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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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    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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    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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    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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    Difference of lithofacies mechanical properties of the fourth member of Shahejie Formation in the Bonan Subsag, Bohai Bay Basin
    LI Zhipeng, BU Lixia
    Petroleum Geology & Experiment    2019, 41 (2): 228-233.   DOI: 10.11781/sysydz201902228
    Abstract   PDF (1472KB)  
    Based on the data of well cores in low permeability reservoirs in the fourth member of Shahejie Formation in the Bonan Oilfield, the rock facies types were studied. Using conventional three axis compression test data of different lithofacies, restored static rock mechanical parameters were established under reservoir confining pressure conditions. The differences of static mechanical parameters and stress-strain relation between lithofacies were analyzed. The low permeability reservoirs in the Bonan Oilfield can be divided into 5 types: coarse grained sandstones, fine sandstones, siltstones, mudstones and carbonate sandstones. In the same rock, with the increasing confining pressure, the Young’s modulus becomes larger, and the Poisson’s ratio increases slightly. With the increase of rock gain size, the Young’s modulus increases and the Poisson’s ratio decreases. However, the Poisson’s ratio of coarse grained sandstones does not follow the overall trend, and is larger than that of fine sandstones and smaller than that of siltstones. As the grain size of rock becomes coarser, the stress-strain relation becomes more linear. And the initial grain rearrangement plastic section and the high stress plastic section become smaller.
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    Pore structure characteristics of the Lower Cambrian black shale in the Cengong block, southeastern Guizhou area
    WANG Ruyue, HU Zongquan, YANG Tao, GONG Dajian, YIN Shuai, LIU Zhongbao, GAO Bo
    Petroleum Geology & Experiment    2019, 41 (2): 207-214.   DOI: 10.11781/sysydz201902207
    Abstract   PDF (2059KB)  
    Based on the mineralogy, organic geochemistry, nitrogen adsorption, physical properties and FE-SEM observation, the pore structure characteristics of the Niutitang and Bianmachong marine shales of the Lower Cambrian in the southeastern Guizhou area were systematically analyzed. The dominant pore types of the organic-lean shale with a high clay mineral content in the Niutitang and Bianmachong formations are plate-like and slit-like inter particle pores with average pore sizes commonly greater than 5 nm. However, the organic-rich shale in the Niutitang Formation mainly contains slit-like and ink-bottle-like pores with average pore sizes less than 3-4 nm, and the specific surface area is 2-3 times of that of the organic-lean shale. In addition, the total pore volume and specific surface area have a positive correlation, and there is also a correlation between clay mineral content and average pore size, but the correlations between total pore volume/specific surface area and clay mineral content/average pore size are negative. Under favorable preservation conditions, the shale has a relatively high development level of organic matter pores, greater values of porosity, pore size and peak diameter with a positive correlation between porosity and permeability, which are represented as “high porosity and low permeability”. Under unfavorable preservation conditions, the reservoir parameters have lower values except the permeability, which leads to the overdevelopment of fractures and has the feature of “low porosity and high permeability”. Besides, the TOC content has a significant control on pore structure and generally has a positive correlation with total pore volume, specific surface area and porosity and a negative correlation with average pore size. Nevertheless, in the intervals with an excessive TOC content, the decrease and increase of pore size and ductility with increasing TOC coupled with compaction and/or unfavorable preservation will result in the atrophy, collapse and close of narrow pores and throats which leads to the negative correlations between TOC and reservoir parameters.
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    Gas migration mode for the central canyon in deep-water Qiongdongnan Basin
    LIU Jingjing, LIU Zhen, WANG Zisong, CAO Shang, SUN Xiaoming
    Petroleum Geology & Experiment    2019, 41 (2): 193-199.   DOI: 10.11781/sysydz201902193
    Abstract   PDF (2665KB)  
    Exploration results showed that the gas in the shallow Neogene central canyon reservoirs of the Qiongdongnan Basin mainly came from the deep Paleogene source rocks in the deep-water area. However, given that the late tectonic activity in the basin was weak, how did the gas in the deep formations migrate to the Neogene reservoirs? Using seismic frequency division technology, the resolution of 3D seismic data was improved. A fracture system below the central canyon was identified, and a gas transport mode was established by combining this interpretation with the development characteristics of regional faults. There were four stages of fault activity in the deep-water area of the basin, with pronounced periodicity. The activity and stationary periods happened alternately. Based on this, this paper proposed a concept of fracture cycle, which includes a shorter activity period and a longer stationary period. A fracture activity corresponds to a fracture cycle, and multiple fracture activities can be superimposed to form a stacking pattern of fracture cycles. Then, studying the difference of the migration mode for fractures in different periods, this paper proposed a fast inflow migration mode during the fault activity period and an effective seepage migration mode during the stationary period, and pointed out that it could enhance the efficiency of gas migration in a overpressure rift basin, if the inflow migration mode and seepage migration mode occurred alternately. In the Lingshui Depression, a series of ladder-like faults developed, connecting source rocks in the deep formations with many high-angle small faults in the shallow formations, which allowed deep natural gas migrate to shallow reservoirs. Thus, a relayed transport mode of “multi-stage fracturing and multiple faults” for gas migration in the central canyon was proposed.
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