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2019 Vol. 41, No. 1

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2019, 41(1): .
Abstract(291) PDF-CN(194)
Abstract:
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
2019, 41(1): 1-9. doi: 10.11781/sysydz201901001
Abstract(1896) PDF-CN(406)
Abstract:
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.
Geochemical characteristics of organic-rich shale in the Dawuba Formation, western Guizhou Province
CHEN Rong, YUAN Kun, ZHANG Ziya, XU Qiufeng, LU Shufan, HE Jingbo
2019, 41(1): 10-15. doi: 10.11781/sysydz201901010
Abstract(1243) PDF-CN(208)
Abstract:
Consideration of the organic-rich shale of the Upper Paleozoic in the southern part of China has been stimulated by the advancement of shale gas exploration and development in China. The organic shale section of the Lower Carboniferous Dawuba Formation in the western part of Guizhou Province, which is widely distributed and thick, is one of the main targets of Guizhou shale gas exploration. In the process of shale gas exploration, the organic matter abundance, maturity and kerogen type of organic-rich shale are the main parameters of shale gas evaluation. In this paper, these three properties were determined on organic shale outcrop samples of the Dawuba Formation and combined with previous data, the organic geochemical characteristics of the Dawuba Formation have been described. The TOC content of organic-rich shale in the Dawuba Formation in the western Guizhou is generally > 1%, and most samples are in the range of 1%-3%. The kerogen in the Dawuba Formation is mainly of type Ⅱ2 and type Ⅲ, and in some parts type Ⅱ1 is present. Ro is generally > 0.6%, mostly distributed in the range of 1.3%-3.0%, which means they are high maturity to over-mature. The regional data show that the organic geochemical properties and the shale gas exploration potential of the Dawuba Formation are better in Liupanshui Shuicheng and Pu'an-Qinglong areas.
Shale gas characteristics of organic-rich shale in Luofu Formation in Guizhong Depression
ZHANG Ziya, WEI Jiaqi, SHI Dishi, QIN Yinglun, ZHAO Yingquan, PANG Chunyu, LIU Yang
2019, 41(1): 16-22. doi: 10.11781/sysydz201901016
Abstract(1175) PDF-CN(230)
Abstract:
The characteristics of organic-rich shale in the Middle Devonian Luofu Formation in the Guizhong Depressionwere studied using whole rock and clay mineral X-ray diffraction, and organic geochemical analyses. The shale was deposited as a black mud shale, carbonaceous shale, siliceous shale and siliceous mud shale. The organic carbon content in the southern Luzhai is higher than 2.55%, and the highest value in the northwest of Heshan-Shanglin is above 3.0%. The organic matter is mainly mixed types I and Ⅱ1, which showed a great hydrocarbon generation potential and a high thermal evolution degree. The analysis of shale gas enrichment factors indicated that the regions close to Nandan-Tian'e and Heshan were favorable for shale gas accumulation, which were exploration targets in the Middle Devonian Luofu Formation in the Guizhong Depression.
