岩心油水两相渗流启动压力梯度实验研究

Experiment Research on Starting Pressure Gradient of Oil-Water Two Phase Flow in Cores

低渗储层油水两相渗流时存在启动压力梯度,充分认清水驱油时启动压力梯度的变化和影响因素对油藏水驱开发至关重要。为了搞清油藏储层油水两相渗流启动压力梯度特点及其影响因素,对不同渗透率、不同含水饱和度、不同润湿性岩心水驱油两相渗流的启动压力梯度进行了室内实验测定,根据实验现象和实验结果,分析了产生启动压力的岩心孔隙内部的阻力效应和微观成因。研究结果表明:气体渗透率小于50×10^(-3)μm^(2)的低渗岩心随含水饱和度增加,启动压力梯度增大;气体渗透率大于50×10^(-3)μm^(2)的中高渗岩心启动压力梯度随含水饱和度变化不大,总体呈下降趋势,且数值较小;对于低渗油藏,启动压力梯度随岩心渗透率降低而增大,随岩心润湿指数增加而减小;岩心边界层液体厚度越大,启动压力梯度越大。产生启动压力的附加阻力效应有油滴毛管力产生的摩擦阻力、静润湿滞后导致油珠变形产生的阻力及液阻效应产生的阻力,其大小和岩石孔喉半径、润湿指数、微观孔隙的油水分布状态、边界层厚度及固液界面张力有关。

Low permeability reservoirs have starting pressure gradient in the oil-water phase seepage,fully understanding the change and influence factor of starting pressure gradient in water driving oil.In order to get a thorough understanding of starting pressure gradient’s characteristic and influence factor in oil-water phase seepage,the starting pressure gradients of different permeability,different water saturation and different wettability cores in two-phase seepage during water flooding were experimentally measured in laboratory,according to the experimental phenomenon,resistance effect and microgenesis generating starting pressure in the cores’hole have been analysed.The result of research shows that the starting pressure gradients of cores that permeability below 50×10^(-3)μm^(2)are incremental with water saturation growing.The starting pressure of cores that permeability above 50×10^(-3)μm^(2)don’t change much with the permeability changing,and the whole trend is declining,the values of starting pressures are small.For low permeability reservoirs,the cores permeability and wettability index are smaller,the boundary layer thickness are larger,the starting pressure gradients are larger.The adding resistance effects producing starting pressure gradient have the frictional drag caused by oil drop capillary pressure,the resistance caused by oil bead deformation from static wetting lag and the resistance caused by liquid resistance effect,whose values are related to pore throat radius,wettability index,oil and water distribution in microscopic pores,boundary layer thickness and solid-liquid interfacial tension.