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Marine and Petroleum Geology 26 (2009) 573–579

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Marine and Petroleum Geology

journal homepage: www.elsevier .com/locate/marpetgeo

Integrating structural geology and petroleum systems modeling – A pilotproject from Bolivia’s fold and thrust belt

Friedemann Baur a,*, Matias Di Benedetto b, Thomas Fuchs a, Carolyn Lampe c, Simone Sciamanna d

a IES, Integrated Exploration Systems, Ritterstr. 23, 52072 Aachen, Germanyb RepsolYPF, Esmeralda 255, Buenos Aires C1035ABE, Argentinac Franz-Kreuter-Str. 4, 50823 Koeln, Germanyd RepsoYPF, E&P, Praia do Botafogo, 300, 22250-040 Rio de Janeiro, Brazil

a r t i c l e i n f o

Article history:Received 7 September 2007Received in revised form27 March 2008Accepted 2 January 2009Available online 15 January 2009

Keywords:BoliviaSub AndeanFold and thrust beltPetroleum systems modelingStructural geologyTecLinkBasin modeling

* Corresponding author. Tel.: þ49 241 5158610; faxE-mail addresses: f.baur@ies.de, baur@lek.rwth-aa

0264-8172/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.marpetgeo.2009.01.004

a b s t r a c t

For the first time, a new approach to petroleum systems analysis is presented which allows full inte-gration of tectonic and palinspastic restoration with three-dimensional (3D), PVT-controlled, multi-component, three-phase petroleum migration analysis through time. A systematic modeling study hasbeen applied to a study area dominated by fold and thrust belts located in the Sub Andean orogeny nearTarija, Bolivia. The project has been performed with a special focus on the simulation technique and onthe correct distribution of temperature, source-rock maturity and pressure development through timewith reference to its input data. This is the first pilot project presenting a 3D numerical model ina compressional structural regime to which the basin modeling approach has been applied to explain theobserved distribution of temperature, pressure, maturity and petroleum accumulations in general.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Nowadays it is becoming increasingly difficult to make newdiscoveries and to predict the location of accumulations, theirvolumes and their composition due to the fact that many of theworld’s new interesting exploration areas are characterized bystructurally complex geologic settings. Therefore, there is a distinctneed to link structural modeling techniques with the petroleumsystems analysis approach to assess complex scenarios and toquantify and improve petroleum charge risk. While this link isalready proved useful and has been successfully tested and appliedin 2D (Lampe et al., 2006; Sciamanna et al., 2005), this paperpresents the first application of such a link in full 3D. The study hasbeen performed using the PetroMod� 3D PetroFlow package,including the TecLink 3D tool developed by IES (Integrated Explo-ration Systems GmbH). PetroMod� TecLink 3D enables thecomplete range of petroleum generation and migration methods,using the hybrid migration simulator (Hantschel et al., 2005), to beapplied in complex tectonic environments such as those affected by

: þ49 241 515860.chen.de (F. Baur).

All rights reserved.

salt- and shale-diapirism, as well as in extensional and especially incomplex compressional tectonic environments such as thrust belts.

The approach was applied to a 45� 25 km area in the SubAndean fold and thrust belt located 120 km northeast of Tarija,southern Bolivia, in order to provide an integrated explorationstudy for a more focused oil and gas exploration.

The pilot project is based on interpretation of seismic data,structural restoration and petroleum systems modeling. The latterincludes the so-called TecLink 3D approach, which is a new, uniqueand innovative technique, avoiding the issue of multiple z-valuesfor an individual layer in the case of thrusted strata, which posesproblems during numerical simulation. It should be noted that thefocus of the project was on development and validation of the newmodeling technique, rather than providing new insights about theregional geology of the study area.

