Porosity of gas shale: Is the NMR-based measurement reliable?

Abstract

Aiming at obtaining an accurate porosity of gas shale, various approaches are attempted. Therein, nuclear magnetic resonance (NMR), being treated as a kind of new-developed technique, possesses the representative significance. However, as a booming technique, the reliability of NMR-based porosity of shale is not exactly defined. Depending on NMR device, this work measured the porosity of shale experiencing different water soaking time, accordingly, judging the reliability of NMR-based porosity. Results indicate the NMR outcomes vary with the water soaking time, making a doubt about the objectivity of NMR-based porosity in reflecting the real shale porosity. Furthermore, some supplementary means were adopted to verify the water soaking-induced variation in the pore system of shale sample, which intensities the suspicion if the NMR-based porosity is reliable or not. To sum up, this work considers that the NMR-based porosity of shale is not reliable enough when water is used as the probe. Besides, this work also offers some suggestions on how to enhance the reliability of NMR-based porosity of shale sample. Basically, this work selects a fresh perspective to analyze the NMR approach in determining shale porosity, which is hopefully helpful in promoting the development of NMR technique in the shale-related field.