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Practices and Cognitions of Petroleum Exploration in Mesozoic,Ordos Basin LUO Anxiang, YU Jian, LIU Xianyang, JIAO Chuangyun, HAN Tianyou, CHU Meijuan Xinjiang Petroleum Geology    2022, 43 (3): 253-260.   DOI: 10.7657/XJPG20220301 Abstract （560）   HTML （31）    PDF（pc） （1437KB）（399）       Knowledge map    Save The Ordos basin is the second largest sedimentary basin in China with abundant oil and gas resources and broad exploration prospects. Typical low-permeability-tight oil reservoirs are develpoed in the Triassic Yanchang formation in the basin,which are difficult to explore. Through continously geological researches on the Mesozoic oil reservoirs in the Ordos basin over the past 50 years,some theories about hydrocarbon accumulation in Jurassic reservoir groups,in large-scale lithologic reservoirs in inland depression lake basins and in continental shales have been formed. By virtue of three strategic shifts,four conventional hydrocarbon provinces with reserves exceeding 10×108 t and a successive zone with shale oil reserves of 20×108 t have been discovered. The proven oil reserves have increased by an average of over 3×108 t per year for 10 consecutive years. Thus,Changqing oilfield in Ordos basin has become an oil and gas province with the fastest increase in reserves and production in China and contributed 12.5% of China's annual oil production,which provides a reference for the petroleum exploration in other similar basins. Table and Figures | Reference | Related Articles | Metrics

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Well Logging Evaluation of Bauxite Reservoirs in Ordos Basin LIU Die, ZHANG Haitao, YANG Xiaoming, ZHAO Taiping, KOU Xiaopan, ZHU Baoding Xinjiang Petroleum Geology    2022, 43 (3): 261-270.   DOI: 10.7657/XJPG20220302 Abstract （490）   HTML （21）    PDF（pc） （4208KB）（239）       Knowledge map    Save Bauxite gas reservoir is a kind of very rare unconventional gas reservoir recently discovered in the Ordos basin, and well logging evaluation plays an important role in its exploration and development. In the early well logging evaluation, bauxite was considered as the weathering crust caprock, but not as a reservoir, and there was no systematic well logging evaluation method suitable for the exploration and development of bauxite gas reservoirs. Based on the aluminous rocks in Taiyuan formation in the Longdong area, southwestern Ordos basin, the well logging evaluation method for bauxite gas reservoirs was studied from five aspects, that is, qualitative lithology identification, mineral composition, reservoir physical properties, quantitative calculation of gas-bearing properties and systematic summary of imaging model-pore structure characteristics. The well logging response for identifying aluminous rock formations was clarified and the aluminous rock identification chart by acoustic time-gamma ray was established. The porosity-permeability-saturation evaluation model for bauxite gas reservoirs was constructed through petrophysical experiments, and the criteria for identifying bauxite reservoir was proposed by combining micro-resistivity scanning imaging and nuclear magnetic resonance logging data. Finally, a well logging evaluation method for bauxite gas reservoirs was formed. Table and Figures | Reference | Related Articles | Metrics

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Main Controlling Factors and Gas Enrichment Area Selection of Ma55 Gas Reservoir in Eastern Sulige Gas Field BAI Hui, YANG Tebo, HOU Kefeng, MA Zhixin, FENG Min Xinjiang Petroleum Geology    2022, 43 (3): 271-277.   DOI: 10.7657/XJPG20220303 Abstract （369）   HTML （15）    PDF（pc） （5950KB）（129）       Knowledge map    Save In order to improve the drilling rate of pay zones in the Ma55 gas reservoir in eastern Sulige gas field, Ordos basin, using the drilling, logging, core and gas production testing data, and analyzing the main factors controlling pay zones such as sedimentary microfacies, diagenesis and paleotopography, the distribution law of dolomite in the Ma55 gas reservoir was clarified. Moreover, the reservoirs were comprehensively classified and evaluated, and the favorable gas enrichment areas in the Ma55 gas reservoir were selected. The research results show that the pay zones in the Ma55 reservoir are distributed as “lens” in local areas, with poor continuity. The most favorable reservoir rocks are granular dolomite and coarse powder crystalline dolomite, and the main storage space consists of intergranular pores, intergranular dissolved pores and structural fractures. Sedimentary facies and diagenesis are the main controlling factors of the Ma55 reservoir, and the grain beach is the most favorable sedimentary microfacies of the Ma55 dolomite. The pay zones are mainly controlled by quasi-contemporaneous dolomitization and buried dolomite diagenesis. The paleoslope on the relatively high position is a favorable area for the development of the Ma55 gas reservoir. Table and Figures | Reference | Related Articles | Metrics

