Journal of Southwest Petroleum University(Science & Technology Edition) ›› 2024, Vol. 46 ›› Issue (2): 26-40.DOI: 10.11885/j.issn.1674-5086.2022.03.07.03

• GEOLOGY EXPLORATION • Previous Articles     Next Articles

Characteristics Analysis and Its Enlightenment of Shale of Low Resistivity in Wufeng Longmaxi Formation in Southern Sichuan Basin

HUANG Lisha1,2,3, YAN Jianping1,2,3, HU Xingzhong4, ZHENG Majia5, ZHONG Guanghai6   

  1. 1. School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China;
    2. National Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China;
    3. Natural Gas Geology Key Laboratory of Sichuan Province, Chengdu, Sichuan 610500, China;
    4. Management Center of Oil and Gas Exploration of Shengli Oilfield Company, SINOPEC, Dongying, Shandong 257000, China;
    5. Southwest Oil and Gas Field Company, PetroChina, Chengdu, Sichuan 610041, China;
    6. Research Institute of Shale Gas, Southwest Oil & Gas Field Company, PetroChina, Chengdu, Sichuan 610041, China
  • Received:2022-03-07 Published:2024-05-11

Abstract: There are low resistivity anomalies of shale gas reservoirs of Wufeng–Longmaxi Formation in Changning and Luzhou areas in southern Sichuan Basin, and the gas production of low resistivity wells in different areas varies greatly. Based on the data of physical properties, geochemistry, X-ray diffraction, thin section, gas content, production test and logging curve, the characteristics, genetic factors and their effects on gas content of different types of low resistivity are studied. The results indicate that the boundary between low resistivity well and normal resistivity well in shale gas reservoir is 15 $\Omega\cdot$m, and the resistivity range of sub low resistivity well is mainly 10$\sim$100 $\Omega\cdot$m. The curve shape characteristics of low resistivity well mainly include ”`continuous decline type" ($R_{\rm t}$<5 $\Omega\cdot$m) and ``first decrease and then increase type" (5$\sim$15 $\Omega\cdot$m). The origin factors of low resistivity mainly include graphitization caused by over mature organic matter, high water saturation, high pyrite content and high clay mineral content, which play a different role in the reduction of resistivity of different types; Low resistivity wells of “continuous decline" generally have poor gas content, but the “first decrease and then return to increase" generally have good gas content. The low resistivity shale at the bottom of the syncline structural belt and at a large buried depth is usually ”continuous decline", and the gas-bearing properties and test productivity are usually very low. It is a type that needs special attention in the risk exploration and development of low resistivity shale gas.

Key words: marine shale, low resistivity, southern Sichuan Basin, Wufeng Longmaxi Formation, organic matter graphitization

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