页岩气渗流中扩散影响机理分析

Mechanism of Diffusion Influences to the Shale Gas Flow

摘要: 基于页岩气藏复杂孔隙结构以及由基质系统向裂缝系统扩散现象，基于物理学理论，通过建立天然气单相流动模型，更加详细分析了页岩气从基质到裂缝的流动机理及扩散对页岩气流动的影响规律。分析表明：达西流动产生气体流量与压力梯度和渗透率成正比；高压条件下，渗流以达西流为主。在低压条件下，扩散产生气体流量所占比例较大；随着地层压力的增大，扩散作用明显减弱。扩散产生体积流量与渗透率大小无关。 Considering the complex pore structure and the diffusion from the matrix system to the fracture system, the single phase flow model of natural gas is established, and one new diffusion coefficient formula is given in the paper. Finally the flow mechanism from the matrix to the fracture and the shale gas flow characteristics affected by the diffusion are analyzed. The results show that: the Darcy flow rate is proportional to the pressure gradient and permeability; and the Darcy flow mainly influences the flow in high pressure, but the diffusion obviously influences the gas flow in low pressure, the proportion of the diffusion flow rate is larger. With the increase of formation pressure, the diffusion flow rate decreases significantly. The diffusion flow rate has nothing to do with the permeability.