岩心油水两相渗流启动压力梯度实验研究

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。研究结果表明：气体渗透率小于50×10-3μm2的低渗岩心具有较大的启动压力梯度，且随渗透率降低，启动压力梯度快速增加，岩心内含水饱和度越高，启动压力梯度越大；气体渗透率大于50×10-3μm2中高渗岩心启动压力梯度随渗透率变化不大，且数值较小，随岩心含水饱和度增加而降低；产生启动压力的阻力效应大小和岩石的润湿性、毛管压力、微观孔隙的油水分布状态、固液界面张力及孔喉半径有关。对于低渗透油藏，岩心的润湿指数越大，含水饱和度越高，固液界面张力越大，所产生的油水两相阻力效应越大，岩心启动压力梯度就越大。

Experiment research on starting pressure gradient of oil-water two phase flow in cores

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 cores in two-phase seepage during water flooding were experimentally measured in laboratory, according to the experimental phenomenon, resistance effect generating starting pressure in the cores’ hole. The result of research shows: The cores that permeability are below 50×10-3μm2 have larger starting pressure, and they increase rapidly with the decreasing of permeability, the water saturations of cores are higher, the starting pressures are larger; The starting pressure of cores that permeability are above 50×10-3μm2 don’t change much with the permeability changing, and the values of starting pressures are small, which decrease with the water saturations increasing; The resistance effects generating starting pressure are related to rock wettability、capillary pressure、oil and water distribution in microscopic pores、solid-liquid interfacial tension and pore throat radius. For low permeability reservoirs, the cores wettability are larger, the water saturations are higher, the solid-liquid interfacial tensions are larger, the resistance effects of oil-water phase are bigger, the cores’ starting pressure gradients are larger.