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Evaluation of pore effectiveness of Quaternary mudstone biogas reservoirs in Sebei area, Qaidam Basin
SIMA Liqiang, MA Jun, LIU Junfeng, YANG Huijie, WANG Liang, ZHAO Ning
2023, Vol.35(2): 1–10
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Sequence filling succession and fluid indication of dolomite reservoirs of the first member of Permian Qixia Formation in Baoxing area, southwestern Sichuan Basin
FENG Mingyou, GAO Ruiqi, WANG Xingzhi, XU Liang, ZHAO Jin, LIU Xiaohong, SHANG Junxin
2023, Vol.35(2): 11–20
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2294 )
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Types and distribution of tight sandstone gas sweet spots of the third member of Upper Triassic Xujiahe Formation in Yuanba area, Sichuan Basin
HUANG Yanqing, LIU Zhongqun, WANG Ai, XIAO Kaihua, LIN Tian, JIN Wujun
2023, Vol.35(2): 21–30
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2378 )
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Hydrocarbon accumulation law and model of Cretaceous clastic rocks in western Tabei uplift
XU Zhuang, SHI Wanzhong, WANG Ren, LUO Fusong, XIA Yongtao, QIN Shuo, ZHANG Xiao
2023, Vol.35(2): 31–46
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2287 )
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Sedimentary characteristics of Jurassic Shaximiao Formation in Wubaochang area, northeastern Sichuan Basin
FANG Rui, JIANG Yuqiang, CHEN Qin, ZENG Lingping, LUO Yuzhuo, ZHOU Yadong, DU Lei, YANG Guangguang
2023, Vol.35(2): 47–58
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Fluid pressure field building process and its petroleum geological significance of Paleogene Shahejie Formatiom in Bonan sag, Jiyang Depression
ZHENG Bin, DONG Ao, ZHANG Yuanzhi, ZHANG Yi, SU Shan, ZHANG Shichao, FAN Jinjin, LUO Yinshan
2023, Vol.35(2): 59–67
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2245 )
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302
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Characteristics and main controlling factors of oolitic shoal reservoirs of Triassic Feixianguan Formation in eastern Kaijiang-Liangping trough, Sichuan Basin
WEN Wen, YANG Xiyan, XIANG Man, TAO Xiayan, YANG Rong, LI Yang, FAN Jiaxing, PU Baiyu
2023, Vol.35(2): 68–79
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2286 )
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Characteristics and main controlling factors of shale oil reservoirs of Triassic Chang 7 member in Heshui area, Ordos Basin
XIAO Ling, CHEN Xi, LEI Ning, YI Tao, GUO Wenjie
2023, Vol.35(2): 80–93
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2271 )
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Hydrocarbon accumulation and evolution characteristics of Paleogene in Yingxiongling area, Qaidam Basin
WANYAN Ze, LONG Guohui, YANG Wei, CHAI Jingchao, MA Xinmin, TANG Li, ZHAO Jian, LI Haipeng
2023, Vol.35(2): 94–102
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2206 )
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Ternary seismic configuration interpretation technology of Paleogene Wenchang Formation in Panyu 4 depression, Pearl River Mouth Basin
HUANG Junli, ZHANG Wei, LIU Lihui, CAI Guofu, ZENG Youliang, MENG Qingyou, LIU Hao
2023, Vol.35(2): 103–112
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2228 )
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High-frequency sequence division and geological significance of dolomiteevaporite paragenetic strata of Cambrian Gaotai Formation in eastern Sichuan Basin
HU Zhonggui, WANG Jixuan, LI Shilin, GUO Yanbo, ZUO Yun'an, PANG Yulai
2023, Vol.35(2): 113–124
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Favorable geological conditions for the formation of ultra-high petroleum columns in petroliferous basins
HAN Yunhao, JIANG Zhenxue, ZHANG Zhiyao, ZHU Guangyou
2023, Vol.35(2): 125–135
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2260 )
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Vertical sealing of Paleogene faults and its control on reservoirs in Chaluhe fault depression, Yitong Basin
YING Kaiying, CAI Chang'e, LIANG Yuqi, CHEN Hong, SHANG Wenliang, SU Guijiao
2023, Vol.35(2): 136–143
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Genesis and exploration enlightenment of Ordovician fracture-vuggy carbonate karst reservoirs in Tarim Basin
NI Xinfeng, SHEN Anjiang, QIAO Zhanfeng, ZHENG Jianfeng, ZHENG Xingping, YANG Zhao
2023, Vol.35(2): 144–158
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Reservoir sensitivity of Neogene Guantao Formation in Zhanhua Sag, Bohai Bay Basin
YAO Xiutian, WANG Chao, YAN Sen, WANG Mingpeng, LI Wan
2023, Vol.35(2): 159–168
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Evaluation of pore effectiveness of Quaternary mudstone biogas reservoirs in Sebei area, Qaidam Basin
SIMA Liqiang, MA Jun, LIU Junfeng, YANG Huijie, WANG Liang, ZHAO Ning
