 425.1.1 Data import and QA/QC of input................................................................ 425.1.2 Creation of surfaces .................................................................................... 425.1.3 Layering and Gridding of surfaces ............................................................. 445.1.4 Matching facies with wells .......................................................................... 455.1.5 Correlation of reservoir logs. ..................................................................... 475.2 STRUCTURAL MODELLING ........................................................................ 485.2.1 Fault modeling ............................................................................................ 485.2.2 Scaling-up of well logs parameters............................................................. 495.2.3 Scaling-up of Net-to-gross. ......................................................................... 535.2.4 Facies modeling .......................................................................................... 545.3 COMPARISON OF THE VARIOUS GEOSTATIC MODELLING METHODS

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60CHAPTER SIX: CALCULATION OF OOIP .................................................................. 626.1 MANUAL CALCULATION OF OOGIP .............................................................. 626.1.1 Connected Reservoir ................................................................................... 646.1.2 Unconnected Reservoir ............................................................................... 656.2 OOIP CALCULATION FROM PETREL .............................................................. 666.1.2 Connected Reservoir ................................................................................... 668RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER SEVEN: UNCERTAINTIES, CONCLUSION ANDRECOMMENDATIONS .................................................................................................. 697.1 UNCERTAINTIES ............................................................................................ 697.1.1 General Reservoir Structure ....................................................................... 697.1.2 Sealing or Non-Sealing of Faults ................................................................ 707.1.3 Reservoir Layering...................................................................................... 707.1.4 Geostatisitcal extrapolation of Petrophysical Parameters ......................... 707.1.5 Position of the Fluid Contacts .................................................................... 707.1.6 Reservoir Fluid Properties ......................................................................... 717.1.7 Sequence Stratigraphy ................................................................................ 717.2 CONCLUSION .................................................................................................. 727.3 RECOMMENDATIONS ................................................................................... 73REFERENCES ................................................................................................................. 749RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

LIST OF FIGURESFigure 1.1 Location of the Paris Basin.............................................................................. 15Fig 1.2: Geological cross section of the Paris basin ......................................................... 16Figure 1.3: General Stratigraphy of the Paris Basin ......................................................... 17Figure 1.4: Petroleum System of the Joana Field ............................................................. 19Figure 1.5: Facies C4a and C4b ........................................................................................ 21Figure 1.6: Log seals of reservoir 1(C4a) and 2(C4b). ..................................................... 22Figure 2.1: The seismic surface of Joana field showing wells and major faults. ............. 25Figure 2.2 Contour map of the Paris basin with the red circle showing the location ofJoana field ......................................................................................................................... 26Figure 4.1: A typical dune-like depositional environment ............................................... 27Figure 3.2: The prehistoric map of Paris basin showing the location of Joana field by the

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blue ring which corresponds with section E-F .................................................................. 30Figure 3.3 The Stratigraphy of Joana field. ...................................................................... 31Figure 3.4: Location of the facies 1 - 9 in their typical depositional environment ........... 32Figure 3.5: The maximum flooding surfaces and sequence boundaries. .......................... 33Figure 3.6: The correlated cross-section of wells; Joana-3, Joana-2, & Joana-6 (partly) . 34Figure 3.7 .The correlated cross-section of facies of the wells in Joana field ................. 35Figure 4.1: The Joana 2D well log .................................................................................... 37Figure 4.2: Cross section of processed logs from Joana-2D showing some computedreservoir properties along the well section. ...................................................................... 37Figure 4.3: Cross section of well logs from Joana fields 3,2,,6 ........................................ 40Figure 5.1: Contour diagram for thickness between MFS 0 and MFS 1 .......................... 43Figure 6.1: Creation of six surfaces .................................................................................. 43Figure 5.3: Layering of surfaces ....................................................................................... 44Figure 5.4: Gridding of the surfaces with dimensions 100*100*1.0 per cell ................... 45Figure 5.5(a): Matching of facies with well log (Joana-2) ............................................... 46Figure 5.5(b): Matching of facies with well log (Joana-3) ............................................... 46Figure 5.6: Reservoir log correlation ................................................................................ 47Figure 5.7: Fault modeling identifying key pillars ........................................................... 48Figure 5.8: final fault model of the Joana field. ................................................................ 49Figure 5.9: Scaling up of porosity using arithmetic mean method. .................................. 50Figure 5.10: Scaling up of porosity along the wells in the model .................................... 50Figure 5.11: Histogram of the porosity distribution for the method used. ....................... 51Figure: 5.12: Up scaling of Gamma ray on the reservoir model ...................................... 52Figure 5.13: Up scaled gamma ray logs in 3D.................................................................. 53Figure 5.14: Histogram obtained from the scaled up net-to-gross.................................... 54Figure 5.15: facies modeling of Reservoir 2 ..................................................................... 55

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Figure 5.16: facies modeling of the Non-Reservoir.......................................................... 55Figure 5.17: Facies modeling using Boolean method for the non reservoir .................... 56Figure 5.18: Facies modeling of the channel the discrete Boolean method .................... 57Figure 5.19: Histogram obtained from the Boolean method ............................................ 57Figure 5.20: facies modeling using Sequential Gaussian Simulation (SGS) .................... 5810RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Figure 5.21: Histogram obtained from Sequential Gaussian Simulation. ........................ 59Figure 5.22: Facies modeling using kriging method ........................................................ 59Figure 6.23: facies modeling using the moving average method ..................................... 60Figure 6.1: The plot reservoir area versus depth assuming connected reservoir. ............. 64Figure 6.2: The plot reservoir layers versus depth for an unconnected scenario .............. 65Figure 6.3: volume calculation settings window .............................................................. 67Figure 6.4: Print screen of the Volume Calculation Report.............................................. 6811RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

LIST OF TABLESTable 3.1: Summary of the properties and reservoir potentials C1 – C9 facies. .............. 28Table 5.1: Representation of the reservoir parameters. .................................................... 60Table 5.2: Comparison of the various geostatistic methods. ............................................ 6112RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER ONEGENERAL INTRODUCTION1.1 OBJECTIVES OF THE STUDYThe objective of this study is to produce a static geological modeling of the Joana field.The field is located in the Paris Basin, about 300 km South-East of France and existedsince the Triassic-Jurassic period though most of its physical changes took place duringthe Cretaceous – Eocene period. The static modeling of the reservoir was achieved withthe industry-acclaimed software, PETREL, produced and patented by Schlumberger.1.2 SCOPE OF THE STUDYThe scope of the project involves the following:Identification of the field location on the Paris BasinExplanation of the field and reservoir parameters of the Joana field.