Micro pore characteristics of Wufeng-Longmaxi shale and their control on gas content: a case study of well Anye 1 in Zunyi area, Guizhou Province
GE Mingna, PANG Fei, BAO Shujing
2019, 41(1): 23-30. doi: 10.11781/sysydz201901023
Abstract(1159) PDF-CN(247)
Abstract:
The Anchang syncline is a complex tectonic area for shale gas exploration in South China, located in the northern part of Guizhou Province. The shale of the Upper Ordovician Wufeng-Lower Silurian Longmaxi formations in the well Anye 1 in Zunyi area of Guizhou Province was studied using argon ion polishing, scanning electron microscopy, N2 low-temperature low-pressure adsorption experiments and organic geochemical, rock and mineral analysis and other supporting experiments to portray microscopic pore type, structure and their controls on the gas content of marine shale reservoirs. There are many kinds of micro and nano pores in the Wufeng-Longmaxi shale, and organic pores and micro cracks are the most abundant. The shale hosts mainly nano pores, and the micro pores are mostly filled with calcite. Organic pores are the main pore types of the Longmaxi shale, and micro cracks are the main pore types of the Wufeng shale. There are two kinds of N2 adsorption-desorption isotherms:type IV-H4 hysteresis loop and type V-H3 hysteresis loop, which are slit pores with a flat structure. The BET specific surface area is between 7.87 and 14.83 m2/g, the total pore volume of BJH is between 0.002 6 and 0.005 2 cm3/g, mainly mesopores, and the average pore diameter is concentrated at 2-5 nm. In the longitudinal direction, microscopic pores have a significant control on the gas content of the Wufeng-Longmaxi shale in the well Anye 1. The shale adsorption amount is positively correlated with the TOC content, and the other parameters have no obvious correspondence with the gas content. Compared with the Wufeng-Longmaxi shale in the Jiaoshiba area, those in the well Anye 1 have different thickness, porosity, permeability and pore throat diameter, which are the main controls for gas content. Through the single well analysis of well Anye 1, it is shown that the Wufeng-Longmaxi formations of the Anchang syncline are superior in geological conditions and have good prospects for shale gas exploration.
Evaluation of shale gas resources of the Sinian Doushantuo Formation in the southern Huangling anticline, western Hubei Province
LI Haohan, CHEN Ke, BAO Shujing, ZHANG Yanlin, SONG Teng, WANG Peng
2019, 41(1): 31-37. doi: 10.11781/sysydz201901031
Abstract(1288) PDF-CN(178)
Abstract:
With the first discovery of the world's oldest shale gas in the Sinian Doushantuo Formation on the southern limb of the Huangling anticline in the western Hubei Province, the gas-bearing properties of the dark shale in this layer have been confirmed. The gas content and density data of the dark shale of the Sinian Doushantuo Formation in the study area were obtained by gas content and rock and mineral analyses of the core samples from the well ZD-1. Based on the interpretation of regional seismic reflection profiles and well data of ZD-1 and ZD-2, we delineated the distribution and thickness variation of the black shale in detail, and defined the volume of the gas-bearing shale. The resource potential of the Lower Sinian Doushantuo Formation on the south limb of the Huangling anticline was determined by the probabilistic volume method. The gas resource was calculated, ranging (85-303)×109 m3, and the median resource was 195×109 m3, which indicates that the layer has a good shale gas resource potential. It was recommended as a shale gas exploration target in the western Hubei Province.
Petrological characteristics and sedimentary environment in the southern Guizhou during the Late Carboniferous
YUAN Kun, CHEN Rong, LIN Tuo, FANG Xinxin, QIN Yinglun, WANG Chao, ZHOU Zhi, SUN Xiangcan
2019, 41(1): 38-44. doi: 10.11781/sysydz201901038
Abstract(1023) PDF-CN(184)
Abstract:
The sedimentary environment changed frequently from carbonate terraces to basin in the Late Carboniferous in the south part of Guizhou. There were two lithologic combinations at the same time, namely the Nandan Formation (black limestones and siliceous shale limestones) and the Weining Formation (light gray limestones and dolomites). However, the sedimentary environment boundary and transitional characteristics between the two formations are not clear yet. The changes and transition characteristics of sedimentary facies in the southern Guizhou were analyzed based on previous research and the analysis of three typical wells, and combined with sedimentary sequence characteristics and rock combination characteristics. It was found that in the Late Carboniferous, the southern part of Guizhou experienced a retreat from basin facies to carbonate terraces facies, and there was a certain intersection and transition between various facies. A retreat process took place in the south-west direction. The appearance of the Weining Formation in the south indicated the shallowing of seawater and the closure of a rift trough.