2. TecLink 3D – method

2.1. Event and Paleo Stepping

The traditional approach in basin modeling uses the present-daygeometry as an input parameter to calculate the initial depositional

F. Baur et al. / Marine and Petroleum Geology 26 (2009) 573–579574

thickness of a layer backwards by applying a decompaction rule(Eq. (1)). To solve the decompaction equation for the first time, thepresent-day porosities are estimated by the program using a fast 1Dsteady-state approach for the present-day geometry only. Theseestimated present-day porosities together with the initial porositiesand the present-day thickness yield the depositional thickness. Theinitial porosities are taken from a PetroMod� internal databasewhere all lithology-dependent parameters are stored.

dPD=dini ¼ ð1� FiniÞ=ð1� FPDÞ (1)

with d¼ thickness, F¼ porosity, ini¼ initial, and PD¼ present-day.After removing and decompacting the entire stack of sediments,

which is called backstripping, sequential, deterministic, forward-modeling is applied to simulate step-by-step from the oldest eventup to present-day geometry. Temperature and pressure develop-ment is taken into account to consider the behavior of compactionin more detail (Welte et al., 1997).

For each time-step, which is determined within the input of thenumerical model as depositional or erosion age, the following sub-steps are performed.

First, the newly deposited sediments are added with their initialporosity.

Next, the pressure equation (Eq. (2) for 1D case) is solved usinga numerical finite-element solver.

v=vzðkvu=vvzÞ � Cðvu=vtÞ ¼ �C vðpl � phÞ=vt (2)

with u¼ overpressure (pore pressure minus hydrostatic pressure),pl¼ lithostatic pressure, ph¼ hydrostatic pressure, k¼ permeabilityof the layer matrix, v¼ fluid viscosity (fluid property), z¼ depth,C¼ compressibility (here equal to l�Fmin where l is Athy’s factorand Fmin is the minimum porosity).

In order to solve this equation one needs to know the change inlithostatic potential, which is the difference between lithostatic andhydrostatic pressure. To calculate the lithostatic pressure, the respec-tive densities of water and rock as well as the porosities are needed. Theporosity is also needed to calculate the permeability, which is assumedto be a function of lithology and porosity. For the new sediments theinitial porosity is used, and for the already deposited ones the calcu-lated porosities from the previous time-step are used.

Once the overpressure is known, the maximum effective stress(s¼ pl� ph� u) can be calculated. This can then be used to applya compaction model (Eq. (3)) which yields the new porosities basedon the overpressure or maximum effective stress.

An equation similar to Athy’s law but more complex andexpressed in terms of overpressure rather than effective stress isused in the software (Eq. (3) shows Athy’s law changed to over-pressure conditions).

F ¼ Fini exp�� lðpl � ph � uÞmax

�(3)

where (pl� ph� u)max is the maximum value attained by theeffective stress. Thus, we have for the compressibility C¼ lF. Forother abbreviations see above.

The solution of Eq. (3) provides the new porosities. From thenew porosities all other related parameters are known, such aspermeability.

The simple relation between porosity and thickness (Eq. (1))gives the new thickness during the forward simulation. Tempera-tures and all other quantities are calculated afterwards. Thesecalculation steps are repeated up to present-day.

If the simulated present-day geometry differs from the giveninput geometry one can perform additional runs. In these runs thecalculated present-day porosities are used in the decompactionequation to determine initial depositional thicknesses, instead of

using the multi-1D calculated porosities; the more runs performed,the better the agreement between simulated and given inputgeometry.

The time framework which controls the calculation steps isgiven by the depositional and erosion ages of the strata. These agesare defined as ‘‘Event Steps’’ and are the basis for a past to presentforward-modeling simulation (Hantschel and Broichhausen, 2002).Therefore, the Event Stepping approach calculates compactionbased on initial conditions such as initial porosity, permeability,fluid viscosity and compressibility as well as additional informationsuch as present-day thickness and ages. This approach (Fig. 1) issuitable for geologic settings dominated by normal deposition anderosion and in extensional basins (Broichhausen, 2004).

In the case of complex paleo-thickness-variations such as, e.g.massive vertical structural movements like salt- and mud-diapir-ism and other complex extensional structures, there is a certainneed for kinematic, palinspastic and structural restorations, takingthese movements of masses into account. The intermediatereconstructed paleo-geometries act in this situation as a guidelinefor the regular forward simulation and can directly be integratedinto the modeling process as so-called ‘‘paleo-models’’. For paleo-models the thicknesses are already predefined (snapshots in time),and solving compaction and its related calculation for thicknessprediction is therefore no longer necessary. Instead of building onemodel with present-day geometry one builds several models withfixed geometries and assigns ages to each model.

