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    Pore characterization of shale in Shanxi Formation, Yan'an area, Ordos Basin
    WANG Zilong, GUO Shaobin
    Petroleum Geology & Experiment    2019, 41 (1): 99-107.   DOI: 10.11781/sysydz201901099
    Abstract   PDF (2336KB)  
    The shale reservoirs in the Upper Paleozoic Shanxi Formation in the Yan'an area of the Ordos Basin were studied. The whole porosity of the shale was characterized in detail using NMR, SEM, high pressure mercury intrusion, nitrogen adsorption and carbon dioxide adsorption. The Shanxi Formation in the Yan'an area mainly developed four types of porosity, i.e. fractures, intergranular, intragranular pores, and organic pores, with intragranular and organic pores in the majority. The T2 NMR curves are mostly single-peaked and almost unchanged after centrifugation, indicating that the samples are dominated by nano pores with poor connectivity. High pressure mercury intrusion, nitrogen adsorption and carbon dioxide adsorption experiments showed that the pore volume is mainly meso pores and macro pores, accounting for about 85% of the total pore volume, while micro pores only account for 15% of the total pore volume. The specific surface area is mainly provided by micro pores and meso pores, with micro pores accounting for 52% of the total specific surface area, followed by meso pores accounting for 48%. Macro pores can be neglected when the surface area is more than 99%. The pore morphology of the samples is mainly parallel plate pores with openings or slits at both ends.
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    Shale gas reservoir geology of the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in western Hubei and northeastern Chongqing
    ZHOU Zhi, ZHAI Gangyi, SHI Dishi, WANG Shengjian, GUO Tianxu, LIU Yimin, WANG Hao
    Petroleum Geology & Experiment    2019, 41 (1): 1-9.   DOI: 10.11781/sysydz201901001
    Abstract   PDF (6968KB)  
    The Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation are important strata for shale gas exploration in the western Hubei and northeastern Chongqing area. At present, no breakthrough has been made in exploration, and the main factors controlling shale gas enrichment are unclear. The spatial and temporal distribution, geochemical features, reservoir properties and gas-bearing capacities of high-quality shale of deep-water continental shelf facies in the Wufeng-Longmaxi formations were studied based on the analysis of drill core and field outcrop data of well JD1 and its adjacent area in Jianshi area. Organic-rich shale was developed well in the Wufeng-Longmaxi formations. The organic-rich shale of deep-water continental shelf facies was mainly found in the Katian, Hirnantian and Rhuddanian stages, which featured substantial thickness, high TOC content, medium maturity, favorable reservoir conditions and medium burial depth, showing a good potential for shale gas enrichment. The organic-rich shale of deep-water continental shelf facies in the Katian, Hirnantian and Rhuddanian stages had a stable structure with few fractures, and a regional cap rock in the Middle and Lower Triassic and these are the main controls for shale gas enrichment in the Wufeng-Longmaxi formations in the western Hubei and northeastern Chongqing area.
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    Multi-stage activity characteristics of small-scale strike-slip faults in superimposed basin and its identification method: a case study of Shunbei area, Tarim Basin
    HUANG Cheng
    Petroleum Geology & Experiment    2019, 41 (3): 379-389.   DOI: 10.11781/sysydz201903379
    Abstract   PDF (4438KB)  
    The strike-slip faults in superimposed basins usually experienced multi-stage activities. The episodic formation and evolution of strike-slip faults match with the important tectonic transformation periods of superimposed basins. Generally speaking, strike-slip fault zones converge (or stretch) in stress fields at different tectonic stages. It will result in the formation of specific associated structural styles of near-surface tectonic layers in the same period. Finally, a complete vertical tectonic sequence is formed. If the strike-slip associated structures peculiar to each tectonic layer are taken as geological records of strike-slip fault activities in the same period, the episodic activity of the strike-slip faults can be restored step by step from the present underground geological structure, and then the active periods of faults can be determined. In addition, during the episodic slip of strike-slip faults, changes in horizontal slip direction and faulted tectonic-sedimentary geological bodies often occur. These two phenomena actually reflect the core content of the kinematic characteristics of strike-slip faults, namely, the direction and distance of slip. It can also be used as an important basis for judging the active stages of strike-slip faults. Therefore, the Tarim superimposed basin is divided into five tectonic layers on the basis of the study of basin tectonic-sedimentary evolution background. On this basis, the vertical structural sequence and main associated structural styles of strike-slip fault system in the study area are determined. The geometric and kinematic characteristics of strike-slip associated structures in different tectonic layers of Tarim superimposed basin are analyzed. Two types with seven applicability techniques for distinguishing active periods of faults based on seismic data have been formed.