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Acquisition, velocity model of and time-depth conversion of the seismic of thefield.Exploration of the fault pattern of the field.Sedimentological study of the field (sequence stratigraphy, heterogeneity andfacies).Petrophysics of the field’s reservoirs (Cut-off, Rw, OWC, ODT, WUT, FWL etc.)Propose a static model for the reservoirs of the field.Carry out a calculation (estimation) of the OOIP (Original Oil In Place) by bothmanual means and the application of the softwareMaking the necessary recommendations and concluding eventually.13RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

1.3 DATA USEDThe data used for this project were all provided by Prof. Bernard Michaud i.e. it hadalready been inputted into the software beforehand. Had it been otherwise, the data wouldhave been inputted by the use of the Petrel Explorer which consists of eight tabs, put intwo separate explorer windows, called First and Second Petrel Explorer. They can beenabled/disabled from the View option in the Menu bar. Two main working tabs in theFirst Petrel Explorer are:Input tab: Where all the input files are placed as well as edits on input data or copies ofinput data. Data created within Petrel and not related to the 3D grid (such as polygons,surfaces, seismic interpretations) will also be stored under this tab. And theModels tab: All data related to the 3D grid (horizons, faults, properties, etc.).Also, the active items in PETREL are shown in bold fonts, and the characteristic thing inPetrel is the active item which is being displayed with bold fonts. Also, the +/- sign isused for the expansion and collapse of icons respectively by clicking the sign before theicon concerned.1.4 METHODS ADOPTEDThe method adopted was entirely the use software to electronically acquire, sort andarrange, process, and interpret the field data for the Joana field save for the manualcalculation of the OOIP (Original Oil in Place) in Chapter Six. This was done to get a feelof the action and verify the accuracy of the work done by the comparison of the ranges ofthe results of the two methods.Having looked at all these, we would now go into the structure of the field, as it were.14RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

1.5 HISTORY OF THE PARIS BASINParis basin is an intracratonic basin – a basin existing in the middle of continents wherethe compressive and extensive forces of the foreland and the extensive basins act out andproduce a net effect. In actual sense, it’s a combination of extensive and compressivebasins. As a matter of fact, the Paris basin was first formed an extensive basin (during theTriassic-Jurassic era) which progressively transformed to a compressed structure tillpresent day. There exist also the distributions of structural traps caused by stresses;Cretaceous-Eocene shortening being the most important and prominent of them.In the basin also several north-west trending folds extend from the basin to the EnglishChannel. Subsidence continued throughout the Triassic and the Jurassic but decreasedsomewhat in the early cretaceous. By the late Cretaceous, the Tethys Sea to the south

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(which got as far as the present-day North Africa) had transgressed and covered much ofFrance. A prominent mark of this transgression is the extensive chalk deposits thatoutcrop in the visibly arid but agriculturally sound Champaign district.15RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 1.1 Location of the Paris Basin

1.6 STRUCTURE OF THE PARIS BASINThe Joana field is located in the Paris Basin located in the intracratonic sag basin withconcentric structures..The basement and carboniferous rocks is over-lain by 3000m ofTriassic to tertiary sediments. Rifting in the Triassic was overlain by a phase of rapidthermal subsidence in the Jurassic which was laminated in the latest Jurassic resulting inthe rise of the Vosges block to the coast. The Vosges is a range of mountains northeasterlyof France that extends190km from South to North, running parallel to the RhineRiver. It has highest elevation of about 1500m.PARIS

Source Rock for Middle Jurassic and Cretaceous =LIASTRIASSICMIDDLEJURASSICLimestoneLOWERCRETACEOUS

16RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

There was a major North-South compression event which is related to the Pyreneanprogeny and a minor NW-SE compressed event which resulted to the Alpine progeny.Most of the important anticlines of the Paris basin were formed during the Pyreneanprogeny.Fig 1.2: Geological cross section of the Paris basin

1.7 STRATIGRAPHY OF THE PARIS BASINThe general stratigraphy of the Paris basin on which Joana field is located is shown in thefigure 1.3 below. This shows that the basement rock is overlain with Triassic sedimentsdeposited in fluvial through marine to evaporitic environment. There was rapid thermalsubsidence in the early Jurassic period which produced a down wrapping of the basincentre and a deposition of transgressive-regressive cycles.The Comblanchean platform and callovian, on which the reservoir of Joanna fieldoverlies, is part of the T8 aggrading and transgressive series. The transgressive phaseshows the classical succession of the lagoonal mud-rich, aggrading sequences and highenergy oolithic-rich back steeping sequence.Joana Field17RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 1.3: General Stratigraphy of the Paris Basin

1.8 THE PETROLEUM SYSTEMBefore hydrocarbon accumulations are formed and retained in the sub-surface, there arerequisite conditions that must be in place. These conditions are what make up thepetroleum system. In essence, the petroleum system is made up of:Presence of a source rock

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MigrationPresence of reservoir rocksSealsTrapsTime and Preservation18RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

The conditions that have to do with flow and movement are called dynamic conditionsand includes migration, trap, time and preservation; while the reverse ones are namedstatic conditions, made up of source rocks, reservoir rocks and seal.The Joana Petroleum system being considered follows the same pattern and falls into thesame description. Figure 1.4 below depicts that:Also shown in the figure are the major geological (in some cases tectonic) incidents thathelped shape the Joana system. Some of these included the Austrian, Pyrenean andAlbine phases, the Tethys rifting, the primary and secondary diagenesis and theirrespective periods, etc. coming back to the different conditions, the next section containstheir explanations firstly on a general basis, and secondly as it relates to the field at hand.19RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 1.4: Petroleum System of the Joana FieldJOANASOURCE ROCK RESERVOIR MIGRATION OROGENIC EVENT SEAL ROCK TRAPSMAASTRICHTIAN Maturation Major phase

riftingSUBSIDENCE

phaseAustrianTethysStMartin-de-BossenayfaultsEarlydiagenesis??Secondary

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diagenesis??phasephaseAlpinePyreneanSTRUCTURAL&STRAIGRAPHC20RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

1.8.1 Source RockSource rocks refer to those fine-grained sediments; mainly organic rich shales that aredeposited on shallow marine environment during low energy transgressive phases ofgeologic basin formation. Hydrocarbons originate from the source rocks.For Joana field, the principal source rocks are several layers of Jurassic Toarcian Schist’scartons and Sineumurian Hettangian. The former (Sineumurian Hettangian) may havegenerated more oil than the latter (Toarcian) because they are more deeply buried andcover a larger area at the centre of the basin which is shown in Figure 1.2. However, thelower Torcian Schist’s cartons are the source rock for Joana field. The phase of oilgeneration began in the late cretaceous.1.8.2 Reservoir RockThe two main reservoir rocks encountered in the Paris basin are sandstones (upperTriassic keuper) and carbonates (middle Jurassic Bathonian). The Jurassic carbonates(which serves as reservoir for Joana field) are complex Oolitic bioclastic limestonereservoirs. They are divided into the upper calcarenitic unit (C4a) and the lowercalcarenitic unit (C4b). As shown in Figure 1.5, Facies C4a is less homogenous thanFacies C4b (Chapter 3 gives a detailed description). These rocks have accounted forabout 40% of the total production.21RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

