AUTHORS

Carolyn Lampe � Ucon Geoconsulting,Piusstr. 22a, 50823 Köln, Germany;c.lampe@ucon4d.com

Carolyn Lampe received her Ph.D. from theUniversity of Cologne in cooperation withthe University of Minnesota. She worked as a

Fault control on hydrocarbonmigration and accumulationin the Tertiary Dongyingdepression, Bohai Basin, China

technical expert for petroleum systems analysiswith the Schlumberger PetroMod Group for

Carolyn Lampe, Guoqi Song, Liangzi Cong, 7 yr before starting her own consulting firm and Xing Mu specializing in all aspects of quantitative nu-merical basin and petroleum systems modeling.She is a consulting professor at StanfordUniversity.

Guoqi Song � SINOPEC (China Petrochem-ical Corporation), 3 Liaocheng Road, Dongying257071, Shandong Province, People’s Republicof China; songguoqi@slof.com

Guoqi Song received his Ph.D. from the Ge-ology and Geophysics Institute of the ChineseAcademy of Science. He is currently the chiefexploration expert at Shengli Oilfield Company,China Petroleum & Chemical Corporation(SINOPEC). He has been involved in the inves-tigation and study of petroleum explorationof Chinese terrestrial fault basins since 1982.His publications include sequence stratigraphystudies and petroleum systems in Chinesefault basins.

Liangzi Cong � Keeping Advanced OiltechLtd., 16 Qinghuadong Road, Beijing 100083,People’s Republic of China;peter@ka-oiltech.com

Liangzi Cong received his Ph.D. from the Re-search Institute of Petroleum Exploration andDevelopment, PetroChina, in 1999. He is nowthe general manager of Keeping Advanced

ABSTRACT

Shengli oil field, the second largest oil and gas field in China, islocated in the Tertiary Dongying graben system in the south-ern Bohai Basin. Three petroleum systems, one for eachmapped source rock, and as many as seven reservoir rocks aredocumented in the Dongying graben system, representing acomplex migration and accumulation pattern. In addition,both the source and the reservoir facies are distributed un-evenly throughout the system, requiring a complex distribu-tion of possible migration pathways. Stratigraphic conduits,that is, sandy and conglomeratic facies, are mostly present inthe northern graben flank area, where coarse sediments pro-vide possible migration pathways. Over most of the basin,however, faults—active at different times throughout basinevolution—add important additional conduits for petroleummigration, as well as acting locally as seals, depending on theirsurrounding lithology and their respective sealing or leakingproperties through time. This article aims to show that theShengli oil field provides an excellent example of how three-dimensional petroleum systems modeling allows the assess-ment of fault behavior and timing to predict the distribution ofhydrocarbons in a system.

Oiltech Ltd. He has conducted petroleum ge-ology studies in numerous Chinese basins since1991. His interests include trap analysis, dy-namic processes from petroleum generation toaccumulation, and well proposals.

Xing Mu � SINOPEC (China PetrochemicalCorporation), 3 Liaocheng Road, Dongying

INTRODUCTION

The Bohai Bay Basin is one of the most petroliferous basins inChina. The Dongying depression (study area) is a constituentpart of the Jiyang depression, one of six major depressions

257071, Shandong Province, People’s Republicof China; muxin@slof.com

Xing Mu received his Ph.D. from the ChinesePetroleum University in 2006. He is now thedirector of the Geophysics Department in the

Copyright ©2012. The American Association of Petroleum Geologists. All rights reserved.

Manuscript received February 18, 2009; provisional acceptance May 8, 2009; revised manuscriptreceived September 12, 2011; final acceptance November 3, 2011.DOI:10.1306/11031109023

AAPG Bulletin, v. 96, no. 6 (June 2012), pp. 983– 1000 983

Geoscience Institute of Shengli Oilfield Com-pany, China Petroleum & Chemical Corporation(SINOPEC). He has been involved in petro-leum exploration for more than 20 yr. His in-terests include geologic modeling and seismicinterpretation.

ACKNOWLEDGEMENTS

We thank Shengli oil field (SINOPEC ChinaPetrochemical Corporation subsidiary), Dong-ying, China, for their kind cooperation, valuableinput, and helpful discussions; in particular, wethank Xiangxing Kong, Xinian Sun, and YongjinGao. We also thank Fujian Ma (SchlumbergerPetroMod group) for helping with translationand communication. Debra K. Higley, BrettFreeman, Carl K. Steffensen, and an anonymousreviewer are gratefully acknowledged for theirconstructive reviews of the manuscript. Wethank Gretchen M. Gillis and the AAPG editorsfor their constructive comments and instruc-tions that helped improve the article. Finally, wethank Jay Schmidt for her careful checking ofthe article. We thank Gretchen M. Gillis and theAAPG editors for their constructive commentsand instructions that helped improve the article.Finally, we thank Jay Schmidt for her carefulchecking of the article.The AAPG Editor thanks the following reviewersfor their work on this paper: Brett Freeman,Debra K. Higley, Dallas B. Spear, and Carl K.Steffensen.

984 Hydrocarbon Migration and Accumulation

within the Bohay Bay Basin (Figure 1). More than 40 oil fields,featuring various trap types, have been discovered in the Dong-ying depression during 40 yr of petroleum exploration (Li,2003). These include several large oil fields with reserves ex-ceeding 800 MMBOE of oil in place, such as Lijin, Shengtuo,Dongxin, and Niuzhuang (Figure 1A–D). Collectively, all theoil fields in the Jiyang depression are referred to as the Shenglioil field and represent the second largest oil and gas provincein China.