Silicon sources and hydrocarbon accumulation in shale, Triassic Yanchang Formation, Ordos Basin
LIU Guoheng, ZHAI Gangyi, ZOU Caineng, HUANG Zhilong, XIA Xianghua, SHI Dishi, ZHOU Zhi, CHEN Rong, ZHANG Cong, YU Shufang
2019, 41(1): 45-55. doi: 10.11781/sysydz201901045
Abstract(1180) PDF-CN(254)
Abstract:
A series of analyses, including major and trace element analysis, X-ray diffraction for bulk and clay mineral composition, Rock-Eval analysis, TOC analysis and scanning electron microscope observation, were conducted in order to determine the different silica sources and hydrocarbon accumulation between the Chang 7 member and Chang 9 member shale of the Triassic Yanchang Formation in the Ordos Basin. The Chang 72 sub-member and the Chang 9 member shale had more similarities in silica sources, mineral composition, element composition and organic geochemical characteristics, while the Chang 73 sub-member shale showed certain differences in the above properties from the other two sets of shale reservoirs. The silica in the Chang 72 sub-member and the Chang 9 member shale came from terrestrial detritus, while the silica in the Chang 73 sub-member shale showed the characteristics of two sources, namely, terrestrial detritus and hydrothermal from vents at the bottom of the lake. Both Chang 7 and Chang 9 shales are high-quality source rocks. However the contents of residual hydrocarbon and kerogen are higher, the type of kerogen is much better, and the oil saturation index is higher under the influence of hydrothermal fluid for the Chang 73 sub-member shale. Hence the Chang 73 sub-member is superior to the Chang 72 sub-member and Chang 9 member shale and has higher exploitation value.
Gas-bearing characteristics and controls of the Cambrian Shuijingtuo Formation in Yichang area, Middle Yangtze region
LUO Shengyuan, LIU An, LI Hai, CHEN Xiaohong, ZHANG Miao
2019, 41(1): 56-67. doi: 10.11781/sysydz201901056
Abstract(1310) PDF-CN(227)
Abstract:
The Yichang area in the Middle Yangtze region is a new exploration target for shale gas outside the Sichuan Basin. The shale of the Cambrian Shuijingtuo Formation has an enormous gas resource potential in view of gas shows in most wells. Gas contents vary in different wells. We investigated the gas-bearing characteristics and controls of shale in the Cambrian Shuijingtuo Formation in the Yichang area integrating geological and geochemical data. The black rock series of the Shuijingtuo Formation in this area is mainly carbonaceous shale and gray shale, about 50-140 m thick. They have a high organic carbon content and are mainly of typeⅠ, generally thermally over-mature, showing a good hydrocarbon generation potential. The on-site measured gas content is 0.32-5.48 m3/t, and the cumulative thickness of shale with gas content >2 m3/t is 44.05 m, which reflects a good overall gas content of shale in this area. The gas-bearing capacity of the Shuijingtuo Formation shale is affected by various factors such as sedimentary facies, organic carbon content, mineral composition, porosity, extent of fracture and formation pressure. The black carbonaceous shale deposited in the continental shelf facies has higher gas content than the gray calcareous shale of the slope facies, while the limited platform facies has the lowest gas content. The gas content has a positive correlation with the organic carbon and quartz mineral contents, a weak negative correlation with the carbonate mineral content, and a poor correlation with the clay mineral content. Organic carbon content has a more significant control on gas content. Shale porosity and pore distribution variations are important factors leading to the differences in gas content. In addition, shale gas content is also closely related to reservoir fracture development and formation pressure.
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
2019, 41(1): 68-75. doi: 10.11781/sysydz201901068
Abstract(1420) PDF-CN(172)
Abstract:
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.
