真三轴应力条件下二氧化碳致裂增渗煤层及驱替瓦斯机理研究

In this project we intend to use anisotropic coal and rock as the research object. Based on the self-developed multi-functional fluid-solid coupling true triaxial stress test system and multi-physical coupling coal and gas simultaneous extraction large-scale test system, we plan to combine laboratory research, theoretical analysis, and numerical simulation and field experiments together to carry out this project. We will investigate the experimental study on fracturing coal seam to enhance permeability with carbon dioxide and displacing in coal seam under true triaxial stress conditions with different stress level, injection rates, and temperature. Thus we could illustrate the correlations between the true triaxial stress, anisotropy of coal and the process of fracturing coal seam to enhance permeability and displacing gas. We could obtain cracking pressure threshold, crack growth and morphology and other key parameters in the process of fracturing coal seam with carbon dioxide. We would establish a seepage model of displacing gas in coal seams with carbon dioxide considering mass exchange rate under temperature-fluid-solid coupled true triaxial stress conditions. Finally we would reveal the Mechanism of fracturing coal seam to enhance permeability with carbon dioxide and displacing gas under true triaxial stress conditions. Combining with the field conditions, we plan to carry out the field test on fracturing coal seam with carbon dioxide and displacing gas to identify its influence scope and real effect. The research results can provide theoretical and technical basis for utilizing carbon dioxide to fracture coal seam to enhance permeability and displace gas, which is of important theoretical and practical significance for the prevention and control of coal and gas simultaneous extraction and gas dynamic disasters in deep coal mining.

本项目拟以各向异性煤岩为研究对象，利用自主研制的多功能真三轴流固耦合试验系统和多场耦合煤与瓦斯共采大型模拟试验系统，采用实验室研究、理论分析、数值模拟和现场试验相结合的方法，开展真三轴应力条件下不同应力水平、不同注入速率和不同温度条件下的二氧化碳致裂增渗煤层与驱替置换煤岩中瓦斯试验研究；阐明真三轴应力、煤体各向异性与二氧化碳致裂增渗煤层及驱替瓦斯的相互关系；获得二氧化碳致裂增渗煤层启裂压力、裂缝扩展规律和形态等关键参数；建立考虑物质交换速率的真三轴热流固耦合条件下二氧化碳驱替煤层瓦斯多孔渗流模型；揭示真三轴应力条件下二氧化碳致裂增渗煤层及驱替瓦斯机理；结合现场实际，进行二氧化碳致裂增渗煤层及驱替瓦斯的试验研究，确定其影响范围与效果。研究成果可为利用二氧化碳致裂增渗煤层及驱替瓦斯提供理论与技术基础，对实现深部煤与瓦斯共采及瓦斯动力灾害的防治具有重要的理论和实际意义。

二氧化碳可以作为一种流体介质改造增透煤层，高压二氧化碳进入煤层后可驱替煤层中的瓦斯，增加煤层瓦斯的抽采效率。研究真三轴应力条件下二氧化碳致裂煤层的裂缝扩展特征以其驱替瓦斯的机理对利用二氧化碳增加煤层瓦斯抽采效率，实现煤与瓦斯共采具有非常重要的意义。本研究利用自主研制的多功能真三轴流固耦合试验系统，开展了真三轴应力条件下二氧化碳致裂增渗煤岩试验研究，分析了二氧化碳致裂煤层的破坏特征及裂缝扩展规律，揭示了多因素影响下二氧化碳致裂煤层的裂缝扩展规律。建立了二氧化碳致裂煤层FDEM数值模型，研究了煤层非均质性和粗糙裂缝网络对流体致裂煤层的影响规律。评价了流体致裂对不同类型储层的致裂效果，得到了影响致裂后含裂纹煤体渗透率的关键因素，建立了考虑裂隙结构的真三轴渗透率模型，对致裂后裂隙煤体渗透率的各向异性进行了分析。开展了二氧化碳驱替煤岩芯甲烷的物理实验，研究了煤层中多组分气体的运移规律。进行了现场二氧化碳致裂煤层试验，提出了气液两相联合致裂增透煤层技术，研究了该技术在大尺度现场煤层致裂增透的效果。四年以来，项目组出版专著1部，发表学术论文23篇，其中：SCI论文22篇，EI论文1篇。项目执行期间新申请国家发明专利20项，其中已获得授权国家发明专利14项。项目相关研究成果获得重庆市科技进步一等奖1项。项目组已培养出站博士后1人、培养博士生5人、硕士生1人。项目成员1人入选中国科协青年人才托举工程，1人获“绿色矿山青年科技奖”，3人获得省部级“优秀博士学位论文奖励”。