TheDongyingdepression covers an area of roughly5700km2

(2201 mi2) and is one of more than 50 faulted Mesozoic–Cenozoic subbasins of the Bohai Bay Basin. Bordered by adominant north-bounding graben fault, it forms an asym-metrical half graben, typical of many graben structures ineastern China and within the Bohai Bay Basin in particular (Li,2004; Wei et al., 2010). The sedimentation of the basin fill iscontrolled by footwall uplift and hanging wall subsidence,consisting of mainly Tertiary terrigenous sediments that gradefrom coarse fluvial graben-shoulder sediments in the north tofiner grained lacustrine sediments in the graben center. Syn-sedimentary movement along the main graben faults resultedin the development of a large number of fault blocks, espe-cially along the northern flank of the structure. Together withthe sedimentary basin fill and the burial history, the faultssubdivide the basin into individual facies regimes (e.g., prox-imal coarse facies in the hanging walls, distal fine-grained fa-cies in the footwalls), thus locally preventing purely lithology-based flow connections. Therefore, faults have to be taken intoaccount to explain the known accumulations. Timing of faultmovement and whether faults are sealing or nonsealing arepoorly understood yet appear to be the primary control forunderstanding the distribution of hydrocarbons within the ba-sin. This article presents the results of a three-dimensional (3-D)petroleum systemsmodeling study, showing that the complexdistribution of hydrocarbons in the Dongying graben systemcan only be explained by incorporating the control that faultshave as both conduits and seals.

GEOLOGIC SETTING

The Bohai Bay Basin developed as a back-arc basin during theMesozoic and evolved into an intracratonic-rifted basin duringthe Cenozoic. The basin and its subbasins resulted from a com-plex polyextension-phase tectonic history. This can be sub-divided into three periods (Figure 2) (Cong and Zhou, 1998).(1) A series of small isolated basins developed along major

in the Dongying Depression (China)

northwest and northeast-trending fault sets duringa late Mesozoic to Paleocene rift stage. Good pe-troleum source and reservoir rocks were formed ina few isolated basins during the later period of thisstage, that is, the Kongdian Formation. (2) Duringa second rift stage, the Eocene toOligocene (65.0–24.6 Ma) synrift, most grabens were isolated al-though with local connections to other grabens.Pronounced vertical fault movement and high sedi-mentation rates characterized these grabens. Dur-

ing this time, more than 50 subbasins can be dis-tinguished that are mostly controlled by footwalluplift and hanging wall subsidence, featuring deepsedimentary depocenters and marginal basementhighs. The most important petroleum generationand accumulation layers of the Shahejie (Es) andDongying (Ed) formations were formed during thisstage. (3) The last stage, the late Tertiary (24.6Ma)to the present-day postrift, represents a phase ofthermal subsidence where rifting ceased. Most

Figure 1. Map (upper) of theBohai Bay Basin with its six majorsubbasins. The Dongying de-pression (lower) is part of theJiyang Subbasin and includesthe Shengli oil field, comprisingknown fields such as the Lijin(A), Shengtuo (B), Dongxin (C),and Nuizhuang (D) oil fields.

Lampe et al. 985

depressions are now connected with only a fewbasement highs, the distribution of which allowsthe subdivision of six superimposed subbasins(Figure 1) (Li and Li, 2003). Two formations,Guantao (Ng, a reservoir rock) and Minghuazhen(Nm, a local seal), were deposited during this stage.

With respect to the stratigraphic evolution andthe sedimentary processes of the Bohai Bay Basin,periods (2) and (3) were the two major tectonicevolution stages. During the synrift stage, sedi-mentation was restricted to the grabens and halfgrabens (Li, 2003), and the Paleogene sedimentswere deposited inmostly lacustrine environments.During the postrift stage, the Neogene sedimentswere widespread and were dominated by fluvialdeposits (Chen et al., 1984).

986 Hydrocarbon Migration and Accumulation in the Dongying

STUDY AREA

All hydrocarbon accumulations discovered in theDongying depression are sourced from and mostlyreservoired in Tertiary strata, which feature a com-plex stacking pattern of source rocks, reservoir for-mations, and cap rocks. These complicated strati-graphic conditions were offset by syndepositionaland postdepositional fault movement, which dis-sected the whole area into individual fault blocks.Thus, a subbasin such as the Dongying depressionmay consist of hundreds of hydrocarbon-bearingfault blocks that vary in size, age, and character,each representing an independent oil-water andpressure system (Zhai, 1997). Strong Mesozoic toearly Cenozoic movements north of the Dongying

Figure 2. Stratigraphy of the Dongying depression. The general stratigraphy is based on Zhai (1997). Also shown are the units and agesconsidered in the numerical model based on SINOPEC Shengli Oilfield Co., Ltd., specifications. The light-gray units represent reservoirrocks; the dark-gray units are source rocks. Their properties are described in the text in the Model Input section. Phases of rifting andthermal subsidence are indicated on the right.

Depression (China)

depression resulted in significant displacement ofthe northern boundary faults, namely the Cheng-nan and Shengbei fault zones (Figure 3), with upto 1200m (3937 ft) of vertical throw. At the sametime, the structural movement in the south wasmuch less, which gave rise to the asymmetric half-graben shape of the depression.

The vast thickness of source rocks (locally upto 2300 m [7546 ft] for an individual source rockinterval) resulted in rich hydrocarbon resourcesandmade theDongying depression one of themostfavorable petroleum subbasins in China. The base-ment in the study area is Archean granite that wasexposed by regional erosion before deposition ofthe Tertiary strata. Quaternary sediments, com-monly consisting of loosely cemented sand and siltand intercalated tight shale, form regional seals andare considered overburden rock.

The Lower Tertiary System

Together with numerous other subbasins, theDongying depression developed in the early Ter-tiary and features individual depocenters of lacus-trine sedimentation and varying fault activity. ThePaleogene (E) includes three formations: the Pa-leocene Kongdian (Ek) Formation, the Eocene toOligocene Shahejie (Es) Formation, which includesthe main petroleum source rocks in the studyarea, and the Oligocene Dongying (Ed) Formation(Figure 2).

