Table of Content

28 February 2018, Volume 39 Issue 1

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Theory of composite sand body architecture and its application to oilfield development

Hu Guangyi, Fan Ting'en, Chen Fei, Jing Yongquan, Song Laiming, Liang Xu, Xiao Dakun

2018, 39(1):  1-10.  doi:10.11743/ogg20180101

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In recent years, the theory of composite sandbody architecture proposed by CNOOC has contributed to several major oil and gas discoveries.This paper systematically introduces the context for proposing this theory, its fundamental concept, main content and characterization method as well as practical application, and discusses the significances of this theory.Ground penetrating radar reveals that the common architecture element of modern and ancient meandering river deposits is point bar composite instead of a single point bar.When their scales being larger than seismic resolution, they commonly correspond to a single channel belt or composite channel belts and represent a sub-layer or sand group.A sand body of this kind is defined as a composite sand body and is treated as a separate development unit.The composite sand body is originated from abrupt change in accommodation and source supply caused by tectonic uplift or subsidence of basin valley.The relationship between depositional process and composite sand body architecture pattern is revealed by river terrace geomorphology.This paper illustrates architecture unit, architecture bounding surfaces, architecture model, scale characteristics and their controlling factors, and defines modern sedimentary geomorphic markers of architecture bounding surfaces.Fine characterization of composite sand body architecture is the key to precisely describing remaining oil distribution and quantifying development index, and further optimizing injection-production pattern and increasing success rate of infilling drilling.

Fault interactions and their significances for hydrocarbon accumulation in offshore Bohai Bay Basin, eastern China

Yu Yixin, Zhou Xinhuai, Xu Changgui, Wu Kui, Zhou Xin, Liu Yubo

2018, 39(1):  11-19.  doi:10.11743/ogg20180102

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A great number of extensional and strike-slip faults of various orientations and scales occur in the offshore Bohai Bay Basin, eastern China.Complex areal and vertical combinations exist between these faults and they play a key role in hydrocarbon accumulation in this area.Based on seismic interpretation and structural mapping, this paper mainly focuses on the regional and local interaction patterns of the extensional faults and strike-slip faults and their significances for hydrocarbon accumulation in the study area.On map view, the regional patterns of fault interaction involve conjugate type, orthogonal crossing type and oblique crossing type, while the local patterns of fault interaction can be divided into broom-shaped transfer type, branch transfer type, en-echelon fault transfer type and transition structure transfer type, of which the last type can be subdivided into three sub-types including ramp, horst type and faulted-block.On sectional view, the fault interaction patterns mainly include X-shaped type, hybrid type and superposition type.The fault interaction not only influences basin architecture, but also impactes trap, reservoir and hydrocarbon migration.This study is of great significance for oil and gas exploration in the offshore Bohai Bay Basin.

Characteristics of S-shaped strike-slip transfer zones and quantitative analysis of their influence on hydrocarbon accumulation in Liaoxi structural belt, Bohai Sea

Liu Yubo, Huang Xiaobo, Xu Changgui, Li Qiang, Wu Kui, Yu Yixin, Zhang Rucai

2018, 39(1):  20-29.  doi:10.11743/ogg20180103

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S-shaped strike-slip transfer zone is widely developed structure in strike-slip strain background.However, previous researches are mainly focused on the classification of strike-slip transfer zones, but its control on hydrocarbon accumulation is poorly understood.Based on 3D seismic data and oil and gas fields analysis, this paper addresses the effects of S-shaped strike-slip transfer zone on hydrocarbon accumulation in the Liaoxi structural belt, Bohai Sea, by using statistical methods.Cenozoic structural deformation of the Liaoxi structural belt is characterized by deformation of NE-trending extension superimposed by NEE-trending dextral strike-slip activities.S-shaped strike-slip transfer zone can be divided into restraining bends and releasing bends.According to different evolution stages, restraining bends can be further divided into 3 subordinate classes, involving transpressional uplifting bend, gentle restraining bend and intense restraining bend.Similarly, releasing bends involve spindle-shaped pull-apart, lazy s-shaped pull-apart and rhomboidal pull-apart.In addition, the strike-slip transfer zones at the end of strike-slip fault zones contain restraining and releasing horsetails.The concept of oil and gas enrichment index (OGEI) is defined, and the positive correlation between master strike-slip fault curvature and intensity of adjusting strike-slip faults is proven.A mathematical model from OGEI is proposed to quantitatively predict oil and gas enrichment.It is a quantitative tool for exploration decision, and has been applied in analysis of LD5-2N oil field successfully.

