oa Shale Gas Migration and Differential Enrichment in Organic-Rich Black Shale, Wufeng-Longmaxi Formation

Understanding the controls on gas migration and enrichment in the organic-rich black shale is critical for exploration. In this paper, the migration path and reservoir conditions of shale gas are analyzed, and the carbon isotope fractionation and organic matter pore differences are compared. Carbon isotopic variations (δ¹³C₁: -28.9‰ to -29.7‰; δ¹³C₂: -26.3‰ to -32.7‰) between wells indicating that micro-migration occurs when shale gas leans upward along the formation towards the structural high point. Image analysis by scanning electron microscopy shows that the pore size and morphology of organic matter in shale under different burial depth conditions vary. Shale in Wells buried deeper has a lower organic porosity (12.3% vs. 15.9%) and pore aspect ratio (∼1.5 vs. ∼2.5), reflecting that the differences in reservoir pore structure is caused by the differential effects of tectonic stress and overburden pressure. Therefore, successful exploration in deep to ultra-deep Wufeng - Longmaxi formation shales requires evaluating of not only favorable initial conditions (high TOC, high quartz, low clay) but also the critical impacts of burial depth, overburden pressure, tectonic deformation history (particularly uplift/compaction) on pore preservation, and the role of gas migration pathways.