The Development of Open and Closed Pores and Their Controlling Factors in the Longmaxi Shale, Chongqing, China: Implications From <scp> N ₂ </scp> Adsorption and <scp>SAXS</scp> Experiments on Bulk and Kerogen Samples

ABSTRACT The Longmaxi Shale is the most productive stratum for shale gas in China. Although its pores have been investigated extensively, their openness and controlling factors remain poorly understood. This study integrates small‐angle x‐ray scattering (SAXS), low‐pressure N 2 adsorption (LPNA) and scanning electron microscopy (SEM) to quantitatively resolve open/closed pore characteristics (1–100 nm) in the bulk and kerogen samples of the Longmaxi shale in the Chongqing area, China, and to identify their geological controls. Results indicate that pore development is primarily governed by TOC, R o and clay mineral content. Closed pores exhibit a significantly high proportion within kerogen, are predominantly mesopores and constitute the main contributor to the total shale porosity. Compared with inorganic minerals, organic matter shows stronger compositional homogeneity, with minimal variability in pore size across samples. For the volume of open pores obtained from N 2 gas adsorption, organic pores contribute 2.8%–34.2% (average 9.58%) to total open pore volume, while inorganic pores account for more than 70%. However, SEM imaging reveals abundant organic pores, suggesting that a substantial proportion of these pores may be closed, with gases trapped in closed organic pores being non‐producible. Consequently, reliance on SEM evaluation alone may lead to significant overestimation of recoverable shale gas reserves, underscoring the critical importance of quantitative assessment of closed pores.