Affiliation:
1. Shale Gas Research Institute, Petrochina Southwest Oil & Gas Field Company, Chengdu 610051, China
2. Sichuan Provincial Key Laboratory of Shale Gas Evaluation and Exploitation, Chengdu 610051, China
3. National Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing), Beijing 102249, China
4. Unconventional Petroleum Research Institute, China University of Petroleum (Beijing), Beijing 102249, China
Abstract
When the thermal maturity of the Longmaxi Formation in the southern Sichuan Basin is too high, the pore structure of shale becomes poor. Therefore, to investigate the effect of organic matter thermal maturity on shale pore structure, a study was conducted. Using the Longmaxi Formation shale in the southern Sichuan Basin as an example, the intrinsic relationship between shale porosity, pore structure parameters, organic matter laser Raman maturity, and organic matter graphitization degree was examined using X-ray photoelectron spectroscopy, particle helium porosity measurement, organic matter micro-laser Raman spectroscopy, and gas adsorption experiments. The results indicate that thermal maturity is the macroscopic manifestation of the graphitization degree of organic matter, and the correlation coefficient between the two is 0.85. A thermal maturity of 3.5% (with a corresponding organic matter graphitization degree of 17%) aligns with the highest values of shale porosity, pore volume, and pore-specific surface area across all pore size conditions. The evolution model of shale pore structure can be divided into two stages. The first stage is characterized by a thermal maturity between 2.0% and 3.5% (with a corresponding degree of graphitization of organic matter between 0% and 17%). During this stage, the number and connectivity of micro-macropores increase with increasing thermal maturity. The second stage is marked by a thermal maturity between 3.5% and 4.3% (with a corresponding degree of graphitization of organic matter between 17% and 47.32%). Basement faults are present, leading to abnormally high thermal maturity, poor preservation conditions, continuous generation of micropores, better connectivity, and a reduced number of pores. Medium macropores with good connectivity suffer from gas loss in the fracture network, leading to the collapse and disappearance of pores. The results mentioned in the statement have an important guiding role in the efficient exploration of shale gas in the Longmaxi Formation in the southern Sichuan Basin.
Funder
PetroChina Southwest Oil and Gas Field and China University of Petroleum-Beijing cooperative project
China Petroleum Natural Gas Group Co., Ltd. science and technology project ‘the new layer of favorable area optimization and exploration evaluation of key technology research’
research project of PetroChina Southwest Oil and Gas Field Company ‘Research on controlling factors of shale gas content difference in different tectonic belts in Luzhou-Yuxi area’
Subject
Geology,Geotechnical Engineering and Engineering Geology
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