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Figure 1.5: Facies C4a and C4b

1.8.3 TrapsThe type of trap existing is stratigraphic and structural in nature. Also porous micritic andconcentric Ooliths are being replaced by radial Oolite types with little reservoir quality.1.8.4 MigrationThe presence of Fault juxtaposition which enables the Hettangian to often make contactwith Triassic sandstones makes migration pathways easy. The thick and widespreadmiddle Jurassic (callovian) shales seal the middle Jurassic carbonate reservoir. Thepresence of this very extensive shale is one of the possible explanation for having nearlyno major oil accumulation above it in the centre of the basin.1.8.5 SealsThe presence of shale seals exists in the upper and lower reservoirs. The facies C2 andC3 seals reservoir 1 while C6 shale with patches of facies C9,C8 and C5(not continuous)acts as a seal for reservoir 2.The log below taken from Joana 5D illustrates this point.22RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 1.6: Log seals of reservoir 1(C4a) and 2(C4b).

1.8.6 TimeThe conversion of oil from the remains of plants and animals to kerogen and then to oiland gas requires the passage of time for its attainment. Also, the migration andaccumulation of oil at a particular reservoir takes time to be achieved.23RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER TWOSEISMIC INTERPRETATION AND ANALYSISThe acquisition of geophysical data for reservoir simulation is usually done in threestages from the seismic report. The three stages are:2.1 PICKING OF TOPSUsually the tops of geological layers (markers) are selected either with the use of verticalseismic profile (VSP) which involves the process of obtaining the travel time of soundwave at one point and extrapolating it to other points or with the use of the logcalculations. In some cases, both the results from the VSP and the log are correlated toarrive at the top of the marking layers.The interpretation of seismic is done by the geophysicist and the geologist each with theirrespective input: the geophysicist understands the mathematics of the process while thegeologist knows the existence of the various markers. The well known layer cakeinterpretation method of analysis comes in handy at this point.2.2 TIME DEPTH CONVERSIONThe respective geological layers are shown with respect to the time taken to reach theirtops and pass through them. Distance (depth) is not shown at this stage. The next taskinvolved is the conversion from time domain to the domain of depth. The knowledge ofthe velocity of the respective layers is now needed. Most times, the average velocities ofthe different layers which have been well researched and documented are used for theconversion. The knowledge of the different layers comes in very important at this stage.24RESERVOIR MODELLING PROJECT REPORT – JULY 2009

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(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

However, care must be taken not to fall prey to the classical velocity hoax, the case ofspurious structures thrown up on the time plot as a result of wide velocity differencebetween two adjacent layers. Clay and salt are usually the common culprits. Thisstructure leads to a false representation of the base of the salt layer as an anticline-likestructure. This is as a result of an adjusting in shape to cancel out the wide velocitydifference. So, the existence of a structure that looks like an anticline should be wellinvestigated so as not to be confused with a salt dome. Or better still, the existence of asalt layer in the field seismic should make the geologist and the geophysicist be preparedto correct for this hoax. This has led to drilling of salt domes with the thought that theywere anticlines.2.3 FAULT PATTERNSThe fault patterns existing in a field are usually very clear in the seismic report. For theJoana field, the two parallel faults were located at the edge of the field. Specifically, thefault is located at the south-west corner of the field. That was strategic. The strategiclocation of the fault could also be used to locate other points in the field. Simply put, thefault pattern was as unambiguous as they were helpful.Despite the three methods enumerated above, none was applied in the Joana field. Thegeophysicist had already prepared the seismic surface. The surface of the presentedseismic map was located on top of the maximum flooding surface correlated as layerMFS 3The seismic surface is as shown in Figure 2.1 below.25RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)-1 0 4 0- 1 0 5 0-1 0 6 0- 1 0 7 0-1 0 8 0- 1 0 9 0-1 1 0 0- 1 1 1 0-1 1 20- 1 13 0-1 1 40J o a n a -4Jo a n a -3Jo a n a -2J oa n a -1EM -2EM -112 0 0 1 60 0 2 00 0 2 4 0 0 2 8 00 3 2 0 0 3 6 0 0 4 0 0 0 4 4 0 0 4 8 0 0 5 2 0 012 0 0 1 60 0 2 00 0 2 4 0 0 2 8 00 3 2 0 0 3 6 0 0 4 0 0 0 4 4 0 0 4 8 0 0 5 2 0 06400 6000 5600 5200 4800 4400 4000 3600 3200 2800 2400 2000 1600 12001200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 64000 2 5 0 5 0 0 7 5 0 1 0 0 0 1 2 5 0 m1 :2 5 0 0 0

Figure 2.1: The seismic surface of Joana field showing wells and major faults.The seismic surface contains a major fault in the South West direction. Such faults arepopular in the basin which is evident in the contour map of the field which shows severalfault planes as shown in Figure 2.2 below.MajorFaults26RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 2.2 Contour map of the Paris basin with the red circle showing the location of Joana field27RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

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CHAPTER THREESEDIMENTOLOGY OF JOANA FIELDThe Paris basin has most of its geological features composed of sediments of finematerials (shales that is) formed in the shallow marine environment (depositionalenvironment) and during the Jurassic era (time).As a typical shallow marine environment that it is, the geological features of thesedimentology of the Joana field is as follows:Dune-like deposition of sediments ( shown in figure 3.1 below)The presence of oolithic and bioclastics sediments (shown in figure 3.1 below)Deposited in the environment of an ancient lagoon; characterized by warmshallow water.Figure 4.1: A typical dune-like depositional environment28RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

In line with the process of obtaining first hand information about the sub-surface, coresamples were collected at different sections of the wells under study. The core samplesfell into facies classification within the beds and were studied in their respective classes.The classes were from facies C1 – C9.The study was quite extensive and covered the various properties of the reservoir rock.However, the summary of it was what concerned the study at hand and exactly that iswhat is presented in the next section. These include:Table 3.1: Summary of the properties and reservoir potentials C1 – C9 facies.FACIETYPEDESCRIPTION RESERVOIRPOTENTIALC1 Fine bioclastic debris mudstone facies; cemented with dolomite.Deposited in low energy open seaGood seal; poorreservoir potentialC2 Micritic matrix mudstones.Deposited in subtidal environmentPoor reservoirpotentialC3 Packer stone with partial dissolution if some bioclasts with verylow porosity and permeabilityDeposited in a high energy environment of platform marginPoor reservoirpotentialC4a Essentially Grainstone and little packestone; well sorted,bimodal distribution with fine and medium granulometryDeposited in submarine duneGood reservoirpotentialC4b Grainstone with chemical compression and pressure dissolutionphenomenaGood reservoirpotentialC5 Sediments from lower reef shoals

