页岩气储层岩石水吸附-扩散实验和数值模拟

xinmeng

页岩气储层岩石水吸附-扩散实验和数值模拟

Advances in Geo-Energy Research, 2019, 3(2): 165-174

原文网址: https://www.yandy-ager.com/index.php/ager/article/view/116

        尽管深层水平钻井和水力压裂在非常规页岩气藏中大幅度增产获得了成功，仍需要深入理解与其基本传输过程相关的不确定性，以便提高采收率和减少环境影响。在水力压裂过程中，大量的水基压裂液被注入页岩气藏，大部分水滞留无法回收影响了天然气生产。

       近日，中国科学院力学研究所沈伟军副研究员、中国石油勘探开发研究院李熙喆教授和美国劳伦斯伯克利国家实验室Abdullah Cihan研究员等人对四川盆地龙马溪组页岩开展了页岩水吸附-扩散实验研究。在实验基础上，他们建立了基于Maxwell-Stefan扩散和Guggenheim-Anderson-de Boer (GAB)等温吸附的计算模型，进一步分析了页岩水吸附-扩散过程。研究表明：页岩的水吸附等温线为Ⅱ型曲线，包括单层吸附、多层吸附和毛细管凝聚，GAB模型可用于较好地描述页岩的水吸附过程。随着相对压力的增大，页岩的水吸附量增加，有机碳的含量和温度增强了页岩的水吸附。水力压裂过程中毛细管压力可达到几百MPa数量级，从而造成大量的压裂液滞留在页岩储层中。此外，页岩的水吸附扩散模拟结果小于实验值，进一步表明页岩水吸附过程中出现了毛细冷凝。

Experimental and numerical simulation of water adsorption and diffusion in shale gas reservoir rocks

Weijun Shen, Xizhe Li, Abdullah Cihan, Xiaobing Lu, Xiaohua Liu

(Published: 2019-03-08)

CorrespondingAuthor and Email: Weijun Shen, wjshen763@imech.ac.cn; ORCID: https://orcid.org/0000-0003-3658-8670

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Citation: Shen, W., Li, X., Cihan, A., Lu, X., Liu, X. Experimental and numerical simulation of water adsorption and diffusion in shale gas reservoir rocks. Advances in Geo-Energy Research, 2019, 3(2): 165-174, doi: 10.26804/ager.2019.02.06.

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ArticleType: Original article

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Abstract：

      Despite the success of deep horizontal drilling and hydraulic fracturing in yielding large production increases from unconventional shale gas reservoirs, uncertainties associated with basic transport processes require understanding in order to improve efficiency and minimize environmental impacts. The hydraulic fracturing process introduces large volumes of water into shale gas reservoirs, most of which remains unrecoverable and interferes with gas production. In this study, the water adsorption and diffusion measurements of the Longmaxi Formation shale were conducted at 30 ℃ and 50 ℃ for relative humidities from 11.1% to 97.0%. Based on the experiment, a computational model based on the Maxwell- Stefan diffusion equation was constructed to analyze water adsorption and diffusion in shale rocks, and the Guggenheim-Anderson-de Boer (GAB) isotherm for gas adsorption was included in the model. The results show that water adsorption isotherms of shales belong to type II curve, including the monolayer, multilayer adsorption and capillary condensation, and the GAB model can be used to describe the water adsorption process in shale rocks. With the increasing of relative pressure, the water adsorption of shale increases, and the organic carbon content and temperature strengthen the water adsorption in shale. The capillary pressure can reach the order of several hundreds of MPa after the hydraulic fracturing process, and it results in a large amount of fracturing fluid retained in shale gas reservoirs. Furthermore, the simulation of water adsorption and diffusion in shale rocks is less than the experimental value, which further indicates that capillary condensation occurs in shale rocks.

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Keywords: Effective thermal conductivity, porous media, rough surfaces, fractal.