Table of Content

25 August 2009, Volume 30 Issue 4

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High-quality source rocks and their distribution prediction in the Bohai Sea waters

Pang Xiongqi, Guo Yonghua, Jiang Fujie, Yin Xiangdong, Ma XingZhi, Guo Enzhen

2009, 30(4):  393-397.  doi:10.11743/ogg20090401

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Although dark mudstones are well developed in the Paleogene of the Bohai Sea waters,the major source rocks are still poorly understood,constraining the planning of exploration strategy.To tackle the problem,researchers redefined the high-quality source rocks and preliminarily developed a systemic method for its evaluation and prediction.The method was applied to the prediction of source rocks in the Paleogene in the Bohai Sea waters.The following understandings were obtained.Vertically,the source rocks in the Shahejie Formation are large in thickness,high in quality and relatively large in proportion to the dark mudstones.In contrast,although the dark mudstones in the Dongying Formation are large in thickness,high-quality source rocks are rare.Laterally,source rocks in the Bozhong depression are the largest in both thickness and distribution,followed by Liao-dong Bay,Qikou and Huanghekou depressions.Source rocks of Es⁴-Ek are mainly developed in Liaodong Bay area,Laizhou Bay and Qikou depressions.In general,the major source rocks in the study area are considered to come from the Shahejie Formation,of which the Es³ is the most important.

Control of source rock on hydrocarbon accumulation and prediction of favorable plays in the Bozhong Depression of the Bohai Sea waters

Xia Qinglong, Pang Xiongqi, Jiang Fujie, Ma Xingzhi

2009, 30(4):  398-404,411.  doi:10.11743/ogg20090402

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According to the geological theory of "source-control" (i.e.,hydrocarbon accumulations are under the control of source rocks),we made geostatistics on distributions of source rocks and reservoirs in China's eastern basins.Based on these statistical data,we brought forward a concept of "hydrocarbon distribution threshold" ,which lays the foundation for concepts such as "probability of hydrocarbon pooling","probability of reserve distribution" and "maximum size of reservoir".A multivariate nonlinear mathematical model was established by using the geostatistics and regression discrimination approaches.We made a comprehensive prediction on the hydrocarbon distribution in the Bozhong depression of the Bohai Sea waters according to the hydrocarbon expulsion threshold,hydrocarbon pooling threshold and hydrocarbon distribution threshold.The results show that,the favorable plays are the Shijiutuo pooling system and the Bodong pooling system.Favorable exploration targets will be traps which are adjacent to the boundary of hydrocarbon expulsion and have an over 80% probability of hydrocarbon pooling.

Method for obtaining key parameters for calculating residual oil amount in carrier beds after oil migration and accumulation in the Liaodong Bay Depression

Tian Lixin, Wu Li, Jiang Zhenxue, Zhou Jingjing, Yao Leilei

2009, 30(4):  405-411.  doi:10.11743/ogg20090403

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The 1st and 2nd member of the Paleogene Shahejie Formation (E3s¹ and E3s²) in the Liaodong Bay depression were taken as examples.We performed geologic and statistical analyses on the residual hydrocarbons and physical properties of the reservoirs.Based on the characteristics of residual hydrocarbons inside and outside the hydrocarbon kitchen and in combination with the relationship between buoyance of oil column in carrier beds and capillary pressure of pores,we determined the height of residual oil column and calculated the amount of residual oil in carrier beds.The results show that the amount of residual oil range from 184 to 259 million tons in the carrier beds of E3s¹ and E3s² in the Liaodong Bay depression,amounting to 7.4%-10.4% of the total hydrocarbon expulsion.Residual hydrocarbon in reservoirs is the main loss of hydrocarbon in the process of secon-dary migration.The key parameters for calculating residual oil have great impact on the accuracy of prediction.