Characteristics of the Cambrian Shuijingtuo shale reservoir on Yichang Slope, western Hubei Province: a case study of well EYY 1
LI Hai, LIU An, LUO Shengyuan, CHEN Xiaohong, CHEN Lin
2019, 41(1): 76-82. doi: 10.11781/sysydz201901076
Abstract(1202) PDF-CN(187)
Abstract:
The characteristics of shale reservoirs on the Yichang Slope in the western Hubei Province were studied using organic geochemistry, mineral X-ray diffraction, field emission scanning electron microscopy and nuclear magnetic resonance methods on black shale samples collected from the Cambrian Shuijingtuo Formation in the well EYY 1. Shale in the study area is mainly composed of quartz, clay minerals and carbonates with high calcium and low siliceous contents. From bottom to top, the contents of clay minerals and carbonates gradually decrease, while the content of quartz gradually increases. Shale porosity has a positive relationship with TOC content, especially in the section with a TOC content higher than 2%. Micro pores and small pores are abundant in the shale. Small pores and meso pores contribute significantly to porosity. The contribution of pores in brittle minerals to the matrix porosity of shale is stable, while the contribution of organic pores and interlayer pores in clay minerals are respectively changing relative to their contents, which means that the contribution of organic pores increases with depth and pores in clay minerals decrease gradually.
Shale gas accumulation in the Upper Permian Leping Formation: a case study of well Ganfengdi-1 in the central Pingle Depression, Jiangxi Province
FANG Chaogang, XU Zhenyu, TENG Long, HUANG Zhengqing, ZHENG Hongjun, XU Feifei
2019, 41(1): 83-93. doi: 10.11781/sysydz201901083
Abstract(1048) PDF-CN(130)
Abstract:
The Upper Permian Leping coal measures are widely developed in the Pingle Depression, Jiangxi Pro-vince, which is a key area for shale gas exploration in the Lower Yangtze region. The core data of well Ganfengdi-1, the first geological survey well in the Pingle Depression, which drilled through the main shale of Leping Formation, were studied in order to determine the shale gas accumulation conditions and exploration potential in the central Pingle Depression. More than 200 core samples were analyzed using non-uniform sampling. By means of thin section observations, organic geochemical analysis, X-ray diffraction analysis of whole rock and clay minerals, argon ion polishing scanning electron microscopy and in situ analysis of shale, it was determined that a large thickness of the black carbonaceous shale of the Leping Formation in the central Pingle Depression has a high content of organic carbon. The type of organic matter is good, and the stage of high maturity gas generation is favorable for shale gas generation and accumulation. In addition, the content of brittle minerals is high. The brittle index I is 26%-53.5%, averaging 37.3%, while the brittle index Ⅱ is 23.3%-52.6%, averaging 39.0%, which indicates that the shale formation has a good compressibility. Organic pores and intragranular pores in clay minerals are well-developed. The internal connectivity of the pores is good, and the specific surface area of the minerals is high, which is of great significance for the occurrence of shale gas. The micro-cracks mainly play a role of communication and diversion to improve the permeability of the shale. By analyzing the exploration potential parameter indexes of the 4 sections of the Leping Formation (Guanshan, Laoshan, Shizishan and Wangpanli), it is considered that the Wangpanli and Laoshan shale have more outstanding gas show, thickness, TOC content, organic matter pore and mineral composition, which can be regarded as favorable shale gas exploration targets in the Leping coal-bearing system in the central Pingle Depression.
Shale gas accumulation conditions and resource potential evaluation of the Cambrian in the Lower Yangtze area
HUANG Zhengqing, ZHOU Daorong, LI Jianqing, WU Tong, XU Feifei
2019, 41(1): 94-98. doi: 10.11781/sysydz201901094
Abstract(1414) PDF-CN(162)
Abstract:
The Cambrian in the Lower Yangtze region is a marine sedimentary stratum with an area of 130×103km2. The Lower Cambrian Hetang Formation (Makufushan Formation) comprisesblack carbonaceous mudstones with a thickness of 276 m and an organic carbon content (TOC) rangingfrom 0.25%-23.52%, averaging 4.54%. The organic matter is mainly of type I, showing favorable conditions for shale gas accumulation. The Lower Cambrian stratum has experienced tectonic movements and transformation duringmagmatic activityduring the Caledonian, Hercynian, Indosinian, Yanshanian and Himalayan periods, and some individual sections have become part of metamorphic rocks. Therefore, the thermal evolution degree of carbonaceous mudstones is high in the Hetang Formation in many areas of the Lower Yangtze region. The maximum vitrinite reflectance (Ro) is 6.32%, indicating for an over mature stage. At the same time, due to large overburden and structural influence, the burial depth of the Hetang Formation also varies. The thickness, burial depth, TOC content and Ro of the carbonaceous mudstones in the Hetang Formation were applied to construct ageological survey and potential evaluation of shale gas in the Cambrian in the Lower Yangtze region. There are mainly three exploration targets including the region from the Shangrao area in the Jiangxi Province to the Tonglu area in the Zhejiang Province, the Yangzhou area in the Jiangsu Province and the Quanjiao area in the Anhui Province, with an estimated resource of 28894×109m3.