2023, Vol.35(2): 1–10
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doi: https://doi.org/10.12108/yxyqc.20230201
Through low-field NMR experiments, the T2 spectra of the Quaternary mudstone biogas reservoirs in the Sebei area of Qaidam Basin were analyzed under saturated water state and gradient drying temperature state, and the NMR response characteristics of pore fluids were clarified to evaluate the effectiveness of pores. The results show that:(1) Based on the T2 spectrum under the saturated water state, the centrifugal bound water T2 spectrum was constructed by fitting the normal distribution function, the T2 cutoff values of movable fluid and capillary bound fluid were determined, the fluid types were divided, and the pore effectiveness evaluation was carried out. (2) The T2 spectral peaks of water-saturated rock samples in the study area are small on the left and large on the right, and the amplitude of the right peak is much larger than that of the left peak, accounting for more than 90% of the T2 spectral amplitude. With the increase of drying temperature, the amplitude of the T2 spectrum decreases and the left shift trend is obvious. The T2 spectrum shape of the bound water is approximately normal distribution, and the starting position basically coincides with the T2 spectrum under the saturated water state.(3) The T2 cutoff value(T2 C1) of movable fluid in the study area is 3.3 ms on average, and the average T2 cutoff value(T2 C2) of capillary bound fluid is 1.8 ms. The pore fluids include movable water, capillary bound water and clay bound water. The clay bound water T2 is less than T2 C2, and the capillary bound water T2 is larger than T2 C2 and less than T2 C1, and the movable fluid T2 is larger than T2 C1. The capillary bound water content is the highest, followed by the clay irreducible water, which account for 84.43%-95.06% of the total pore fluids, and the movable water content is low.(4) The effective pores of the reservoir in the study area account for 54.99% of the total pores and are mainly capillary-bound pores, and clay-bound pores are ineffective pores. The higher the clay content, the smaller the effective porosity.
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Sequence filling succession and fluid indication of dolomite reservoirs of the first member of Permian Qixia Formation in Baoxing area, southwestern Sichuan Basin
FENG Mingyou, GAO Ruiqi, WANG Xingzhi, XU Liang, ZHAO Jin, LIU Xiaohong, SHANG Junxin
2023, Vol.35(2): 11–20
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doi: https://doi.org/10.12108/yxyqc.20230202
Dolomites of Qixia Formation of Middle Permian in Baoxing area of southwestern Sichuan Basin display a complex diagenetic alteration and complex genesis of high-quality reservoirs. The filling characteristics of dolomite reservoirs in the study area were analyzed based on field investigation, macroscopic and microscopic petrological characteristics, cathodoluminescence and fluid inclusion measurement. The results show that:(1) The dolomites of the first member of Qixia Formation of Middle Permian are composed of subhedral medium to coarse-grained dolomites, with zebra texture and tectonic breccia developed. The reservoir spaces are mainly residual intercrystalline pores, residual intercrystalline dissolved pores and dissolved fractures, followed by expanding dissolved fractures and geodes, with porosity of 1%-4%.(2) The dolomite reservoirs in the study area are mainly filled with medium to coarse-grained saddle dolomites and bright crystal calcites, followed by a small amount of quartzs. Locally, medium to coarse-grained dolomites are distributed in the fractures together with calcites in a belt shape. In general, the distribution of dolomites is obviously controlled by faults, and the fractures and caves are relatively developed, and the filling sequence is coarse-grained saddle dolomite-quartz-calcite.(3) During the Middle-Late Triassic period, the Mg-rich thermal brine in deep basin entered the formation along faults and replaced original rock to form hydrothermal dolomites. The hydrothermal cooling effect carried out the dissolution transformation of the early reservoirs, and accompanied by the pressure reduction, led to the precipitation of coarse-grained saddle dolomite and a small amount of calcite. Under the influence of Yanshan movement at the end of Jurassic, the silicon-rich hydrothermal solution in deep basin entered the reservoir and replaced some saddle dolomites and a small amount of quartzs filled holes. In the late Yanshanian period, the carbon dioxide rich fluids with high-temperature and low salinity were supersaturated due to tectonic uplift and precipitated late calcites, which greatly reduced the reservoir space.(4) The reservoirs are intense densification after episodic fluid alteration, and part of the residual vugs or fracture networks are relative porous for hydrocarbon accumulation and migration.