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    Prospects for ultra-deep oil and gas in the “deep burial and high pressure” Tarim Basin
    GU Yi, WAN Yanglu, HUANG Jiwen, ZHUANG Xinbing, WANG Bin, LI Miao
    Petroleum Geology & Experiment    2019, 41 (2): 157-164.   DOI: 10.11781/sysydz201902157
    Abstract   PDF (990KB)  
    Ultra-deep oil and gas exploration technology is developing, and the thermal evolution of source rocks under high pressure in the Tarim Basin has become the focus of ultra-deep oil and gas resource evaluation and hydrocarbon generation theory research. Simulated hydrocarbon generation from source rocks under high temperature and pressure, combined with the geological conditions of “deep burial and high pressure” of the Shuntuoguole Uplift in the Tarim Basin, a study was carried out on the hydrocarbon generation, evolution and retardation under high pressure of marine source rocks in the Tarim Basin. Ever since the Yanshan period, the Cambrian source rocks still have geological conditions for generating high-maturity liquid hydrocarbon in the Shuntuoguole Uplift. The boundary conditions for thermal evolution retardation include: ①Long-term stable closed system; ②Source rocks deeper than 6 500 m with the fluid pressure above 60 MPa, and a low temperature with a gradient less than 20 ℃/km in the later period; ③Marine source rocks with type I and type Ⅱ1 kerogen. The ultra-deep Cambrian marine source rocks in the Tarim Basin are mainly type I and type Ⅱ1 kerogen, and the degree of inhibition is more obvious under high pressure. The scope and potential of the oil generation window are much higher than the traditional theoretical value. Therefore, the prospect for ultra-deep oil and gas exploration is considerable.
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    Sedimentary characteristics and geological significance of tempestites in the Upper Cambrian Xixiangchi Formation, Chengkou area, northern margin of the Yangtze Platform
    WANG Han, LI Zhiwu, LIU Shugen, SONG Jinmin, RAN Bo, LAI Dong, HAN Yuyue
    Petroleum Geology & Experiment    2019, 41 (2): 176-184.   DOI: 10.11781/sysydz201902176
    Abstract   PDF (3865KB)  
    The Upper Cambrian Xixiangchi Formation has been considered as a potential target for hydrocarbon exploration in the Sichuan Basin, but little is known about its sedimentary facies and controls on reservoir quality. The tempestite deposition found in the Xixiangchi Formation at the northern margin of the Yangtze Platform may provide some important constraints for that. Through field survey and thin section analysis, we present a detailed description on the tempestite deposition of the Upper Cambrian Xixiangchi Formation in Chengkou area on the northern margin of the Yangtze Platform, and further discuss the significance for paleogeography and implications for hydrocarbon reservoir in the northeastern Sichuan Basin. Many diagnostic sedimentary structures can be recognized in these Upper Cambrian tempestites of the Xixiangchi Formation in Chengkou area, such as basal scour-and-fill structures, rip-up clasts, hummocky cross stratification (HCS), graded bedding, and so on. Five types of tempestite sequences were recognized in terms of variant assemblies of storm-induced sedimentary structures, with a gradual transition from Type 1 at the bottom to Type 5 on the top. According to tempestite deposition, lithological association and sedimentary sequence, combined with the classical mode of tempestites developed in shallow water carbonate environments, we suggested that the sedimentary environment of tempestites of the Upper Cambrian Xixiangchi Formation in Chengkou area were dominated by middle ramp, and evolved from inner ramp at the bottom to mid-outer ramp on the top, with a deepening-upward trend. Integrated with regional geological background, it is speculated that the Upper Cambrian Xixiangchi Formation on the northern margin of the Yangtze Platform is dominated by mid-outer ramp facies to the northeast of Chengkou, and inner-ramp facies to the southwest. This implies that there were many geologic advantages for high quality shoal reservoirs in the Upper Cambrian Xixiangchi Formation developed in the northeastern Sichuan Basin to the southwest of Chengkou, worthy to be explored in the future.