Pore characterization of shale in Shanxi Formation, Yan'an area, Ordos Basin
WANG Zilong, GUO Shaobin
2019, 41(1): 99-107. doi: 10.11781/sysydz201901099
Abstract(2219) PDF-CN(267)
Abstract:
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.
Prediction of brittle index and its relationship with log data in marine-terrigenous shale of Qinshui Basin
FU Juanjuan, GUO Shaobin
2019, 41(1): 108-112. doi: 10.11781/sysydz201901108
Abstract(1164) PDF-CN(134)
Abstract:
Rock brittleness, as a key factor affecting the fracture properties of shale, is one of most important parameters for shale gas reservoir evaluation and "sweet spot" prediction. At present, the brittleness evaluation of shale reservoirs in the Qinshui Basin is mostly based on qualitative analysis because of its simple well logging series and limited number of cores for XRD based mineral composition. In this paper, a brittleness index (BI) was firstly calculated based on mineral composition information from XRD data. Then the relationship between logging data and BI was analyzed. Finally, a model for calculating the BI of the Carboniferous and Permian shale is established. The results show that the brittleness in the studied area is related to quartz, dolomite, pyrite and clays. The contents of quartz, dolomite and pyrite have a positive correlation with BI, whereas the clay minerals, which increase the ductility of rocks, are negatively correlated with BI. Different logging responses reflect different degrees of BI. The BI is positively related to the density, whereas it is negatively correlated with natural gamma signal. The relationship of BI with resistivity and interval transit time is not strong, showing a weakly negative correlation. The BI calculated using a multiple linear regression method is in a good agreement with that obtained by the mineral method.
Laminated texture of shale and its storage space significance in Western Depression, Liaohe Basin
MAO Junli, ZHANG Jinchuan, LIU Tong, DING Jianghui
2019, 41(1): 113-120. doi: 10.11781/sysydz201901113
Abstract(1128) PDF-CN(158)
Abstract:
Almost all organic-rich shale contains stratigraphic structures to varying degrees, reflecting different sedimentary facies, shale organic matter abundance, hydrocarbon generation capacity, reservoir space and gas content. The organic matter (OM) can be divided into three types of occurrence state, namely continuous lamellae, discontinuous lamellae and scattered lamellae, based on the sedimentary characteristics of organic-rich shale in lacustrine rift basins and the heterogeneity of the OM distribution. The black shale stratigraphic structure of the Western Depression of Liaohe Basin was studied using core observation, thin section analysis and scanning electron microscopy, and combined with statistical analysis. The organic-rich shale in the fourth member of Shahejie Formation (Sha-4) was mainly deposited in a semi-deep lake under brackish water conditions, developing carbonate-curved continuous laminae and clay-type flat continuous laminae. The Sha-3 shale, deposited in a freshwater deep-semi-deep lake, is dominantly composed of felsic interlaced laminae and dispersed laminae. The continuous carbonate-mixed lamellar shale can be related to chemical interactions, biochemical interactions caused by algae, or a combination of these two. The organic-rich clay shale is mainly composed of seasonal lamellae formed by climate change. The discontinuous striated layers usually consist of clay lamellae, and silt and clay are seasonally input in the form of advection or inter-layer flow. The shale lamellar morphology largely determines hydrocarbon generation capacity and characteristics, and further may influence reservoir capacity. The continuous lamellae are generally characterized by high carbonate content as well as being prone to dissolution, high TOC abundance, strong hydrocarbon generation ability and abundant organic pores. The organic pore-micro-seam reservoir system would contribute to oil and gas accumulation, and carbonate content is positively correlated with hydrocarbon content. In addition to the development of various inorganic pores, the discontinuous lamellae also develop organic pores, bedding cracks, and mineral cleavage cracks, which lead to the development of shale reservoir space and superior shale gas-bearing conditions. The dispersed lamellae are less prone to dissolution and cracking, so the reservoir space is relatively undeveloped and the gas-bearing conditions are relatively poor.