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Sedimentary Characteristics and Sand Body Architecture of Shallow Delta Front in Ordos Basin: A Case Study of Chang 9 Member in Shiwanghe Section in Yichuan REN Yilin, ZHAO Junfeng, CHEN Jiayu, GUAN Xin, SONG Jinggan Xinjiang Petroleum Geology    2022, 43 (3): 310-319.   DOI: 10.7657/XJPG20220307 Abstract （359）   HTML （8）    PDF（pc） （5476KB）（236）       Knowledge map    Save As an important reservoir for storing oil and gas,the sand bodies in delta front are found with enormous petroleum exploration potential. However,there are few studies on architecture of sand bodies in shallow delta front through field outcrops. Guided by sedimentology and reservoir architecture theories,the outcrop observation and sampling was combined with the results of laboratory experiments and statistical analysis to clarify the sedimentary characteristics and sand body architecture of Chang 9 member in the Shiwanghe section in Yichuan,Ordos basin. The results show that during the deposition,the Chang 9 member in Shiwanghe section lied in a warm and humid environment,especially an oxidation to weak-reduction transitional freshwater environment that was not obviously stratified,and shallow delta front subfacies was mainly developed,including microfacies such as underwater distributary channel,estuary bar,sheet sand and interdistributary bay. The single sand bodies of shallow delta front in Chang 9 member in the study area can be divided into two vertical stacking styles such as non-connected and connected,and two lateral contact styles such as butted and cut-stacked. The accommodation growth rate and sediment supply rate jointly controlled by terrain slope and lake level rise/fall are important factors affecting the spatial development style of the composite sand bodies. The gentle slope allows the channels to incise weakly and present the characteristics of plane intersection. The rise of lake level and the decrease of source supply increase the ratio of accommodation growth rate to sediment supply rate,which may lead to the weakening of sand body connectivity. The architecture models of sand bodies like river-river cut stacking and river-bar cut stacking are favorable for hydrocarbon accumulation. Table and Figures | Reference | Related Articles | Metrics

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Shale Oil Enrichment Mechanism and Sweet Spot Selection of Fengcheng Formation in Mahu Sag，Junggar Basin JIN Zhijun, LIANG Xinping, WANG Xiaojun, ZHU Rukai, ZHANG Yuanyuan, LIU Guoping, GAO Jiahong Xinjiang Petroleum Geology    2022, 43 (6): 631-639.   DOI: 10.7657/XJPG20220601 Abstract （353）   HTML （27）    PDF（pc） （5508KB）（197）       Knowledge map    Save The Fengcheng formation in the Mahu sag is an alkaline lake sediment，and is divided into Feng 1 member，Feng 2 member and Feng 3 member from bottom to top. In the Fengcheng formation，the lithology vertically changes rapidly，the mineral composition is complex，and the organic-rich shale source is integrated with the shale reservoir. The formation bears oil universally，but the sweet spots are scattered. The results of formation testing for single layers are not satisfied，showing an unclear production potential. According to core slices and geochemical analyses，the Fengcheng formation in the Mahu sag is dominated by lamellar silty shale intercalated with dolomite，which are mainly composed of terrigenous clastic minerals and carbonate minerals. With the variation of burial depth，the pore volume changes consistently with the variation of surface area of pores，and the pore volume is mainly contributed by macropores (pore diameter > 50 nm). The source rock is dominated by Type Ⅱ organic matter，and the vitrinite reflectance ranges from 0.85% to 1.40%，indicating a peak oil generation period. There are many shear fractures with middle to high angles in the Feng 2 member，and shear fractures with middle to high angles and structural fractures with low angles in the Feng 3 member，whose formation and development degree are controlled by lithology，mineral composition，rock mechanical properties，etc. Based on the characteristics of lithologic assemblage，reservoir property and oil-bearing property，four relatively concentrated sweet spots have been identified. When performing multi-interval formation testing and production testing in vertical wells，it is necessary to select sweet spots with good oil content and more fractures to conduct geological research and geology-engineering integration technology research，and to perform production improvement tests in horizontal wells，so as to realize comprehensive breakthrough for shale oil exploration and development in the Fengcheng formation in the study area Table and Figures | Reference | Related Articles | Metrics