The sedimentary cycle with each formationbegins with (1) alluvial fan deposits, followed by(2) fluvial deposits, (3) coastal lake deposits,(4) shallow to deep lake deposits, (5) ephemerallake and river deposits, (6) delta-plain deposits, and(7)marsh deposits (Chen et al., 1984).Deltaic fans

Figure 3. South-north–trending cross section through the model cube, showing the stratigraphy, facies distribution (finer lithologies inthe deeper part of the basin and in the footwalls, coarser toward the basin shoulder and in the hanging walls), and general half-grabenstructure with some of the major faults. Refer to Figure 5 for fault details.

Lampe et al. 987

and turbidites are commonly associated with thebounding faults along the steep northern flank ofthe basin and are excellent petroleum reservoirrocks. The lowerTertiary formations represent threemain cycles (Figure 2): (1) the Kongdian cycle (E1k),(2) the lower part of the Shahejie cycle (E2s4–E2s2L), and (3) the upper part of the Shahejie(E2s2U–E2s1U) through theDongying cycle (E3s2U–E3d). Because of the marginal position of theDongying depression within the Bohay Bay Basin,the Es1 and Ed formations are very thin and aretherefore combined in the model (Figure 2). Partof the upper Dongying Formation was subsequentlyeroded.

The Upper Tertiary System

The sedimentary environment of the Bohai BayBasin in the late Tertiary is different from that inthe early Tertiary in that all subbasins, includingthe Dongying depression, were subject to thermalsubsidence and provided a widespread cross-basinfluvial depositional environment (Li andLi, 2003).

Two formations were deposited in the BohaiBay Basin during the late Tertiary (N). These arethe lower Guantao (Ng) and the upper Ming-huazhen (Nm) formations. The Guantao Forma-tion is characterized by coarse-grained braided-riverdeposits. It is also the uppermost petroleum-producing formation in the Dongying depression.The Minghua Formation features mostly fine-grained sediments, deposited by ameandering riversystem. It serves as the regional cap rock in theDongying depression.

NUMERICAL SIMULATION

The petroleum systems studywas performed usingthe PetroMod 3-D PetroFlow package of Schlum-berger’s PetroMod Software Suite. A model wasconstructed to forward model the pressure, tem-perature, andmaturity history of the basin, includingfully pressure-volume-temperature (PVT)–controlledmulti-component migration. Special focus was put

988 Hydrocarbon Migration and Accumulation in the Dongying

on the faults with respect to geometry, properties(sealing versus nonsealing), and timing of faultactivity.

Model Input

The model covers an area of 27 (east-west) × 23(north-south) km (17 × 14 mi) in the northernpart of the Dongying depression (Figure 1). Thegeographic extent was chosen to include the pre-dominant half-graben structure of the basin fromthe basin shoulders in the north to the depocenterin the south (Figure 3). It also includes the mainboundary fault (Shengbei fault zone) and othermajor faults (Shengnan and Lijin fault zones) thatare known to be relevant for the distribution ofthe known accumulations. The model extent waschosen to calculate the known accumulations inthe area and to predict possible new prospects.

Themodel comprises 10 original horizons, withdata derived from well picks and interpretation ofnumerous seismic two-dimensional (2-D) lines. Toaccount for intermittent seal and reservoir layers(Ed-Es1), as well as a basement, two of the layerswere subdivided to account for a total of 11 layers.

Based on well data, facies maps were con-structed for 6 of the 11 layers, namely, Es4U,Es3L, Es3M, Es3U, Es2, and Ed-Es1, to model thecommonly small-scale variations of lithology dis-tribution caused by changes in depositional envi-ronment and fault displacement. The remaininglayers were assigned to have a uniform (single)lithology. The individual lithologies are composedof shale (seal, commonly a source rock), shaly lime-stone, limestone, mixed sandstone and siltstone,sandstone (reservoir), sandy conglomerate (reser-voir), and conglomerate (reservoir). An example isshown in Figures 3 and 4.

Three source rocks are considered in themodelthat comprise parts of the Eocene Es4L, Es3L, andEs3M formations (Figure 2). Each of those for-mations features a variation of different lithologies,where the source rock facies represents only a frac-tion of the formation (Figures 3, 4). These sourcerocks are mostly thick lacustrine deposits contain-ing mixed-type kerogen derived from algae and

Depression (China)

higher land plants. The source rock properties—mapped total organic carbon (TOC) and hydro-gen index (HI) from key wells—vary within thefacies and are unevenly distributed throughout thesource rock. The Es4U has a TOC ranging between1 and 5.5 wt. %, with an HI of as much as 625 mghydrocarbon (HC)/g TOC. The Es3L has a TOCbetween 1 and 5.6 wt. %, with an HI of as much as215 mg HC/g TOC (Figure 4). The Es3M fea-tures TOC values up to 1.3 wt. % and HI valuesof up to 410 mg HC/g TOC. A generic type-II ki-netic model for the conversion of kerogen to pe-troleum from Burnham (1989) is assigned to eachsource rock.

Seven potential reservoir rocks are included inthe model, namely, in the Es4U, Es3L, Es3M,Es3U, Es2, Ed-Es1, and Ng formations (Figure 2).Their average in-situ vertical permeabilities rangebetween 1.5 and 3 logarithmic millidarcys (log[mD]), with capillary entry pressures approxi-mately 0.01 MPa (petroleum-water system). The

distribution of the reservoir rocks, like that of thesource rocks, is highly dependent on the facies var-iation within the individual formations (Figure 4).

The shale facies in the individual layers, com-monly coinciding with source rocks, function aslocal seals, which were defined in the model by lowpermeabilities (between −7 for the deeper sectionand −1.5 vertical log[mD] for the shallower sec-tion) and high capillary entry pressures (between2.8 MPa for the deeper section and 0.75 MPa[petroleum-water system] for the shallower sec-tion). The lowerOligocene Ed-Es1 and the PlioceneNm formations serve as regional seals (Figure 3).

