Experimental and Modeling Study of Methane Adsorption onto Partially Saturated Shales

Abstract

Shale gas equilibrates through gas‐liquid‐solid interactions in reservoirs, but the role of moisture is rarely investigated. To determine how adsorbed water influences methane behavior, three carboniferous shale samples from the Qaidam Basin, China, were humidified at five levels up to a relative humidity of 89%, and their methane capacities at pressures up to 12 MPa were studied. The experimental results indicate that two water‐related mechanisms, “water blocking for methane transport” and “surface competition for gas‐solid interaction,” are primarily responsible for the methane capacity variations. A compositional comparison suggests that a high abundance of clay minerals plays a favorable role in methane migration by retaining water in interlayer pores. Based on the experimental data, an optimized method for calculating the adsorption amount based on an approximation of density distribution is proposed. The model predicts the average thickness of the adsorption layer and the adsorbed methane density distribution on the surface at a given pressure. The methane adsorption layer “thins” in a stepped pattern by up to 45% in the presence of water, with little further change observed at relative humidities greater than 75% in the studied samples.

Effect of Pre-Adsorbed Water on Methane Adsorption Capacity in Shale-Gas Systems

“…Merkel et al (2015) conducted the similar experiments and arrived at the same conclusions reported by Gasparik et al (2013). Wang et al (2018) investigated the influences of water on methane adsorption in three partially saturated shales. They found that a hint of water affects the methane adsorption less in samples with lower water contents and when the water content is increased, water clearly impedes methane adsorption.…”

“…Thus, methane adsorption experiments on moisture-equilibrated shale samples were produced. Some researchers carried out equilibrium moisture treatment on rock samples prior to the experiments (Ross and Bustin, 2009;Gasparik et al, 2013;Merkel et al, 2015;Wang et al, 2018;Tian et al, 2020). For example, Ross and Bustin (2009) studied the methane adsorption capacity of shale under moistureequilibrated condition and reported a 20-90% reduction compared to the value under dry condition.…”

Experimental Investigation of Spontaneous Water Imbibition into Methane-Saturated Shales under Different Methane Pressures

“…S i decreases with increasing methane pressure from 0.1 to 5 MPa. Previous studies on gas adsorption in shales have indicated that the adsorption capacity of shale rocks increases with increasing gas pressure − and that the adsorbed gas may account for more than 50% of the total gas storage . More methane molecules are adsorbed onto the pore surface of the sample with increasing methane pressure, resulting in the wettability of the pore surface changing from water-wet to oil-wet.…”

Effect of Surface Coverage of Water Molecules on Methane Adsorption on Muscovite and Pyrophyllite: Molecular Dynamics Study

“…Several factors contributing to the adsorption amount have been reported to date (for example, ref ). According to previous experimental studies, total organic carbon (TOC), − thermal maturity, and clay content ,, are positively correlated with the adsorption amount, while temperature − and moisture content ,− have a negative correlation with the adsorption amount.…”