Distribution features of current geothermal field in the Bohai Sea waters

Qiu Nansheng, Wei Gang, Li Cuicui, Zhang Yuan, Guo Yonghua

2009, 30(4):  412-419.  doi:10.11743/ogg20090404

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The average geothermal flow in the Bohai Sea waters is (60.9±8.7)mW/m².It is up to 70～80 mW/m² in the Shijiutuo,Shaleitian and Bonan uplifts,65-75 mW/m² in the Bozhong sag,the Huanghekou sag and the Qinnan uplift,while lower than 65 mW/m² in the Liaodong bay,Miaoxi,the Laizhou bay,Qikou,Sha'nan and Chengbei.The geothermal gradient varies in different structural units of the Bohai Sea waters and averages at 30.8℃/km.Higher geothermal gradient 32-42℃/km,is tested in the Shaleitian uplift,Bozhong,the Laizhou bay,Qikou,Sha'nan and Chengbei.In contrast,it is low in the sags,22-32℃/km on average.The distribution of geothermal field coincides with the structural configuration in the Bohai Sea waters,roughly reflecting the structural form of the NNE-trending Tan-Lu Fault.

An analysis on fluid inclusions and hydrocarbon migration in JZ 25 area of Liaodong Bay waters

Deng Jinhui, Huang Xiaobo, Li Huiyang, Ju Yongtao

2009, 30(4):  420-424,430.  doi:10.11743/ogg20090405

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A study of hydrocarbon charge history was carried out in JZ25 area,Liaodong Bay waters,by using homogenization temperature of fluid inclusions.The results indicate that the area had experienced two stages of hydrocarbon charge.The first one happened during the period prior to a secondary outgrowth of quartz and mainly in form of liquid-hydrocarbon inclusions of low abundance and low maturity.The second stage happened during the period after the secondary outgrowth of quart and organic inclusions of high abundance were mainly distributed along the micro-fractures that cut through quartz grains and their outgrowth rims or in the dissolution pores of feldspar grains.Hydrocarbon reservoirs in JZ25 area is considered to be formed mainly during the second stage,which is 23-21 Ma from nowadays.An analysis of excess pressure system and hydrocarbon pathway of source rocks in third member of the Shahejie Formation in the study area was then performed based on the above understanding.A model illustrating hydrocarbon migration controlled by both reservoirs and faults was also established and served as an important guidance for the exploration of large-scale hydrocarbon reservoirs in JZ25 area.

Control of structure-paleogeomorphology on the deposition of the lower part of the third member of the Paleogene Shahejie Formation in the Qingdong Sag of the Bozhong Depression

Li Guifan, Li Jianping, Wang Genzhao, Cheng Jianchun, Gong Huijie

2009, 30(4):  425-430.  doi:10.11743/ogg20090406

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Based on seismic and log data,we used back-stripping technology and trend analysis method to restore structure-paleogeomorphology of the Qingdong sag during the sedimentation of the lower part of third member of the Paleogene Shahejie Formation (E3s³).We also explained the control of structure-paleogeomorphology on sedimentary systems.Controlled by the Tan-Lu fault and its induced faults,the Qingdong sag subsided as a whole during the sedimentation of the lower part of E3s³.It was a dustpan-shaped rift which was faulted in its eastern part and overlapped in its western part.Within the sag,there were three near east-west-trending sub-uplifts which separated the Qingdong sag into four sub-sags.From south to north,the size of these sub-sags became larger gradually.Controlled by structure-geomorphology,fan deltas were developed in the east of the Qingdong sag,while braided deltas were developed in the west and in the south during the deposition of the lower part of E3s³.The major part of the delta sedimentary system was obviously controlled by the sub-sags.Arenaceous sediments of fan delta and braided delta facies overlapped,in various degrees,the sub-uplifts because of the small size of the sag and sufficient supply of deposits.The shallow water and strong energy resulted in the arenaceous beach-bar facies of different scales on the sub-uplifts.Favorable reservoir conditions and traps are found in delta sandbodies developed on the eastern ramp,braided delta sandbodies developed on the western gentle slope and arenaceous bench bar deposits developed on the sub-uplifts.These sandbodies should be the major exploration targets.