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Types and distribution of tight sandstone gas sweet spots of the third member of Upper Triassic Xujiahe Formation in Yuanba area, Sichuan Basin
HUANG Yanqing, LIU Zhongqun, WANG Ai, XIAO Kaihua, LIN Tian, JIN Wujun
2023, Vol.35(2): 21–30
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doi: https://doi.org/10.12108/yxyqc.20230203
Through core observation, thin section identification and logging analysis and other geophysical technologies, the characteristics of tight sandstone reservoirs of the third member of Upper Triassic Xujiahe Formation in western Yuanba area of Sichuan Basin were studied. Combined with gas well productivity characteristics and main controlling factors in the study area, the types and causes of gas reservoir sweet spots were summarized, and the distribution of the sweet spots was predicted. The results show that:(1) There are various sandstones of the third member of Xujiahe Formation, among which medium-coarse-grained calcareous lithic sandstone and fine conglomerate are high-quality reservoirs. There are various types of fractures, mainly low angle shearing cracks and diagenetic contraction joints.(2) There are two types of sweet spots, such as medium-coarse-grained calcareous lithic sandstone type and fine conglomerate type, which can be further subdivided into six types combined with fracture characteristics. There are differences in geological characteristics, test methods and trial mining characteristics of various sweet spots.(3) The formation of sweet spots is mainly controlled by sedimentation, diagenesis and tectonism. The medium-coarse-grained calcareous lithic sandstone and fine conglomerate are mostly distributed in the distributary channel near the boundary between delta plain and front. Differential recrystallization is the reason for the formation of gravel-edge fractures. The distribution of fractures is controlled by faults and stratum flexure caused by tectonic activity.(4) The medium-coarse-grained calcareous lithic sandstone and fine conglomerate are characterized by low GR, low CNL, medium-high Rd and medium AC values. The S-wave impedance of high-quality reservoirs and μρ(μ stands for shear modulus, ρ stands for density) are medium-high, and the sweet spots of medium-coarse-grained calcareous lithic sandstone, fine conglomerate and superimposed through gravel cracks are widely distributed in strip shape, while the other four types of sweet spots are sporadically distributed.
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Hydrocarbon accumulation law and model of Cretaceous clastic rocks in western Tabei uplift
XU Zhuang, SHI Wanzhong, WANG Ren, LUO Fusong, XIA Yongtao, QIN Shuo, ZHANG Xiao
2023, Vol.35(2): 31–46
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doi: https://doi.org/10.12108/yxyqc.20230204
Based on core observation and physical property, geochemical analysis and 3D seismic data, through sedimentary facies analysis of single well and well-tie profile, fine seismic interpretation and identification of dominant sand bodies, the hydrocarbon accumulation law and model of Cretaceous clastic rocks in western Tabei uplift were studied from the aspects of oil source, oil and gas charging characteristics, transport system and reservoircap assemblage. The results show that:(1) The Cretaceous oil and gas in the study area has the characteristics of terrigenous origin. The oil mainly comes from Triassic lacustrine source rocks in Kuqa Depression, the gas mainly comes from Jurassic coal-measure source rocks in Kuqa Sag, while the deep Triassic marine source rocks contribute a little to oil and gas.(2) The Cretaceous oil and gas charging in the study area lasted for a long time, and the accumulation period was late. The accumulation can be divided into two phases:oil generation in the early period and gas accumulation in the late period. Oil accumulation occurred in the Miocene(4.0-22.0 Ma), and gas accumulation occurred in the early Pleistocene(3.5-11.0 Ma). Affected by the structural uplift of 2.6-3.5 Ma, the gas reservoir maturity was low.(3) The oil and gas transport system in the study area is well developed. Faults and unconformities are used as the main migration channels in southern Tianshan Mountains. The unconformity surface and thin sand bodies of Baxigai Formation are the migration channels in Shunbei area.(4) The reservoirs in the study area are mainly developed in Shushanhe Formation and Baxigai Formation, with sand content generally higher than 60%, which constitute a good reservoir-cap assemblage with the continuous mudstone developed in the upper part. The distribution of high-quality reservoirs is controlled by sedimentary facies. The high-quality reservoirs in southern Tianshan Mountains are mainly distributed in the front sand bar and beach-bar of fan delta, while the high-quality reservoirs in Shunbei area are mainly distributed in front lobe of braided river delta. At present, the exploration wells are not at the highest part of the lobe, and the oil and gas shows are relatively poor. the reservoir properties in Shunbei area are better.(5) Due to different fault activities and reservoir-cap assemblages, there are obvious differences in the types of oil and gas reservoirs between southern Tianshan Mountains and Shunbei area. The oil and gas reservoirs in southern Tianshan Mountains are mainly low-amplitude structural and structural-lithologic composite reservoirs. The oil and gas reservoirs in Shunbei area are mainly lithologic reservoirs with small scale.