Characteristics and major control factors of natural fractures in carbonate reservoirs of Leikoupo Formation in Pengzhou area, western Sichuan Basin

Zhao Xiangyuan, Hu Xiangyang, Xiao Kaihua, Jia Yuewei

2018, 39(1):  30-39,152.  doi:10.11743/ogg20180104

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Several types of natural fractures occur in the reservoir of the Leikoupo Formation in Pengzhou area, western Sichuan Basin, and their major controlling factors are very complex.Geological, geophysical and experimental data are integrated to study the genetic types and characteristics of these fractures, and analyze the geologic factors controlling the formation of tectonic factures.In the reservoir of the Leikoupo Formation, the predominant fracture type is tectonic facture, followed by diagenetic fracture.The tectonic factures can be classified into three types:high angle fractures, oblique fractures and low angle fractures.Each type of fracture has its own specific dominant orientation, indicating that they are resulted from multiple stages of tectonic movement.The fractures are effective in general.High angle fractures are all effective, while some low angle fractures and oblique fractures are ineffective.Fractures are highly developed in dolomite, but are poorly developed in limestone.Due to the impacts of differences of fracture genetic mechanisms and the timing of fracture formation and reservoir diagenetic evolution, the development of high angle fractures and oblique fractures are mainly controlled by faults and their disturbed stress field, thickness of rock mechanics layer and physical properties of reservoirs, while that of the low angle fractures are mainly controlled by occurrences of local strata and structures and sedimentation.

Influence of maceral composition on organic pore development in shale: A case study of transitional Longtan Formation shale in eastern Sichuan Basin

Cao Taotao, Liu Guangxiang, Cao Qinggu, Deng Mo

2018, 39(1):  40-53.  doi:10.11743/ogg20180105

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A sequence of organic-rich shale of transitional facies can be observed in the Longtan Formation of eastern Sichuan Basin.In order to investigate the characteristics of the organic pores and their controlling factors in the shale, we performed experiments and analyses on shale samples to study TOC, mineral composition, vitrinite reflectance, and organic petrological parameters through low-pressure nitrogen adsorption and scanning electron scanning combined with argon ion milling and etc.The results show that the mineralogy of shale samples from coastal-swamp, lagoon-tidal flat and shallow shelf facies is dominated by clay minerals with low content of quartz.The organic matters in the samples are mostly vitrinites with poorly-developed organic pores.However, some micro-cracks were found to occur within or along the rims of organic matter grains.In contrast, the shale of deep shelf facies was characterized by high quartz and low clay mineral contents and orgnic matters with well-developed pores being dominated by sapropelinite and solid bitumen.There is an inverse relationship or insignificant correlation between the microscopic pore volume and TOC of shale of the coastal-swamp, lagoon-tidal flat and shallow shelf facies.In contrast, the pore volume is positively correlated with TOC for shale of deep shelf facies.In combination with previous works, we propose that vitrinite and solid bitumen are not the main contributors to organic pores during the high maturity stage of the samples, while sapropelinite is the most favorable for orga-nic pore development.Thereforoe, the organic maceral composition should be taken into consideration when studying shale reservoir properties of this transitional facies in eastern Sichuan Basin as well as other areas.