Inorganic geochemical characteristics and paleoenvironment of Chang 7 oil shale in Yanchang Formation, Tongchuan area, Shaanxi Province
QIAO Shihai, LI Yuhong, GUO Wang, ZHANG Yunpeng, WANG Yong
2019, 41(1): 121-126. doi: 10.11781/sysydz201901121
Abstract(1063) PDF-CN(128)
Abstract:
The geochemistry of shale core samples from the 7th member (Chang 7) of Triassic Yanchang Formation were analyzed in order to study the characteristics of sedimentary palaeoenvironment such as salinity, redox condition, depth, hydrothermal activity and palaeoclimate when the Chang 7 member was deposited in the Tongchuan area, Shaanxi Province. The content of Sr is 198.28×10-6, Sr/Ba is 0.39, V/Ni is 4.50, the equivalent boron content by the Walker method in most samples is less than 200×10-6, and the lowest value is about 40×10-6. Based on the above characteristics, it can be concluded that the Chang 7 oil shale was deposited in a brackish fresh water and anaerobic environment. The quantitative determination of cobalt indicated that the sedimentary environment was a lake with a maximum water depth of 40-70 m. The average Sr/Cu ratio is 4.28, which means that the paleoclimate was warm-wet and semi-humid. P, Cu, Co, Ni, V and Rb were enriched. The total REE was low, and the HREE was enriched. Ce showed a negative anomaly. Most of the La/Yb-REE plots were located near the intersection of basalt, granite and sedimentary rocks. All these characteristics strongly confirmed the existence of hydrothermal sedimentation in the lake.
Occurrence and controls of shale absorbed gas in Liupanshan Basin
HAN Wei, AI Ning, LI Yuhong, ZHANG Yunpeng, GUO Wang
2019, 41(1): 127-133. doi: 10.11781/sysydz201901127
Abstract(938) PDF-CN(115)
Abstract:
The Liupanshan Basin has potentially favorable conditions for oil and gas exploration. An absorbed gas model and other methods were used to study the mud shale in the Cretaceous Madongshan Formation in the well GY 1 in the Liupanshan Basin in order to discuss the occurrence and controls of the shale absorbed gas. The Cretaceous shale in the basin has a relatively low content of organic matter, but the maximum methane adsorption capacity ranges from 1.73 to 2.35 m3/t with a mean value of 2.03 m3/t indicating a relatively high gas storage capacity. The adsorption capacity of the shale increases first and then decreases with increasing depth. There is a deep inflection point. Pressure plays a major role in shallow formations, while temperature plays a major role at depth. The occurrence conditions of shale absorbed gas were mainly affected by six factors, among which the influence of organic matter abundance, maturity and moisture content were not significant, while mineral content, microscopic properties, temperature and pressure were the main influencing factors. When the external geological conditions are suitable, the gas enrichment degree of the shale reservoir in the Liupanshan Basin could be relatively high and very favorable for exploration.
