考虑岩石变形效应的页岩气渗流模型

页岩气藏孔渗结构具有强烈的多尺度性,渗流机理复杂,纳米级基质孔隙克努森扩散效应、裂缝应力敏感效应,以及气体解吸收缩效应等多重机制对页岩气多尺度流动特征及页岩气产能模型都有一定影响。建立考虑纳米级基质孔隙克努森扩散流、裂缝应力敏感变形、基质解吸收缩效应协同作用的非线性渗流数学模型。应用全隐式有限差分和牛顿-拉普森迭代法进行数值求解。对相关因素分析得到,裂缝变形负相关于中前期气体产能;而基质解吸收缩正相关于中后期气体产能。实际生产过程中,应当结合不同生产阶段,合理调整页岩气生产条件;协同考虑裂缝变形和基质解吸收缩耦合效应,最终优化页岩气生产制度,提高页岩气采收率。

Seepage Character Research for Shale Gas Reservoirs with Consideration of Rock Deformation

The porous structure of shale possess intensive multi-scale, seepage mechanism is extremely complex. Knusen diffusion which occurs inside nano-scale matrix, stress sensitivity of fracture and matrix shrinkage induced by gas desorption have certain impacts on multi-scale flowing and productivity model.With comprehensive consideration of Knusen diffusion, stress sensitivity and matrix shrinkage induced desorption, this paper establishes the nonlinear seepage mathematical model of multi-fractured horizontal shale gas well ,and obtains the numerical solution via the numerical difference and Newton iterative methods.The relevant analysis demonstrates that fracture deformation has negative relationship with gas productivity at the early-intermediate stage; However, matrix shrinkage has positive relationship with gas productivity at the intermediate-late stage. During the process of real production, based on different production stage, justifying production condition, and comprehensively considering the effects of fracture deformation and matrix shrinkage, as a result, we can optimize the production and enhance gas recovery.