Paleo-structure features in the 1st member of the Upper Paleozoic Shanxi Formation and its influences on gas accumulation in southwestern Ordos Basin

Zhang Yuhang, Zhao Jingzhou, Wang Yongwei, Liu Tao, Wang Wenqiang, Tang Wen

2018, 39(1):  54-65.  doi:10.11743/ogg20180106

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Based on the latest seismic data, geological understanding and exploration results in the Southwestern Ordos Basin, paleo-deformation characteristics of the 1st member of the Upper Paleozoic were studied using tectonic evolution analysis and paleo-structure restoration, and controlling effects of paleo-structure on hydrocarbon distribution were analyzed.According to the strata correlation, the sedimentary, deformation, and subsidence characteristics of the 1st member of the Permian Shanxi Formation are identified.The tectonic evolution and hydrocarbon accumulation stages revealed that the key periods of the Upper Paleozoic tectono-hydrocarbon accumulation are the Late Jurassic and the end of the Early Cretaceous in the Southweste.Through the restoration of Shan 1 paleo-structure in different tectonic evolution stages, the ancient structure of the Upper Paleozoic Shan 1 in Late Triassic, Late Jurassic and end of Early Cretaceous share similarities but also demonstrate gradual evolution through time.The paleo-uplift and paleo-slope are widely developed in the late Jurassic, while the western slope gradually narrowed and the Tianhuan Depression is formed at the end of the Early Cretaceous.Based on the analysis of tectonic deformation and hydrocarbon accumulation stages, it is believed that the Late Jurassic Shan 1 paleo-structure is the key factor controlling the distribution of the Upper Paleozoic gas reservoirs in the Southwest Ordos basin.Due to the lack of long-distance migration of the gas in the Upper Paleozoic reservoirs in the study area, the Early Cretaceous hydrocarbon charge is focused around the Late Jurassic ancient structure highs of Shan 1 member.Thus the hydrocarbon accumulation model is characterized by near-source or intra-source accumulation.

Sequence stratigraphy and sedimentary characteristic analysis of Qiaotou sandstone of Tayuan Fm in Linxing area, eastern margin of Ordos Basin

Wu Peng, Gao Jixian, Guo Junchao, Zhou Yuzhe, Hu Xiaoxian

2018, 39(1):  66-76.  doi:10.11743/ogg20180107

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Sedimentary characteristics and location within sequence framework of the Qiaotou sandstone of the Taiyuan Formation in Linxing area, eastern margin of Ordos Basin, determine the reservoir type and trap area.The Taiyuan Formation is divided into one complete long-term cycle (LSC1) and four complete medium-term cycles (MSC1, MSC2, MSC3, MSC4) based on identification of sequence boundaries and flooding surfaces by using seismic, logging, outcrop and outcrop data.The Qiaotou sandstone is within the descending half cycle of MSC1 and is dominated by coarse-grained and coarse-to-medium grained quartz sandstones.The cumulative probability curve of the grain size is typical of the two-way flow.Core observation reveals typical tidal current sedimentary structure and pinnate, massive, graded and composite bedding.The sand bodies show lenticular geometry on section and appear as bands parallel with shorelines on map.The Qiaotou sandstone is believed based on a comprehensive analysis to be tidal channel and barrier bar deposits, which are quality reservoirs of marine facies.The sand body parallels shoreline in northwest-southwest direction and all wells that penetrate it test high gas flow.The area of traps are controlled by the sand body boundary and show the characteristics of lithologic traps.This study is of great significance for guiding exploration and development of tight sand gas in Linxing area, eastern margin of Ordos Basin.

Enhancement of ultra-deep tight sandstone reservoir quality by fractures: a case study of Keshen gas field in Kuqa Depression, Tarim Basin

Wang Junpeng, Zhang Huiliang, Zhang Ronghu, Yang Xuejun, Zeng Qinglu, Chen Xiguang, Zhao Jianquan