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Inversion of Fracture Parameters and Formation Pressure for Fractured Horizontal Wells in Shale Oil Reservoir Based on Soaking Pressure WANG Fei, WU Baocheng, LIAO Kai, SHI Shanzhi, ZHANG Shicheng, LI Jianmin, SUO Jielin Xinjiang Petroleum Geology    2022, 43 (5): 624-629.   DOI: 10.7657/XJPG20220517 Abstract （340）   HTML （7）    PDF（pc） （884KB）（188）       Knowledge map    Save A fractured horizontal well in shale oil reservoir should be soaked before it is put into production. In order to quickly evaluate the effect of volume fracturing, a post-frac evaluation method based on the data of soaking pressure of shale oil reservoirs was proposed. Through numerical simulation of well soaking, the pressure diffusion and fluid migration in the stimulation area controlled by the fractured horizontal well were characterized, and a post-closure linear flow calculation model and a fracture storage control calculation model were established. Then a calculation method for inverting fracture parameters and formation pressure was formed. The results show that after pump is stopped, the stimulation area goes through 9 flow stages such as flows controlled by fractures in end section of wellbore, by fractures in the whole wellbore and by reservoir matrix, and the pressure drop derivatives appear as multiple straight-line segments with different slopes in log-log coordinates. This method has been applied to four typical shale oil horizontal wells in Jimsar sag, which proves that the data of soaking pressure can be used for the inversion of fracture parameters and formation pressure, and also verifies the applicability of the proposed method. The study results provide a reference for evaluating fracturing effect and optimizing well spacing. Table and Figures | Reference | Related Articles | Metrics

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Deformation and Favorable Area Evaluation of Shunbei No.4 Strike-Slip Fault Zone in Tarim Basin LI Haiying, HAN Jun, CHEN Ping, LI Yuan, BU Xuqiang Xinjiang Petroleum Geology    2023, 44 (2): 127-135.   DOI: 10.7657/XJPG20230201 Abstract （340）   HTML （39）    PDF（pc） （7486KB）（240）       Knowledge map    Save The Shunbei No. 4 strike-slip fault zone which is located in the Shuntuoguole low uplift of the Tarim basin and extends northward to the Shaya uplift is characterized by deep burial，horizontal segmentation，vertical stratification，multi-stage activities，and complex structure. Through the interpretation of high-quality 3D seismic data from the Shunbei No. 4 strike-slip fault zone，the stratification，segmentation，staging，activity and favorable area evaluation of the fault zone were carried out. The results show that the Shunbei No. 4 strike-slip fault zone has a 4-layer structure in the Paleozoic，roughly bounded by the top of the Middle Ordovician，above which echelon faults are found and below which high-steep strike-slip faults are developed. The strike-slip fault zone is visibly segmented into the northern segment，the middle segment，and the southern segment according to the strike，showing an overall characteristic of compressed in south and extended in north. In the Paleozoic，the strike-slip fault zone successively experienced four periods of activity，namely，EpisodeⅠof the middle Caledonian，Episode Ⅲ of the middle Caledonian，late Caledonian，and Hercynian. By combining the main controlling factors (e.g. source-reservoir connectivity，reservoir size，and late adjustment) for hydrocarbon enrichment and accumulation in the Shunbei area，the favorable areas in the Shunbei No. 4 strike-slip fault zone were evaluated. Multiple favorable areas have been identified and then verified by actual drilling. Table and Figures | Reference | Related Articles | Metrics