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    Transmission model of secondary gas reservoir on the basin margin of Jiyang Depression
    ZHANG Weizhong, ZHANG Yunyin, WANG Xingmou, ZHA Ming, DONG Li, LIU Haining, QU Zhipeng, YU Jingqiang
    Petroleum Geology & Experiment    2019, 41 (2): 185-192.   DOI: 10.11781/sysydz201902185
    Abstract   PDF (2317KB)  
    Heavy oil and gas have an association in a shallow fault basin reservoir. More than 50% of shallow gas reservoirs came from the biodegradation of heavy oil. However, there is little research on the migration process from the heavy oil reservoir to the shallow gas reservoir. Through the study of the carrier system type, distribution and elements of heavy oil and shallow gas reservoirs, two models were established, and the migration controls were clarified. There are two carrier system types: lateral and vertical. Lateral migration mainly developed in the high convex belt of the basin, and the shallow gas reservoir was distributed over the side of the heavy oil reservoir. The transmission process was dominated by lateral migration. Vertical migration also took place through diffusion along faults. Vertical migration mainly developed in the depression and low convection zone, and the shallow gas reservoir was located directly above the heavy oil reservoir. The transport process is dominated by vertical migration through faults.
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    Tectonic evolution characteristics of Yingjisha and Pishan areas and the influence on petroleum accumulation in the southwest depression, Tarim Basin
    XIE Qiaoming, WANG Zhenliang, YIN Chengming, LI Qingyao, LIAO Xiao, ZHAO Zilong, ZHANG Kuaile
    Petroleum Geology & Experiment    2019, 41 (2): 165-175.   DOI: 10.11781/sysydz201902165
    Abstract   PDF (4102KB)  
    The oil and gas exploration degree in the southwestern depression of the Tarim Basin is low overall. Complex tectonic evolution is one of the key factors that restrict the hydrocarbon accumulation and exploration in this depression. There are no major discoveries in the Yingjisha and Pishan areas that are geologically similar to those found in the oil and gas fields of Akmomu and Kekeya. Using a balanced section technology, and the geological circumstances and single well burial history as the constraints in the field, the tectonic evolution characteristics of the Yingjisha and Pishan areas and their effects on hydrocarbon accumulation were analyzed. Since the Permian, the Yingjisha area has undergone three stages of tectonic nappe, and developed tectonic styles such as imbricate thrusts, V-belt and fault related folds. It has the strongest nappe effect in the Miocene, with a strata shortening of 22.4%. The Pishan area has experienced four stages of tectonic thrust, developing styles such as imbricate thrusts and fault related folds. The strongest thrusting took place during the Pliocene with a strata shortening of 12.5%. There is a certain difference in time and intensity of tectonic movement in the Yingjisha and Pishan areas since the Miocene. Since the Neogene, the strong thrusting of the Yingjisha and Pishan areas has caused the formation of thick Cenozoic strata in the foreland depression, making the underlying source rocks enter the high-maturity and over-mature stage, resulting in large-scale hydrocarbon generation. Oil and gas migrated along faults and unconformities into anticline structures to form reservoirs. The difference in tectonic effects between the Yingjisha and Pishan areas since the Neogene has led to some differences in the conditions for hydrocarbon accumulation. The initial charging period of hydrocarbons and the main formation time of structural traps in the Yingjisha area were both in the Miocene epoch, and the primary oil and gas reservoirs were easily damaged in the Pliocene epoch. In the Pishan area, the initial charging period of hydrocarbons and the main formation time of structural traps were both in the Pliocene epoch, and the primary oil and gas reservoirs showed a low damage risk.