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Sedimentary characteristics of Jurassic Shaximiao Formation in Wubaochang area, northeastern Sichuan Basin
FANG Rui, JIANG Yuqiang, CHEN Qin, ZENG Lingping, LUO Yuzhuo, ZHOU Yadong, DU Lei, YANG Guangguang
2023, Vol.35(2): 47–58
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doi: https://doi.org/10.12108/yxyqc.20230205
Based on the principle of base level cycle change, the data of field outcrop, drilling, logging and seismic stratigraphic slice were used to analyze the sequence structure, river channel composition characteristics under different accommodation spaces and river type conversion model of the second member of Jurassic Shaximiao Formation in Wubaochang area of northeastern Sichuan Basin. The results show that:(1) There are mainly one third-order and three fourth-order base level cycles developed in the second member of Jurassic Shaximiao Formation in Wubaochang area of northeastern Sichuan Basin. Each fourth-order sequence is a thick layered stacked box type sand body under the low accommodation space. With the base level rising, the accommodation space increases, and it transits to a relatively isolated sand body deposition at the top of the sequence.(2) The paleoclimate of the second member of Shaximiao Formation was dry. Due to the near provenance deposition, the sandstone was coarse and the maturity was low, the strong hydrodynamic structure was developed, it was parallel reflection on seismic profile, and the fluvial facies characteristics were obvious. There are many braided river sedimentary systems with discontinuous positive rhythms superimposed on each other in low accommodation space and meandering river sedimentary systems with binary structure in high accommodation space.(3) The fluvial facies strata of the second member of Shaximiao Formation have a "braid curve" transformation law from bottom to top, which is specifically shown as follows:under the low accommodation space, sand bodies are distributed in a large area, and the seismic geomorphology is shown as mutually overlapping braided river channels. When the base level rises rapidly, the accommodation space increases, and the seismic geomorphology shows a relatively isolated meandering river channel.(4) The accommodation space and sediment supply ratio(A/S) is mainly affected by strong tectonic activity and change from warm and humid to hot and dry climate in Daba Mountain provenance area.
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Fluid pressure field building process and its petroleum geological significance of Paleogene Shahejie Formatiom in Bonan sag, Jiyang Depression
ZHENG Bin, DONG Ao, ZHANG Yuanzhi, ZHANG Yi, SU Shan, ZHANG Shichao, FAN Jinjin, LUO Yinshan
2023, Vol.35(2): 59–67
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doi: https://doi.org/10.12108/yxyqc.20230206
The fluid inclusions in shale and tight sandstone of Paleogene Shahejie Formation in Bonan sag of Jiyang Depression were tested for Paleopressure, the fluid pressure evolution process was restored, and its petroleum geological significance was discussed. The results show that:(1) The third member of Shahejie Formation(Es3) in Bonan sag experienced four pressure field reconstruction processes in Guantao Formation and subsequent sedimentary periods. The duration of each pressure field reconstruction is 3-4 Ma, showing the characteristics of low sequence episodic pattern.(2) Different from the low sequence episodic pressure field building process of Es3, the Es4 has a high threshold for pressure field reconstruction under the sealing of overlying gypsum rocks. Two pressure field reconstruction processes occurred during the sedimentary period of Dongying Formation and the end of Guantao Formation, showing the characteristics of high sequence episodic pressure field.(3) The low sequence episodic pressure field building process of Es3 i ndicates an open fluid environment and strong acid dissolution. The physical properties of Es3 r eservoir with low sequence episodic pressure field are higher than those of the upper Es4 r eservoir with high sequence episodic pressure field. The hydrocarbon source rocks of Es3 n ot only discharge a large number of hydrocarbons, but also contains hydrocarbons in its own reservoir space, so as to form enrichment areas of conventional oil and shale oil.