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Accumulation Conditions and Exploration Direction of Lower Jurassic Tight Sandstone Gas Reservoirs in Taibei Sag CHEN Xuan, WANG Jufeng, XIAO Dongsheng, LIU Juntian, GOU Hongguang, ZHANG Hua, LIN Lin, LI Hongwei Xinjiang Petroleum Geology    2022, 43 (5): 505-512.   DOI: 10.7657/XJPG20220501 Abstract （338）   HTML （29）    PDF（pc） （3198KB）（196）       Knowledge map    Save The Turpan-Hami basin has great potential of oil and gas resources in the Lower Jurassic strata, with a large quantity of remaining resources. The discovered oil and gas reservoirs are mainly distributed in the positive structural belts around the Shengbei and Qiudong subsags in the Taibei sag, and they are primarily structural reservoirs. Less researches on the oil and gas resources in the hinterland of the subsags have been performed. Based on the dissection of known reservoirs, a systematic study was carried out on the depositional system, source rock, reservoir rock and accumulation conditions of three major hydrocarbon-rich subsags in the Taibei sag. The results show that the coal-measure source rocks are widely developed in the Shuixigou group in the Taibei sag and are in broad contact with the braided river delta sandstones, which is conducive to the formation of near-source tight sandstone gas reservoirs. There are two types of tight sandstone gas reservoirs in the Lower Jurassic, namely, trap-type and continuous-type. The hinterlands of the subsags are favorable areas for the formation of continuous-type tight sandstone gas reservoirs. Therefore, the exploration should be switched from the source-edge positive structure to the hydrocarbon-rich subsag, and from the above-source conventional oil reservoirs to the in/near-source tight sandstone gas reservoirs. The hinterlands of the Shengbei and Qiudong subsags have the conditions to form large gas reservoirs, so they are favorable areas for exploring near-source tight sandstone gas reservoirs in the lower Jurassic. Table and Figures | Reference | Related Articles | Metrics

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Reservoir Characteristics and Controlling Factors of Shan 1 Member in Qingyang Gas Field, Ordos Basin DUAN Zhiqiang, XIA Hui, WANG Long, GAO Wei, FAN Qianqian, SHI Wei Xinjiang Petroleum Geology    2022, 43 (3): 285-293.   DOI: 10.7657/XJPG20220305 Abstract （323）   HTML （8）    PDF（pc） （6467KB）（137）       Knowledge map    Save In the Qingyang gas field, Ordos basin, which is a typical tight sandstone gas field, the major pay zone is the first member of the Permian Shanxi formation. Its sedimentary sand bodies change rapidly with small thickness, making the prediction of reservoir distribution difficult, which restricts the productivity construction of the gas field. In this paper, sedimentary sand body characterization and thin layer prediction were carried out using logging-seismic combination, the main factors controlling reservoir development were discussed, and favorable reservoir distribution areas were identified. The results show that the paleogeomorphology and paleo-flow direction jointly controlled the distribution of delta sand bodies, the underwater distributary channel sand bodies with developed dissolution facies are the most favorable reservoirs, and the local micro-amplitude nose uplift structure is the natural gas enrichment area. Based on the factors such as sand body distribution, reservoir physical properties, diagenesis and structural characteristics, a set of standards for classifying reservoirs in the study area was established, by which two Type I reservoir enrichment areas were defined in the southern and central parts of the study area. Table and Figures | Reference | Related Articles | Metrics

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Exploration Progress and Potential Evaluation of Deep Oil and Gas in Turpan-Hami Exploration Area ZHI Dongming, LI Jianzhong, CHEN Xuan, YANG Fan, LIU Juntian, LIN Lin Xinjiang Petroleum Geology    2023, 44 (3): 253-264.   DOI: 10.7657/XJPG20230301 Abstract （317）   HTML （537）    PDF（pc） （2522KB）（256）       Knowledge map    Save To realize the shift of oil and gas exploration from shallow-middle to deep strata, and from conventional to unconventional resources, and then to promote the exploration of deep oil and gas resources in the Turpan-Hami exploration area, the tectonic-lithofacies palaeogeographical evolution of Turpan-Hami basin, Santanghu basin, and Zhundong block of Junggar basin were analyzed, the characteristics and exploration potential of the petroleum systems in these basins were evaluated, the main exploration targets were determined, and the fields for strategic breakthrough were selected. In the Carboniferous-Permian period, the Turpan-Hami exploration area was a unified sedimentary basin with similar sedimentary environments and structures. In the Triassic-Jurassic period, the study area was separated into several independent foreland basins. With the tectonic-lithofacies palaeogeographical evolution, three sets of source rocks (marine-transitional facies of Carboniferous, lacustrine facies of Permian, and lacustrine-coal measure of Jurassic) were formed, contributing to three major petroleum systems. The change in exploration ideas has promoted significant progress in petroleum exploration in deep strata. Significant breakthroughs have been made in the exploration of Shiqiantan formation marine clastic oil and gas reservoirs, Permian shale oil reservoirs and conventional sandstone oil reservoirs in the Zhundong block, and the Middle-Lower Jurassic large-scale tight sandstone gas reservoirs in the Turpan-Hami basin, which enables the discovery of large-scale high-quality reserves and the orderly succession of strategic resources. Future exploration should be carried out at three levels: strategic preparation, strategic breakthrough, and strategic implementation, with a focus on 10 favorable directions. Table and Figures | Reference | Related Articles | Metrics