Control of the Dongying Formation mudstone upon the distribution of hydrocarbon accumulations in the Liaodong Bay Depression

Xu Changgui, Zhu Xiuxiang, Shi Cui'e, Wang Haijun

2009, 30(4):  431-437.  doi:10.11743/ogg20090407

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The Liaodong Bay depression is located in northeastern Bohai Bay Basin.Hydrocarbon-bearing layers in the depression present a trend of becoming younger from north to south.Most hydrocarbon accumulations in the northern and central parts of the depression are distributed in the Dongying and Shahejie formations—a pattern closely related with the mudstone (thicker in the north and thinner in the south) in the Dongying Formation.Considering the structural features,evolution of depositional systems,and formation development in the Liaodong Bay depression,we studied the overpressure created by the mudstone in the Dongying Formation and the configurations of the mudstone with carrier systems such as sand bodies,faults,unconformities,and discussed the controlling effect of the mudstone on hydrocarbon accumulations in the Liaodong Bay depression.The result shows that the mudstone,together with faults,oil sources and sandbodies,control the distribution of oil and gas accumulations.Of these factors,the overpressure created by the thick mudstone has a strong presence in affecting the distribution of accumulations in the northern and central parts of the depression,causing most of them occurring in the Dongying Formation and its underlying layers.

Distribution characteristics and origin of carbonate cements in the middle and deep clastic reservoirs of the Paleogene in the Bozhong Depression

Wang Qingbin, Zang Chunyan, Lai Weicheng, Wang Bo, Wang Xuelian, Zhao Xiaojiao

2009, 30(4):  438-443.  doi:10.11743/ogg20090408

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Carbonate cements are the most important cements in the Paleogene sandstone reservoirs of the Bozhong depression.Analysis on thin sections shows that the main cements of the middle and deep clastic reservoirs are siderites,dolomites,calcites,ferrodolomites and ferrocalcites.According to the statistical data,carbonate content gradually rises with the increase of depth.A sharp increase of carbonate content occurs in the Paleogene Dongying Formation.When the carbonate content exceeds 10%,it will have a great impact on physical properties of reservoirs.Analysis on thin sections and isotopes reveals that the siderites mainly occur as pores fillings and particle rim cements and were mainly formed in the synsedimentary period or at the early stage of the early diagenesis.The calcites mainly occur as particles or poikilitic cements.The relative calcite content has negative correlation with δ¹⁸O values,indicating that most of the calcites were formed late.The ferrocalcites mainly occur as particles.The ferrocalcite-dominant samples correlate with low δ¹⁸O values and relatively high temperature of precipitation.The dolomites mainly occur as intergranular pore-filling particles in patches,and its relative content has obvious positive correlation with δ¹⁸O value.Its temperature of precipitation is relatively low and the time of forming is relatively early.The ferrodolomites mainly occur as dispersed particles,and its relative content has obvious positive correlation with δ¹⁸O value and its temperature of precipitation is relatively low.

An integrated seismic-geological approach to predict lacustrine carbonate rock in the Bohai Sea waters

Song Zhangqiang, Lai Weicheng, Niu Chengmin, Xue Jinbao, Shen Hongtao, Yu Shengjie

2009, 30(4):  444-449.  doi:10.11743/ogg20090409

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Under the guidance of lithofacies paleogeography and sedimentology,we analyzed the data of wells in the Bohai Sea waters and concluded that the development of lacustrine carbonates is influenced by factors such as paleogeomorphology,paleoclimate,provenance,tectonic evolution and basement characteristics.The lacustrine carbonates were found to distribute separately and be limited in certain areas.The results of forward modeling show that the lacustrine carbonates are characterized by strong reflection or mounded reflection.Our research proves that it is feasible to predict the distribution of lacustrine carbonate reservoirs with the integrated seismic-geological method under the guidance of geological model.This method has been successfully applied to the B22 area and the B13 area in the Bohai Sea waters.