2018, 39(1):  77-88.  doi:10.11743/ogg20180108

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Kuqa Depression in Tarim Basin is one of the major gas sources for the west-east national gas transmission project.The Lower CretaceousBashijiqike Formation in the Keshen gas field is the major pay zone with a burial depth exceeding 6 000 m and low matrix porosity and permeability (<0.1×10^-3 μm²).Fractures can tremendously improve the permeability of reservoirs.Therefore, a thorough analysis and quantitative description of fracture growth and accurate prediction of the spatial distribution pattern of fracture permeability of the Formation are critical to natural gas development in the study area.Methods including drilling and coring, FMI imaging, carbon oxygen isotopic chronological analyses, fracture modeling through holograhic laser scanning of outcropwere combined with experimental analysis procedures such as CT scanning, SEM, cathode luminescence, laser scanning confocal microscope, high pressure mercury injection and electron microprobe to study both qualitativelyand quantitativelythe enhancement ofreservoir propertiesof the Formation by fractures.The fractures in the gas field aredominated by half-filled shear fractures with an effective opening ranging between 0.1 and 1.5 nm.There arethree stages of structural fractures developed in the Formation, and the fractures of each stage line up in different patterns at different structural locationsunder the control of structural stress.The fractures have a general porosity of less than 0.1%, but they caneffectively improve the permeability of the reservoirs by 1 to 3 orders of magnitude and result inthe formation of high-permeability reservoirs 150 m below the unconformity face.Fractures formed during early and middle stages served as pathways of fluids for tight reservoir diagenesis and cementation, unfavorable for the preservation of connective pores and throats.Those formed during later stage were accompanied by oil and gas charging processes and enlarged pore throats in reservoir matrix through dissolution.Micro-fractures had limited effect upon the connectivity of pores and throats in the reservoirs (only effectively connecting pore-throats with aperture between 10 to 100 times).In summary, fracture network formed during the late stage is the key to high productivity of the gas field.

Differential deformation and its control mechanism of fault structures in Yakela fault-salient, Tarim Basin

Yang Yong, Tang Liangjie, Diao Xindong, Xie Daqing

2018, 39(1):  89-97.  doi:10.11743/ogg20180109

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Based on the interpretation of 3D seismic data, the differential deformation characteristics of faults in Yakela fault-salient were studied and the controlling factors were discussed.Controlled by the thick mudstone of the Cretaceous and gypsum rocks of the Jidike Formation, the development of different faults is observed in different in vertical domains.Large basement involved thrust faults were developed in the lower structural section.Echelon-distributed extensional-shear faults were developed in the middle structural section.Capping-sliding faults were developed in the upper structural layers.The intensity of fault deformation gradually decreased from bottom to top.Formation of the faults experienced 4 critical stages:thrust faults development stage in late Paleozoic, thrust faults rejuvenation stage in Mesozoic, extensional-shear faults development stage in early Neogene and capping-sliding faults development stage in late Neogene.The late Paleozoic thrusting was largely related to the collision between the Tarim continental block and the peripheral terrains due to the closing of the North Kunlun Ocean at the end of the early Ordovician, followed by the closing of the South Tienshan Ocean at the end of Permian.The fault activities in Mesozoic and Cenozoic were the tectonic response of the far-field effect of the India-Eurasia collision.

Mechanism of strike-slip faulting and hydrocarbon accumulation in northern slope of Tazhong area

Ning Fei, Jin Zhijun, Zhang Zhongpei, Yun Jinbiao, Zhang Jibiao

2018, 39(1):  98-106.  doi:10.11743/ogg20180110

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A series of NE trending strike-slip faults developed in northern sloped of Tazhong area.In order to unravel the forming mechanism and its implication on hydrocarbon accumulation of strike-slip faults, detailed analysis upon geometric styles of strike-slip faults was performed, and the evolutional process of NE trending slip-faults in northern Tazhong area was simulated by using physical analogue model method.The results show that development of different planar and sectional structural styles of strike-slip faults is induced by differential pushing and basement shear effect under simple contractional stress field.Segmentation of characteristics is also observed along faults trending.It is concluded by physical analogue results integrated with structural background analysis that the forming mechanism of strike-slip faults in northern slope of Tazhong area was controlled by two factors.Firstly, the segmentation of Tazhong I fault gave the northern slope of Tazhong area a differential pushing stress in NE direction at the late Caledonian-early Hercynian.Secondly, NE trending basement faults activity in northern Tazhong area resulted in basement shear effect, which drag overlying upper Ordovician, Silurian, Devonian strata sinistrally.The existence of NE trending strike-slip faults contribute to hydrocarbon accumulation in northern slope of Tazhong area.On the one hand, high-angle structural faults development induced by strike-slip faults connects reservoir sections.On the other hand, faulting of strike-slip facilitates multi-layers hydrocarbon accumulation in northern slope of Tazhong area.