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Characteristics and Hydrocarbon Generation Potential of Chang 9 Source Rocks on Yishaan Slope, Ordos Basin LUO Lirong, LI Jianfeng, YANG Weiwei, MA Jun, LI Huan, WU Kai Xinjiang Petroleum Geology    2022, 43 (3): 278-284.   DOI: 10.7657/XJPG20220304 Abstract （315）   HTML （7）    PDF（pc） （746KB）（141）       Knowledge map    Save A number of favorable oil-bearing areas have been discovered in the lower assemblage adjacent to the Chang 9 source rocks on Yishaan slope, Ordos basin. In order to promote the petroleum exploration of the lower assemblage in this area, it is urgent to deepen the research on the characteristics and hydrocarbon generation potential of the Chang 9 source rocks. The distribution of the Chang 9 source rocks were analyzed using well logging, mud logging and core data. The geochemical characteristics and hydrocarbon generation potential of the Chang 9 source rocks were studied by various methods such as rock pyrolysis analysis, total organic carbon analysis, kerogen maceral analysis, and biomarker analysis by saturated hydrocarbon gas chromatography-mass spectrometry. The results show that the Chang 91 source rocks are distributed in Wuqi, Jingbian, Zhidan, Ansai and other areas, with the maximum thickness of over 20 m, and the Chang 92 source rocks are mainly developed in Ganquan-Luochuan area, with the maximum thickness of over 12 m. The Chang 9 source rocks hold a high abundance of organic matters that were originated from lower aquatic organisms and terrestrial higher plants. With Type Ⅰ and Ⅱ1 organic matters in dominance, which are in the mature stage, the Chang 9 source rocks exhibit high hydrocarbon conversion rate and especially strong hydrocarbon generation capability in Zhidan-Ansai area. The Chang 9 source rocks are mostly good and locally high-quality rocks with strong hydrocarbon generation and expulsion capacities, which provides a material basis for hydrocarbon accumulation in the lower assemblage of Yanchang formation on Yishaan slope. Table and Figures | Reference | Related Articles | Metrics

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Sedimentary System of Permian Fengcheng Formation in Hashan Area in Northwestern Margin of Junggar Basin YU Hongzhou, WANG Yue, ZHOU Jian, XUE Yan Xinjiang Petroleum Geology    2022, 43 (4): 396-403.   DOI: 10.7657/XJPG20220403 Abstract （312）   HTML （13）    PDF（pc） （12519KB）（135）       Knowledge map    Save The Fengcheng formation in the Hashan area in the northwestern margin of Junggar basin experienced strong tectonic deformation and structural displacement. There are few studies on the sedimentary system of the Fengcheng formation, which restricts the oil and gas exploration in this area. The 3D seismic, drilling, logging and core data in the Hashan area were systematically analyzed, and the structural evolution of the Fengcheng formation in different parts of the Hashan area was investigated, so that the original stratigraphic position of the Fengcheng formation was restored, the sedimentary facies types were analyzed and compared, and finally the original sedimentary system of the Fengcheng formation in this area was restored. The results show that in the Hashan area the tectonic compression strength gradually weakens from west to east, and the shortened distances of the Lower Permian from the Early Permian to the present in the western, central and eastern parts due to the compression are 33.0-40.0 km, 25.0-30.0 km and 15.0-20.0 km, respectively. Three types of sedimentary facies such as fan delta, beach bar and lake are developed and volcanic rocks of a certain scale are found in the Fengcheng formation. During the deposition of Feng 1 member, large-scale fan deltas and shore-shallow lakes were developed in the northern part of the Hashan area, semi-deep to deep lakes and beach bars in a small range in the central-western part, and volcanic rocks in the central-eastern part. During the deposition of Feng 2 member, the sedimentary range of semi-deep to deep lakes expanded significantly, thick layers of dolomitic mudstone was developed, and the distribution range of fan-delta sandy conglomerate and volcanic rocks decreased. During the deposition of Feng 3 member, the provenance supply capacity was enhanced, large-scale contiguous fan-delta sandy conglomerate was developed in the northern and western parts and semi-deep to deep lakes and beach bars were found locally. Table and Figures | Reference | Related Articles | Metrics

