Origin and Evolution of Clay Mineral and Its Impact on Shale Oil Enrichment: Insight from Qingshankou Formation, Songliao Basin, NE China.

Abstract

Shale oil exploration in China's clay-rich shale formations has gained attention, but the origin and impact of clay minerals on reservoirs remain unclear. This study examines the Qingshankou Formation in the Songliao Basin using Nanomin analysis, X-ray diffraction, X-ray fluorescence analysis, TOC analysis, rock pyrolysis, and FE-SEM to investigate the origin, the evolution, and the pore structures of clay mineral. Illite and I/S mixed layers dominate the matrix, while compaction disrupts their authigenic structures. Illite and I/S mixed layers primarily originate from detrital deposition and transformation of smectite. Chlorite is mostly authigenic and increases with thermal maturity. Illite and I/S mixed layers form elongated intergranular pores and microfractures, which significantly contribute to pore space, with their aligned axes pores playing a key role in microfracture formation. Authigenic chlorite primarily fills pores, while detrital chlorite exhibits discrete boundaries and alignment within the matrix. In comparison, authigenic chlorite pores are larger and more significant for reservoir porosity than detrital chlorite pores. Detrital clay mineral deposition promotes organic matter enrichment, while feldspar and quartz detritus deposition hinder it. These findings enhance the understanding of clay mineral evolution and the mechanisms of continental shale oil reservoir formation and organic matter enrichment.