基于非线性渗流的低渗透油藏极限注采井距计算方法

Calculation Method of Limit Injection-Production Well Spacing in Low Permeability Reservoirs Based on Nonlinear Seepage

注水已成为低渗透油藏高效开发的重要方式之一,原油在低渗储层中渗流时存在启动压力梯度以及压敏效应的影响,导致低渗透油藏注水开发效果差。为了明确注采井之间压力分布、确定合理注采井距,基于油水两相渗流理论,建立了注水井与生产井(压裂直井)之间的压力分布计算模型,并根据注采井间压力分布计算了低渗透油藏极限注采井距。以DG油田Z区块为例开展了实例应用,分析了启动压力梯度、渗透率、注采压差、原油黏度以及压敏效应对极限注采井距的影响,验证了极限井距与启动压力梯度、原油黏度呈负相关关系,与渗透率、注采压差和压敏效应呈正相关关系。应用该方法计算的一注一采条件下的极限井距与实际生产相符合,验证了方法的准确性和可靠性。该方法为低渗透油藏布置合理的注采井距以及实现效益开发提供了理论依据。

Water flooding is one of the main strategies to develop low permeability reservoirs.Due to the influence of starting pressure gradient and pressure sensitive effect,crude oil seepage in low permeability reservoir will lead to poor waterflood development effect.In order to determine the pressure distribution and rational well spacing between injection and production wells,based on the theory of oil-water seepage,the calculation model of pressure distribution between injection production wells(fractured vertical wells)is established.The limit well spacing is calculated according to the pressure distribution between injection and production wells.The calculation model was used on the Z block of DG Oilfield,and the effects of starting pressure gradient,permeability,the pressure difference between injection and production wells,oil viscosity and pressure-sensitive effect to limit well spacing were analyzed.It proves the limit well spacing is negatively correlated with starting pressure gradient and oil viscosity,but positively correlated with permeability,the pressure difference and the pressure-sensitive effect between injection and production wells.The limit well spacing calculated based on the condition of one production well and one injection well is agreement with the field condition,verified the accuracy and reliability of the method.The method provides a theoretical basis for rational injection-production well spacing and beneficial development of low permeability reservoirs.