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Characteristics and Formation Mechanism of Traps in K1g1 Reservoir in Changshaling Structural Zone, Jiuquan Basin WEI Jun, YAN Baonian, DU Wenbo, ZHOU Xiaofeng, ZHOU Zaihua, LI Tiefeng, XIE Jingyu Xinjiang Petroleum Geology    2022, 43 (4): 379-386.   DOI: 10.7657/XJPG20220401 Abstract （310）   HTML （21）    PDF（pc） （7073KB）（147）       Knowledge map    Save With the meanings such as core observation, casting thin section identification and scanning electron microscope imaging, and based on the analysis of sandstone in light of petrological characteristics, diagenesis, pore types and dissolution fluid sources, the trap formation mechanism was investigated. The results show that the traps in the sandstone reservoir of the first member of the Cretaceous Xiagou formation (K1g1) in the Changshaling structural zone, Jiuquan basin, are diagenetic traps, the reservoir space is dominated by secondary pores, and the barrier is tight sandstone cemented by calcite in the early diagenetic stage. Atmospheric fresh water carrying smectite particles infiltrates through faults and dissolves the calcite cements and feldspar particles in tight sandstone, creating secondary intergranular pores and intragranular pores and clay-rich reservoir forms. The tight sandstone which is far from faults and has non-contact with atmospheric fresh water becomes the barrier. The traps are elongated and distributed along the fault trend, with the characteristics of “large sand bodies and small traps”. For the K1g1 sandstone reservoir, the diagenetic traps controlled by faults should be preferentially explored and wells should be deployed in the areas close to faults. Table and Figures | Reference | Related Articles | Metrics

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Characteristics and Genesis of Condensate Reservoirs of Lianggaoshan Formation in Fuling Area, Southeastern Sichuan Basin LI Mingyang, LI Chengyin, QU Dapeng Xinjiang Petroleum Geology    2022, 43 (4): 387-395.   DOI: 10.7657/XJPG20220402 Abstract （299）   HTML （14）    PDF（pc） （1211KB）（159）       Knowledge map    Save In the condensate gas reservoirs of the Lower Jurassic Lianggaoshan formation in the Fuling area, southeastern Sichuan basin, the fluid properties are complex and the gas-oil ratios from multi-well testing differ greatly. In this paper, the basic characteristics of oil and gas were clarified by using the data such as crude oil chromatography-mass spectrometry, gas composition, carbon isotopes and fluid inclusions. The gas reservoir properties and phase states were determined with the empirical calculation method for gas compositions and through the experiments simulating PVT fluid phase state. On this basis, the genesis and forming process of condensate gas reservoirs were discussed. The results show that the gas reservoirs in the Lianggaoshan formation are mainly condensate gas reservoirs without oil rings, where hydrocarbons are mainly primary condensate oil and gas generated from Type Ⅱ2 kerogens in the mature stage, and cracking gas is found locally. The thermal evolution degree of source rocks and the differences in the present temperature and pressure conditions of formation are the main contributors to different reservoir properties. The superimposed areas of the relatively deep-burial areas during the hydrocarbon accumulation period on the areas with relatively high pressure at present are favorable targets for future exploration. Table and Figures | Reference | Related Articles | Metrics

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Influences of Shale Rheology on Pore Structures of Qiongzhusi Formation in Chengkou Area, Northeastern Sichuan Basin YU Shuyan, WANG Yang, FENG Hongye, ZHU Hongjian Xinjiang Petroleum Geology    2022, 43 (5): 513-518.   DOI: 10.7657/XJPG20220502 Abstract （299）   HTML （10）    PDF（pc） （14955KB）（209）       Knowledge map    Save In order to determine the influence of natural rheology of shale on microscopic pore structure, taking the marine shale of the Lower Cambrian Qiongzhusi formation in the Chengkou area, northeastern Sichuan basin as an example, the types and characteristics of rheological structure and microscopic pore structure in the shale and their relationship were studied by using rock thin sections, focused ion beam scanning electron microscope and low temperature liquid nitrogen adsorption experiment. The microstructures of shale rheology mainly include porphyroclast system, cataclastic flow, pressolutional stylolites, microscopic fold, S-C fabric and crenulation cleavage, and the micro-nano structures include mylonite zone, micro-hybrid zone, and rotating porphyroclast. Rheological shale is dominated by nanoscale intergranular pores, and most of the primary pore structure is difficult to preserve under rheological action. Ductile rheology leads to a decrease in the number of pores, pore diameter, pore volume and pore specific surface area of shale, which reduces the storage performance of shale. Table and Figures | Reference | Related Articles | Metrics