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Deposited by very strong tidal currentsPoor reservoirpotentialC6 Micritic mudstone and wackestone.Deposited in subtidal environmentPoor reservoirpotentialC7 Reworked limestone particles coming from high energy dunelikeconstructionsPoor reservoirpotential29RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

C8 Facies containing bioclasts and wackestoneDeposited close to platform margin in high energy barFair reservoirpotential in fairsorted levelsC9 Bioclastic shale wackestoneDeposited in low energy open platform marginPoor reservoirpotentialFrom the table 4.1 above, most of the facies from the cores were deposited in dunes inshallow marine environment. There was equally the record of the presence of oolithiclimestone and bioclastics. These are intrinsic properties of dune-like depositions.A prehistoric surface map of the Paris basin was also available for the study of thesedimentology of Joana field. The map was presented in figure 3.2 below. The ringedarea is the location of Joana field and its depositional environment corresponds withsection E-F as equally shown below in figure 3.2 below.The figure indicates that the transgression and regression of the sea in prehistoric timesaround the coast and in the shallow parts of the sea played a major role in the depositionof sediments which formed Joana field. As shown in the figure 3.2, the Ladiox sediments,which was deposited in the shallow sea, formed the Callovian formation. The reservoirsof Joana field are contained within this Callovian formation.In conclusion, the sedimentology of the Joana field is that of limestone deposits.30RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 3.2: The prehistoric map of Paris basin showing the location of Joana field by the blue ring whichcorresponds with section E-F

3.2 STRATIGRAPHY OF JOANA FIELDThe stratigraphy of Joana field is a description of the succession of bed and formationwithin the field. This is represented diagrammatically in figure 4.3 below. The beds withgood reservoir are located within the lower Callovian formation, while the Bathonianformation forms the bottom seal of the reservoir. These formations were of the upperJurassic era, and are extensions of the Paris basin stratigraphy.31RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 3.3 The Stratigraphy of Joana field.Upper Callovian

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formationC1 – C2 C1 – C2 :Mudstone asMicritic limestone,tight formationC3 C3:Highly cementedlimestone; 2-3 porosity,low permeabilityC4A C4A: Coarse grainstones, well sorted; about15% porosityC6 C6:Micritic limestonewith brachiopod, wakestone corals andnumerous broken piecesC4B C4B: Grainstone andlittle packestonemodified by compressionand pressure dissolutionBATHOLITHS Upper Bathonian32RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

3.3 CORRELATIONSequence stratigraphy was used to create a chronological reconstruction of thesedimentary processes which gave rise to the reservoirs in Joana field.First, the classes of the facies were located in their typical depositional environment asshown in figure 4.4 below.Figure 3.4: Location of the facies 1 - 9 in their typical depositional environmentIn effect, the given facies collected from the seven wells, as cores, were arranged in orderof increasing depositional energy. The order was in this mannerC4A, C4B, C8, C9, C5, C7, C3, C6, C2, C1Increasing energy of depositionC 1C 2C 3C 4C 6C 7C 8C 9C 533RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

For each log of the seven wells under consideration, the positions of the facies along thewell log column was marked and an arrow was used to connect the marked facies in theprovided column as shown in figure 4.5 below for the well section of Joana 5D. Thedirections of the arrows were coordinated which culminated in the identification of themaximum flooding surfaces and the sequence boundaries.Figure 3.5: The maximum flooding surfaces and sequence boundaries.SB 3Sequence BoundaryMFS 3

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Maximum Flooding SurfaceSB 2Sequence BoundaryMFS 2Maximum flooding surfaceSB 1Sequence BoundaryIncreasing Energyof Deposition

34RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Using Petrel, the two well cross-sections under study were displayed and the maximumFlooding surfaces across the logs correlated using the following lines MFS 3, MFS 2MFS 1 and MFS 0 in figure 3.6.Figure 3.6: The correlated cross-section of wells; Joana-3, Joana-2, & Joana-6 (partly)35RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

The correlation of the well cross-sections in figure 3.6 yielded the following:There are three main maximum flooding surfaces across all the logs in the sevenwells under study (of which the cross-section of three is shown) as shown infigure 3.6 and above.The first maximum flooding surface correlated depth is MFS 3. Its correlation lineindicates the top of the Bathonian formation.The lower reservoir sand lies above MFS 3 correlation depth. This lower reservoiris marked as facie C4b. It was deposited when the sea regressed after themaximum flooding surface of MFS 3 was attained.The next maximum flooding surface above the Bta 5 is MFS 2. It was alsocorrelated across all the logs. It indicates the maximum deposition of C6 facie asthe sea transgressed.After MFS 2 maximum flooding surface, the sea regressed to deposit thesediments of facie 4A which formed the upper reservoir.Then the sea transgressed to reach the maximum flooding surface of MFS 2,which covered the entire area to deposit sediments of facie C3, C2 and C1 as seal.Figure 3.7 .The correlated cross-section of facies of the wells in Joana fieldJ1J3J2 J5J6J7GDJ436RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER FOURPETROPHYSICS4.1 LOGS AND INTERPRETATIONLogs obtained from well logging activities on the wells in the Joana field includedgamma ray logs, resistivity logs and neutron density logs. The primary aim of such logswas to identify the reservoir and non-reservoir zones. Usually, the identification of

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reservoir zones is accomplished by the correlation of all of these above-named logs. Nosingle log on its own can identify and confirm the existence of such. Truth be told, theuse of these, and many other logs cannot overrule the uncertainty that still lurks aroundthe corner. We are aware of that and a section would be dedicated to this concept.However, based on what was done, Figure 4.1 shows one of well logs from Joana 2Dwell. Using Petrel, analysis of this well log together with the well logs from the othernine wells was interpreted, and interpretation result extrapolated to describe the entirefield. The next two sub-sections would explain in slight details how the reservoir andnon-reservoir portions of the field were identified with the use of logs. Added to thesealso is the use of some of the appropriate reservoir engineering terms such as the cut-off,the water saturation, volume of shale calculation, the water salinity, the free water level,oil-water contact, the oil down to, water up to, and so on. All these would be spokenabout in the light of the field under consideration.37RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)CALI_14 IN 14

GR_10 GAPI 100

BS_14 IN 1415151520153015351540154515551560156515701580152515501575

1510.21585.0DEPTHMETRES

IMPH_10.2 OHMM 2000

IDPH_10.2 OHMM 2000

DT_1140 US/F 40

NPHI_10.45 V/V -0.15

RHOB_11.95 G/C3 2.95

DRHO_1-0.35 G/C3 0.15

PEF_10 B/E 20

TENS_111000 LBF 1000

Porous ReservoirsShale9m8m

Very low PorosityLimestone < 6%12m

Low Porosity19m Limestone (6-9%)Compact LSLOWER CALLOVIANBATHONIANFacies C4aFacies C4bFaciesComblanchienWELL: J-2DFacies C6