Boundary Conditions

Thermal boundaries at the top (surface tempera-ture) and the base (basal heat flow) of the modelweredefined to allow the simulation of temperatureand source rockmaturity through time. The surface

Figure 4. Key wells used forcalibration of the three-dimensionalmodel, as well as examples offault distribution, lithology distri-bution, and source rock proper-ties (hydrogen index [HI] and totalorganic carbon [TOC]) for var-ious formations in the study area.HC = hydrocarbon.

Lampe et al. 989

temperature was determined using PetroMod’s in-tegrated sediment-water-interface-temperature cal-culator (Wygrala, 1989). This trend incorporatescontinental drift and passage through various cli-mate zones. Calculation is based on the present-dayposition of the study area (Southeast Asia, 37°N).Because of the mostly terrestrial character of thedepositional systems, a correction for water depthwas not necessary.

Several key wells (Figure 4) with measuredvitrinite reflectance data and corrected bottom-hole temperatures were used to assemble a repre-sentative vitrinite reflectance curve. Various heat-flow scenarios were tested to fit the calibrationdata. Lithospheric stretching modeling by He andWang (2003) showed that the heat flow duringbasin evolution varied between 51 and 63mW/m2,with a slight cooling trend from the Oligocene tothe present day, which resulted in a moderatethermal background heat flow of 61 mW/m2.This cooling trend is also constrained by apatitefission track and vitrinite reflectance analyses con-ducted by Hu et al. (2001). Hu et al. (2001) andWang et al. (2002) state similar heat flows, rang-ing between 63.8 and 65.8mW/m2 and paleo–heatflows (>25 Ma) possibly ranging between 70 and90 mW/m2. The model applies a constant heatflow of 60 mW/m2, which agrees well with thecalibration data.

Fault Concept and Fault Properties

Faults are present in basically every subbasinthroughout the Bohai Bay Basin and cause basinarchitecture and sedimentation to be mostly con-trolled by footwall uplift and hanging wall sub-sidence. The faults feature a wide variety of extent,depth, throw, shale gouge ratio (SGR), and relatedproperties. They have an important function forpressure development and fluid flow andmay haveconsiderable impact on migration. They can act asmigration pathways (open faults) or as seals (closedfaults), where they can trap petroleum and holdcolumn heights depending on their sealing orleaking properties. Five generalized fault zonesare included in the model (Figure 5): (1) northern

990 Hydrocarbon Migration and Accumulation in the Dongying

Chengnan; (2) central Shengbei, representing themajor graben fault in the study area; (3) the ad-jacent Tuogu; (4) southeastern Lijin; and (5) west-ern Tuo.

Faults have extremely complex 3-D structuresand can occur not only over large vertical and/orhorizontal distances but also consist of more or lesswide fault zones instead of a distinct fault plane(Manzocchi et al., 2010). The petrophysical prop-erty distribution within these structures relevantfor fluid flow and fault-seal analysis is equally com-plex, which is why this model requires gross sim-plifications for both geometries and properties re-garding the fault zones in the Dongying depression.

GeometryFault planes were constructed from fault lines oneach horizon (mapped intersections of faults andhorizons), which were derived from seismic in-terpretation. These fault lines were connected toform 3-D fault planes, which represent boundaryelements (2-D membranes) between individualcells in themodel (Hantschel andKauerauf, 2009).Instead of forming a smooth curved fault plane, thenumerical fault geometry is simplified, followingthe shape of the model’s cell faces, with horizontalmembranes on layer surfaces and vertical mem-branes between layers, thereby forming a stair-stepgeometry. The model faults have zero volumebetween the volumetric model cells, that is, noactual fault rock is present, yet they can have flowproperties assigned to them that are different fromthe surrounding wall rock, for example, they cantheoretically be a vertically and horizontally trans-missive conduit for flow surrounded by an other-wise sealing lithology. This simplification allows asatisfactory approximation of the fault behaviorwith respect to petroleum migration or pressurecompartmentalization.

PropertiesThe two flow properties related to faults acting asseals or conduits in themodel are permeability andcapillary threshold pressure, also referred to as faultcapillary pressure (FCP) (Hantschel and Kauerauf,2009). Permeability and capillary pressure can beexpressed by the so-called gouge composition,

Depression (China)

Figure 5. Classification of the individual fault zones in the study area with respect to location and properties. The modeled faultproperties changed between (1) the tectonically active rift phase (100–14 Ma), where fault activity was mainly governed by their positionwithin the basin relative to the graben center or shoulder; and (2) the quiet postrift phase (14–0 Ma), where faults were assigned tocorrespond to their principal surrounding lithologies. FCP = fault capillary pressure; SGR = shale gouge ratio.

Lampe et al. 991

which is a mixture of all the rocks surrounding orpassing the faults during movement. Informationabout the basin lithology (derived fromwell data oroutcrop), a thorough stratigraphic interpretation ofthe subsurface, and the evolution of fault displace-ment through time provide the necessary infor-mation to quantify the sealing or leaking potentialof the faults. An important factor for determiningthe flow properties of the fault is the shale contentof the rock surrounding the faults between the footand the hangingwall, which greatly depends on theprevailing layer-by-layer juxtaposition and the faultdistance or throw. All these parameters can beexpressed by applying the SGR (Yielding et al.,1997). The SGR, given in percent of shale content,is a fault seal attribute, which is an estimate of clayconcentrationwithin fault gouge, typicallymappedacross the surface of a fault (Yielding et al., 1997;Harris et al., 2002). This clay concentration de-pends on the lithologies surrounding the fault atany given point in space and may thus vary greatlyeven on a small scale.

