Logging evaluation method of geological-engineering sweet spot parameters for deep shale gas based on petrophysical facies: A case study of the Wufeng-Longmaxi Formation in LZ block of Sichuan Basin
ZHANG Shaolong1,2, YAN Jianping2,3, GUO Wei4, ZHONG Guanghai5, HUANG Yi6, LI Zhipeng7
1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China; 2. School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China; 3. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China; 4. Research Institute of Exploration and Development, PetroChina, Beijing 100083, China; 5. Shale Gas Research Institute, PetroChina Southwest Oil & Gas Field Company, Chengdu, Sichuan 610051, China; 6. Southwest Branch, CNPC Logging Company Limited, Chongqing 400021, China; 7. Institute of Exploration and Development, Shengli Oil Field, SINOPEC, Dongying, Shandong 257015, China
Abstract:Marine deep shale gas (with a burial depth of greater than 3500 m) reservoirs are affected by deposition, diagenesis, tectonism, biological processes, and other factors, and the formation mechanism of their sweet spots is very complicated. As a result, conventional divisions of sedimentary microfacies and lithofacies are difficult to carefully describe their strong heterogeneity,which further increases the difficulty in the fine logging evaluation of geological-engineering sweet spot parameters.Therefore, this paper takes the shale gas reservoir in LZ block in the south of Sichuan Basin as an example and analyzes the connotation, factors,and core indicators of petrophysical facies of marine shales.Then,with rock thin sections, whole-rock diffraction,total organic carbon (TOC) data,and logging response characteristics,the paper obtains three types of petrophysical facies(Ⅰ,Ⅱ,and Ⅲ) and further divides them into six subcategories (Ⅰ1,Ⅰ2,Ⅰ3,Ⅱ1,Ⅱ2,and Ⅲ),so as to explore their characteristics and dominant facies. In addition, the random forest algorithm is used to develop a method for identifying petrophysical facies in continuous logging profiles and establish a fine logging calculation model of geological-engineering sweet spot parameters based on different types of petrophysical facies.The results indicate that:1Ⅰ1 deve-loped at the top of Wufeng Formation and the first and third sub-members of the first member of Longmaxi Formation, namely,l11-l13,and Ⅱ1 developed at the fourth sub-member of the first member of Longmaxi Formation ①14 are favorable facies, and they usually feature high TOC, large porosity, rich gas content, and strong brittleness.②The logging identification results of petrophysical facies based on the random forest classification algorithm are better than that of conventional logging crossplot identification methods, and the accuracy rate is above 90%.③The calculation accuracy of geological-engineering sweet spot parameters based on a random forest regression model with classified petrophysical facies is high, and the correlation coefficient of calculated and measured parameters all exceeds 0.9. The proposed method effectively solves the difficulty in obtaining geological-engineering sweet spot parameters of marine deep shale gas reservoirs, realizes the accurate calculation of well profiles of sweet spots, and lays a foundation for selecting favorable layers and optimal targets of horizontal wells and estimating resource amounts.
张少龙, 闫建平, 郭伟, 钟光海, 黄毅, 李志鹏. 基于岩石物理相的深层页岩气地质—工程甜点参数测井评价方法——以四川盆地LZ区块五峰组—龙马溪组为例[J]. 石油地球物理勘探, 2023, 58(1): 214-227.
ZHANG Shaolong, YAN Jianping, GUO Wei, ZHONG Guanghai, HUANG Yi, LI Zhipeng. Logging evaluation method of geological-engineering sweet spot parameters for deep shale gas based on petrophysical facies: A case study of the Wufeng-Longmaxi Formation in LZ block of Sichuan Basin. Oil Geophysical Prospecting, 2023, 58(1): 214-227.
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