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

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 NMRbased 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. (c) 2022 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Automated summary

This study compares the results of nuclear magnetic resonance (NMR) measurements on shale samples with different water soaking times, revealing a correlation between NMR porosity and soaking time, which raises doubts about the objectivity of NMR-based porosity in reflecting the actual shale porosity. Supplementary methods were used to verify the changes in the pore system of shale samples induced by water soaking. The study concludes that NMR-based porosity of shale is not reliable enough when water is used as the probe and suggests ways to enhance its reliability.