The SGR can directly be converted to capillarythreshold pressures and permeabilities as a basisfor flow simulation (Yielding, 2002; Hantschel andKauerauf, 2009; Manzocchi et al., 2010). In gen-eral, fault zones with higher clay content, equiva-lent to higher SGR values, can support higher cap-illary threshold pressures and thus possess bettersealing qualities. An SGR value between 15 and20% is interpreted to represent a threshold valuebetween nonsealing and sealing faults (Yielding,2002).

Fluid Flow and Fault Seal PropertiesThe fault properties relevant for migration vary inspace (lateral facies variations) and time (faultactivity through time). This allows the faults to beopen or closed during different stages of modeledbasin evolution as well as in different sectionswithin the same fault zone.

For this model, neither SGR nor FCP was ac-tually measured because relevant data such as V-shale (volume fraction of shale) logs were notavailable for the study area. Instead, the fluid-flowproperties along or across the modeled faults wereapproximated based on the major tectonic stages

992 Hydrocarbon Migration and Accumulation in the Dongying

during basin evolution in theDongying depressionand the spatial variations of the depositional en-vironment and its respective lithologies.

Most of the faults have been simplified to beeither perfectly sealing (closed faults: SGR > 95%,FCP > 50 MPa) or perfectly leaking (open faults:SGR < 18%, FCP < 0.1MPa) while changing fromsealing to leaking or vice versa based on the pre-vailing tectonic activity in the basin (variation intime). For intermediate faults with spatial SGRand FCP variations (e.g., the Lijin fault system),FCP values from the immediately surrounding li-thologies were used based on the fact that faultdisplacement is rather small. The FCP values werethen translated to an approximate fault SGR basedon Yielding (2002). The fault seal properties forthe individual fault systemswere derived as follows.

The Shengbei fault features the most signif-icant throw and appears to be active throughoutthe entire basin evolution. In addition, it transectssandy or conglomeratic sediments associated withthe graben flanks. It is therefore thought to beopen, that is, nonsealing, during the entire interval.The Chengnan, Tuogu, and Tuo fault zones arecomparatively shallow, that is, the faults do notreach as deep as the Shengbei fault; they generallycut across fewer stratigraphic units and they showcomparatively small throws. These faults are in-terpreted to be active (nonsealing) during the riftstages and the subsequent uplift and erosion of thebasin (65–14Ma)whereas they are subject to theirrespective surrounding lithologies (coarser non-sealing SGR values toward the basin sides, finersealing SGRvalues toward the basin center) duringthe following thermal subsidence state when tec-tonic activity ceased. The Lijin fault zone occurs inthe deepest part of the basin, and although it doesnot have a significant throw, it cuts across a varietyof laterally varying facies assemblages, ranging fromcoarse-grained conglomerates and sandstone nearthe basin edges toward finer grained silt and shalelithologies toward the basin center. Little verticaldifference is assumed between the hanging walland the footwall lithology, so the fault propertiesare based on the immediately surrounding lithol-ogy. The Lijin fault zone is thus expected to featurelateral spatial variations of sealing versus nonsealing

Depression (China)

properties, and its fault seal character is approxi-mated by SGR values throughout the entire basinevolution. These values range gradually from 70%SGR (perfectly sealing) in the mostly shaly basincenter to 0% SGR (perfectly leaking) toward thedominantly sandy and conglomeratic basin margin.

Migration modeling both within the sedimen-tary column and along the faults is performedusinginvasion percolation. This migration method isbased on mapping the threshold pressure of eachpore to an occupation probability (Wilkinson andWillemsen, 1983; Hantschel and Kauerauf, 2009).Flow is thus mostly controlled by the capillarythreshold pressure of individual cells (lithologyand fault parameters) in the model.

Fault ModelsNumerous sensitivity studies were performed totest different fault property scenarios in the studyarea. These included end-member scenarios where(1) all faults are closed, (2) all faults are open withrespect to fluid flow, (3) no faults are present, or(4) the faults show varying properties that changeboth spatially depending on the surrounding faciesand through time in accordance with the differentperiods of tectonic activity in the Dongying de-pression. To account for the variations of faultproperties, both FCP- and SGR-type faults havebeen assigned. Although FCP-type faults are eitherclosed (high capillary threshold pressure, sealing)or open (low capillary threshold pressure, conduit),the SGR-type faults allow a more “natural” approx-imation of the SGRwith respect to the surroundinglithologies (facies variations) and are thus assignedwhere significant spatial variations of lithologyproperties (permeability, capillary pressures) areto be expected. This is especially the case for thosefaults, which cut basin formations that show atransition from more marginal (coarse, conduit)to more central (fine-grained, sealing) sediments(Lijin fault zone, Figure 5).

RESULTS

Based on the petroleum system concept ofMagoonand Dow (1994), the study area within the Dong-

ying depression consists of three petroleum sys-tems, one for each mapped source rock (Figure 6).Those source rocks contribute petroleum to up toseven reservoir layers, thus representing a complexmigration and accumulation pattern (Figure 7).

Both the source and the reservoir facies aredistributed unevenly throughout the system, re-quiring an intricate distribution of possible mi-gration pathways. Stratigraphic conduits, that is,sandy and conglomeratic facies, are only located inthe northern graben flank area, where coarse sedi-ments provide possiblemigrationpathways. Inmostof the basin, however, faults—active at differenttimes throughout basin evolution—constitute themost likely conduits for hydrocarbon migration.

Three types of faults are included in themodel:

1. The main graben faults (Chengnan and Sheng-bei fault systems) act as possible conduits forhydrocarbons throughout the entire basin evo-lution. These faults reach from the basement allthe way up to the Pliocene overburden rock(Nm), thus allowing the petroleum to migrateand be trapped in the upper Oligocene Ed-Es1and the lower Miocene Ng reservoirs.

