考虑非达西渗流的复合页岩气藏试井模型

Well testing model for composite shale gas reservoir considering non-darcy percolation

对于缝网改造的近井地带出现的非达西效应,在综合考虑页岩气解吸、扩散、非达西渗流(内区)和达西渗流(外区)基础上,建立多重机制作用下的复合页岩气藏不稳定试井模型,利用Laplace变换与分数阶虚宗量贝塞尔函数等方法对模型进行求解,利用Stehfest数值反演编程绘制井底压力动态曲线,对渗流指数、内区半径、内外区流度比、储容比、扩散系数、Langmuir吸附体积等参数进行敏感性分析。结果表明:流体在储层中的渗流可以划分为纯井筒储集影响阶段、过渡阶段、内区径向流阶段、内区径向流向外区径向流的过渡阶段、外区径向流阶段5个阶段。渗流指数越大,过渡段和内区径向流段压力及压力导数曲线位置越低;内区半径越大,内区非达西渗流段持续时间越长;内外区流度比越大,外区径向流段压力导数曲线抬升幅度越大;储容比越大,内外区过渡段后期出现的小"驼峰"的峰值越大;扩散系数越大,外区径向流段压力导数曲线位置越低;Langmuir吸附体积越大,内外区过渡段后期出现的小"驼峰"位置越低。该结果可应用于页岩气井的试井解释。

Based on the non-Darcy effect of near-wellbore region caused by hydraulic fracturing,with comprehensive consideration of desorption,diffusion,non-Darcy flow(inner region)and Darcy flow(outer region)of shale gas,well test model of composite shale gas reservoir is built and solved by using Laplace transformation and fractional-order imaginary-measure Bessel function.The dynamic pressure curve of bottom hole pressure is drawn by using Stehfest numerical inversion programming.Based on curve characteristics and transformation mechanism,five flow regimes can be identified which includes wellbore storage period,transition flow period,radial flow period in the inner region,transition flow period between two regions,and radial flow period in the outer region.The influence of relevant parameters such as seepage index,radius of inner region,mobility ratio of inner and outer region,storativity ratio,diffusion coefficient and Langmuir volume were analyzed.The larger the seepage index,the lower pressure and derivative curves are in the transition period and inner-region radial flow period.The larger inner-region radius,the longer duration is in the non-darcy flow period.The larger mobility ratio,the higher derivative curves is in the outer-region radial flow period.The larger storage ability ratio,the higher hump is in the later transition period from inner-region radial flow to outer region radial flow.The larger the diffusion coefficient,the lower derivative curve is in the outer-region radial flow period.The lager Langmuir adsorption volume,the lower hump is in the later transition period from inner-region radial flow to outer region radial flow.A new model is built in this paper for well test analysis of shale gas wells,and the model can be used for well test interpretation to obtain some important parameters of gas reservoir and gas well.