非达西渗流效应对低渗透气藏水平井产能的影响

Impact of non-Darcy flow on the deliverability of horizontal wells in low-permeability gas reservoirs

水平井作为提高低渗透气藏单井产能的重要手段在实际生产中得到广泛运用。文献调研表明,低渗透气藏受其储层物性的影响,普遍存在复杂的非线性渗流效应,如滑脱效应、启动压力梯度及应力敏感效应;目前已有的低渗透气藏水平井产能预测模型中均没有考虑气体滑脱效应的影响,究竟这些效应是如何影响低渗透气藏水平井产能的还缺乏相应的评价手段。为此,针对低渗透气藏的渗流特征,引入新的拟压力函数,建立综合考虑气体滑脱效应、启动压力梯度、应力敏感效应共同影响下的水平气井产能模型,并以某低渗透气藏为例,分析了这些效应分别对水平气井产能的影响程度。结果表明:应力敏感对水平气井产量影响较大,但是气体滑脱效应与启动压力梯度对水平气井产能的影响也不能忽略;应力敏感会使水平气井产量大幅下降,最大可下降12%;气体滑脱效应会使水平气井产量上升,增加幅度在1.96%左右;启动压力梯度会使水平气井产量下降,下降幅度约1.43%。所建立的水平井产能评价方法为深入认识低渗透气藏水平井产能变化特征提供了重要的评价手段。

The horizontal well technology is widely applied in fields to enhance the deliverability of gas wells especially in the low permeability gas reservoirs.An investigation into the related literatures shows that complicated non-linear seepage effects such as slippage effect,threshold pressure and stress sensitivity are ubiquitous in the low permeability gas reservoirs due to their physical properties.However,in the existing deliverability forecast models for such horizontal wells,the influence of slippage effect has never been considered for lack of the corresponding evaluation criteria of what impact the above-mentioned effects have on the productivity of low permeability gas reservoirs.Therefore,in view of the percolation feature of low permeability gas reservoirs,we introduced a novel pseudo-pressure function and built a new deliverability forecast model for horizontal wells with slippage effect,threshold pressure and stress sensitivity taken into account.In a case study of a low permeability gas reservoir,we analyzed how these effects influence the deliverability of horizontal wells.This analysis result shows that stress sensitivity has a rather greater impact on the deliverability of horizontal wells while the slippage effect and threshold pressure can not be ignored.Specifically,stress sensitivity will result in a significant decrease of the deliverability of horizontal wells with a maximum rate of 12%;slippage effect will increase the deliverability of horizontal wells with an amplitude of 1.96 %;threhold pressure will also result in a decrease of the deliverability of horizontal wells with an amplitude of 1.43%.The proposed evaluation model is of great significance to a better understanding of the varying characteristics of the unsteady deliverability of horizontal gas wells in low permeability gas reservoirs.