Abstract:

Chang 7 and Chang 9 shales are the main reservoir for shale gas enrichment in the Yanchang Formation of Ordos Basin. The heterogeneity of the macro framework, geochemical parameters, microscopic pore structure and mechanical parameters was analyzed on the basis of the core analytical data and logging interpretation results of lacustrine shale. The results show that the density and frequency of siliceous lamina are high and the heterogeneity is strong. The siliceous lamina can effectively improve the property of shale, and provide favorable space for free gas enrichment and migration. Shale section with stronger heterogeneity has better physical properties for the free gas seepage and enrichment. There are more siliceous lamina developed in the shale section with weak heterogeneity where the physical properties are poor. The stranded hydrocarbon content is high. There is no hydrocarbon migration and hydrocarbon expulsion is difficult, so adsorbed gas gets more and more, and it is easy to be enriched. Therefore, the lacustrine shale gas enrichment mechanism is controlled by its heterogeneity. Strong heterogeneity shows high content of brittleness mineral, which is advantageous to the shale reservoir fracturing.

Key words: Lacustrine shale, Heterogeneity, Siliceous lamina, Organic geochemical characteristics, The pore distribution, Mechanical parameter