微裂缝性特低渗透油藏单向稳态渗流压力分析

Pressure analysis of stable single direction flow in micro-fractured ultra-low permeability reservoirs

为研究微裂缝性特低渗透油藏特殊的流体渗流规律,重新建立了考虑启动压力梯度和压敏效应综合影响的渗流运动方程,并在此基础上建立了完整的微裂缝性特低渗透油藏一维单向稳态渗流的数学模型,采用Kirchhoff变换,获得了压力分布解析公式。最后采用算例,对压力分布特征及影响因素进行了分析。结果表明,微裂缝性特低渗透油藏一维单向渗流的压力分布影响因素比较多,如启动压力梯度、变形系数、生产压差和排距等,并且这些因素均以非线性方式产生综合影响。单向渗流的压力分布不再是直线形式,而是凸形曲线。等压线分布亦不均匀,近井附近压力消耗严重。启动压力梯度大时,压力损失主要是沿程损失;启动压力梯度小时,压力损失主要由压敏效应消耗在近井区域。远离井底仍然是近似直线压降。放大生产压差和减小排距能够在一定程度上缓解启动压力梯度和压敏效应的影响。

A large number of experiments of microcosmic porous flow have proved that the special rule exists in micro-fractured ultra-low permeability reservoirs.The motion equation considering thepressure-sensitive effect and threshold pressure gradient was established again.Then the integrated mathematical model about one-dimension one-way stable percolation was established.Applying the method of the Kirchhoff transform,the analytical formulas of pressure distribution were obtained.Finally the characteristics of pressure distribution and the affecting factors were analyzed from four examples.The factors that affect pressure distribution of one-dimension one-way stable percolation in micro-fractured ultra-low permeability reservoirs are much more,such as threshold pressure gradient,deformation coefficient,well spacing,producing pressure drop,and so on.And these factors affect it synthetically in nonlinearity.The pressure distribution of single direction flow is not right line but convex curve,and the contours are heterogenetic that are dense at immediate vicinity of well-bore.If the threshold pressure gradient is the major factor,the pressure loss is mainly on way;if the pressure-sensitive effect is the major factor,the pressure loss is mainly converged at immediate vicinity of wellbore.Approximate linear pressure drop presents far away from the bottom hole still.And enlarging the producing pressure drop and diminishing the well spacing are effective in relieving the influence of threshold pressure gradient and pressure-sensitive action.