页岩气储层压裂水平井非线性渗流模型

Non-linear Porous Seepage Model of Multi-fractured Horizontal Well in Shale Gas Reservoir

水平井+体积压裂技术已经成为目前高效高速开发页岩气藏的主要技术手段。针对页岩储层存在的吸附扩散效应和应力敏感效应以及流体的滑脱效应和高速紊流效应,建立了水平井多级压裂复合渗流模型,并获得了其在Laplace空间的解析解;通过Stefest数值反演和Duhamel原理,得到了考虑井筒储集效应和表皮效应影响下的实空间无因次产量模型,从而绘制了无因次产能模型图版并进行了产能影响因素敏感性分析。根据实践应用结果显示,模型能够预测水平井产量并具有更高的预测精度。研究结果表明:页岩气藏压裂水平井产能可划分为三个渗流区域和五个流动阶段,前期由裂缝线性流占主导地位,产量高但递减速度快;中期由天然裂缝供气,是处于基质和裂缝供气的过渡阶段;后期由基质线性流占主导地位,产量低但递减缓慢。启动压力梯度对水平井前期产量影响较大,而储层应力敏感性对后期产量影响较大。模型为认识体积压裂水平井复杂渗流规律、预测页岩气藏压裂水平井产能、评价压裂效果以及优化水平井压裂参数提供了有效的科学依据和理论支撑。

The technology of multi-fractured horizontal well is the one of the most effective and efficient methods to develop shale gas reservoir. Referring to absorption/diffusion effect,stress sensitivity effect in shale formation and slippage effect,a compound flow model of multi-fractured horizontal well was built and its analytic solution in Laplace space was also obtained. Using Stefest numerical reversion technology and Duhamel principle,taking wellbore storage and skin effect into consideration,a non-dimensional productivity model in real space was built and its solution was resolved,thus drawing standard template of non-dimensional productivity model and carrying out sensitive analysis of influencing factors. According to the consequences of realistic application,this model can predict real productivity of a multi-fractured horizontal well and the forecast accuracy is high enough to solve real problem.The results show that production of multi-fractured horizontal well in shale gas can be divided into three seepage zones and five stages. In the first stage when linear flow in artificial fractures is dominant,production relatively high whereas the decline rate is also high;in the middle stage when linear flow in nature fractures or micro-fractures is dominant,production and decline rate are both decreasing;in the final stage when linear flow in matrix is predominant,production period long with low production rate. Foundation for learning complicated seepage law of multifractured horizontal well was built,forecasting productivity of multi-fractured horizontal well in shale gas reservoir,revaluating result of artificial fracturing and optimizing fracturing parameters of horizontal well.