Characteristics and controlling factors of Lower-Middle Ordovician Reservoirs in Yubei area, Tarim Basin

Liu Hongguang, Liu Bo, Cao Jianhua, Huang Chenjun, Liu Geyun

2018, 39(1):  107-118.  doi:10.11743/ogg20180111

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The Lower-Middle Ordovician carbonates in the Yubei Area, Tarim Basin, are considered promising exploration targets.However, the complexity of the controlling factors and distribution patterns of the reservoirs hindered the exploration process in the area.By using petrologic, physical and geochemical methods, we classified the reservoirs into five types:cavern type, dissolution pore type, fracture-vug type, vug-fracture type and fracture type.The main controlling factors of the reservoirs were determined to be dissolution, dolomitization and fracturing.It is suggested that the relative low stand sea level during the Early-Middle Ordovician caused the relative paleogeomorphic highs being repeatedly exposed to penecontemporaneous dissolution, which resulted in the formation of centimeter-scale caves, millimeter-scale mold pores, along-bedding dissolution and geopetal cements that are not cotrolled by single uniform exposure surface.The dissolution degree in the Penglaiba Formation was overly stronger than that in the Yingshan Formation.The dolomitization processes that mainly occurred in penecontemporaneous and shallow burial stages strengthened the resistance of carbonates to compaction and pressure dissolution, thus provided favorable condition for the preservation of early dissolution pores and caves and contributed indirectly to the forming of reservoirs in the area.The fractures formed through multiple tectonic stages.The fractures formed before the Late Hercynian epoch were filled up by calcite, dolomite and silica and made less contribution to the formation of reservoirs.However, the fractures formed during the Late Hercynian and Himalayan epoch were effective in contributing to the formation of reservoirs due to weak diagenetic processes.

Investigation of igneous rock reservoir petrophysical parameter model and oil reservoir identification standard: A case study on the Carboniferous samples of the Chepaizi Uplift in the Junggar Basin

Zhu Yong, Yu Yixin, Wang Shuang, Wang Yong

2018, 39(1):  119-128.  doi:10.11743/ogg20180112

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Igneous rock oil reservoir distributed in the Carboniferous system of Chepaizi uplift in the Junggar Basin, but its reservoir lithology and petrophysical characteristics is very complex.Firstly, taking method of petrology, lithology identification, core measurement, oil testing, imaging and conventional logging, the pore and fracture characteristics of the igneous rock reservoir were summarized.The total petrophysical property is the matrix porosity, permeability and porosity.The total permeability of the reservoir is contributed by both fracture permeability and matrix permeability, while the permeability of un-fractured reservoir roughly equals matrix permeability.Secondly, using tri-porosity curve regression and FMI effective fracture identification with the constraints from core measurement, a model have been established to calculate the physical parameters of matrix, fracture and bulk reservoir of the igneous rock.Data is compared with core measurements.The model is proved to be reasonable and practical when applied to igneous rock reservoir physical property evaluation in the Chepaizi Uplift.This method can also be used to evaluate other areas.At last, based on the model of reservoir physical parameter, together with analysis on drilling, mud logging and oil testing data, a standard for igneous rock oil reservoir diagnose in the Chepaizi Uplift has been established.

