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

Abstract

The presence and content of water will certainly affect the gas adsorption capacity of shale and the evaluation of shale gas content. In order to reasonably evaluate the gas adsorption capacity of shale under actual reservoir conditions, the effect of water on methane adsorption capacity needs to be investigated. Taking the Da’anzhai Member of the Lower Jurassic Ziliujing Formation in the northeastern Sichuan Basin, China as an example, this study attempts to reveal the effect of pre-adsorbed water on methane adsorption capacity in shale-gas systems by conducting methane adsorption experiments in two sequences, firstly at different temperatures under dry condition and secondly at different relative humidity levels under the same temperature. The results show that temperature and relative humidity (i.e., water saturation) are the main factors affecting the methane adsorption capacity of shale for a single sample. The key findings of this study include: 1) Methane adsorption capacity of shale first increases then decreases with depth, reaching a peak at about 1,600–2,400 m. 2) Lower relative humidity correlates to greater maximum methane adsorption capacity and greater depth to reach the maximum methane adsorption capacity. 3) 20% increase of relative humidity results in roughly 10% reduction of maximum methane adsorption capacity. As a conclusion, methane adsorption capacity of shale is predominately affected by water saturation, pore type and pore size of shale. This study could provide a theoretical basis for the establishment of a reasonable evaluation method for shale adsorbed gas content.

Pore Water and Its Multiple Controlling Effects on Natural Gas Enrichment of the Quaternary Shale in Qaidam Basin, China

“…This is because water molecules are larger in volume than methane molecules, and water molecules will occupy part of the pore space, limiting the entry of methane molecules into the pores. In addition, increased water saturation also leads to an increase in the wettability of the pore wall surface, which reduces the adsorption capacity of methane molecules on the pore wall surface [50]. Methane molecules and water molecules have the characteristics of competitive adsorption on quartz, clay minerals, and other components in shale.…”

Experimental investigations of CO2 adsorption behavior in shales: Implication for CO2 geological storage

“…The characteristic of CO 2 adsorption in shales are essential for the CO 2 -ESGR field application results and CO 2 geological storage safety. Isothermal adsorption measurement is the most commonly used method for providing CO 2 adsorption characteristics in shales (Wang et al, 2016;Chen et al, 2021;Liu D et al, 2022). The analysis models to study CO 2 adsorption properties include the classical statistical mechanics-based Freundlich model, monolayer adsorption-based Langmuir model, multilayer adsorption BET model, and micro-pore filling adsorption D-R model (Du et al, 2021;Liu J et al, 2021;Shi et al, 2022).…”