Water Uptake Behavior and Influence Factors of Longmaxi Shale: Implications from Water Physisorption and Imbibition Measurements
Changhai Hou, Bingsong Yu, Li Liu, Yanran Xu, Yifan Zhang, Linhao Zhang, Jiale Zhao, Xiang Zhao, Quanwen Zuo, Mengdi Sun
Abstract
Water uptake behavior can greatly impact gas migration in shale reservoirs. In this work, we combined water vapor sorption (including adsorption and desorption) and spontaneous imbibition (SI) to systematically investigate the water uptake behavior and influence factors of samples from the Longmaxi shales in the northern Guizhou Province, China. The model of fracturing fluid loss was divided into two stages: (i) SI stage—fracturing fluid is drawn into fractures by capillary forces, then into large pores, and finally into small pores; (ii) water vapor adsorption (WVA) stage—here an increase in relative humidity (RH) causes water vapor molecules to be initially absorbed into hydrophilic pores via monolayer adsorption, followed by multilayer adsorption, and finally cluster formation and/or capillary condensation when both hydrophilic and hydrophobic pores are filled. The results also show that pore size distributions derived from WVA exhibit unimodal distributions, which are generally greater than that obtained from N2 adsorption because of clay swelling. The illite–smectite mixed-layer mineral is the main WVA site within clay minerals. Moreover, the controlling factors of WVA vary with RH. At low RHs, clay is the main controlling factor for WVA by providing strong intermolecular bonding for monolayer vapor molecules, while at high RHs, porosity and pore volume become the main controlling factors by providing more space for capillary condensation. Specifically, the pores with sizes of around 3 nm mainly contribute to WVA under high RHs. This work should therefore improve the understanding of fracturing fluid loss process and influence factors, contributing to the optimization of shale gas production.