Estimation of Porosity in Gas Shale Using ¹H NMR Measurement: Implications for Enhanced Shale Gas Recovery

Abstract

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.

Adsorption Models for Shale Gas: A Mini-Review

“…NMR method, as a nondestructive method to detect hydrogen-containing fluids in porous media, can characterize pore structures, analyze fluid behavior, and quantify the porosity and permeability in shale. − In the 1 H NMR system, the 1 H atoms jump to a higher energy level after absorbing the excitation energy of electromagnetic radiation, and transverse relaxation happens when the excitation stops, with the atomic magnetic moment perpendicular to the external magnetic field being zero. This process is related to the intermolecular and surface interactions in the fluid system, and the transverse relaxation spectrum amplitude of pure methane increases linearly with increasing pressure.…”

“…Jiang et al 108 used NMR to quantitatively classify the pore system of shale gas reservoir by combining high-speed centrifugation with cores drying gradually, as shown in Figure 7. Yang et al 105 studied the variation characteristics of adsorption film density based on isothermal adsorption experimental data of shale gas obtained by NMR. Kang et al 109 used NMR spectra combining with machine learning to predict the components and types of kerogen in shale.…”