Figure 4.1: The Joana 2D well log15151520153015351540154515551560

15251550DEPTHMETRESGR_1

0 GAPI 100RT_1

0.01 OHMM 1000K_CORE_1

0.01 MD 1000SWE_1

1 V/V 0SWE_1

1 V/V 0PHIE_1

0.2 V/V 0VOL_UWAT_1

0.2 V/V 0PHI_CORE_1

0.2 V/V 0VSH_1

0 V/V 1PHIE_1

1 V/V 0CALCI_3MN_1

100 0EF_EZT_1

0 10FACIESLITH.VALUE_1SHOWS_1CORE_NO_1SAND_10 1.2RESERVOIR_10 1.7PAY_10 3PERFS.DESCRIPTION_1-1090-1095

-1100-1105-1110-1115-1120

-1125ELEVATION(TVD)METRES1515Call_Sup1522Call_Inf1552Bathonien

Core PermeabilityCore PorosityWater SaturationSWEffective PorosityPHIEShale Content VSHCore HC ShowsElectro- FaciesEasyTraceGeologicalFaciesMeasured Depth1525m1550mWELL: J-2DRw=0.5 @ 52 C=> Salinity = 7 kppmVSHGR

High RtSW < 60%GR Rt SW PHIE VSH EFacies Geol

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FaciesHCShows

Core CalcimetrySW

Figure 4.2: Cross section of processed logs from Joana-2D showing some computed reservoir propertiesalong the well section.38RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

4.1.1 Identification of the Reservoir zonesThe reservoir sections of well logs are generally characterized and identified based on theanalyses made on the measurements taken from the respective logs::Low gamma ray (this is at a value far below the minimum called the cut-off)Caliper size less than bit sizeRHOB (density log) lying on the left of NPHI (neutron porosity log)PEF (Photoelectric factor log) reading of about 1.8 units ( within sandstone), 5.1( within limestone) & 3.1 (within dolomite)LLD (Laterolog Deep resistivity) lying on the left of MSFL (Micro SphericallyFocused Log)SP (Spontaneous Potential) log having values which are not close the baseline –where the base line is chosen as the shale line.Most times, the results shown above apply to the pure reservoir rocks (i.e 100%sandstone or limestone) without any contaminant. In nature, however, that rarely occurs.To account for the volume of the impurities present (mostly shales), the volume of shalecalculation is done. This actually a factor (always less than one) which shows the volumeof the reservoir that is has shale impurity. The remaining would now be the pure reservoirrock.Also contained in the reservoir region is the contacts (the water-oil contact WOC, thegas-water contact GWC etc). WOC is determined by the difference between the LLD andthe MSFL. That is, at the contact, the distance between the two logs widens moreshowing a variation in their resistivities. The MSFL which measures predominantly theresistivity of water starts reducing while the LLD which measures both the resistivity ofoil and water starts increasing. This point usually becomes clear if the two super imposedon one another. The WOC is also the last point of 100% water saturation in the reservoir.39RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

The free water level, FWL, on its part is also a point of 100% water saturation. However,it is marked in reservoir engineering as the point of zero capillarity pressure.The water up to, WUT, is the last point that pure water reaches to in the reservoir. It mayor may not be equal to either the FWL or the WOC depending on the reservoir rock typeand pore spaces.Also, the oil down to, ODT, is the lowest point of oil in the reservoir. It also could beequal to the WOC or not depending on the rock properties and the pore size distribution.4.1.2 Identification of Non-reservoir areas (shale zones)The non-reservoir sections of well logs are generally characterized by the followingproperties:Caliper size greater than bit size.High gamma ray log.PEF (photoelectric log) reading of about 3.4 units.SP (spontaneous potential log) on the baseline

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RHOB (density log) lying on the right of NPHI (neutron porosity log).The use of the shale cut off value – a value of the gamma ray above which the sectionsare taken to be shaly is used. The non-reservoir portions are usually of almost oppositeproperties to the reservoir sections.4.1.3 Summary of the Petrophysical Analysis of the LogsFollowing the highlighted points above, the logged sections of the wells were analyzed.The reservoir and non-reservoir sections were identified and correlated as shown in figure4.3 below.40RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Using the gamma ray log and the density-neutron log overlay, two reservoir sectionswere identified. The reservoir sections were separated by a thick shale beds. Thereservoir sections were limestone bearing formations as indicated by the position of theneutron log lying on the left of the density logs along the reservoir sections. The gammaray log values along the reservoir sections were v low indicating clean formations. Usingquick look analysis, the average porosity along the identified reservoir sections was about19 percent. Also, the reservoir sections were bearing hydrocarbons formations asindicated by the high resistivity readings from the resistivity log as shown for Joana 2Din figure 4.2 above.Subsequent analysis of the saturation of the reservoir section showed that the averagewater saturation of the hydrocarbon bearing sections was about 30 percent, indicating thatit was rich in hydrocarbons.Figure 4.3: Cross section of well logs from Joana fields 3,2,,641RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER FIVESTATIC RESERVOIR MODELINGPetrel software was used for the static modeling of the Joana field. A three-dimensionalmodel was chosen owing to its ability to assist in the visualization of reservoir moreclearly. That is, it’s easier for the modeler to get a feel of his model while it’s being donein three dimensions. On a normal operation, the workflow for the static (or geostatic)modeling of a reservoir is as follows:5.1 DATA QC/QA AND ANALYSISData import and QC/QA of inputCreation of matching geographical surfacesCorrelation of reservoir on logsIntersection mapCreation of isochors map for reservoir5.2 STRUCTURAL MODELINGFault modelingUpscaling of logsFacies modelingPetrophysical modelingGrid Design5.3 COMPARISON OF THE GEOSTATIC MODELLING METHODSThe above have been the outline of the different sections. They would now be explored in

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details in the subsequent sections. In the course of our geostatic modeling, we carried outthe following activities:42RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