Control of the Tan-Lu fault zone on hydrocarbon accumulation in the Bohai Sea waters

Wang Guimei, Zhou Donghong, Tang Liangjie

2009, 30(4):  450-454,461.  doi:10.11743/ogg20090410

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In the Bohai Sea waters,near the Tan-Lu fault zone,the Bonan and Liaodong Bay exploration areas have great potential for hydrocarbons.While apart from the Tan-Lu fault zone,the Boxi exploration area has less oil and gas.In addition,the existing discoveries are all distributed surrounding the Tan-Lu fault zone.From the above-mentioned facts,we can conclude that,near the Tan-Lu fault zone,there is a great potential for hydrocarbon exploration.Balanced-cross sections show that the Tan-Lu fault zone of the Bohai Sea area shows tectonic features of extension in the Paleogene and strike-slip in the Neogene.The Paleogene extensional activities controlled the development of hydrocarbon kitchens and promoted the fast maturation of source rocks.Later,the Neo-gene strike-slip activities shaped many structural traps and helped the hydrocarbon migration and late accumulation.The Bohai Sea waters show great potential for hydrocarbon exploration,while to date,only a small amount of the total resources have been proved.

The Cenozoic folding in the Bohai Sea waters

Chen Shuping, Lü Dingyou, Tang Liangjie, Wang Yingbin, Sun Mengsi, Qu Dongmeng, Yang Xianfan,

2009, 30(4):  455-461.  doi:10.11743/ogg20090411

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This paper summarizes the types of the Cenozoic folding,their controlling factors and distribution in the Bohai Sea waters based on seismic data interpretations.According to their mechanical genesis,the folding can be classified into four types which are respectively related to extension,wrench,compression induced by gravity sliding,and compaction and diapirism caused by gravity.Extension-related folding and compression-rela-ted folding happened during the Paleogene and these two types of folds are distributed along the long-active main faults and slopes respectively.Wrench-related folding happened during the Neogene and the folds are distributed in the eastern part of the Bohai Bay Basin where the Tanlu fault zone passes by.Among the gravity-related fol-ding types,the drape folding had been active in the whole Cenozoic and the folds are distributed on the salient.While the salt diapirism folding was restricted to certain areas and the faults occur only in the Laizhou Bay sag at the south of the basin.The current exploration results in the Bohai Sea waters show that traps located along the faults and related to the wrench folds of the Late Neogene are favorable for oil and gas accumulation.

Fault activities and hydrocarbon migration and accumulation during the Neotectonic period in the Bozhong-Bonan segment of the Tanlu fault zone

Jiang Lina, Zou Huayao

2009, 30(4):  462-468,482.  doi:10.11743/ogg20090412

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The Tanlu fault zone was very active in the process of the Neotectonic movement.Although the tecto-nic movement was intense,several medium-and large-sized oil fields were formed in the Bozhong-Bonan segments of the Tanlu fault zone,indicating that fault activity played a key role in the migration and accumulation of hydrocarbons during this period.This paper,starting with the activity differences between the major and secondary faults in different tectonic settings,uses the fault activity rate (FAR) method to analyze and summarize the relationship between fault activities and hydrocarbon migration & accumulation during the Neotectonic period and to reveal the mechanism of late hydrocarbon accumulation in the study area.The results show that fault activities vary across different segments of the zone.The main faults with weaker activities are favorable for hydrocarbon accumulations,while those with stronger activities are the opposite,as it is easy for hydrocarbons to escape.A combination of active main faults with secondary faults of weaker activity is considered good for hydrocarbon migration,accumulation,and preservation.

Relationship between faulting and hydrocarbon pooling during the Neotectonic movement around the central Bohai Bay

Zhou Xinhuai, Niu Chengming, Teng Changyu

2009, 30(4):  469-475,482.  doi:10.11743/ogg20090413

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The area around central Bohai Bay is an important prolific zone,where faults are well developed and faulting during the neotectonic movement played a significant role in migration and preservation of hydrocarbons.The fault activity rate (FAR) method was used to study the relationship between faulting activity and hydrocarbon accumulation/preservation in the area based on analysis of activity changes along the strike of main fault and combinations of faults with different FAR within the zone.In addition,the controlling mechanisms of hydrocarbon accumulation were also discussed in respects of the locations of spill points,the definition of fault carrier systems and FAR,and the relationship between fault throw and thickness of regional caprock.The results indicate that hydrocarbon accumulations in the area are mainly located near faults with moderate or weak activities(FAR<25 m/Ma),while they seldom occur near faults with strong activities(FAR>25 m/Ma) because these faults served mainly as vertical migration pathways,making it hard to form shallow oil accumulations.For these faults,only in areas with relatively weak fault activities can hydrocarbon accumulation occur.

