Nanoscale pore network evolution of Xiamaling marine shale during organic matter maturation by hydrous pyrolysis

A suite of hydrous pyrolysis experiments was conducted on low-maturity organic-rich shale samples (with a total organic carbon (TOC) content of 6.9 wt % and marine-derived type I kerogen) from Xiamaling Formation to investigate the pore network evolution across a maturation gradient. Scanning electron microscopy and low-pressure gas physisorption (CO2 and Ar) were applied to observe the pore morphology and quantify the pore structure. On the basis of the geochemical properties and yields of the pyrolysis products, organic matter (OM) thermal maturation includes the following four stages: bitumen generation (unheated to 350 °C), oil window (350–410 °C), oil cracking (410–480 °C), and wet gas cracking (480–550 °C). The nanoscale pore network evolution shows a good correspondence to stages of hydrocarbon generation. Overall, the total pore volume increased in the bitumen generation stage and the oil window, followed by a decrease in the oil cracking stage, but then again increased in the wet gas cracking sta...