Instead of applying the Event Stepping method all the way fromthe oldest to the present-day geometry, the simulation optimizesonly up to the first (i.e. oldest) paleo-model (optimizing in that casemeans an iterative improvement to match the predefined inputthickness, thus the thickness of the oldest paleo-model). With thedefinition of the first paleo-model the forward-modeling approachchanges from the Event Stepping mode to the so-called ‘‘PaleoStepping’’ approach (Fig. 1). From that point, the simulator useseach given paleo-model and calculates temperature and pressureconsidering its duration and shape (see also Section 2.3), beginningwith the oldest geometry and simulating forward in time (Hant-schel and Kauerauf, 2009). The resolution of the model with respectto time is now determined by the number of paleo-models and isno longer controlled by depositional ages. Of course it is possible tohave deposition of additional layers at the top of the strata duringPaleo Stepping but this new geometry has to be provided as anadditional paleo-model.

To include transient effects for maturity, temperature or pres-sure, the calculated values from the previous paleo-model areconsidered and transferred to the next paleo-model. This is donefor each parameter taking into account both vertical and lateralinfluences for the changing geometries through time. This proce-dure of applying first the Event Stepping approach at depositionaltimes and using the Paleo Stepping approach, which meansswitching from one paleo-model to the next, during movements ofmasses, describes the simplest scenario of a TecLink model (Hant-schel and Kauerauf, 2009). More complex is the situation in cases ofnot only vertical but also relative contrary lateral movements ofmasses, e.g. during thrusting and compression. In such a situationof lateral displacement of rock masses thrust faults are indispens-able and the problem of multiple z-values for the same layer occurs.In this situation the ‘‘block-concept’’ has to be introduced to avoidthe vertical repetition of a layer.

2.2. The block concept

Models which undergo significant shortening (thrust) due tocompressional tectonics need to be subdivided in a way thatmultiple depth-values are eliminated. This can be realized by

Fig. 1. Schematic diagram depicting the handling of compaction and subsequent pressure calculation for two different approaches. (1) Event Stepping: during normal deposition allgeologic events are defined by depositional (or erosional) ages. Compaction through time is calculated in steps using a deterministic forward-modeling approach which is thencompared to the initial model input data. In case of a mismatch, an iterative improvement of the match between the input thicknesses and the final model thicknesses is performed.Pressure is calculated as a function of load, converted into stress, and a compaction model provides porosity and thickness. (2) Paleo Stepping: during compression all geologic agesare defined through paleo-models, i.e. predefined geometries that change through time. Pressure, stress and porosity are defined as described for the Event Stepping approachexcept that porosity is not used for thickness calculation.

F. Baur et al. / Marine and Petroleum Geology 26 (2009) 573–579 575

subdividing the model into individual ‘‘thrust-blocks’’ (also called‘‘fault blocks’’). Each fault block corresponds to an individual thrustsheet representing a geometrical unit without vertically repetitivestrata. While each fault block represents an individual sub-model onthe input side, all blocks are combined into a single integrated modelduring the simulation. The thermal and pressure regime as well asmigration are calculated for the entire model including its mutualand overlapping effects at the block-boundaries. Hence, blocksretain their structural integrity during the model’s tectonic evolu-tion but are connected with respect to all geophysical andgeochemical parameters. Information about the age, shape, locationand hierarchy of all blocks throughout both space and time needs tobe determined within the input in the form of the geometry itselfand some extra information. This extra information has to beintroduced to handle the generic exchange of information amongthe paleo-models during Paleo Stepping. This can be realized bydetermining three additional kinds of data/information to allowa correct assembly of the paleo-models at a certain age and position.The extra information is (1) the age assignment for the paleo-modelsto put them into the correct chronological order, (2) the block orderassignment to stack the blocks within each paleo-model on top ofeach other and (3) the so-called parent–child-block concept, whichcontrols the affiliation and derivation of each block in the case ofblock splitting. This information is fundamental for allowinga correct exchange of data between the corresponding blocks for allparameters which are calculated for the numerical model.

