特低渗透油藏非线性渗流模型

Non-linear seepage flow models of ultra-low permeability reservoirs

启动压力梯度和介质变形是油气在低渗透、特低渗透储集层中渗流规律偏离达西定律的主要原因。基于介质变形、启动压力梯度特征物理模拟实验,定义了新的应力敏感系数,分析了应力敏感系数和启动压力梯度(单相和油水两相条件下)的变化规律。建立了考虑启动压力梯度和介质变形的特低渗透油藏单相和油水两相非线性渗流数学模型,对于单相渗流,给出了定产量、变产量和定流压条件下模型的解;对油水两相非活塞驱替,给出了分流量方程、油水前缘位置方程及压力、产量方程,并给出了求解方法。模型的油藏工程应用表明:低渗透油藏产能递减速度高于中高渗油藏;渗流速度比较小时,非线性因素对油水两相渗流影响显著。利用该模型,还可确定油田的合理注采井距。

Non-linear seepage flow is caused chiefly by medium deformation and threshold pressure gradient （TPG） in low and ultra-low permeability reservoirs. According to laboratory experiment on medium deformation and TPG, a new stress sensitive coefficient is defined, and the variation rules of the coefficient and TPG （including single phase and oil-water two phases）are analyzed. The non-linear seepage models of single phase and oil-water two phases are set up with consideration of medium deformation and TPG. The single phase model is solved on the condition of constant flow rate, changing production rate, and constant bottom-hole pressure respectively. For oil-water non-piston displacement flow, the fractional flow equation, oil/water front equation, pressure equation and production equation are put forward with solultions. The reservoir engineering application shows that the production rate decline in low permeability formations is more serious than that in medium-high permeability formations, and non-linear factors exert serious influence on oil-water two phases flow when the velocity is low. Moreover, reasonable injector producer distance can be determined by the models.