煤层气井排采阶段储层渗透率动态变化特征

Dynamic variation characterization of reservoir permeability in drainage andextraction stage of CBM wells

煤储层渗透率是决定煤层气井产能的关键参数,以鄂尔多斯盆地延川南煤层气田2号煤储层为例,根据不同煤体结构煤储层性质,通过物质平衡方程确定煤层气井排采阶段煤储层压力,基于P&M渗透率模型分析煤层气井排采阶段储层渗透率动态变化特征。结果表明,原生结构煤储层、碎裂煤储层的杨氏模量大,煤基质收缩效应占主导地位,煤储层渗透率增加,压降径向传播距离长,排泄半径有效延伸,提高了煤层气井产能;原生结构煤储层单位压降渗透率增加量高于碎裂煤储层,具有更高的煤层气井产能;原生结构煤储层渗透率主要受产气量控制,碎裂煤储层渗透率受产气量、产水量共同控制;碎粒煤储层的杨氏模量小,有效应力效应占主导地位,煤储层渗透率降低,主要受产水量控制,压降径向传播距离短,排泄半径未有效延伸,抑制了煤层气井产能。该研究可为不同煤体结构煤储层的煤层井排采制度优化提供理论依据。

Coal reservoir permeability is a key parameter in determining the productivity of CBM wells.Taking the No.2 coal reservoir in Yanchuannan CBM field in Ordos Basin as an example,based on reservoir properties of different coal body structures,reservoir pressure in drainage and extraction stage was determined by material balance equation,and dynamic variation characterization of reservoir permeability in drainage and extraction stage was analyzed based on P&M permeability model.The results show that the Young modulus is large in primary structural coal reservoir and fragmented coal reservoir,the matrix shrinkage effect dominates,and coal reservoir permeability increases.The radial propagation distance of pressure drop is long,and the drainage radius is effectively extended,improving the productivity of CBM wells.The increase in permeability per unit pressure drop is higher in primary structural coal reservoir than that in fragmented coal reservoir,which is responsible for the higher productivity in primary structural coal reservoir.The permeability of primary structural coal reservoir is mainly controlled by gas production,while the permeability of fragmented coal reservoir is controlled by the combination of gas production and water production.The Young modulus of granulated coal reservoir is small,and the effective stress effect dominates.The permeability of coal reservoirs decreases,mainly controlled by water production.The radial propagation distance of pressure drop is short,and the discharge radius is not effectively extended,which suppresses the production capacity of coalbed methane wells.This study can provide a theoretical basis for optimizing the drainage system of CBM wells with different coal structures.