2.3. Special pressure handling

Pressure and porosity in TecLink models are calculated withinthe Paleo Stepping approach via predefined paleo-models and their

subsequent change in overburden which is inherent to their givengeometry (Fig. 1). Thus, it is desirable that the changes in layerthickness (overburden) between individual paleo-models areaccounted for during their palinspastic reconstruction. Whileswitching from one paleo-model to the next, the change in over-burden can be calculated from the actual and previous paleo-modelby adding up the weight of the overburden column heights andtaking into account the lateral movement. For the lateral movementthe cell values are transformed accordingly by taking into accountthe lateral length changes of each layer. With the first paleo-modela pressure regime is already available derived from the traditionalcalculated Event Stepping approach. Additionally, the porositiesand permeabilities and all other parameters are available as well.For the second paleo-model (second eldest) the change in over-burden represents the change in lithostatic and hydrostatic pres-sure and the porosities are taken from the previous paleo-modeland used by the simulator to solve Eq. (2). Overpressure is usedonce again to calculate effective stress (s¼ pl� ph� u), which isthen used to obtain the new porosities. This workflow is knownfrom the traditional Event Stepping approach.

The only difference to Event Stepping is that in the Paleo Step-ping approach porosity is not directly related to thickness viacompaction, which means compaction and porosity decrease aredecoupled (Hantschel and Kauerauf, 2009). Instead, the porosity isdirectly connected to the effective stress, whereas the thickness isused as it is predefined.

In the case of an incorrect structural reconstruction, wherea layer is buried continuously but the thickness does not decreaseaccordingly, compaction can be compensated and controlled bychanging the amount of rock matrix material to end up with thecorrect porosity at a certain/given thickness.

F. Baur et al. / Marine and Petroleum Geology 26 (2009) 573–579576

3. TecLink 3D – application

3.1. The study area

The 1125-m2 study area is located 120 km northeast of Tarija,Bolivia and lies amidst the Sierras Subandinas within the SubAndean Zone at the eastern margin of the Andean orogeny. Asedimentary sequence of up to 8 km in thickness has beendeposited from Early Ordovician to Late Pliocene, featuring anactive foreland basin stage from Early Miocene on (Corneliuset al., 2005). The area is characterized by north–northeasttrending narrow anticlines and thin-skin tectonic deformation,which has been active since the Late Miocene (6–7 Ma) and hasgenerated a hinterland duplex geometry cut by out-of-sequencethrusting during the very last deformation stage (Sempere et al.,1990; Baby et al., 1992). The relative timing used for the pal-inspastic reconstructions has been established based on growingstrata, paleo-magnetic data and isotopic data of volcanic ashes(Echavarria et al., 2003). A simplified sequence stratigraphy hasbeen used not only for the structural reconstruction but also forthe numerical basin model, which comprises 20 layers. The SubAndean fold and thrust belt is controlled by two major incom-petent layers, the Silurian Kirusillas and the shallower upperDevonian Los Monos Formation. Both layers cause detachmentlevels (Sempere, 1995; Echavarria et al., 2003; Moretti et al.,2006) and are realized in the model. At the same time theseshale-dominated detachment levels act as source rocks togetherwith a third, lower Devonian, source rock. All source rocks consistof siliciclastic detritus and have been deposited in a semi-restricted anoxic, marine, extensional basin (Lindquist, 1998). Thesource rocks are preserved throughout the area with thicknessesranging from hundreds to thousands of meters, and havea maximum cumulative thickness of around 2 km (Lindquist,1998; Moretti et al., 1996, 1995).

Silurian and younger reservoir rocks are widely distributedwithin the Sub Andean orogeny. They are characterized by fair tovery good porosity at shallower depth due to high quartz contentand a slow rate of dissolution at low temperature. They have goodpermeabilities at greater depths as a result of geomechanicalfailure, i.e. fracturing (Jordan and Alonso, 1987; Moretti et al., 2000;Labaume and Moretti, 2001b; Florez-Nino et al., 2005). Regionaland locally distributed seals were deposited during the entirePaleozoic throughout the study area and often alternate with thesandstone reservoirs (Jordan and Alonso, 1987).