5.1 DATA QC/QA AND ANALYSIS5.1.1 Data import and QA/QC of inputThe data for carrying out the modeling are generally imported into the software frommany formats. Notable among them is the ASCII file format. Data can be imported asWell data (Well Tops), or Well logs. Also, the data could be copied from existing Petrelproject. The quality assurance of the data is ensured by the use of the Import DataSpreadsheet (which can be edited by the text editors Notepad, WordPad, Word andExcel) to verify the data and their units.However, for the project at hand, the data has already being imported and set for furtheranalysis. That is, the quality of the data has already been assured. The input data was thenused to create the surfaces for the modeling.5.1.2 Creation of surfacesThis is a process of gridding data into surfaces, and editing same to display on a window.This is not just related to pre-processing of data, but as a way of preparing the input data.The several types of data that could be converted to surfaces, include lines/point data,well tops/fault cuts etc. for our own case, the data was in the form of well tops.From the process window, the attribute to be created was chosen as the well depth. Thegeometry was then defined and the size of the boundary defined. The input type was alsochosen as seismic lines. Three sequence boundaries were identified along log sections forthe wells provided for this study as shown in figure 4.3 above. The sequence boundarieswere named MFS 3, MFS 2 and MFS 1. The surface MFS 0 was also identified.Together the references for the top and bottom surfaces were also provided. Thethickness between the surfaces MFS 0 and MFS 1 is shown below as a representative ofthe other surfaces to give an idea of the contour system in the reservoir (figure 5.1)43RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.1: Contour diagram for thickness between MFS 0 and MFS 1The other six surfaces are also shown in the next figure 5.2 below. It shows the surfacesthat were created.Figure 6.1: Creation of six surfaces44RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

5.1.3 Layering and Gridding of surfacesGridding refers to the use of cells to represent the reservoir models. Considerations forthe choice of the grid is that the reservoir was fairly heterogeneous limestone deposited ina dune-like manner as discussed in sedimentology of Joana field in Chapter three. Thus,to represent the heterogeneities associated with the reservoir and considering theprocessing speed of our computer systems, 100 * 100 grids was used for the geostaticmodel as diagrammatically represented in figure 5.5 below.With respect to the layering, 1.0 thickness was used to represent the heterogeneities in avertical section of the model. This gave rise to six layers as show in figure 5.3 below. Thewindow used for the selection of the thickness is as shown in figure 5.4 below.

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Thus, the grid dimension of the cells used for the geostatic model was 100*100*1.0 percell.Figure 5.3: Layering of surfaces45RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.4: Gridding of the surfaces with dimensions 100*100*1.0 per cell

5.1.4 Matching facies with wellsThe nine facies that were identified and sufficiently studied and explained (ChapterThree) from the core data of wells were matched with the logs. From the matches, thesequence boundaries were then identified. This was done using the displaying the datatool, then to the well section tool. The logs chosen for display were the gamma ray, theresistivity, the neutron porosity log and the density log. Also, the respective wellparameters: the permeabilities, the well names, the depth is TVD subsea etc were allentered. The colourful log was later displayed as shown in figure 4.3 above.46RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.5(a): Matching of facies with well log (Joana-2)Figure 5.5(b): Matching of facies with well log (Joana-3)47RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

5.1.5 Correlation of reservoir logs.Sequence stratigraphy was used to correlate the logs obtained from the various logs in theJoana field. With the knowledge of the respective maximum flooding surfaces, thecorrelation of the logs obtained from the various wells in Joana field was done Well Topswindow as shown in figure 5.6 below. The different layers, showing their differentformation types and characteristics (shown by their colours) were added. This is anaddition to the one earlier which contained the layers without the characteristics of theformations (figure 4.7)Figure 5.6: Reservoir log correlation48RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

5.2 STRUCTURAL MODELLING5.2.1 Fault modelingThis was the first stage in structural modeling. Here, the process involved the generationof a faulted 3D grid and inserting the horizons, zones and layers of the field into it. Thishas to be done first by defining the shape of each of the faults to be modeled i.e.generating the key pillars. The choice of the key pillars was done so as to have the faultdiagram cut through a section of the Joan field as shown in figure 5.7 below while stillretaining the grid shape of the field.Figure 5.7: Fault modeling identifying key pillarsThe final fault model using the fault sticks digitized on the x-section is shown below.Care was taken in the development of the fault sticks (key pillars) to use as few pillarsand shape points as possible, using just enough to show the fault’s form. The model isalready complex, and we don’t intend adding to this by a microscopic fine-tuning of thefault model. The model is just an approximation of the fault itself. This is shown in figure5.8 below.49

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RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.8: final fault model of the Joana field.

5.2.2 Scaling-up of well logs parametersHaving created the 3D grid and the fault model, values were added to the empty 3D gridsto build the geostatic model. First, we scaled up the well the well logs. In scaling up thelogs, the simple method was used: that is assigning a value to each grid which the logpassed through. The open hole log provided for the study were neutron log, density log,gamma ray log and sonic log. Each log was scaled up along vertical direction of the wellsusing volume arithmetic average methods as shown in figure 5.9 for the neutron-porositylog. This plot showed the up scaling process for the value and the graphicalrepresentation of the logs.50RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.9: Scaling up of porosity using arithmetic mean method.Figure 5.10: Scaling up of porosity along the wells in the model51RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

As shown in figure 6.9, the distributions of the scaled-up properties of the neutronporosity log were closely comparable with the original log. Also, the distribution for thescaled-up well sections of the neutron log was obtained by three methods of averaging:the sequential Gaussian, the Boolean and the Krigig methods. This is shown in figure5.10 with the sequential Gaussian clearly showng a better approximation of the porositydistribution.Figure 5.11: Histogram of the porosity distribution for the method used.52RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

For the Gamma Ray Log , it was up scaled using the using the acclaimed appropriatesequential Gaussian method. This is used despite the fact that porosity mostly a normaldistribution whereas most other reservoir parameters are lognormal. From figure 5.11below, the up scaled logs matched the actual logs within the limits of the structure of ourmodel.Figure: 5.12: Up scaling of Gamma ray on the reservoir model53RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

The 3D model (figure 6.12) also adds to the explanation of this point, showing thedistribution of the gamma ray properties of the fields in the field.Figure 5.13: Up scaled gamma ray logs in 3D

5.2.3 Scaling-up of Net-to-gross.The net-to-gross property was also scaled up using the arithmetic mean method. 5.13show the histogram where the scaled up net-to-gross values of the well logs wascompared with the original well logs and the up scaled cells. An appreciable comparisonwas obtained which implies that the scaled up net to gross is representative of thereservoir heterogeneity.54RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.14: Histogram obtained from the scaled up net-to-gross

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5.2.4 Facies modelingHere, the log properties and the facies properties were extrapolated across Joana field.Three methods usually are applied in achieving this namely: Sequential GaussianSimulation (SGS), Kriging and the Boolean method.However, because of the reasons given above about the appropriateness of the SequentialGaussian method to the simulation being carried out and time constraints, it was the onlymethod adopted. The figures 5.14(a) and 5.14(b) show the input window for theformation parameters for the reservoir (named Reservoir 1) and the shaly non-reservoirregion (Non –Reservoir).55RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.15: facies modeling of Reservoir 2Figure 5.16: facies modeling of the Non-Reservoir56RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.17: Facies modeling using Boolean method for the non reservoirThe facies modeling was carried out in order to build a geological model of Joana field.The up scaled log properties were complemented with given facie data for the field. Sixfacies were provided for the field and were inputted in the model as shown in figure 5.17above where the input for both the reservoir and the non-reservoir zone are shown.For the channel (the meandering river), the geostatistic method adopted is the Boolean.The Boolean method is usually used for definite objects in an area where its influenceends. For example, the meandering river starts and ends in the channel, and not even aninch outside it. The map of this is shown in figure 5.18 below. Equally substantiating thisproperty of the Boolean method is the Histogram 5.19 which shown little or no variation.The distribution of the properties for both the original data and the up scaled data showedelements of being discrete.57RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.18: Facies modeling of the channel the discrete Boolean methodFigure 5.19: Histogram obtained from the Boolean method58RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

