双重低渗介质含启动压力梯度不定常渗流研究

A study on transient flow under threshold pressure gradient in dual-pore media with low permeability

建立了考虑启动压力梯度和动边界共同影响的双重低渗介质储层非达西不定常渗流模型,通过引入新定义的无量纲压力线性化压力扩散方程,采用Laplace变换结合Stehfest数值反演算法对模型进行解析求解,得到井壁压力分布和动边界传播规律。对低渗双重介质敏感参数进行了分析,结果表明:启动压力梯度对动边界传播、井壁压力及压力导数动态曲线有很大影响,启动压力梯度越大,动边界传播越慢、压力损失越大,并且井壁压力导数曲线在后期有上翘特征;不同弹性储容比和窜流系数下低渗双重介质井壁压力导数曲线区别于中高渗双重介质的特征在于其后期出现上翘。运用Duhamel褶积和有效井径模型建立了不稳定试井分析典型曲线图版。

A model of non-Darcy transient flow in dual-pore media with low permeability has been built under consideration of the comprehensive effects from threshold pressure gradient and moving boundary.By introducing a new-defined pressure diffusion equation linearized by dimensionless pressure,Laplace transform in combination with Stehfest numerical inversion algorithm is used to solve this model,by which the pressure distribution on wellbore wall and the moving boundary propagation can be known.Analyses of the sensitive parameters for dual-pore media with low permeability have indicated that the threshold pressure gradient has great influences on moving boundary propagation,wellbore-wall pressure and its dynamic derivative curve,and that the higher the threshold pressure gradient,the slower the moving boundary propagation and the larger the pressure drop,with an upwarp feature in the derivative curve during later flow.Under various elastic storativity ratios and interporosity flow coefficients,the difference of wellbore-wall pressure derivative curve in dual-pore media with low permeability from that in dual-pore media with middle-high permeability is indeed this upwarp feature.In addition,Duhamel convolution and effective wellbore diameter models are applied to establish typical curve charts for the analyses of pressure transient testing.