Adsorbed and free methane not only occur in the shale gas enrichment and accumulation process but also in the decompression−desorption−diffusion−seepage process during shale gas production. In this work, we elaborate the optimization and combination of low-field nuclear magnetic resonance (NMR) and isothermal adsorption experiments on shale samples to quantitatively identify multiphase methane in the adsorption−desorption process. NMR signatures from individual matrix components, which comprise shale, are investigated to gather data to better estimate its petrophysical parameters. The T 2 signal is the highest for montmorillonite, followed by Illite, and the T 2 signals of bitumen and chlorite are relatively similar. Kaolinite and kerogen have the lowest NMR signals because they do not contain crystal water. The 1 H signal of kerogen mainly stems from its methyl, methylene, carboxyl, and hydroxyl groups. The types of clay minerals will profoundly affect the wettability of pores, thereby further influencing the relaxation mechanism of shale. By analyzing the T 2 spectrum of the injected and produced CH 4 from the shale sample, we revisit the possible mechanisms that could arise in shale and examine the adsorption−desorption process based on the tested sample. The results reveal that methane is present in three different states in shale, among which T 2 (0.1−1 ms) indicates the adsorbed methane and T 2 (3−20 ms) indicates the free methane in pores, along with T 2 (80−110 ms), indicating the free methane in fractures. The practical exploitation process of shale gas exhibits notable pressure and desorption hysteresis characteristics. The T 2 spectrum of methane in the different states in the adsorption−desorption process can be better simulated with a mathematical model. The ultimate goal of this study is to develop a holistic multidisciplinary methodology to assess multiphase methane in the adsorption−desorption process of shale gas.

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The identification of shale porosity is of fundamental significance for evaluating reservoir quality in gas-shale plays, where the various methods rarely discern the adsorbed porosity and free porosity. Comprehensive measuring campaigns, as well as reliable isothermal adsorption data sets, show that the adsorbed porosity and free porosity can be validly identified by using 1 H NMR (nuclear magnetic resonance) and isothermal adsorption experiments. Here, we show that the T 2 distribution of individual T 2 peaks in "CH 4 -saturated shale", adsorbed film density, and Boyle's law can be applied to calculate the adsorbed porosity, free porosity, and total porosity. We estimated the adsorbed porosity and found that NMR measurements have remarkable capacity dynamics for characterizing CH 4 saturation in shale samples. Furthermore, the adsorbed film density can be optimized by isothermal adsorption data. The novel method established in this paper directly computes the adsorption film density according to the physical characteristics of the measured isotherm adsorption. The purpose of this investigation is to unravel some of the mysteries surrounding the assessment of the adsorbed and free porosities of unconventional hydrocarbon development. The integrated analysis of these measurements helps us to better understand the adsorbed porosity, free porosity, and total porosity of samples from conventional and unconventional shale plays.