The reservoir model using the Sequential Gaussian method as shown in figure 5.20 and5.21 below. Sequential Gaussian method of geo statistics is applicable for data that arediscrete and vary as well. It is not for continuous and deterministic data. Simply put, itinvolves simulation (similar to the Monte Carlo simulation) to arrive at its selecteddistribution of data. The choice of this method over the collocated kriging method wasthat the Collocated kriging has to make use of two distributions of data in which one ofthem is being made to concur with the other. For example, constraining of a seismic mapto become porosity map. The sequential Gaussian, on its part, allows the variation andjust shows it. This is acceptable in the modeling of reservoirs because of its attendantuncertainties.Figure 5.20: facies modeling using Sequential Gaussian Simulation (SGS)59RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 5.21: Histogram obtained from Sequential Gaussian Simulation.

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Figure 5.22: Facies modeling using kriging method60RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)Figure 6.23: facies modeling using the moving average method

5.3 COMPARISON OF THE VARIOUS GEOSTATIC MODELLINGMETHODSTable 5.1: Representation of the reservoir parameters.Region Bounding MFS Horizons Check Best LayeringParameterReservoir 1 MFS3,MFS2 Horizontal Gamma Ray Proportionallayering (15)Non-Reservoir MFS2,MFS1 Vertical Gamma Ray ProportionalLayering (5)Reservoir 2 MFS1,MFS0 Horizontal Gamma Ray ProportionalLayering (12)61RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Table 5.2: Comparison of the various geostatistic methods.GEOSTATISTIC MODEL CHARACTERISTICSDeterministic (moving average) It gives a single map and most times asingle value for the estimation of parameterof interest.Kriging It usually gives a single value most of thetimes. It does not give a distribution with arange of possible values.Stochastic (sequential Gaussian) This is a stochastic as well as a simulationmethod. Single values are not usuallyprovided, but a range of possible values; aprobability. The variation in data is wellrecognised and factored into any design.The process is similar to the famous MonteCarlo simulation.Boolean It is similar to the stochastic method, but itis usually confined within a particularregion for a particular object of interest.For e.g., the modelling of the variation ofporosity in a river channel.62RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER SIXCALCULATION OF OOIPFor this chapter our work would be to calculate the Original Oil in Place (OOIP) in thereservoir. There would be two methods adopted for doing such. The first would be to doso manually based on the information available from the logs of Joana field. This is initself a two-pronged approach as there would two different values for the manualcalculation based on the assumption made about the connectedness or not of the

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reservoirs of the field.Then, the static modeling software, Petrel, would be used to perform the same calculationbased on the model created. The two results would then be compared for similarities orotherwise.6.1 MANUAL CALCULATION OF OOGIPStatic reservoir modeling most times is done to obtain a geological structure of thereservoir as well as an estimate of the Original Oil and Gas in Place (OOIGP). For theJoana field, same was done as has been shown in the previous five chapters. To calculatethe volume of oil in the field, the knowledge of the two reservoir layers separated bysome non-reservoir beds was used. The process was done for two cases: connected andunconnected reservoirs. Which among the cases is correct? No one can really say, itdepends on who is looking at the report and what information is being sought. This wouldbe explored more under the section on uncertainties (section 6.2).63RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

The OOGIP is given by the formula below:OOIGP = bbls RVBSGNo

o 6.29 1Where:GN=Net-to-gross Ratio= ratio of the whole rock that is in the reservoir.= Porosity (fraction)o S = Saturation of Oil (fraction)o B = Formation Volume FactorRV= Rock Volume (in m3)6.29 = conversion factor from m3 to barrels (the commercial unit of oil).Data obtained from the logs of Joana field gave the following value for the petro physicalproperties:GN=0.70; =19%; o S =0.80 and o B = 1.2 Rb/STB.These values were considered to be average values across the reservoir beds in Joanafield.For the Rock Volume, the table of values for the top surface area of the topmost reservoirat various depths was provided. These values were plotted on the graph sheet shown infigure 6.1 below. From the plotted top surface line, the base of the topmost reservoir, andthe top and bottom of the reservoirs below were marked and extrapolated parallel to theplotted topmost surface line. The actual shape of the plot and hence the rock volume,depends on whether connection is assumed or not.64

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RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

6.1.1 Connected ReservoirFigure 6.1: The plot reservoir area versus depth assuming connected reservoir.For the connected reservoir case shown above (figure 6.1), the number of squares of thegraph paper were counted. They were then multiplied with the magnitude a unit square(in volume units) and 2,500,000,000 m3 was obtained as the Rock Volume.The OOGIP is then calculated by substituting the following values in the governingequation:0.70GN, 0.19, o S 0.80, o B 1.2Then,OOIGP = 6 .29 2500 ,000 ,0001 .210.70 0 .19 0 .80 bbls = 1,394,000,000 bbls= 1,394 MM bbls65RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Going a step further in calculating the hydrocarbon reserves (or recoverable oil); arecovery factor of 0.25 was assumed.Reserves = 0.251,394106bbls= 349 MM bblsTo bring the calculation to realistic, economic terms, we assume a price of $65.00 perbarrel of oil. Then:Revenue = 6 6534910= $22.70 billion (by approximation)6.1.2 Unconnected ReservoirFigure 6.2: The plot reservoir layers versus depth for an unconnected scenarioFor the unconnected reservoir case, by manual counting of the grids (within the yellowzones in figure 6.2 above) and multiplication with unit volume of the grids, the volumerepresenting the unconnected section of the reservoir was 60,000,000 m3.

66RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Thus the reference volumes for the unconnected and connected reservoir portions ofJoana field are considered to be 600,000,000 m3.OOIGP = 6.29 600 106

1.211.000.190.80bbls = 478,000,000 bbls= 478 MM bblsGoing a step further in calculating the hydrocarbon reserves (or recoverable oil); arecovery factor of 0.25 was assumed.Reserves = bbls 6 0.2547810

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= 120 MM bblsTo bring the calculation to realistic, economic terms, we assume a price of $65.00 perbarrel of oil. Then:Revenue = 6 6512010= $7.77 billion (by approximation)6.2 OOGIP CALCULATION FROM PETRELThe calculation of OOGIP from Petrel was done in these two steps:6.1.2 Connected ReservoirUnder the process window, the make contacts icon was chosen, from then to the contactset and the contact level was then entered. The contact level chosen was entered to be thesame for all segments and same for all zones. The flow was in this manner:Definition of Contacts: this was done as a new contacts set since none had beendefined earlier.67RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

Definition of the Contact Type: the contacts were defined as Gas Oil Contact andOil Water Contact.0.19, o S 0.80, o B 1.2Definition of Contact level: Gas Oil Contact = 1625mOil Water Contact = 1945mFrom the common settings tab, the properties of the reservoir that are user-defined wereentered. They are as follows:o S 0.80, o B 1.2Figure 6.3: volume calculation settings window68RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

On completion, the volume calculation report was generated and the print screen is asshown in figure 6.4 below.Figure 6.4: Print screen of the Volume Calculation Report.From the figure 6.4 above, the Original Oil in Place from Petrel was 64 million cubicmetres of oil. Apply the same recovery factor used above; we have revenue of $6.5billion.69RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

CHAPTER SEVENUNCERTAINTIES, CONCLUSION ANDRECOMMENDATIONS7.1 UNCERTAINTIESThe uncertainties that exist in the modeling of this field and by extension, the calculationof the OOIP include:7.1.1 General Reservoir StructureThe modeling of the field was done on the assumption of the classical anticlinal structurefor the reservoirs. The layers that were used to create the structure of the reservoir wereassumed to be formed in this manner with the bottom water in place.Also, the seismic interpretation that yielded most of the information used to define the

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field could have been erroneous also. This is because the layers were not explicit andthere presence was inferred majorly based on experience.The time depth conversion that yielded the depths of the different layers is also not foolproof,bearing in mind the classical velocity hoax in salt domes.The compartmentalization of the reservoirs to different pressure regimes is also subject toerror.70RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

7.1.2 Sealing or Non-Sealing of FaultsThe fault that ran through the south-west of Kandie field was assumed to be sealing. Thatwent into the modeling of the fault, the reservoirs in the field and the calculation of theOOIP. It could have been non sealing leading to the migration of fluid that was expectedto have been trapped there. That could lead to an error in the OOIP7.1.3 Reservoir LayeringUniform layering was assumed for the reservoirs of the field that resulted in the divisioninto three major layers i.e. the top and bottom reservoir and the middle non-reservoir. Thegamma ray was used to quality check the layers which is an approximate itself. Thelayers are not as homogenous as the model might have assumed.7.1.4 Geostatisitcal extrapolation of Petrophysical ParametersThe use of geostatistics to extrapolate most of the reservoir petrophysical parameters isnot without its own errors. Parameters such as porosity, permeability, fluid saturations etcwere all extrapolated using either the deterministic or probabilistic methods ofgeostatistical analysis. The use of the methods of estimation such as the moving average,the kriging, the collocated kriging; the simulation methods of the sequential Gaussian andthe Boolean all involve either estimating a value to represent a whole group of numbersor the use of the distribution of values to extrapolate the others7.1.5 Position of the Fluid ContactsThe fluid contacts chosen for the calculation of the OOIP were given based on theinterpretation of logs and the seismic survey, coupled with the knowledge of the geologyof the area (which can never be exhaustive). The water level used for the calculationscannot be clearly said to be Oil Water Contact. It could be the Water Up To or the FreeWater Level. This is because despite the sophistication of the tool used, there is aloophole for uncertainties.71RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

7.1.6 Reservoir Fluid PropertiesThe fluid (gas, oil and water) properties that were used in the description of the reservoirsand in the calculation of the OOGIP were, at best, estimates. This is because no matterhow perfect a sampling process is, the result would still have errors. Samplings areusually done on the premise of homogeneity; such could not be said with certainty aboutthe field.Also, the Pressure, Temperature, and Volume (PVT) properties of reservoir fluids varywith the parameters of the environment. So, the samples taken, and used could not be saidto be perfectly representative. Parameters involved in this include the Formation VolumeFactor (both for oil and gas), the solution gas ratio etc.

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7.1.7 Sequence StratigraphyThe determination of fluid contacts (and other reservoir properties) is usually done at thedrilled wells with certainty. The other points between the wells have their propertiesdetermined by correlation and sequence stratigraphy. The correlations could be wrongand any OOIP calculated with such wrong correlations would be useless.72RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

7.2 CONCLUSIONAt the end of the week-long static modelling of the Joana field, we were able to defineand model the reservoir and non-reservoir compartments culminating in the calculation ofthe OOIP of 1398 MM bbls and 478 MM bbls respectively for the connected andunconnected reservoirs. Also, the use Petrel for modeling gave an OOIP of 402.56 MMbbls (i.e. a reserve of 120 MM bbl). From the data presented above, two things becomeevidently clear:The quantity of OOIP calculated depends on the person calculating and theassumptions made in the calculation. For example, assuming a connectedreservoir gives a value about thrice that of an unconnected reservoir. These are theuncertainties discussed in the previous section.Also, the more of the uncertainties that one takes care of determines the accuracyor not of the calculated OOIP. The use of the software Petrel appeared to give abetter result because of the number of uncertainties as against the manual methodof calculation. The use of geostatistics to make intelligible and reasonablepredictions based on the response of the reservoir cannot be over-emphasized.The parameters (e.g. Porosity is more distributed under Petrel than the arithmeticaverage assumption of the manually calculated method.Synthesizing the two points above, it suffices to say that a reservoir could have a widerange of the cost implications depending on which method of calculation as theconnected reservoir is worth about $15billion more than the unconnected one. So, thepreferred calculation is the Petrel calculation because of its recognition of uncertaintiesand giving a more realistic quantification of the reservoir OOIP.73RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

7.3 RECOMMENDATIONSBased on the above, we recommend that:The facies modelling be repeated with another geostatistic method so as to arriveat the optimal method of reservoir properties extrapolation.The model be fine-tuned with a smaller upscaling ratio in order to arrive at betterresults. A higher model of the Petrel software can suffice, at this point.The uncertainties identified in the study be investigated upon for furtherinformation. The ones that relate to the change of scales of observation can alsobe studied too.The model can still be upscaled to a dynamic model, based on the favourableeconomic outlook of the OOIP, which could still updated as field data is gathered.74RESERVOIR MODELLING PROJECT REPORT – JULY 2009(BY NWATU, VICTOR OKECHUKWU AND OLAJIDE, FESTUS OLATEJU.)

REFERENCES31

Lecture Notes on Original Oil in Place (OOIP) Calculation and Reservoir Uncertainties(2009), Bernard Michaud, IPS/IFP, Port-Harcourt, Nigeria.Petrel for Reservoir Engineers, Reservoir Engineering Course v.2004 (course ed. 1),Schlumberger Information Solutions, 1st July 2005, 5599 San Felie, suite 1700, Houston,TX 77056-2722.

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