Experimental study on the wettability of Longmaxi gas shale from Jiaoshiba gas field, Sichuan Basin, China

Wettability plays a significant role in exploration and exploitation of shale gas. However, the characterization and evaluation of the wettability of gas shale is a challenge due to the complexity and heterogeneity of components and pore structure. The objective of this paper is to characterize the wettability of gas shale and analyze its relationships with mineral composition, total organic carbon (TOC), and nuclear magnetic resonance (NMR) T2 spectrum by a series of parallel experiments of oil (water) contact angles, NMR, and rock composition analysis on core samples of Longmaxi Formation drilled from shale gas wells in Jiaoshiba gas field, Sichuan Basin, China. The study shows that: ① the gas shale is both water-wet and oil-wet and prone to be oil-wet with water contact angle (θw) ranging from 32° to 41.5°; ② the mineral composition together with TOC jointly affects θw; the quartz mineral and TOC have a negative effect on θw, whereas clay minerals have a positive influence on θw of gas shale; ③ the θw shows distinctive correlations to the characteristic of T2 spectrums; Recognized as a crucial parameter describing the characteristic of the T2 spectrum, the geometric mean of T2 spectrum (T2 g) is considered as a preferable model parameter to relate the θw and the T2 spectrum. Thus, novel equations for predicting contact angle by NMR are proposed.