Investigation of Methane Desorption and Its Effect on the Gas Production Process from Shale: Experimental and Mathematical Study

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• 作者：Jinjie Wang ; Mingzhe Dong ; Zehao Yang ; Houjian Gong ; Yajun Li
• 刊名：Energy & Fuels
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：31
• 期：1
• 页码：205-216
• 全文大小：495K
• ISSN：1520-5029

文摘

A number of potential gas reserves are present in shale reservoirs around the world. The gas production process is more complex in shale reservoirs than in conventional reservoirs, mainly because of the ultralow permeability of the matrix, complex pore structure, and organic components that cause desorption. Long-term gas production comes from both free gas expansion and adsorbed gas desorption. In addition to the estimation of the gas content reserve in a reservoir, an accurate description of the effect of adsorbed gas on the dynamic gas production process is meaningful for predicting gas production from shale. Experimental and mathematical efforts have been undertaken to obtain an accurate description of the gas production process. This paper investigates desorption and diffusion, which are two of the key mechanisms in the shale matrix during gas production. The experimental results suggest that the gas production process from shale can be divided into two stages: free gas expansion from inorganic micropores in the early stage and the subsequent desorption–diffusion-dominated stage in the matrix. Furthermore, the effects of production pressure (equal to the external pressure), temperature, and particle diameter on the dynamic gas production process were examined based on the variable-volume volumetric method (VVM). Both higher external pressure and higher temperature lead to the lower contribution of desorbed gas to the total gas production. Moreover, the delayed adsorption diffusion model, which considers the dynamic gas desorption/adsorption, is presented to adequately represent the measured dynamic experimental data. The calculated gas production curves are in good agreement with experimental observations. Mathematical calculations of the production rate also suggest and confirm the two-stage process of gas production. This paper enables operators to develop a primary understanding of how gas desorption affects the performance of a shale gas well and provides insights into the analysis of the gas flow regime and more accurate forecasting for shale gas production.