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Characteristics and main controlling factors of oolitic shoal reservoirs of Triassic Feixianguan Formation in eastern Kaijiang-Liangping trough, Sichuan Basin
WEN Wen, YANG Xiyan, XIANG Man, TAO Xiayan, YANG Rong, LI Yang, FAN Jiaxing, PU Baiyu
2023, Vol.35(2): 68–79
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doi: https://doi.org/10.12108/yxyqc.20230207
Based on core observation, micro thin section identification and scanning electron microscope analysis, combined with sequence division, the reservoir characteristics and controlling factors of Triassic Feixianguan Formation in eastern Kaijiang-Liangping trough of Sichuan Basin were studied. The results show that:(1) The reservoirs of Triassic Feixianguan Formation are dominated by oolitic dolomite and fine silty dolomite in TieshanpoPuguang area, and oolitic dolomite(with gravel, sand and bean grains) in Dukouhe -Qilibei area, and the original structural components of oolitic rocks are better preserved.(2) The reservoirs in the study area are characterized by multi-stage development. The reservoirs in Tieshanpo-Puguang area are developed in ssq1, ssq2 and ssq3 sequences, with the characteristics of early development, large thickness and wide distribution area, and type Ⅰ, Ⅱ and Ⅲ reservoirs are developed. The reservoirs in Dukouhe Qilibei area are developed in ssq2 and ssq3 sequences, which are late developed, small in thickness and limited in distribution area, and are dominated by type Ⅱ and Ⅲ reservoirs.(3) Sedimentary palaeogeomorphology and sea-level change control the development stages and thickness of oolitic shoal reservoirs in the study area. When sea-level began to decline in the middle and late stages of ssq1, oolitic shoal reservoirs began to develop in the paleogeomorphic highlands with large thickness and obvious dolomitization.(4) The water energy in steep slope and gentle slope margin slope zones affects the types of oolitic shoal sediments, provides a material basis for diagenetic dissolution and dolomitization, and thus controls the physical properties and scale of the reservoir.
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Characteristics and main controlling factors of shale oil reservoirs of Triassic Chang 7 member in Heshui area, Ordos Basin
XIAO Ling, CHEN Xi, LEI Ning, YI Tao, GUO Wenjie
2023, Vol.35(2): 80–93
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doi: https://doi.org/10.12108/yxyqc.20230208
Heshui area in Ordos Basin is the main zone for the exploration and development of shale oil in Chang-qing Oilfield. Based on the data of cast thin section, physical property analysis, scanning electron microscopy, high-pressure mercury compression and nuclear magnetic resonance, the characteristics and main controlling factors of shale oil reservoirs of Triassic Chang 7 member in Heshui area of Ordos Basin were analyzed. The results show that:(1) The shale oil reservoir of Chang 7 member in Heshui area is mainly a set of dark gray-black fine siltstone, mainly lithic arkose, and the average volume fraction of fillings is 16.71%. The rock physical properties are poor, with an average porosity of 8.15% and an average permeability of 0.102 mD. It is an ultra-low porosity, extra-low porosity and ultra-low permeability reservoir.(2) The reservoir pores in the study area are mainly feldspar dissolved pores and residual intergranular pores. Sub-micron pores(0.1-1.0 μm) are the main reservoir space, accounting for 75.56% of the total pores, followed by nano pores(with diameter less than 0.1 μm), accounting for 17.94% of the total pores. The throat type is relatively complex, and the tube-shaped throats caused by dissolution and the flake and curved flake throats caused by compaction are the main throat types of the reservoir. (3) Sedimentation, diagenesis and tectonism jointly control the quality and distribution of shale oil reservoir of Chang 7 member in the study area. Sedimentation provides the material basis for the reservoir. The reservoir is mainly formed in the deep-water gravity flow sedimentary environment, which can be divided into two types:sandy clastic flow sand bodies and turbidite sand bodies. The medium-strong compaction and cementation reduce the physical properties of the reservoir. The dissolution has a certain positive effect on improving the physical properties of the reservoir. The fractures formed by tectonism improve the percolation capacity of the reservoir and are of great significance for the later fracturing and reconstruction of the reservoir.
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Hydrocarbon accumulation and evolution characteristics of Paleogene in Yingxiongling area, Qaidam Basin
WANYAN Ze, LONG Guohui, YANG Wei, CHAI Jingchao, MA Xinmin, TANG Li, ZHAO Jian, LI Haipeng
2023, Vol.35(2): 94–102
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doi: https://doi.org/10.12108/yxyqc.20230209
Through the study of structural evolution characteristics, combined with the analysis of hydrocarbon inclusions and fine dissection of typical oil and gas reservoirs, the formation and evolution process of oil and gas reservoirs in the upper member of Paleogene Xiaganchaigou Formation in Yingxiongling area of Qaidam Basin were analyzed. The results show that:(1) The upper member of Xiaganchaigou Formation in Yingxiongling area experienced a semi saline lake, saline lake and salt lake environment during the Paleogene period, and formed a large area of source-reservoir type oil and gas reservoir dominated by laminated calcite dolomite which is rich in organic matters.(2) The upper member of Xiaganchaigou Formation in the study area has experienced three stages of oil and gas filling. The hydrocarbon inclusions in the first stage are single liquid oil inclusions, reflecting the migration and filling of early low mature crude oil. The hydrocarbon inclusions in the second stage are single liquid oil inclusions, which reflects the migration and filling of medium mature crude oil. The hydrocarbon inclusions in the third stage are gas-liquid two-phase oil inclusions, reflecting an episode of filling of highly mature crude oil.(3) The oil and gas in the study area are characterized by three stages of accumulation. In the middle and late stages of the deposition of Shangganchaigou Formation, reservoirs with low saturation and low maturity formed in the upper member of Xiaganchaigou Formation. In the sedimentary period of Shangyoushashan Formation, low mature to mature oil and gas accumulated to the salt reservoirs and high permeable zones, forming a high oil and gas production area. During the sedimentation period of Shizigou Formation to Qigequan Formation, maturehighly mature oil migrated to the upper member of Ganchaigou Formation and above through the transport of double layer faults to form structural oil and gas reservoirs.