Rock mechanical properties and fracability of continental shale in Zhanhua Sag, Bohai Bay Basin
XIA Zunyi, MA Haiyang, FANG Kun
2019, 41(1): 134-141. doi: 10.11781/sysydz201901134
Abstract(1331) PDF-CN(124)
Abstract:
The rock mechanical properties and fracability of a shale reservoir play an important role in the development of shale oil and gas. There is limited literature on the rock mechanical properties and fracability of continental shale. The mineral composition, compressive strength, Young's modulus and Poisson's ratio of the continental shale in the Shahejie Formation in the Zhanhua Sag were measured by X-ray diffraction and rock mechanical tests under different maturities and confining pressures. The content of carbonate minerals in the shale is the largest, with an average of 44.93%. The content of brittle mineral is slightly higher than that of clay mineral, Which is 30.98% and 24.09%, respectively. The failure mode of shale is predominantly splitting under uniaxial compression, which easily forms a fracture network. With additional confining pressure, the failure mode changed to shear mode. The compressive strength, Young's modulus and Poisson's ratio all increased with the increase of confining pressure, but the fracability decreased. The fracability of shale is positively correlated with thermal maturity. By considering mineral composition, mechanical properties, diagenesis and confining pressure, a mathematical model of the fracturing coefficient was established to evaluate the fracability of shale reservoir, which can provide a reference for the selection of fracturing layer.
Lithofacies characteristics and impact on pore structure of the Shahezi Formation shale, Changling Fault Depression, Songliao Basin
ZHANG Yinghan, LI Zhuo, LIU Dongdong, GAO Fenglin, JIANG Zhenxue, LIANG Zhikai, YANG Dongxu, YU Hailong
2019, 41(1): 142-148. doi: 10.11781/sysydz201901142
Abstract(1532) PDF-CN(125)
Abstract:
A lithofacies classification was established based on TOC and XRD data on cores of the Shahezi Formation in the Changling Fault Depression of the Songliao Basin. There are 7 lithofacies in the study area. Scanning electron microscopy, CO2 and N2 adsorption and high pressure mercury intrusion experiments were applied to quantitatively characterize pore structure. Shale pores were developed in the Shahezi Formation, and the pore types of different lithofacies were also different. Organic matter pores were mainly developed in argillaceous shale. Shale pore size exhibited a multi-peak distribution. Mesopores were the main contributors to pore volume, accounting for an average of 50.9%. Micropores were the main contributors to specific surface area, accounting for an average of 67.8%. The development of micropores was mainly controlled by clay minerals, the development of mesopores was controlled by carbonate minerals, while the development of macropores was controlled by the combination of siliceous and clay minerals. The organic-rich argillaceous rock influenced the surface area and pore volume, and played a major role in controlling shale pore development of the Shahezi Formation.
Micro-pore characteristics of shale in Zhanhua Sag, Bohai Bay Basin
MA Haiyang, XIA Zunyi, WEN Qingzhi, ZHANG Pengyu
2019, 41(1): 149-156. doi: 10.11781/sysydz201901149
Abstract(1138) PDF-CN(109)
Abstract:
The micro-pore structure of shale is a key contol of shale oil and gas accumulation and seepage. The micro-pore structure of the continental shale in the Shahejie Formation in the Zhanhua Sag was analyzed by using argon-ion polishing SEM, CO2 adsorption, N2 adsorption, MIP and NMR. The shale displays six kinds of pores, including organic, intergranular, intragranular, intercrystalline, dissolution pores and micro-cracks. Micropores, mesopores and macropores are all developed. The micropore specific surface area accounts for about 61.52% of the total specific surface area, providing the main space for shale oil and gas adsorption. The mesopores and macropores provide most pore volume, accounting for 49.99% and 41.19%, respectively, which play a major role in the storage and migration of shale oil and gas. The shale porosity is 4.08%-7.04% and the effective porosity is 0.11%-0.64%, which means that pore connectivity is poor.
2019, 41(1): 157-157.
Abstract(353) PDF-CN(83)
Abstract:

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