2. Secondary graben faults such as the Tuo andTuogu fault zones were modeled as being openduring the active rift stage of the graben for-mation and are later mostly sealing because ofthe mostly fine-grained central basin sedimentsthey are transecting. They allow horizontal flowduring the early basin stage (Eocene,Oligocene)and result in fault-controlled accumulations inthe younger Miocene and Pliocene stages.

3. The southern Lijin fault zone has the mostvariation in facies distribution in the area so thatits migration character depends on the surround-ing lithology with sand-dominated SGR valuesin the western part and a shale-dominated SGRin the central and eastern parts of the basin. Thisfault system allows trapping significant hydro-carbon accumulations in the upper Eocene Es2reservoir facies in the western and central partsof the basin (Figure 8). Had this fault systembeen simply open or closed through time (i.e.,no spatial variation), too little or too muchpetroleumwould have been trapped (Figure 9).

Lampe et al. 993

Four different fault scenarios were modeledto show their relative effect on the petroleumdistribution in the study area (Figure 9). Thehydrocarbon balance for each scenario is shownin Table 1.

1. Closed faults (i.e., all faults are consideredsealing throughout the entire basin evolution)retain too much petroleum in the southern partof the basin directly above the main kitchenareas. Lateral northward cross-fault flow is in-hibited. The known shallow accumulations inEs2, Ed-Es1, and Ng did not develop.

2. Open faults (i.e., all faults are considered non-sealing throughout the entire basin evolution)resulted in too little petroleum retained in thegraben. Less than 3% of the generated petro-leum accumulates; most petroleum is lost ver-

994 Hydrocarbon Migration and Accumulation in the Dongying

tically along the faults. The known accumula-tions south of the Lijin fault zone get drained.

3. A model that included no faults showed thatmigration is mostly northward (updip) directed,where mostly horizontal migration is controlledby the individual facies types and the morphol-ogy of the sealing surfaces at regional scale. Notenough petroleum is retained in the southernpart of the basin, whereas the northern part issignificantly overcharged.

4. Only assigned faults (i.e., variation of fault prop-erties through time and space) allowed signif-icant accumulations to develop in the northernpart of the study areawhile producing the knownreservoir distribution in the southern part of thebasin (Lijin oil field). Although the three mainreservoirs—Ed-Es1, Es2, and Es3U—are basicallyrepresented by all four scenarios (Figure 9), only

Figure 6. Modeled source rock transformation ratio and present-day level of thermal maturity (pod of active source rock) for the threesource rocks. Note that the eastern system is only marginally represented by the Es4U source rock, resulting in an underestimation of theShengtuo oil field charge (Figure 1).

Depression (China)

the assigned faults model manages to fill theknown accumulations (Figure 8).

The eastern Shengbei oil field (Figure 8, Ed-Es1 and Es2 formations) is only marginally rep-resented by the model, which is caused by the factthat the kitchen area for this oil field lies mostlyoutside the model dimensions and that the chargeof the respective accumulation is therefore greatlylimited. Modeling results show that this kitchenarea is also mostly responsible for filling the north-ern accumulations in the Ed-Es1 formation, whichtherefore remain undercharged in the model.

DISCUSSION

Modeling studies conducted in the offshore Bo-zhong Subbasin north of the Dongying depressiontogether with oil-source correlations in the Penglai19-3 (PL19-3) oil field, the largest offshore oil fieldin China, revealed extensive mixing of petroleum

derived from separate source rocks or individualkitchens within the same source rock, chargingmultiple reservoir rocks in the vicinity of a highlyactive fault zone (Hao et al., 2007, 2009). Zhanget al. (2004) propose the concept of a “fault-fracturemesh petroleum play” in the Jiyang depression,where hydrocarbons in the younger Neogene reser-voirs are derived directly from Eocene–Oligocenesource rocks or from the redistribution of preexist-ing oil accumulations in the deeper reservoirs viafault-related migration. These investigations sup-port a complex, commonly fault-related, migrationand accumulation history within the Bohai BayBasin and are in accordance with the presentedmodel results.

One might argue that for faults being activeduring migration, there will be intermittent shortperiods where their porosity, permeability, andcapillary structure will be enhanced (Dewhurstet al., 1999;Mildren et al., 2002; Lyon et al., 2005;Langhi et al., 2010). During these times, theycould behave as conduits. However, this may pose

Figure 7. Extended essential elements diagram showing all three petroleum systems present in the study area with relation to tectonicactivity and general fault behavior. The source rock transformation ratio and the critical moment (set at 50% transformation ratio,measured in the deepest part of the basin) for each petroleum system indicate that all three systems comply with the requirements topotentially generate and trap petroleum. Although the two older systems (Es4U and Es3L) reached maximum transformation in the basincenter, the younger system is still mostly immature. All three systems are still active (see also Figure 6).

Lampe et al. 995

a difficulty because once the fault rock is oil wet,one might assume that it will be oil wet for theentire period that oil migration occurs in the sys-tem, in which case a fault that acted as a conduit inthe early part of migration would be transmissiveto oil over a geologic time frame regardless of itsSGR (Aplin and Larter, 2005). However, if trans-

996 Hydrocarbon Migration and Accumulation in the Dongying

missive (open) faults were assumed throughout themigration history of the basin, none of the knownaccumulations in the southernpart of the study areacould bemodeled. Therefore, simple oil-wet (open)faults are unlikely, and a combination of FCP and,for example, relative permeability of the seal maybe responsible for the observed accumulations

Figure 8. A three-dimensional view of the “assigned faults” model at present day, showing the faults and all accumulations, includingtheir migration pathways (left). The map view (right) shows the reservoir distribution for the three main reservoir layers in comparisonwith the known accumulations (polygons) and the respective fault distribution.

