期刊
JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING
卷 196, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.petrol.2020.107631
关键词
pore evolution; pore size distribution; organic-matter pores; thermal maturation; lacustrine shale; Ordos Basin
资金
- State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Chengdu University of Technology) [PLC20190505]
- Unconventional Oil and Gas Geological Research from University Research Innovation Team of Sichuan Provincial Department of Education [14TD0008]
- One-year Visiting Scholar Research Fellowship from Earth Science Sub-project of Double-First Class University Project [10800-18Z0102]
- Young and Middle-aged Teacher Development Fund of Chengdu University of Technology
The study found that different types of pores undergo systematic evolution during the thermal maturation of shale, and the evolution of pore type and size is critically controlled by multiple diagenetic processes, including mechanical compaction, cementation, mineral dissolution, clay mineral transformation, and organic matter thermal maturation.
The study of pore network evolution is an important aspect of tight shale reservoir characterization. Pore spaces in shales consist of three major types: interparticle pores and intraparticle pores associated with mineral matrix and organic-matter pores. In this study, the evolution of pore networks for each pore type in lacustrine shales during thermal maturation was studied based on a suite of 19 Triassic Yanchang Formation shale samples from the Ordos Basin across a maturation gradient from immature to late mature (vitrinite reflectance (R-o) from 0.36 to 1.30%). The results show that different pore types follow systematic evolutions during thermal maturation and that the evolution of pore type and pore size is critically controlled by multiple diagenetic processes such as mechanical compaction, cementation, mineral dissolution, clay mineral transformation, and organic matter thermal maturation. Specifically, at immature and early mature stages (R-o < 0.55%), pores associated with mineral matrix are abundant and have moderate pore sizes. Interparticle pores exhibit preferential orientation along clay platelets. At the mature stage (0.55% < R-o < 1.15%), pores associated with mineral matrix have the smallest size, and interparticle pores become less common and show reduced preferential orientation because of mechanical compaction and cementation. Organic-matter pores start to develop at a maturity level of R-o 0.77% and higher. The total porosity and BET specific surface area show minimum values at R-o 1.12%, mainly because pre-existing matrix-related pores are destroyed by mechanical compaction and filled by migrated bitumen and liquid hydrocarbons, and then they increase when R-o exceeds 1.12%, which likely results from the development of secondary organic-matter nanopores due to the generation and expulsion of gaseous hydrocarbons. An increase in pore size of matrix-related pores at the late mature stage (1.15% < R-o < 1.30%) could be a result of dissolution by organic acid generated during organic matter thermal maturation.
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