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Lithofacies Paleogeography and Petroleum Exploration of Fengcheng Formation in Western Central Depression of Junggar Basin HE Haiqing, TANG Yong, ZOU Zhiwen, GUO Huajun, XU Yang, LI Yazhe Xinjiang Petroleum Geology    2022, 43 (6): 640-653.   DOI: 10.7657/XJPG20220602 Abstract （295）   HTML （16）    PDF（pc） （18669KB）（153）       Knowledge map    Save In order to evaluate the petroleum exploration prospects of the Fengcheng formation in the western Central depression of the Junggar basin, the lithology assemblage and sedimentary facies of the Fengcheng formation were studied by means of analyzing the trace element, core, rock thin section, paleomorphology, logging facies and seismic facies of the formation. The results show that the Fengcheng formation in the study area is fan delta-alkaline lake deposition which formed in an arid-semi-arid climate, foreland tectonic setting and geological environment with periodic changes in water salinity and water depth. From the edge to the center of the Central depression, basin-marginal fan-delta clastic rocks, outer-slope front dolomites, slope-highland volcanic rocks, low-uplift dolomitic calcareous beach-bar peperites, and the central lake-basin alkali rocks are found in sequence. According to the sedimentary characteristics, an evolution model for the fan delta-alkali lake deposition was established for the Fengcheng formation. Based on the sedimentary facies, lithofacies and petroleum exploration status, the Fengcheng formation in the study area can be divided into 5 areas such as conventional hydrocarbon area in basin-margin ultra-denudation belt, tight hydrocarbon area in outer-slope front, shale oil/gas area in lake basin, conventional hydrocarbon area in low-uplift dolomitic calcareous beach-bar and conventional hydrocarbon area in highland volcanic rocks. The favorable exploration area with the depth less than 7 000 m reaches 1.2×104 km2, with hydrocarbon reserves of more than one billion tons, which demonstrates huge exploration potential of the total petroleum system of the Fengcheng formation in the study area Table and Figures | Reference | Related Articles | Metrics

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Method for Calculating Single-Well Producing Geological Reserves and Single-Well Technically Recoverable Reserves in Tight Sandstone Gas Reservoirs: A Case of Carboniferous-Permian Gas Reservoirs in Yanchang Gas Field, Ordos Basin CHEN Zhanjun, REN Zhanli Xinjiang Petroleum Geology    2022, 43 (3): 360-367.   DOI: 10.7657/XJPG20220315 Abstract （294）   HTML （12）    PDF（pc） （711KB）（153）       Knowledge map    Save The Carboniferous-Permian sandstone gas reservoirs in the Ordos basin are tight, with obvious different gas saturations from part to part of the reservoir unit, complex gas-bearing pattern, non-uniform reservoir pressure systems, and highly heterogeneous distribution of reserves as a whole. This paper compared the geological and development characteristics between Carboniferous-Permian tight sandstone gas reservoirs and the conventional sandstone gas reservoirs in Yanchang gas field in Ordos basin. It is found that there is a threshold pressure gradient during the development of the Carboniferous-Permian tight sandstone gas reservoirs, and the single-well produced geological reserves and the single-well reserves producing radius increase with the decrease of the bottom hole pressure. When the abandonment pressure is reached, the single-well produced geological reserves and the single-well reserves producing radius reach the maximum values. Accordingly, by analyzing the distribution of reserves during the development of tight sandstone gas reservoirs, the material balance equation under the condition of threshold pressure gradient was established, and the relationship between cumulative production and bottom hole pressure was obtained. Furthermore, two methods for calculating the threshold pressure gradient were analyzed. On this basis, the method for calculating the single-well producing geological reserves and the single-well technically recoverable reserves in tight sandstone gas reservoirs was proposed, which provides a theoretical basis for the optimization of well pattern to develop tight sandstone gas reservoirs. The theoretical calculation method has been improved to form a simplified method for calculating single-well producing geological reserves, which is referential for well pattern deployment in undeveloped blocks. Table and Figures | Reference | Related Articles | Metrics

