Insights into Pore Types and Wettability of a Shale Gas Reservoir by Nuclear Magnetic Resonance: Longmaxi Formation, Sichuan Basin, China

Reservoir properties, such as pore types and wettability, are essential for shale gas reservoir evaluation. However, advanced nuclear magnetic resonance (NMR), which has been routinely used in petrophysical characterization of reservoirs, is barely used to estimate these properties in shale gas reservoirs. In this study, several sets of specially designed NMR measurements, together with total organic carbon (TOC), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and contact angle tests, are used to study the pore types and wettability of Longmaxi shale gas reservoir. Results show that the NMR transversal relaxation time (T2) spectrum can be used to characterize pore types and wettability of gas shale. Three identified T2 spectral peaks (0.01–0.4 ms, 0.4–15 ms, and >15 ms) separately correspond to organic pores, inorganic pores, and microfractures, which is consistent with the results of FE-SEM. The T2 spectra in as-received and water/oil-imbibition states qualitatively prove ...