Controlling effect of a strike-slip transform belt on hydrocarbon accumulations in the Huanghekou Sag,the Bohai Sea waters

Zhu Xiuxiang, Lü Xiuxiang, Wang Deying, Zhang Jie

2009, 30(4):  476-482.  doi:10.11743/ogg20090414

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The Huanghekou sag,located in the southeast of Bohai Sea waters,is cut through at the center by the west branch of the Tanlu fault zone,forming a strike-slip transform belt in the central uplift.This belt,according to recent exploration results,is considered as one of the key hydrocarbon-bearing structural zones in the sag.Studies on the structures and their evolutionary characteristics in the belt,in addition to the analysis of the hydrocarbon accumulation patterns inside the belt,indicate that the transformation belt controls hydrocarbon accumulation in the central uplift through controlling the development of traps,the distribution of sandbodies,and the formation of carrier systems.The controlling effect of the transform belt is therefore regarded as a useful clue for finding hydrocarbon-bearing areas and for improving exploration efficiency.

Characteristics and modeling of the Cenozoic right-lateral slip deformation in the Liaodong Bay segment of the Tan-Lu fault zone

Yang Qiao, Wei Gang, Ma Baojun, Qi Jiafu

2009, 30(4):  483-489,496.  doi:10.11743/ogg20090415

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The Tan-Lu fault belt is a regional deep fault belt.Geophysical data show that the main shift zone of the Tan-Lu fault goes roughly along the eastern margin of the Liaodong Bay depression.Several steep and near-vertical faults were developed along both sides of the Liaodong uplift in the eastern part of the Liaodong Bay depression.These faults cut all strata from the basement to the Neogene,and some of them even cut the Pleistocene and Holocene.In the southern part of the Liaodong uplift,the faults occur as a broom-like fault complex diverging to the south-west and converging to the north.In section,all the faults show features of normal fault displacement.In contrast,in the northern part of the Liaodong uplift,the faults occur as a feather fault complex diverging to the north-northwest and converging to the south.In section,some faults in the west show distinct characteristics of thrust fault displacement.Fault complex in the sedimentary cover of the basin near the Liaodong uplift reveals that,during the Cenozoic,the north-northeast-trending faults experienced obviously right-lateral slip activities.Sandbox simulation experiment indicates that the fault complexes along the northern and southern parts of the Liaodong uplift may be related to the Cenozoic right-lateral slip movement of the Tan-Lu fault.The differences in fault complex and movement may be related to changes of strikes of the main shift zone of the Tan-Lu fault.

Structural characteristics and hydrocarbon accumulation in the buried hills of the Liaoxi low salient,the Liaodong Bay Depression

Lü Dingyou, Yang Minghui, Zhou Xinhuai, Wei Gang, Liu Le, Li Chunxia, Zheng Xiaofeng

2009, 30(4):  490-496.  doi:10.11743/ogg20090416

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The Liaoxi low salient in Bohai presents clear structural segmentation characteristics and can be divi-ded into southern,middle,and northern parts.The buried hills there present a typical structural style of tilting fault-block and a three-layer architecture consisting of the Archaean metamorphic rocks,Cambrian-Ordovician carbonates,and Mesozoic volcanic rocks.Hydrocarbon accumulations in the buried hills of Liaoxi low-salient are mainly determined by two factors:development of reservoirs in the Paleogene and abundance of hydrocarbon resources in the Liaozhong sag.Therefore,large-scale hydrocarbon accumulations in buried hills occur mostly in circumstances that hydrocarbon supply from the main fault-troughs is plentiful and high-quality reservoirs are absent in the Paleogene.

