Critical geological characteristics and gas-bearing controlling factors in Longmaxi shales in southeastern Chongqing, China

2016 ◽  
Vol 34 (1) ◽  
pp. 42-60 ◽  
Author(s):  
Tieya Jing ◽  
Jinchuan Zhang ◽  
Shisen Xu ◽  
Zhujiang Liu ◽  
Shuangbiao Han
Keyword(s):  
Controlling Factors ◽  
Geological Characteristics ◽  
Gas Bearing

scholarly journals Analyzing the Origin of Low Resistivity in Gas-Bearing Tight Sandstone Reservoir

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yanjiao Jiang ◽  
Jian Zhou ◽  
Xiaofei Fu ◽  
Likai Cui ◽  
Chao Fang ◽  
...  
Keyword(s):  
Controlling Factors ◽  
Gas Reservoirs ◽  
Tight Sandstone ◽  
Internal Factors ◽  
Low Contrast ◽  
Low Resistivity ◽  
Low Degree ◽  
Fluid Properties ◽  
Internal And External Factors ◽  
Gas Bearing

Complex characteristics exist in the resistivity response of Gs reservoirs in the central inversion belt of the Xihu Sag, East China Sea Basin. Some drilling wells have confirmed the existence of abnormally low resistivity in gas reservoirs of the area; and the electrical logging response was unable to reflect fluid properties of the reservoir accurately. Therefore, it is necessary to analyze the origin of the low resistivity and determine its controlling factors. Based on experimental data of core analysis and numerical simulations of mud invasion, this study thoroughly explores the origin of low resistivity in the subject gas-bearing reservoir considering both internal and external factors. The results indicated that when there is no or a low degree of mud invasion, the fine lithology, complex pore structure, additional clay mineral conductivity, and high content of pyrite are the main internal factors driving the conditions present in the studied gas reservoir. When mud invasion occurs, the invasion of highly saline mud is the main external cause of low resistivity. The numerical simulation results indicated that a formation with good permeability and high overbalance pressure has a deep invasion depth. The resistivity around the well is obviously reduced after the invasion, and low resistivity would form easily. Combined with actual data of several wells, the main influencing factors of the reservoir’s electrical characteristics were analyzed, and the main controlling factors of low resistivity in the gas reservoirs are given. This study provides valuable support for studying the low-contrast complex reservoir conductivity mechanism. The study also offers novel ideas for accurate calculation of saturation and the meticulous evaluation of reservoir for subsequent studies.

scholarly journals Integrated Assessment of Marine-Continental Transitional Facies Shale Gas of the Carboniferous Benxi Formation in the Eastern Ordos Basin

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8500
Author(s):  
Weibo Zhao ◽  
Zhigang Wen ◽  
Hui Zhang ◽  
Chenjun Wu ◽  
Yan Liu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Shale Gas ◽  
Ordos Basin ◽  
Gas Content ◽  
Organic Carbon Content ◽  
Geological Characteristics ◽  
Core Samples ◽  
The Ordos Basin ◽  
Gas Bearing ◽  
Benxi Formation

In the Benxi Formation of the Carboniferous system of the Upper Paleozoic in the Ordos Basin, there are many sets of coal measures dark organic-rich shale, being marine continental transitional facies, with significant unconventional natural gas potential. Previous studies are only limited to the evaluation of tight sandstone reservoir in this set of strata, with no sufficient study on gas bearing and geological characteristics of organic-rich shale, restricting the exploration and evaluation of shale gas resources. In this study, analysis has been conducted on the organic carbon content, the major elements, the trace elements, and the mineral composition of core samples from the Benxi Formation in key drilling sections. In addition, qualitative and quantitative pore observation and characterization of core samples have been conducted. The sedimentary environments and reservoir characteristics of the shale of the Benxi Formation have been analyzed. Combined with the gas content analyzing the results of the field coring samples, the shale gas resource potentials of the Benxi Formation have been studied, and the geological characteristics of the Benxi Formation shale gas in the eastern Ordos Basin have been made clear, to provide a theoretical basis for shale gas resource evaluation of the Benxi Formation in the Ordos Basin. The results show that (1) in the Hutian Member, Pangou Member, and Jinci Member of the Benxi Formation, organic-rich shale is well developed, with the characteristics of seawater input as a whole. There is a slight difference in sedimentary redox index, which shows that the reducibility increases gradually from bottom to top. (2) There is an evident difference in the mineral characteristics of shale in these three members. The Hutian Member is rich in clay minerals, while the Jinci Member is high in quartz minerals. (3) The pores are mainly inorganic mineral intergranular pores, clay interlayer fractures, and micro fractures, and organic matter pores are developed on the surface of local organic matter. (4) The mud shale in the Jinci Member has a large cumulative thickness, has relatively high gas-bearing property, and is rich in brittle minerals. The Jinci Member is a favorable section for shale gas exploration of the Benxi Formation.

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