Depression (China)

Figure 9. Distribution of all petroleum accumulations in the study area based on different fault parameters (closed, open, no faults, andassigned faults). The bar diagrams show the relative petroleum contribution of each source rock to the respective reservoir layers(petroleum-source correlation). Although some of the pool distributions are similar in extent and position, they differ in composition, andvice versa. HC = hydrocarbon.

Lampe et al. 997

(Manzocchi et al., 2010), the interrelation ofwhichis beyond the scope of this article.

Not assuming faults, it could be argued thathydrocarbons appear to have migrated verticallyby stair stepping from hanging wall to footwall andvice versa at reservoir-reservoir contacts in differ-ent reservoir units. In this way, they can migrateupstructure and upsequence from source to trapwithout ever flowing along the fault surface itself(Manzocchi et al., 2010). However, the observedaccumulations in the southern part of the studyarea cannot be modeled assuming such a “nofaults” scenario, where only the facies distributionand relative reservoir juxtaposition is responsiblefor vertical petroleum migration. Only the “as-

998 Hydrocarbon Migration and Accumulation in the Dongying

signed faults” scenario allows modeling these pe-troleum accumulations satisfactorily.

Both scenarios, although feasible, do not seemto govern migration in the Dongying depression.Instead, primarily fault-controlled migration, pos-sibly in combination with the aforementionedmechanisms, seems to be the most plausible ex-planation. Additional data, such as measured faultproperties (e.g., Vshale), actual volumetric faults(Fachri et al., 2011), geomechanical fault analysis(Hillis et al., 2000; Mildren et al., 2002), morecarefully interpreted high-resolution stratigraphyand facies variations, as well as further higher reso-lutionmodelingwouldbe required to fully test thesehypotheses.

Although the parameters in the presented pe-troleum systems model were simplified with re-spect to, for example, fault geometry, SGR and/orFCP variations, or fault timing, based on the model,a new discovery was made north of the Shengbeifault (Guoqi Song, 2007, personal communication,Shengli oil field). This serves as an excellent (andrarely communicated) proof of the concept.

CONCLUSIONS

The petroleum system modeling presented hereshows that the migration pathways in the Dong-ying depression seem to be mostly controlled bythe faults and their respective properties, allowingor inhibiting cross- and along-fault flow. Althoughfaults generally have very complex structures andpetrophysical property distributions, even applyinga highly restricted and simplified set of parametersthat uses rules-of-thumb instead of measured data,faults need to be addressed instead of—as so com-monly is the case—ignored in basin-scale petro-leum systems models. The study shows that mi-gration without considering the faults and theirgeometry, timing, and sealing properties cannotproduce the observed distribution of accumulationsin the Dongying depression. Varying fault proper-ties, both in space and time, and fault activity area prerequisite to account for the complex reser-voir distribution in the study area. The study, sup-ported by the new discovery, provides an excellent

Table 1. Hydrocarbon Balance for the Four Model Scenarios*

HydrocarbonBalance (mass %)

ClosedFaults

OpenFaults

NoFaults

AssignedFaults

Total Expelled

Es3M 5.5 Es3L 22.2 (56.7) Es4U 29.0

Total Accumulated inReservoirs

4.5

2.6 4.6 3.3

Total Losses

52.5 54.1 52.1 53.4

Reservoirs (% of accumulated HC)

Ng — 23.7 — 14.5 Ed-Es1 0.9 16.9 48.1 14.3 Es2 74.8 42.4 24.2 56.0 Es3U 12.8 13.5 23.9 11.6 Es3M 0.2 0.4 0.7 0.3 Es3L 10.6 2.7 4.3 2.7 Es4U 0.7 0.4 — 0.6

*With the exception of the “no faults” scenario, Es2 contains most of the hy-drocarbons accumulated in the study area (bold numbers).

Depression (China)

example of how addressing faults in petroleumsystems modeling can aid the understanding of aprospect area, help to gainmore insight into futureexploration tasks, and ultimately support businessdecisions.

REFERENCES CITED

Aplin, A. C., and S. R. Larter, 2005, Fluid flow, pore pres-sure, wettability and leakage in mudstone cap rocks, inP. Boult and J. Kaldi, eds., Evaluating fault and cap rockseal: AAPG Hedberg Series 2, p. 1–12.

Burnham, A. K., 1989, A simple kinetic model of petroleumformation and cracking: Lawrence Livermore NationalLaboratory Report UCID-21665, 11 p.

Chen, C., Huang, J. Chen, J., and X. Tian, 1984, Deposi-tional models of tertiary rift basins, eastern China, andtheir applications to petroleum prediction: SedimentaryGeology, v. 40, p. 73–88, doi:10.1016/0037-0738(84)90040-X.

Cong, L., and H. Zhou, 1998, Polyphase pull-apart structuresof active rift in the Nanpu depression and their relation-ship to oil and gas (in Chinese with English abstract):Oil and Gas Geology, v. 9, no. 4, p. 296–301.

Dewhurst, D. N., Y. Yang, and A. C. Aplin, 1999, Permeabil-ity and fluid flow in natural mudstones: Geological So-ciety (London) Special Publication 158, p. 23–43.

Fachri, M., J. Tveranger, N. Cardozo, and Ø. Pettersen, 2011,The impact of fault envelope structure on fluid flow: Ascreening study using fault facies: AAPG Bulletin, v. 95,no. 4, p. 619–648, doi:10.1306/09131009132.

Hantschel, T., and A. I. Kauerauf, 2009, Fundamentals ofbasin modeling: Berlin, Germany, Springer-Verlag,425 p.

Hao, F., H. Zou, Z. Gong, and Y. Deng, 2007, Petroleummigration and accumulation in the Bozhong Subbasin,Bohai Bay Basin, China: Significance of preferentialpetroleum migration pathways (PPMP) for the forma-tion of large oil fields in lacustrine fault basins: Marineand Petroleum Geology, v. 24, p. 1–13, doi:10.1016/j.marpetgeo.2006.10.007.