Petrophysical facies of Toutunhe Formation in Fudong slope area, Junggar Basin

Yu Jingwei, Fu Huan, Zhang Zongbin, Wu Aicheng, Liu Ni, Wen Huaguo

2018, 39(1):  129-139.  doi:10.11743/ogg20180113

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Core, thin section, logging and drilling data were integrated to study and identify sedimentary facies, diagenetic facies and pressure facies of the reservoir rocks in the Toutunhe Formation of Fudong slope area, Junggar Basin.On this basis, we divided petrophysical facies, performed comprehensive evaluation of the reservoirs, and predicted favorable reservoir development areas.A total of 15 petrophysical facies were identified according to the sedimentary faices, diagenetic facies and pressure facies.Quantitative discriminant functions were built for each of the 15 types of petrophysical facies by using GR, acoustic, density, compensated neutron and deep resistivity logs, and in combination with Fisher typical discriminant, and the correctness of the identification result was tested.The petrophysical facies of the three members in this Formation were mapped based on thin section observation.The reservoirs in the Toutunhe Formation were comprehensively evaluated and classified into four types in combination with production test results, realizing prediction of favorable reservoirs of the Toutunhe Formation.

Progress of research on deep-water mass-transport deposits

Qin Yanqun, Wan Lunkun, Ji Zhifeng, Li Fuheng, Xu Hailong, Ba Dan

2018, 39(1):  140-152.  doi:10.11743/ogg20180114

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Prevalent deep-water mass-transport deposits (MTDs) are important components of sedimentary formation on continental margins around the world.A systematic study on the depositional system is helpful to deeply understanding deep-water transport process, opening up new deep-water plays and reducing risks of offshore engineering facilities.Based on an literature review, deep-water MTDs refer to assemblage of all underwater gravity flow deposits except for turbidite deposits.They can be structurally segmented into three parts, namely head, body and toe.Besides, they can be divided into different types according to transport processes and sediment origins.Sediment gravity flow conditions are essential for deep-water MTDs to form, and their deformation processes should conform to the characteristics of Bingham Plastics.These depositional systems have different scales and contain various kinematic indicators, which can be generally recognized by using seismic, core and well logging data.Deep-water MTDs can form both seals and reservoirs, thus are potential exploration targets in deep-water area.A comprehensive analysis indicates that many problems still exist in the study of deep-water MTDs.For example, (1) the understanding of deep-water mass-transport process should be further deepened and unified;(2) the study on their forming conditions in different settings should be strengthened;(3) the differences between deep-water MTDs and turbidites should be more thoroughly understood;(4) the differences and commonalities between ancient and modern deep-water MTDs should be clear;and (5) the understanding of lithofacies types and lithofacies associations should be unified.It is proposed that future studies should focus on:(1) multi-scale characterization with data of multiple sources;(2) forming conditions, especially triggering mechanisms;(3) integrated research of underwater mass transport mechanism, deposit composition and deep-water gravity-flow deposits;(4) forming conditions of source, reservoir or cap rocks;(4) fine description of ancient deep-water MTDs;and (5) assessment on erosional ability and geological risks.

Characteristics of the large-scale high-amplitude reflections and its significance in hydrocarbon exploration in the Huangliu Formation of Dongfang area of the Yinggehai Basin, South China Sea

Liao Jihua, Wu Keqiang, Guo Gang, Gan Huajun, Sun Ming, Cai Lulu, Zhu Shilei, Liu Ziyu

2018, 39(1):  153-164.  doi:10.11743/ogg20180115

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Based on substantial cores, drilling data, well logging, 2-D and 3-D seismic data, the geometry, facies associates, depositional phases, distribution and evolution of the large-scale high-amplitude seismic reflection package in the 1st member of the Huangliu Formation of Dongfang area were studied.In addition, characteristics of the favorable reservoirs was revealed and its significance in hydrocarbon exploration was discussed.Finally, the exploration strategy of Dongfang area was suggested.The results show that the large-scale high-amplitude reflection packages were gravity flow fan deposit.It consists of turbidite channel fill, overbank deposits and levee.Furthermore, it can be subdivided into three phases vertically.From the first phase to the third, the fan size increased gradually, while the fan migrated toward northwest step by step, with concurrent movement in the direction of southeast.Turbidite channel sand fill bodies are the most important reservoirs in Dongfang area proved by drilling, which were widely distributed and three-phases superimposed.The overpressure played an important role to improve reservoir properties in the 1st member of the Huangliu Formation in Dongfan area.There are mainly updip pinchout lithologic reservoirs in the flaps of diapiric domes, and lenticular sandstone lithologic reservoirs in western Dongfang area which is not associated with diapiric domes.Both of them are associated with the large-scale high-amplitude reflection and have very great exploration potential.

