摘要
因页岩气开采过程中形成的复杂流动缝网系统,导致甲烷气体向浅层地下水迁移,从而引起地下水甲烷含量超标,引发的地下水污染问题是当前备受关注的环境问题之一.因页岩储层结构的复杂性与随机性,且非均质性较强,甲烷在页岩储层中的运移规律有待深入研究.甲烷在基岩中以扩散为主,在裂缝中以渗流为主,从流动建模的角度来看经典对流-扩散模型不能有效刻画甲烷气体的运移规律.针对强非均质性页岩储层结构特点,本文建立能够准确描述具有历史依赖性的运移过程的变时间分数阶导数模型,揭示甲烷在非均匀介质中的反常扩散特征,模拟甲烷的浓度穿透曲线,有效刻画甲烷运移规律.结果表明:变阶数α(t)能够表征甲烷运移过程的时间记忆性,刻画浓度穿透曲线具有的明显拖尾特征及停滞效应.本研究解决了传统整数阶方程无法准确描述的反常扩散现象,为预测双碳目标下的页岩气开采过程中的地下水污染风险提供一种理论指导.
CH_(4)transports to shallow groundwater due to the complex flow network system formed during shale gas extraction.The problem of groundwater pollution caused by excessive CH4 in groundwater is one of the current environmental issues of great concern.Due to the complexity and randomness of the shale reservoir structure and the strong non-homogeneity,the CH_(4)transport law in shale reservoirs needs to be studied in depth.CH_(4)diffusion dominates in matrix and seepage dominates in fractures.From the perspective of flow modeling,the classical convection-diffusion model cannot effectively describe the migration law of CH_(4).In view of the highly heterogeneous structural characteristics of shale reservoirs,a time variable fractional derivative model is established to accurately describe the historically dependent migration process.It can well reveal the anomalous diffusion characteristics of CH_(4)in heterogeneous media,simulate the concentration breakthrough curve,and effectively describe the migration law.The results show that the variable orderα(t)can characterize the temporal memory of methane migration,and describe the obvious tailing and stagnation effect of concentration breakthrough curve.This study addresses the anomalous diffusion phenomenon that cannot be accurately described by traditional integer order equations and provides a theoretical guidance for predicting the groundwater pollution risk in the shale gas exploitation process under the double carbon target.
作者
常爱莲
黄乐
张郡铄
姜天奇
邵明鲁
CHANG Ailian;HUANG Le;ZHANG Junshuo;JIANG Tianqi;SHAO Minglu(School of Mechanical Engineering and Rail Transit,School of Intelligent Manufacturing,Changzhou University,Changzhou 213164,Jiangsu,China;Jiangsu Province Engineering Research Center of High-Level Energy and Power Equipment,Changzhou University,Changzhou 213164,Jiangsu,China;School of Petroleum and Natural Gas Engineering,School of Energy,Changzhou University,Changzhou 213164,Jiangsu,China)
出处
《力学季刊》
CAS
CSCD
北大核心
2024年第3期825-833,共9页
Chinese Quarterly of Mechanics
基金
国家自然科学基金(12302509)
江苏省自然科学青年基金(BK20220615)
江苏省高等学校基础科学面上项目(22KJB130001)
常州大学大学生创新创业训练计划(202310292240B)。
关键词
变分数阶导数模型
页岩气储层
甲烷
数值模拟
反常扩散
variable fractional derivative model
shale gas reservoirs
CH_(4)
numerical simulation
anomalous diffusion