3.2. Geometry

Seven 2D sections as well as two local 3D seismic surveys fromproduction areas have been interpreted and combined to a 21/2Dstructural model which acts as the basis for a 3D palinspasticreconstruction. The structural reconstruction, which ended up with14 restored paleo-models, ranging in time between 6.7 and 1 Ma(Fig. 2), have been performed using 3D Move, developed byMidland Valley Exploration Ltd. The present-day input model forthe structural restoration also acts as the present-day geometry forthe basin model in PetroMod�. This present-day geometry consistsof 10 blocks, with a total of 84 blocks for the entire model includingall paleo-models. Each paleo-model comprises 20 different strati-graphic layers, each consisting of one facies representing onespecific lithology. This is in fact a simplification but this study wasdesigned to test and apply the TecLink approach to a compressioncontrolled 3D data set, rather than focusing on geological detail.Each block comprises both source and reservoir rocks. The initialgrid distance is set to 200 m but the simulation has been performedon a sampled grid.

3.3. Input data

Three major source rocks are considered in the model. Theywere deposited under restricted anoxic, marine conditions andhave been defined to be the Silurian Kirusillas Formation, the EarlyDevonian Icla and the Middle Devonian Los Monos Formation withinitial TOC (Total Organic Carbon) contents of 2 wt.% and HI(Hydrogen Index) values ranging between 400 and 630 mg HC/gTOC (Illich et al., 1981). All intervals are type II to type III, mixed oil-and gas-prone source rocks (Dunn et al., 1995). A generic type IIkinetic model, which fits to all source rocks, has been assigned forconversion of kerogen into petroleum to keep the model as simpleas possible (Vandenbroucke et al., 1999).

The Los Monos Formation also acts as a regional seal due to itslow permeability and is responsible for maintaining the observedoverpressure. The main reservoirs are the fractured Early Devonianquartzites of Huamampampa and the Late Devonian Iquiri Forma-tion. The Santa Rosa, Ichoa and Machareti Formations are alsoassumed to be potential reservoirs. Thrust faults are used as block-boundaries to which properties can be assigned. Due to the fact thatsome of the faults, which cut the reservoir, do not outcrop at thesurface, the assignment of fault properties has been decoupledfrom the existence of a block boundary. It is possible to assignproperties to selected parts of the existing block-boundaries. Thecurrent pilot project, however, was simulated without extra prop-erties, thus the behavior of the faults is controlled by the neigh-boring lithologies.

3.4. Boundary conditions

A constant heat flow of 42 mW/m2 through time with a higherheat flow of 47 mW/m2 for the Holocene has been assumed to fitthe calibration data. This coincides with values from publishedliterature (Husson and Moretti, 2002).

The paleo-water-depth is defined as zero for the periods ofdeposition between 490 and 6.7 Ma. Uplift and thrusting lifted themodel above sea level starting at 6.7 Ma, to give a final averageelevation of w1000 m at present-day. In addition to the present-day surface two paleo-surfaces have been implemented into themodel. The remaining paleo-models have flat but inclined simplepaleo-surfaces. The sediment water interface temperature isdetermined considering the global temperature distributionthrough time as well as the virtual geomagnetic polar wanderingpath for the corresponding continent. The obtained surfacetemperature through time is corrected for the paleo-water-depthbased on a standard temperature depth profile (Wygrala, 1989)which is extrapolated for elevations above sea level.

4. Results

Vitrinite reflectance is one of the primary calibration parametersfor the thermal evolution of sedimentary deposits to reconstructtheir burial history and maturity. The EASY%Ro algorithm ofSweeney and Burnham (1990), has been used to calculate andcalibrate vitrinite reflectance.

The model’s maturity has been calibrated comparing allmeasured vitrinite reflectance data from wells with calculatedtrends (Fig. 3). The transient effect of vitrinite reflectance (Fig. 3)can be seen clearly in the very left block of the upper left modelcube representing the present-day situation. This block was up-lifted just 2 million years ago, thus the maturity offset is caused bythe thrusting of highly mature over less mature material along thethrust fault.