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Ternary seismic configuration interpretation technology of Paleogene Wenchang Formation in Panyu 4 depression, Pearl River Mouth Basin
HUANG Junli, ZHANG Wei, LIU Lihui, CAI Guofu, ZENG Youliang, MENG Qingyou, LIU Hao
2023, Vol.35(2): 103–112
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doi: https://doi.org/10.12108/yxyqc.20230210
Under the framework of source-to-sink system, the sedimentary facies, palaeogeomorphology and seismic configuration attribute slices of Paleogene Wenchang Formation in Panyu 4 depression of the Pearl River Mouth Basin were studied based on seismic configuration analysis, the sedimentary units were divided, the boundaries of each sedimentary unit were defined qualitatively and semi quantitatively, and two exploration potential zones were selected. The results show that:(1) Three types of source-to-sink systems of Paleogene Wenchang Formation were found in Panyu 4 depression of the Pearl River Mouth Basin. A gentle slope divergent source-to-sink system is developed in the northwest, which is characterized by the dynamic evolution of fan delta, lake and braided river delta in the vertical direction, and the seismic configuration changes from medium-strong reflection sheet filling to medium-weak amplitude parallel reflection, and then to high-frequency medium amplitude progradation reflection. A long axis convergent source-to-sink system is developed in the southwest, and the braided river delta is developed stably, which is mainly wedge-shaped in configuration. A steep slope parallel source-to-sink system is developed in the hanging wall of fault controlling depression with stable multi-stage overlapped fan delta, which is generally characterized by a wedge-shaped configuration, reflecting the sedimentary characteristics of fan delta plain-front under the background of abundant sources.(2) The sedimentary palaeogeomorphology of Wenchang Formation in the study area is generally faulted in the east and superposed in the west. During the deposition of the fifth and fourth members of Wenchang Formation, it was in a strong fault depression period. Local tectonic movement raised the northwest and southeast, and a structural ridge and two sub depressions formed in the central part. During the deposition of the third and second member of Wenshan Formation, it entered fault depression period, the sedimentation center moved eastward as a whole, the lake basin shrank, and the western strata were denuded.(3) Seven sedimentary units are developed in the gentle slope divergent source-to-sink area of the study area, which are mainly superimposed underwater distributary channels and thin sheet sand in fan delta front. Four sedimentary units are developed in the long axis convergent source-to-sink area, which are dominated by underwater distributary channels and widely distributed front sheet sand in braided river delta front. In the steep slope parallel source-to-sink area, there are four sedimentary units, including underwater fan, fan delta front, turbidite fan.(4) The long axis convergent source-to-sink system in the southwest and the gentle slope divergent source-to-sink system in the northwest are the exploration potential areas in the study area.
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High-frequency sequence division and geological significance of dolomiteevaporite paragenetic strata of Cambrian Gaotai Formation in eastern Sichuan Basin
HU Zhonggui, WANG Jixuan, LI Shilin, GUO Yanbo, ZUO Yun'an, PANG Yulai
2023, Vol.35(2): 113–124
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doi: https://doi.org/10.12108/yxyqc.20230211
The dolomite-evaporite paragenetic strata are rich in oil and gas resources. Based on the principle of sequence stratigraphy, combined with drilling and thin section data, and on the basis of third-order sequence division, INPEFA and wavelet transform technologies were used to identify and divide the high-frequency sequences of dolomite-evaporite paragenetic strata of Cambrian Gaotai Formation in eastern Sichuan Basin. The results show that:(1) The dolomite-evaporite paragenetic strata of Cambrian Gaotai Formation in eastern Sichuan Basin can be divided into three third-order sequences which are respectively Sq1, Sq2 and Sq3 from bottom to top, and can be further divided into six fourth-order sequences(ssq1-ssq6). The Gaotai Formation is mainly in a carbonate platform sedimentary environment, with mixed tidal flats, confined-evaporative platforms and open platform facies deposits developed in turn from west to east.(2) There are four types of intergrowth rock assemblages of Cambrian Gaotai Formation in the study area, including:thick-layered evaporite overlying dolomite, thick-layered dolomite interbedded with evaporite, interbedded dolomite and evaporite, and thick-layered dolomite overlying evaporite. The dolomite-evaporite paragenetic strata are developed at the contact interface of the fourth-order sequence, and are mostly developed in the highstand systems tract inside the sequence, reflecting a strong disturbance of sea level, especially the relative decline of sea level, which is conducive to the deposition of dolomite and evaporite. (3) The rock assemblage sequence of the dolomite-evaporite paragenetic strata of Gaotai Formation can generate response characteristics on the GRinpefa and wavelet transform curves. The corresponding 64-scale wavelet coefficient curve fluctuates smoothly, and the energy clusters are weak yellow-blue. The GRinpefa curve shows lithological difference between evaporite and dolomite in the form of "notch".
