Journal
JOURNAL OF ASIAN EARTH SCIENCES
Volume 193, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jseaes.2020.104271
Keywords
Shale gas; Lithofacies; Organic-rich shales; Pore structure; Sichuan Basin
Categories
Funding
- National Natural Science Foundation of China [41690134, 41702155, 41821002, 41690131]
- National Science AMP
- Technology Specific Project [2016ZX05034002-003]
- Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) [CUGQYZX1712]
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Shales from Ordovician Wufeng and Silurian Longmaxi groups in the Sichuan Basin were analyzed by using the field emission-scanning electron microscopy, helium pycnometry, and low-pressure gas adsorption experiments. There are mainly three lithofacies in the studied shale reservoirs: clay-rich siliceous shale (S-3), argillaceous/ siliceous mixed shale (M-2), and silica-rich argillaceous shale lithofacies (CM-1). The organic-rich S-3 shales have the highest porosity (averaging 5.4%), the largest pore volume (averaging 0.024 mL/g), and the highest specific surface area (averaging 21.6m(2)/g). Organic matter (OM) pores contribute 62.6% to the porosity of S-3 shales. M-2 shales have the moderate pore structure with porosity averaging 4.3%, pore volume averaging 0.019 mL/g, and specific surface area averaging 16.7m(2)/g. Organic matter and clay minerals contribute 49.5% and 36.8% to the porosity of M-2 shales, respectively. The CM-1 shales have the lowest porosity (averaging 4.1%), the smallest pore volume (averaging 0.017 mL/g), and the lowest specific surface area (averaging 15.6m2/g). The organic-lean CM-1 shales are dominated by clay mineral pores. Clay minerals contribute 56% to the porosity of CM-1 shales. OM pores are well developed in the S-3 shale lithofacies, while most of OM pores are destroyed or compacted in CM-1 shale lithofacies. The effect of compaction on porosity of CM-1 shales is stronger than that of M-2 and S3 shales because of the highest clay minerals content and the lowest siliceous minerals content. Considering the pore spaces and hydraulic fracturing operation, the S-3 shales is more suitable to shale gas exploration than M-2 and CM-1 shales. Certainly, the M-2 and CM-1 shales also have certain amounts of hydrocarbon storage capacity, and could be considered as the candidate targets for shale gas exploitation.
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