Quantitative Characterization of Inorganic Pores in Sinian Doushantou Dolomitic Shale Based on FIB-SEM in Western Hubei Province, China.

Abstract

Unlike traditional shale gas reservoirs, where organic matter pores dominate, inorganic pores are the primary reservoir space in the Sinian (Ediacaran) high-maturity Doushantou dolomitic shale in western Hubei Province, China. The inorganic pore characteristics of Doushantuo shale and its influence on shale gas aggregation were investigated by examining the TOC content, thermal maturity, mineralogical composition, and field-emission scanning electron microscopy (SEM) and focused ion beam scanning electron microscopy (FIB-SEM) of drill cores. The results show that the shale mineral composition in the study area is primarily dolomite and plate-shaped interparticle-intercrystalline pores associated with dolomite are widespread inorganic pores in dolomitic shale. Interparticle-intercrystalline pores account for 75% of the total pores, with a pore size distribution mainly between 50 and 300 nm, as extracted from the 3D pore network model (PNM). Compared with organic pores, interparticle-intercrystalline pores provide greater space for gas storage and have a strong coupling relationship with the hydrocarbon generation and evolution of organic matter. Therefore, the inorganic pores in the Doushantuo Formation play a vital role in the enrichment and accumulation of shale gas. This study aims to establish a scientific basis for understanding the enrichment mechanism of shale gas in Doushantuo dolomitic shale and other inorganic pore-dominated shales in southern China.