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    Reef control factors and new seismic prediction techniques of Changxing Formation, east of Kaijiang-Liangping trough, Sichuan Basin
    PENG Cai, ZHENG Rongcai, CHEN Hui, WANG Lanying, LUO Jing, LIANG Hong
    Petroleum Geology & Experiment    2019, 41 (4): 614-620.   DOI: 10.11781/sysydz201904614
    Abstract   PDF (2297KB)  
    The sedimentary characteristics, main controlling factors and reef reservoir facies of the Upper Permian Changxing Formation reef on the eastern side of the Kaijiang-Liangping trough in the northeastern Sichuan Basin were studied using comprehensive seismic prediction technology.Through the study of single well sedimentary facies, it is found that there are two stages of longitudinal development of the reefs in this area. The paleogeomorphology of the Changxing Formation has a controlling effect on the development and migration of the reefs:the larger the slope, the thicker the reefs.Early paleo-geomorphology controlled the development of reefs. In the northern steep slope zone, early reef strips developed, while in the southern gentle slope zone, late reef blocks developed. Late paleotopography controlled the migration of reefs to the platform, resulting in the second row of reefs.Targeted prediction techniques were used to account for differences in sedimentary environments in different regions. In the central transitional belt, the amplitude property on the top of Changxing Formation on the platform margin was optimized to predict reef thickness. In the southern gentle slope sedimentary zone, the bioreef is predicted by the seismic-based interpretation technique. The predicted results have been confirmed by actual drilling, and many wells have obtained high-yield gas flow.
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    Fault characteristics and controls on hydrocarbon accumulation in Changling Faulted Depression, Songliao Basin
    ZUO Zongxin, LU Jianlin, WANG Miao, LI Ruilei, LI Hao, ZHU Jianfeng
    Petroleum Geology & Experiment    2019, 41 (2): 200-206.   DOI: 10.11781/sysydz201902200
    Abstract   PDF (1076KB)  
    Multiple types of oil and gas reservoirs have been found in the Changling Faulted Depression, and the reservoir types and pool size are variable in different areas. Fault characteristics, forming mechanisms and activity periods were studied based on seismic interpretation. The fault controls on hydrocarbon accumulation were discussed, and the main exploration targets in different areas were identified. Three types of fault were formed during the fault, depression and inversion periods. Under a NNE direction sinistral strike-slip and tension stress background, many NE, NS-NNW and NW direction secondary faults were generated. The fault activity characteristics varied in different areas. Due to fault activities, multiple types of structural traps were formed. The faults have a great influence on oil and gas migration and accumulation in the Changling Faulted Depression. In the areas that the faults are inactive and the tectonics are stable during the depression and the inversion periods, primary reservoirs were well preserved. As a result, the primary reservoirs in the Huoshiling, Shahezi and Yingcheng formations are main exploration targets. The secondary reservoirs are important exploration directions for the long duration of fault activity, especially in the deep faults and strike-slip faults.
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    Shale pore characteristics and controls in well Qian XY 1, Zunyi City, Guizhou Province
    XIE Ting, ZHANG Cong, YANG Yuru, XIA Xianghua, LI Qi, WANG Xianghua, YU Weixin
    Petroleum Geology & Experiment    2019, 41 (1): 68-75.   DOI: 10.11781/sysydz201901068
    Abstract   PDF (6485KB)  
    Twenty-two intact shale core samples from 1 029.91-1 140.4 m in the well Qian XY 1 in the Zunyi City of the Guizhou Province were studied using FE-SEM combined with PerGeos. Qualitative and quantitative analyses of pore development characteristics and main controlling factors were identified based on the organic matter content and maturity, as well as the energy spectrum data of mineral components. The Longmaxi Formation shale in the well Qian XY 1 has a high organic matter abundance and is highly mature to over mature. It mainly developed three types of pores:inorganic mineral pores, organic pores and micro-cracks. The inorganic mineral pores include intragranular, intergranular, intracrystalline, mold and dissolution pores, while the micro-cracks include structural micro-cracks, diagenetic shrinkage joints, organic matter hydrocarbon-discharge joints and artificial cracks. The main controlling factors affecting shale pore development are organic matter content, thermal evolution of organic matter and burial depth.
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