Hao, F., X. Zhou, Y. Zhu, X. Bao, and Y. Yang, 2009,Charging of the Neogene Penglai 19-3 field, Bohai BayBasin, China: Oil accumulation in a young trap in an ac-tive fault zone: AAPG Bulletin, v. 93, no. 2, p. 155–179,doi:10.1306/09080808092.

Harris, D., G. Yielding, P. Levine, G. Maxwell, P. T. Rose, andP. Nell, 2002, Using shale gouge ratio (SGR) to modelfaults as transmissibility barriers in reservoirs: An examplefromtheStrathspey field,NorthSea:PetroleumGeoscience,v. 8, no. 2, p. 167–176, doi:10.1144/petgeo.8.2.167.

He, L., and J. Wang, 2003, Cenozoic thermal history of theBohai Bay Basin: Constraints from heat flow and coupledbasin-mountain modeling: Physics and Chemistry of theEarth, v. 28, no. 9, parts A/B/C, p. 421–429, doi:10.1016/S1474-7065(03)00062-7.

Hillis, R. R., S. D. Mildren, and J. J. Meyer, 2000, Boreholegeomechanics in petroleum exploration and develop-ment: From controlling wellbore stability to predictingfault seal integrity: Preview, v. 89, p. 3–34.

Hu, S., P. B. O’Sullivan, A. Raza, and B. P. Kohn, 2001,Thermal history and tectonic subsidence of the BohaiBasin, northern China: A Cenozoic rifted and local pull-apart basin: Physics of the Earth and Planetary Interiors,v. 126, no. 3–4, p. 221–235.

Langhi, L., Y. Zhang, A. Gartrell, J. Underschultz, and D.Dewhurst, 2010, Evaluating hydrocarbon trap integrityduring fault reactivation using geomechanical three-dimensional modeling: An example from the TimorSea, Australia: AAPG Bulletin, v. 94, no. 4, p. 567–591, doi:10.1306/10130909046.

Li, D. S., and D. W. Li, 2003, Tectonic types of oil and gasbasins in China, 2d ed.: Beijing, China, Petroleum Indus-try Press, 188 p.

Li, D. W., 2004, Neotectonism and Neogene oil and gaspools in the Bohai Bay Basin (in Chinese with Englishabstract): Oil and Gas Geology, v. 25, p. 170–174, doi:CNKI:SUN:SYYT.0.2004-02-008.

Li, P., 2003, Petroleum geology and exploration of continen-tal fault basins (in Chinese): Beijing, China, PetroleumIndustry Press, 203 p.

Lyon, P. J., P. J. Boult, R. R. Hillis, and S. D. Mildren,2005, Sealing by shale gouge and subsequent sealbreach by reactivation: A case study of the Zema Pros-pect, Otway Basin, in P. Boult and J. Kaldi, eds., Evalu-ating fault and cap rock seals: AAPG Hedberg Series 2,p. 179–197.

Magoon, L. B., andW. G. Dow, 1994, The petroleum system,in L. B. Magoon and W. G. Dow, eds., The petroleumsystem: From source to trap: AAPGMemoir 60, p. 3–24.

Manzocchi, C., C. Childs, and J. J. Walsh, 2010, Faults andfault properties in hydrocarbon fluid models: Geo-fluids, v. 10, p. 94–113, doi:10.1111/j.1468-8123.2010.00283.x.

Mildren, S. D., R. R. Hillis, and J. Kaldi, 2002, Calibratingpredictions of fault seal reactivation in the Timor Sea:Australian Petroleum Production and Exploration Asso-ciation Journal, v. 42, p. 187–202.

Wang, L., S. Liu, W. Xiao, C. Li, H. Li, S. Guo, B. Liu, Y.Luo, and D. Cai, 2002, Distribution feature of terrestrialheat-flow densities in the Bohai Basin, east China: Chi-nese Science Bulletin, v. 47, no. 10, p. 857–862, doi:10.1360/02tb9193.

Wei, H., J. Liu, and Q. Meng, 2010, Structural and sedimen-tary evolution of the southern Songliao Basin, northeastChina, and implications for hydrocarbon prospectivity:AAPG Bulletin, v. 94, no. 4, p. 533–566, doi:10.1306/09080909060.

Wilkinson, D., and J. F. Willemsen, 1983, Invasion percola-tion: A new form of percolation theory: Journal of Phys-ics, v. A, p. 3365–3376, doi:10.1088/0305-4470/16/14/028.

Wygrala, B. P., 1989, Integrated study of an oil field in thesouthern Po-Basin, northern Italy: Ph.D. Thesis, Univer-sity of Cologne, Germany, Berichte des Forschungszen-trums Jülich, v. 2313, 217 p.

Lampe et al. 999

Yielding, G., 2002, Shale gouge ratio: Calibration by geohis-tory, in A. G. Koestler and R. Hunsdale, eds., Hydrocar-bon seal quantification: Norwegian Petroleum SocietySpecial Publication 11, p. 1–15.

Yielding, G., B. Freeman, and D. T. Needham, 1997,Quantitative fault seal prediction: AAPG Bulletin, v. 81,no. 6, p. 897–917, doi:10.1306/522B498D-1727-11D7-8645000102C1865D.

1000 Hydrocarbon Migration and Accumulation in the Dongyin

Zhai, G., 1997, Petroleum geology of China: Beijing,China, Petroleum Industry Press, 650 p.

Zhang, S., Y. Wang, D. Shi, H. Xu, X. Pang, and M. Li,2004, Fault-fracture mesh petroleum plays in theJiyang superdepression of the Bohai Bay Basin, east-ern China: Marine and Petroleum Geology, v. 21,p . 651–668 , do i : 10 .1016/ j .ma rpe t geo .2004.03.00.

g Depression (China)