煤层气藏煤与砂岩层间窜流模型构建及影响因素分析

Development of crossflow models between coal and sandstone in coalbed methane reservoirs and influence factors analysis

为了解决多煤层气藏开发中的层间干扰问题,达到能准确预测多煤层气井产能的目的,基于耦合理论,采用达西定律和煤岩动态渗透率模型,构建了煤层与砂岩层的气相和水相的窜流量模型,使用Matlab软件计算了不同条件下的窜流量,并对影响煤层与砂岩层间窜流强度的因素敏感性进行了理论研究。研究结果表明:煤岩原始渗透率、弹性模量以及煤岩与砂岩厚度对砂岩-煤岩层间窜流量的影响比较大,郎格缪尔压力和砂岩渗透率对层间窜流量的影响较小,而在煤岩低弹性模量(2 000MPa)条件下,窜流量随平均孔隙压力的增大而增大,在煤岩高弹性模量(>2 500 MPa)条件下,窜流量随平均孔隙压力的增大先减小后增大,同时当平均孔隙压力介于3~4 MPa时,砂岩层厚度对层间窜流的影响最小。

The interlayer interference in multi-layer coal seams during exploitation of coalbed methane affects the accuracy of gas production prediction. In order to investigate the interlayer interference between coal seams and sandstone seams,the authors built crossflow models of gas phase and water phase. The model is based on the coupling theory and applies the Darcy’s Law and dynamic permeability model of coal.The model was then implemented in Matlab,and cross flows under different conditions were computed. Factors that influence the interference intensity of coal seams and sandstone seams were analyzed. The simulation results show that permeability,elastic modulus of coal,and thickness of coal seams and sandstone seams have more significant influence on cross flow,while the Langmuir pressure of coal and permeability of sandstone have less significant influence on crossflow. On the condition of lower elastic modulus of coal( 2 000 MPa) cross flow between coal seams and sandstone seams increases with the increment of the average pore pressure. The crossflow between coal seams and sandstone seams decreases firstly and then increases as the average pore pressure increases when the elastic modulus of coal is higher than 2 500 MPa.The thickness of sandstone seams has little influence on the cross flow when the average pore pressure is between 3 MPa and 4 MPa.