基于物质平衡修正的页岩气藏压裂水平井产量递减分析方法

基于压裂水平井非结构PEBI网格,引入尘气模型建立了综合考虑页岩气藏吸附/解吸、扩散和达西流的运移数学模型,结合控制体有限差分法和全隐式法推导了页岩气藏无限导流压裂水平井产量递减数学模型,并考虑了页岩吸附/解吸作用修正Blasingame现代产量递减分析方法中的物质平衡拟时间,将该方法扩展到页岩气藏,计算获得了页岩气藏无限导流压裂水平井Blasingame产量递减典型曲线。结果表明:与物质平衡修正后的产量递减曲线相比,修正前的页岩气藏无限导流压裂水平井产量递减曲线值偏小,并且边界拟稳定流出现的时间更早,计算出的单井控制储量偏小;页岩气藏无限导流压裂水平井Blasingame产量递减典型曲线可划分为早期裂缝线性流、早期径向流、复合线性流以及拟稳定流4个流动阶段;页岩吸附/解吸作用对产量递减典型曲线有显著影响,其中Langmuir压力对其影响是非线性的,而Langmuir体积对其影响为线性的。

Production decline analysis method of fractured horizontal well in shale gas reservoirs based on modifying material balance

Based on the non-structural PEBI grid of fractured horizontal well, dusty-gas model is introduced to establish the mathematical model of migration in comprehensive consideration of adsorption/desorption, diffusion and Darcy flow in shale gas reservoirs. On this basis, using both control volume finite difference method and fully implicit method, the production decline mathematical model is derived for the infinitely conductive fractured horizontal well in shale gas reservoirs. Furthermore, shale adsorption/desorption effect is considered to modify material balance pseudotime in the Blasingame modern production decline analysis method. This method is extended to shale gas reservoirs, by which the Blasingame typical production decline curves of infinitely conductive fractured horizontal well are calculated and obtained. The results show that compared with the production decline curves after the modification of material balance, the infinitely conductive fractured horizontal well has smaller production decline curve values prior to modification; the boundary quasi-steady flow appears earlier; the single-well control reserve is smaller. The Blasingame typical production decline curves of infinitely conductive fractured horizontal well are divided into four flow stages, i.e., early fissure linear flow, early radial flow, composite linear flow and pseudo-radial flow. The shale adsorption/desorption has significant influences on the typical production decline curves, such as Langmuir pressure with non-linear effect while Langmuir volume with linear effect.