Hydrocarbon distribution features and main controlling factors in the Bohai Sea waters

Liu Xiaoping, Zhou Xinhuai, Lü Xiuxiang, Zhu Xiuxiang, Wang Haijun,

2009, 30(4):  497-502,509.  doi:10.11743/ogg20090417

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Among the proved reserves in Bohai Sea waters,those from structural hydrocarbon pools account for the most,taking up 66.8% of the total,while complex pools contain second largest reserves (25.9%).The number of the large/medium-sized fields only accounts for 34% of the total,while their proven reserves account for 84.4% of the total.Proven reserves are most numerous in structures of low salient,swell in sag,and salient,accounting for 45.3%,24.9% and 22.0% respectively.Vertically,about 61.0% of the proven oil reserves and 55.0% of the proven gas reserves are distributed in the Neogene.About 93.2% of the proven oil reserves and 85.0% of the proven gas reserves are distributed in the shallow to medium reservoirs with burial depth less than 3 000 m.The hydrocarbon distribution in Bohai Sea waters is the result of a series of geological processes,involving hydrocarbon source rock,depositional systems,structures,as well as fault systems.The hydrocarbons migrated in short distance and accumulated around the hydrocarbon kitchens.Factors such as favorable sedimentary facies belts,high-quality lithofacies,and favorable physical properties played important roles in the development of high-quality reserviors in Bohai Sea waters.The Tanlu fault and its induced faults controlled the formation and development of hydrocarbon kitchens,traps and carrier systems in the study area.

Genetic features of drape anticline oilfields in the Bozhong Depression

Xue Yong'an, Wu Xiaohong, Lü Xiuxiang, Zhou Xinhuai, Wei Gang

2009, 30(4):  503-509.  doi:10.11743/ogg20090418

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Oil-bearing horizons of the drape anticline oilfields in the Bozhong depression are mainly the Neogene Minghuazhen and Guangtao formations,and they are mainly distributed in structures such as salient and low sa-lient.The Bozhong kitchen is the major hydrocarbon source for PL19-3,QHD32-6 and CFD11-1 oilfields in the Bozhong depression.The drape anticline oil/gas fields generally have the genetic features such as being adjacent to hydrocarbon kitchen,quality reservoirs,good reservoir-seal combinations,favorable structural locations and excellent carrier systems.In combination with the analysis of the factors resulting in the failure of exploratory wells on the salient and low salient structures,we believe that the analysis of hydrocarbon migration conditions is the key to searching for large drape anticline oilfields in the Neogene,while the analyses of reservoirs and reservoir-seal combinations are the focus in the Paleogene.

Late-stage near-source preponderant hydrocarbon pooling pattern in the Huanghekou Sag of the Bohai Sea waters

Peng Wenxu, Sun Hefeng, Zhang Rucai, Yu Hongzhong, Zhang Xintao

2009, 30(4):  510-518.  doi:10.11743/ogg20090419

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Being a hydrocarbon kitchen,the Huanghekou sag in the south of Bohai Sea waters had seen many oil and gas discoveries featuring in shallow to middle burial depth (1200-1800 m),moderate crude API,high productivity(as high as 455.3 m3/d of gas from the Neogene),etc.Most of its oil and gas reservoirs were formed through near-source vertical migration and the pooling process has started since 5.1 Ma.Its major reservoirs are apparently controlled by stratigraphic sequences and most of the reservoirs are located below the maximum flooding surface.The pooling pattern can be generalized into "near-source,late-stage,and preponderance".During the period of 2004 to 2008,success rate of exploration in the sag was up to 85%,and 3P geological reserves of single exploratory well averaged at 7.13 MMCM.By the end of 2008,about 100 exploration wells had been drilled.In addition to the discoveries obtained during the 1980s to early 1990s,such as Bozhong 25-1/S,Bozhong 34-2/4,Bozhong 28-1 and Bozhong 26-2,several medium-sized discoveries including Bozhong 34-1,Bozhong 28-2S,Bozhong 29-4 and Bozhong 26-3 have been found in layers with shallow to middle burial depth,initiating a new surge of oil and gas discoveries in the south part of Bohai Sea waters.