High-precision coherence technique in fault system analysis in ultra-deepwater area of the ZhuⅡDepression, northern South China Sea

Zhao Zhao, Tang Liangjie, Zhao Zhigang, Yang Haizhang, Yang Dongsheng, Huang Xuan

2018, 39(1):  165-174.  doi:10.11743/ogg20180116

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The geological conditions of the ultra-deepwater area are complex, and the seismic data is disturbed by many factors.The faults have multiple interpretation solutions, so the accuracy of the structure interpretation is seriously affected.According to the fault characteristics of the 3D working area in ultra-deepwater region, the coherence technique is used for fault interpretation and fault analysis, in order to better understand and more accurately interpret the structure characteristics of the whole Baiyun Sag.It is indicated that the along-horizon coherent slice could apparently reveal the planar distribution of the fault system developed in certain periods.The top surface of Enping Formation (T₇⁰) is a regional unconformity and the rift to sag transition interface of Baiyun-Liwan Sag.The faulting and rifting phase of Baiyun Sag ended in early Oligocene, then sag and depression became the dominate characteristics afterwards.The study demonstrates that the rift to sag transition interface T₇⁰ of Baiyun-Liwan Sag has significant control on hydrocarbon accumulation in the ultra-deepwater area of ZhuⅡDepression.

Sedimentary characteristics and spatial distribution of coarse clastic rocks of fan delta in Changdi fault zone in Gubei sub-sag, Jiyang Depression

Qiu Longwei, Jia Jicheng, Ma Lichi, Yang Yongqiang, Sun Chao, Xin Ye, Wang Xin, Yang Shengchao

2018, 39(1):  175-182,191.  doi:10.11743/ogg20180117

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Fan delta coarse clastic rocks on steep slopes of faulted lacustrine basins have large variability in spatial distribution due to the joint control of various geological factors.Various data including core, log and seismic data are integra-ted to investigate the spatial distribution characteristics and the main controlling factors on formation of the fan delta coarse clastic rocks in the 2^nd to the Upper 4^th Member of the Eocene Shahejie Formation on the periphery of Changdi fault zone in Gubei sub-sag.The study results show that the development of fan delta coarse clastic rocks are controlled by the intensity of fault activity, change of lake level and sediment supply.The contributions of each influential factor are different in different areas, resulting in the differences of distribution of these fan delta coarse clastic rocks.In the northern part of Changdi fault zone, fault activities are strong and sediment supply is sufficient, thus the fan delta deposits are large in scale and are characterized by vertical aggradation of multiple stages on sectional view.In addition, large slump turbidite fans are common in fan front.On the contrary, in the southern part of the fault zone, faulting is relatively weak and sediment supply is insufficient, thus the fans are small in scale and show a superimposition pattern of early retrogradation and late progradation.Owing to the alternative activity of secondary faults, the fan delta coarse clastic rocks are characterized by wedge-shaped superimposition of multiple stages in the direction of perpendicular to provenance.In general, the distribution of oil and gas in the study area are controlled by favorable sedimentary facies zones, lateral pinch out of the fans and sealing of top mudstone.

