The Longmaxi Formation is one of the major exploration horizons of shale in China at present. The gas-bearing sediments in the Lower Paleozoic Longmaxi Formation in the Yangtze area, South Sichuan are characterized by low resistivity. Therefore, it is difficult to distinguish the gas-bearing sediments from aquifers only using logging response. Given this, this study investigated the genetic mechanisms of low-resistivity gas-bearing sediments in the study area in depth using existing data of conventional logging, core drilling, and production-related dynamic conditions, as well as a large number of core analyses and experiments, including casting thin sections, QEMSCAN, and X whole-rock diffraction. According to the study results, three major controlling factors in the low-resistivity gas-bearing sediments of the Lower Paleozoic Longmaxi Formation in the Yangtze region, South Sichuan include the additional conductivity of clay minerals, the complete graphitization of over-mature organic matter, and the distribution pattern of organic matter laminae. The practical application results indicate that the low-resistivity gas-bearing sediments in the study area were formed due to the organic matter laminae developing and the partial graphitization of organic matter. That is, the low resistivity of the shale gas reservoirs tends to be caused by the mutual superimposition and effects of multiple factors. Therefore, it is necessary to analyze the geological, logging, and core data according to various zones and horizons and employ the correlation between upper and lower horizons and between adjacent wells to determine the major controlling factors of the low resistivity of the shale gas reservoirs.
崔瑞康, 孙建孟, 刘行军, 文晓峰. 低阻页岩电阻率主控因素研究[J]. 物探与化探, 2022, 46(1): 150-159.
CUI Rui-Kang, SUN Jian-Meng, LIU Xing-Jun, WEN Xiao-Feng. Major controlling factors of low-resistance shale gas reservoirs. Geophysical and Geochemical Exploration, 2022, 46(1): 150-159.
Sun J M, Xiong Z, Luo H, et al. Mechanism analysis and logging evaluation of low resistivity in lower Paleozoic shale gas reservoirs of Yangtze region[J]. Journal of China University of Petroleum:Edition of Natural Science, 2018,42(5):47-56.
Wang C J. Study on the formation mechanism of low resistivity of continental shale gas reservoir in Yanchang area[C]. Xi’an Shiyou University, Shaanxi Petroleum Society. 2019 International Conference on Oil and Gas Exploration and Development. 2019: 642-643.
杨凯. 四川盆地海陆相页岩岩相特征及电学特征差异性研究[D]. 成都:成都理工大学, 2018.
Yang K. Study on the difference of lithofacies and electrical characteristics of Marine and terrestrial shale in Sichuan Basin[D]. Chengdu: Chengdu University of Technology, 2018.
Wang W B, Guo D K, Chen X F, et al. Genesis analysis and identification methods of Chang 6_ 1 low resistivity oil pays in Yanchang Formation in Wuqi area, Ordos Basin[J]. Petroleum Geology and Recovery Efficiency, 2017,24(2):38-45,89.
Zheng H, Li Y P, Xu J X, et al. Geological genetic mechanism and identification of low resistivity reservoir in Bohai sea area: a case study of LD—A Oilfield in Liaodong Bay[J]. Fault-Block Oil & Gas Field, 2018,25(1):22-28.
Luo X P, Su D X, Wang Z L, et al. Application of NMR logging in low-resistivity reservoir evaluation: A case study of Toutunhe Formation on the Eastern Fukang Slope, Junggar Basin[J]. Xinjiang Petroleum Geology, 2017,38(4):470-476.
黄涛. 页岩岩心复电阻率实验室测试与分析[D]. 成都:成都理工大学, 2016.
Huang T. Complex resistivity of shale core laboratory testing and analysis[D]. Chengdu: Chengdu University of Technology, 2016.
王香增. 陆相页岩气[M]. 北京: 石油工业出版社, 2014.
Wang X Z. Continental shale gas [M]. Beijing: Petroleum Industry Press, 2014.
Liu T L, Jiang Z X, Zhang K, et al. Method and apparatus for identifying graphitization degree of Marine shale [P]. CN107064230A, 2017-08-18.
Kethireddy N, Heidari Z, Chen H. Quantifying the Effect of Kerogen on Electrical Resistivity Measurements in Organic-Rich Source Rocks[C]//SPWLA 54th Annual Logging Symposium. Society of Petrophysicists and Well-Log Analysts, 2013.
Shao L Y, Liu L, Wen H J, et al. Characteristics and influencing factors of nanopores in the Middle Jurassic Shimengou Shale in Well YQ-1 of the Northern Qaidam Basin[J]. Earth Science Frontiers, 2016,23(1):164-173.
Li T T, Zhu R K, Bai B, et al. Characteristics and Research Significance of Fine Lacustrine Sedimentary Rock Laminations of Xiagou Formation in Qingxi Depression of Jiuquan Basin[J]. China Petroleum Exploration, 2015,20(1):38-47.
Shi Z S, Qiu Z, Dong D Z, et al. Laminae characteristics of gas-bearing shale fine-grained sediment of the Silurian Longmaxi Formation of Well Wuxi 2 in Sichuan Basin, SW China[J]. Petroleum Exploration and Development, 2018,45(2):339-348.