The included 1D extraction (Fig. 3) along one well shows a cali-brated maturity profile vs. depth. The profile shows a sudden

Fig. 2. Three of 14 paleo-models are shown. The progressing deformation becomes evident from left to right. Left: beginning of compressional deformation (6.5 Ma); centre:intermediate timestep (5.5 Ma); right: the present-day situation. The upper set of images shows the palinspastic reconstruction of individual horizons used as input data for thenumerical model; the lower images show the actual petroleum system model with all properties, such as lithology and petrophysical properties and boundary conditions. The greyshades depict individual stratigraphic layers.

F. Baur et al. / Marine and Petroleum Geology 26 (2009) 573–579 577

decrease in maturity at the top of each block, which marks thetransition from the thrusting hanging-wall block to the lyingfootwall block. At transitions where no obvious difference inmaturity occurs, it can be debated whether the displacement wasnot strong enough or has been obscured during the geological past(e.g., at the boundary between Block II and III in Fig. 3).

For porosity, a retrograde distribution of values within allthrusted blocks, stacked on top of each other, can be observed(Fig. 4). Within each individual block porosity decreases from top to

Fig. 3. Development of vitrinite reflectance through time of the model-cubes: at 6.5 Ma, 5.2strata for younger ages. Note the maturity offset on the left side of the present-day cube, whfault. 1D extraction of a calibration well, (the extraction goes beyond its original depth). The etrend (solid line) after Sweeney and Burnham (1990).

bottom due to mechanical compaction. The porosity has beencalibrated for all wells based on log-derived porosity data. Aftera successful fit between measured and simulated data for porositythe pressure has been calibrated while changing the defaultpermeability–porosity relationships for some individual litholo-gies, each corresponding to one facies or one layer, respectively.

Overpressure simulation and prediction is still one of the mostchallenging tasks in petroleum systems modeling. The applicationof the new technique (described in 2.1 and 2.3) that converts the

Ma, 2 Ma and at present-day situation. Maturity iso-lines are cutting across the tiltedich is caused by the thrusting of highly mature over less mature material along a thrustxtraction shows measured vitrinite reflectance data (stars) and the calculated maturity

Fig. 4. Porosity (left) and pressure (right) in two wells. The displacement of blocks becomes evident in the vertical porosity distribution. Two sets of pressure calibration data areshown: mud-weight (dots) and RFT (diamonds). The calculated pore pressure (solid line) matches the in situ measurements of RFT very well.

Fig. 5. These are cell extractions taken from source-rock cells located at the top ofdifferent anticlines in different blocks (thrust sheets) of different locations and ofdifferent depths (not from well positions). The critical moment (CM) is indicated by anarrow for two source rocks (SR): Silurian¼ dotted line, Lower Devonian¼ dashed lineand Upper Devonian¼ solid line. The Upper Devonian SR has not reached its CM yet,whereas the Silurian had its CM already in the Permian. The figure shows clearly thatpetroleum has been continuously generated over a long period of time. Parts of thesource rocks, depending on their relative position within the fault and thrust belts, areonly just at the beginning of the petroleum window and show ongoing transformation,and have still a large potential for HC generation.

F. Baur et al. / Marine and Petroleum Geology 26 (2009) 573–579578

change of overburden or load into pressure and porosity andsubsequently into effective stress for each single cell allowstracking the pressure and all related parameters through all paleo-geometries, of the model (Fig. 4). The pressure has been calibratedto all available repeat formation tester (RFT) data to explain themodel and to provide a good base for pressure gradient drivenDarcy migration analysis.

Maturity, source-rock transformation ratio and generatedvolumes of petroleum are influenced not only by the basal heat-flow, but also to a great extend by the relative position of the sourcerocks within the individual blocks and the entire model. Since theblocks move both vertically and laterally through time, the sourcerocks shift position and move successively in and out the petroleumwindow. The thrusting of the blocks causes tilting of the stratawhich causes the individual parts of source rocks to become matureat different times and in different positions. Therefore, it is virtuallyimpossible to define a single critical moment (Magoon and Dow,1994) for the study area. Whereas most of the Silurian source rockhad its critical moment in the Permian, parts of the lower Devoniansource rock reached the required transformation ratio of 50%within the Cenozoic. Some parts of the upper Devonian source-rockappear to have potential for generating wet gas and methane atpresent-day (Fig. 5).