Effects of sulfate reduction on the formation of iron-bearing authigenic minerals in a methane seepage setting

Bei Keqi, Xu Tianfu, Shang Songhua, Wei Mingcong, Jin Guangrong, Cao Yuqing, Tian Hailong

2018, 39(1):  183-191.  doi:10.11743/ogg20180118

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Seabed methane seepage is common in areas with gas hydrate potential.Methane anaerobic oxidation and sulfate reduction occurring in these areas not only control the leakage of methane, but also facilitate the formation of authigenic minerals, which presenting itself as the enrichment of iron-bearing authigenic minerals in sediments rich in iron.This paper discussed the effect of sulfate reduction on the formation of iron-bearing authigenic minerals in a marine methane seepage environment through lab tests of methane-water-rock-bacteria reactions in a low-temperature and high-pressure reactor that simulated seabed sediment environment.The results showed decrease of pH, ORP and increase of HS^- and HCO₃^- concentration, indicating sulfate reduction and anaerobic oxidation of methane in the reactor.The total iron content in the solution decreased by about 7.5 mg/L before and after the tests, indicating iron-related precipitation.SEM images also showed precipitation of mostly iron sulfide with some ankerite and siderite.The paper suggested that a close relationship exist between the formation of authigentic minerals and microbial effect and that the interaction between sulfate reduction and anaerobic oxidation of methane play a positive role in the formation of iron-bearing authigenic minerals.This study may help in understanding further the forming mechanism of iron-bearing authigenic minerals in methane-seepage areas and its significance for gas hydrate prospecting.

Dynamic prediction model of steam flooding in extra heavy oil reservoirs

Fu Jingang, Du Dianfa, Zheng Yang, Ba Zhongchen, Li Dongdong

2018, 39(1):  192-197.  doi:10.11743/ogg20180119

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Steam flooding is one of the most effective and mature methods for the development of super-heavy oil reservoirs.The displacement mechanisms of steam flooding and its technical processes are well understood at present.However, the study of mathematical model and performance prediction model still needs to be further strengthened.Based on the theory of steam chamber growth and the study of subsurface heat loss, the reservoirs in steam flooding process are divided into steam zone, transition zone and crude oil zone.The energy conversion and conservation principles are used to get the expressions of physical parameters in each zone of steam flooding and build injection-production models for steam flooding.At the same time, a performance prediction model is built for five-spot well pattern according to well patterns and the influences of cyclic steam stimulation before steam flooding.The model is solved by programming and the actual data of Zhong32 Block in Xinjiang are used to test it.The results show that the model can accurately predict the locations of fronts of steam chamber and oil-water transition zone.In addition, it also can predict oil and water production.

Post-stack seismic fracture prediction under constraint of shale stress field: A case from the shale reservoir in Wufeng Fm-1^st member of Longmaxi Fm in Jiaoshiba area

Wang Mingfei, Su Kelu, Xiao Wei, Chen Chao, Liu Xiaojing, Wang Jingbo

2018, 39(1):  198-206.  doi:10.11743/ogg20180120

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Seismic prediction of fractures with small scale and low dip in shale is difficult.Taking the shale gas reservoir of the Wufeng Fm-1^st member of Longmaxi Fm in the Jiaoshiba area of Fuling shale gas field as an example, we explored post-stack seismic fracture prediction method under constraint of stress field.Firstly, the post-stack seismic data were processed to enhance the structure response, so as to improve the ability of identifying faults and fractures, then the high precision seismic curvature volume was tracked to describe the level of fracture development.Secondly, the distribution characteristics of present stress field was simulated to reveal the orientation and strain strength of fractures.Finally, the seismic curvature and stress field attributes were normalized to build a fracture prediction model for accurate identification of orientation and intensity of fracture in the shale reservoirs.The results show that NE-trending fractures with moderate to weak intensity dominate the shale reservoir in the Wufeng Fm-1^st member of Longmaxi Fm in the major part of the Jiaoshiba box anticline structure and NE-trending and NW-trending fractures with moderate to strong intensity occur locally on the flanks of structure and fault (fold) belt.The prediction results are in accordance with the geologic understandings.Well-to-seismic calibration reveals that the fracture prediction results correlate well with the fracture leakage zones identified during drilling, further validating the effectiveness and applicability of the method.It can be used to guide the comprehensive evaluation of shale gas reservoirs and drilling engineering.