The pore size distribution and its relationship with shale gas capacity in organic-rich mudstone of Wufeng-Longmaxi Formations, Sichuan Basin, China

The pore size distribution for the 23 fresh outcrop shale samples collected from Shuanghe Town and Changning County, as well as the 14 core samples collected from the Qianqian 1 core well in southeast Chongqing, Sichuan Basin were investigated by means of low-pressure nitrogen adsorption. The main factors controlling pore development and gas accumulation in shales were discussed by integrating total organic carbon (TOC), mineralogy, and shale gas content. The results showed that open, slit-like, and parallel plate structure are major pore types that posses an average pore diameter of 3.76-8.53 nm; chiefly 2-30 nm for mesopores. The BET surface area and total pore volume are high in the Wufeng Formation and in the lower part of the Longmaxi Formation, and it's a bit lower in the upper part of the Longmaxi Formation. Consistent with the trends of TOC, that organic matter is the key controlling factor in the shale pore development. In addition, samples with higher content of clay minerals, but comparative TOC content have a larger specific surface area where clay mineral hosted pores are present. The Wufeng Formation and lower part of the Longmaxi Formation in the Sichuan Basin are preferred layers of shale reservoir fracturing due to high TOC, high rock brittleness, and high gas content.