As stated above, the present model does not comprise any extrafault-property assignment, thus the behavior of the block-bound-aries is controlled by the facies, respectively, by the lithologies,which are neighboring each other at the block-boundaries. Whiledoing so the faults are often controlled by shaly lithologies of layers,which heave along the thrust faults (block-boundaries) and makethe faults less permeable or closed.

The modeled hydrocarbon distribution within the study areamatches the known distribution of accumulations very well. Theoccurrence of shows is in different blocks and at different strati-graphic levels. More calibration with respect to composition, phase

behavior and HC quality (GOR and API gravity) needs to be done inthe future.

5. Discussion and summary

The geometry and its development through time is the domi-nant factor in the study, controlling not only typical parameterssuch as temperature and maturity but also pressure build-up due tothe compartmentalizing effects of sealing faults and layers. Whilesome secondary migration methods, such as Darcy migration, arenot overly sensitive to details of geometry, others, such as flowpathmigration, are very sensitive. The impact of the given geometry onflowpath migration is quite effective because in a reservoir layerwithout a significant pressure gradient the controlling migration

F. Baur et al. / Marine and Petroleum Geology 26 (2009) 573–579 579

factor is buoyancy, which forces the fluids to follow along thegeometry of the overlying seal.

Although simplifications have been applied both to the struc-tural reconstruction and the basin model, the geometry has beentreated as carefully as possible to keep such artificial effects ata minimum. Due to the fact that the TecLink approach usesreconstructed geometries as a basic input parameter for thenumerical basin model, the basin model quality very muchdepends on the reconstructed input geometries.

The assumption of having predominantly closed faultscontrolled by impermeable lithologies fits the observations ofMoretti et al. (2002). They attributed the low permeabilities of thefaults as being due to diagenesis and cementation processes, asdescribed in Labaume and Moretti (2001a,b) and Labaume et al.(2001). In the current study, however, the shaly lithologies neigh-boring these faults are responsible for their low permeabilities, andthis seems to provide reasonable fault behavior.

Although the use of only one lithology per stratigraphic layer isa simplification, it was possible to calibrate all pressure data for allwells. Due to the fact that the entire pressure calculation is mainlybased on vertical effective stress, the fracturing level for the Hua-mampampa could not be reached during the first simulation runs.Therefore high permeability values were assigned to a relativelypoor porosity to emulate the fracturing effect. This leads to thegeneral problem of all basin modeling software that no stress-tensors are taken into account for the pressure analysis. Up to nowthere was no need to do this because basins dominated by exten-sional processes are almost exclusively controlled by verticaleffective stress. To imitate the compressional regime during fault-ing and thrusting it is possible to assign certain pressure boundaryconditions, which have been tested before in 2D TecLink modelsbut not yet for a 3D TecLink model. Ongoing research andimprovement aims to integrate a full stress-tensor calculationwithin the pressure solution, which will be of great benefit forcompressionally dominated numerical basin models.

In general it can be said that the new technique works andproduces reasonable results. Calculated results coincide with themeasured calibration parameters such as temperature, maturity,permeability, porosity and pressure. The model, which covers partsof the Sub Andean fold and thrust belt, stands for a successfulapplication of a novel simulation technique, which enables a fullpressure, temperature and maturity solution in 4D (space and time)for compressional geological settings. A further application to otherstudy areas where structural modeling has been already performedis needed to test different geological settings and to improve thenovel approach of 3D TecLink.

Acknowledgements

The authors thank Repsol-YPF (Buenos Aires), PAE (Pan Amer-ican Energy L.L.C.) and BG (British Gas) for their kind permission topublish the project data. This paper benefited from the thoroughreviews by Isabelle Moretti and Harry Doust.

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