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Favorable geological conditions for the formation of ultra-high petroleum columns in petroliferous basins
HAN Yunhao, JIANG Zhenxue, ZHANG Zhiyao, ZHU Guangyou
2023, Vol.35(2): 125–135
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doi: https://doi.org/10.12108/yxyqc.20230212
Petroleum column height is one of the important indicators to determine the degree of hydrocarbon enrichment. Based on the data of hydrocarbon accumulation in major petroliferous basins worldwide, a systematic analysis of petroliferous basins with ultra-high petroleum columns was conducted. The favorable geological conditions for the formation of ultra-high petroleum columns in petroliferous basins were analyzed in combination with hydrocarbon supply capacity, reservoir-cap assemblages and hydrocarbon migration patterns. The results show that:(1) Most of the typical oil and gas fields in the world with ultra-high petroleum columns are dominated by carbonate formations, accounting for 78% of the total. This is because carbonate formations are relatively easy to develop large-thickness stacked reservoirs, which are conducive to the formation of ultra-high petroleum columns.Typical oil and gas fields with ultra-high petroleum columns abroad are mainly distributed in Persian Gulf Basin, Pre-Caspian Basin and Western Siberian Basin, while mainly distributed in Sichuan Basin, Bohai Bay Basin and Tarim Basin in China.(2) The favorable conditions for the formation of ultra-high petroleum columns include sufficient hydrocarbon supply, vertically stacked large-thickness reservoirs, extensive overlying caprocks, vertical network transport system, favorable migration conditions and good source-reservoir configuration.(3) Many ultrahigh petroleum columns have been found in the deep strata of Tarim Basin. Taking the Fuman oilfield as an example, the sufficient hydrocarbon supply from the Lower Cambrian source rocks, the thick reef tuff reservoirs and tight mudstone caprock of Middle and Upper Ordovician, and the favorable migration conditions such as deep and large faults, are the main reasons for the formation of ultra-high petroleum columns in this area.
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Vertical sealing of Paleogene faults and its control on reservoirs in Chaluhe fault depression, Yitong Basin
YING Kaiying, CAI Chang'e, LIANG Yuqi, CHEN Hong, SHANG Wenliang, SU Guijiao
2023, Vol.35(2): 136–143
Abstract
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doi: https://doi.org/10.12108/yxyqc.20230213
Based on the data of logging and oil test, the vertical sealing of Paleogene faults controlling reservoir in Chaluhe fault depression of Yitong Basin was evaluated by using the method of normal pressure of fault plane. The results show that:(1) The present normal pressure of fault plane of oil and gas reservoirs can be calculated by the data of burial depth, average density of overlying strata and fault dip angle. In the Paleogene, the present normal pressure of Paleogene reservoirs in Chaluhe fault depression of Yitong Basin ranges from 13.3 MPa to 56.0 MPa, and the normal pressure during the reservoir forming period was 3.8-13.1 MPa, showing the characteristics of "ancient opening and present closing". As the greater the pressure on the fault plane, the tighter the fault, thus forming a vertical seal, otherwise open.(2) The minimum value of present normal pressure of fault plane of the reservoirs in the study area is 13.3 MPa, which is defined as the critical value of the vertical sealing of Chaluhe fault depression, and the present critical burial depth of the faults controlling reservoir is further determined to be 2 262 m.(3) The normal pressure of fault plane is positively correlated with the fault tightness index, the vertical sealing critical pressure value, critical burial depth and fault tightness index can be used to quantitatively evaluate the sealing ability of the faults controlling reservoir in the study area.(4) The fault can not only serve as the hydrocarbon migration pathway, but also provide shelter for the formation of reservoirs. The faults controlling reservoir of C43 reservoir in the northwestern margin of Chaluhe fault depression showed a vertical opening during the accumulation period, which coincided with the period of hydrocarbon generation and expulsion, with the function of connecting oil sources and migrating oil and gas. The faults controlling reservoir in well region C43-C48 are now in a vertical sealing state, which can effectively seal oil and gas.