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Core Experiment and Stimulation Mechanism of Unstable Waterflooding in Low Permeability Reservoirs ZHOU Jinchong, ZHANG Bin, LEI Zhengdong, SHAO Xiaoyan, GUAN Yun, CAO Renyi Xinjiang Petroleum Geology    2022, 43 (4): 491-495.   DOI: 10.7657/XJPG20220417 Abstract （289）   HTML （11）    PDF（pc） （1256KB）（203）       Knowledge map    Save According to the typical characteristics of low permeability reservoirs in Changqing oilfield, parallel core and double-layered core experiments were carried out to simulate the effect of unstable waterflooding in heterogeneous low permeability reservoirs. Due to the poor visibility of core experiments, numerical models for simulating interlayer and intralayer heterogeneous reservoirs were established, which may reveal the stimulation mechanism of unstable waterflooding according to the change of flow field. The results show that for interlayer heterogeneous reservoirs, compared with continuous waterflooding, unstable waterflooding can promote the advancement of the flooding front in the layers with lower permeability, and give full play to capillary force in oil displacement, so unstable waterflooding can significantly improve the oil recovery of the layers with lower permeability, and the pattern of short-term injection combined with long-term quit can enhance the recovery rate the most. For intralayer heterogeneous reservoirs, unstable waterflooding can generate pressure oscillations in the layers to enable the fluid percolation between the higher permeability layers and the lower permeability layers, so that the sweep efficiency of injected water in the lower permeability layers is increased and the recovery rate of the lower permeability layers is enhanced, thereby increasing the total oil recovery rate of the reservoir. Table and Figures | Reference | Related Articles | Metrics

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Characteristics and Connectivity of Fault-Controlled Fractured-Vuggy Reservoirs: A Case Study of Unit T in Tuofutai Area, Tahe Oilfield LI Jun, TANG Bochao, HAN Dong, LU Haitao, GENG Chunying, HUANG Mina Xinjiang Petroleum Geology    2022, 43 (5): 572-579.   DOI: 10.7657/XJPG20220509 Abstract （289）   HTML （10）    PDF（pc） （3554KB）（229）       Knowledge map    Save Fault-controlled fractured-vuggy reservoirs are extremely heterogeneous and exhibit the diversity and complexity in inter-well connectivity. Clarifying the influence of faults and karsts on reservoirs is conducive to reservoir connectivity analysis and injection-production strategy adjustment. Taking Unit T in the Tuofutai area of Tahe oilfield as an example, the development characteristics of reservoirs were systematically analyzed based on the results of seismic interpretation and the analysis of overlying water system and production performance responses. It was clarified that the reservoir development is mainly controlled by faults and surface water systems. The difference in karstification intensity leads to different characteristics of the reservoirs, which makes development wells show different production behaviors and inter-well connectivities. Based on the analysis of dynamic and static data, an inter-well connectivity model suitable for fault-controlled fractured-vuggy reservoirs was established, which can provide a basis for the adjustment of subsequent treatments. Table and Figures | Reference | Related Articles | Metrics

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Sedimentary Characteristics and Connectivity of Upper Wuerhe Formation in Wellblock Ke 75, Karamay Oilfield LIU Nianzhou, LI Bo, ZHANG Yi, WU Min, WANG Quan, SU Hang Xinjiang Petroleum Geology    2022, 43 (4): 417-424.   DOI: 10.7657/XJPG20220406 Abstract （288）   HTML （13）    PDF（pc） （2524KB）（179）       Knowledge map    Save The upper Wuerhe formation in Wellblock Ke 75 in Karamay oilfield, Junggar basin has strong heterogeneity and varying connectivity between adjacent wells, and the understanding of sand body distribution in the formation is greatly different from the previous one. It is necessary to study the sedimentary facies and sand body connectivity to clarify reservoir distribution. Taking the upper Wuerhe formation in the Wellblock Ke 75 as an example, the characteristics and styles of the 4th-order architectural elements for each subfacies belt of alluvial fan controlled by both debris flow and braided channel were discussed according to the principles of sedimentology, and the sedimentary characteristics and sand body connectivity of each architectural style were analyzed. The research shows that when the electrical properties and sedimentary cycle characteristics of neighboring wells in the sheet flow zone at fan root are consistent, the sand body connectivity is good, and when the cross flow sand bodies or cross flow fine-grained sediments are developed, the sand body connectivity is poor, leading to difficulties in forming effective reservoirs. The research confirmed a Class I favorable gas reservoir area in the Wellblock Ke 75 in Karamay oilfield. Table and Figures | Reference | Related Articles | Metrics