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Genesis and exploration enlightenment of Ordovician fracture-vuggy carbonate karst reservoirs in Tarim Basin
NI Xinfeng, SHEN Anjiang, QIAO Zhanfeng, ZHENG Jianfeng, ZHENG Xingping, YANG Zhao
2023, Vol.35(2): 144–158
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doi: https://doi.org/10.12108/yxyqc.20230214
Based on core thin section, experimental analysis, drilling, logging and seismic data, the Ordovician carbonate karst reservoirs in Tarim Basin were classified according to the reservoir genetic mechanism, and the distribution, space types and main control factors of various reservoirs were analyzed. The results show that:(1) The Ordovician fracture-vuggy karst reservoirs in Tarim Basin can be divided into five types according to their genesis:(quasi-) syngenetic karst reservoirs, interlayer karst reservoirs, bedding karst reservoirs, buried hill(weathering crust) karst reservoirs and fault-controlled karst reservoirs.(2) (Quasi-) syngenetic karst reservoirs, also known as reef-shoal karst reservoirs, are the reservoir formed by short-term(transient) exposure and leaching of reefshoal facies granular limestone at the platform edge or within the platform due to sea level drop, with matrix pores, dissolved fractures and dissolved caves being developed. They are usually superimposed with later interlayer karst or buried hill karst to form complex karst reservoirs.(3) The interlayer karst reservoirs are developed in the inner zone, and they are related to the parallel(micro-angle) unconformity surface in the carbonate strata and distributed quasi-stratified. The reservoir space is mainly cave type, followed by fracture-vuggy type and vuggy type.(4) The bedding karst reservoirs are related to the slope background, pre-existing pores and fractures around the buried hill, and the surrounding of the buried hill is distributed in a ring band, dominated by vuggy type and fracture-vuggy type, and more than 90% of the dissolved pores and caves are connected through faults and fractures.(5) The buried hill(weathering crust) karst reservoirs are developed in buried hill area. They are related to medium to long-term angle unconformity and greatly affected by faults and fractures. They are quasi-stratified and have obvious characteristics of peak and hill geomorphology. According to the lithology of the surrounding rocks, they can be divided into limestone buried hill karst reservoirs and dolomite weathering crust karst reservoirs. The limestone fracture-vuggy system is developed, the matrix pores are not developed, and the dolomite fracture-vuggy is underdeveloped, mainly consisting of dolomite intercrystalline dissolved pores and fractures.(6) Controlled by faults, karst reservoirs are mainly developed in the fault development area of inner zone. The fractures and vuggy are developed with large burial depth, large scale and long span, and they are distributed in a grid-shape along the faults, dominated by fracture-vuggy type, followed by fault-cave type. The more developed the faults and fractures are, the more developed the dissolved vuggy and caves are, and the higher and more stable the single well oil testing productivity is.(7) Karst reservoirs in the study area are largely developed in the interior area, mainly bedding karst reservoirs and karst reservoirs controlled by faults, with great exploration potential.
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Reservoir sensitivity of Neogene Guantao Formation in Zhanhua Sag, Bohai Bay Basin
YAO Xiutian, WANG Chao, YAN Sen, WANG Mingpeng, LI Wan
2023, Vol.35(2): 159–168
Abstract
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doi: https://doi.org/10.12108/yxyqc.20230215
Reservoir sensitivity analysis is an important means to evaluate the degree of reservoir damage, which is of great significance for the later efficient development and remaining oil tapping. The core samples from Neogene Guantao Formation in Kenxi oilfield of Zhanhua Sag in Bohai Bay Basin were selected to analyze the damage index and sensitivity characteristics of reservoirs of Guantao Formation in combination with thin section observation, X-ray diffraction analysis, mercury injection test and flowing water drive experiment. The results show that:(1) The Guantao Formation in Zhanhua Sag of Bohai Bay Basin is loosely cemented. The pore structure is characterized by large pore size, uniform distribution of pore throat and good connectivity. The rock minerals are mainly composed of quartz, plagioclase, K-feldspar and rock debris, and the clay minerals mainly include kaolinite, illite, chlorite and chlorite-illite mixed layer. The upper member of Guantao Formation is dominated by fine grains, while the lower member is dominated by medium grains.(2) The reservoirs of Guantao Formation are generally characterized by medium velocity sensitivity, weak alkali sensitivity and weak salt sensitivity. The acid sensitivity characteristics of the upper and lower members are quite different. The upper member has non-acid sensitivity characteristics, while the lower member has strong acid sensitivity characteristics with index of 78.25%.(3) The content of ankerite and chlorite and pore structure of Guantao Formation in the study area control the reservoir sensitivity.(4) Controlling of injection-production flow rate is an important content of the development plan in the study area, while the reservoir damage caused by acid sensitivity in the lower member of Guantao Formation should be protected and treated.