西峰特低渗油藏流体渗流特征影响因素实验研究

Experimental study on the factors of influencing the seepage feature of the fluid in Xifeng extra-low permeability reservoir

西峰特低渗油藏原油含蜡量和油气比相对较高,地饱压差小,生产过程中近井地带生产压差下降过快导致溶解气逸出,造成流体间热交换量增大,引起近井地带储层温度降低,原油中蜡等重质组分析出使得近井地带有机垢堵塞严重.根据渗流力学和边界层理论,对西峰特低渗油藏不同温度下油、水两相及单相渗流特征进行了实验研究.实验结果表明:温度和压力降低导致原油中重质组分在孔隙表面吸附量增大,流体边界层增厚,致使油相和水相渗流的启动压力梯度增大,油水流度比增大,油水两相区变窄,岩心润湿性由水湿向油湿转变,驱油效率明显降低,最终导致油井产能降低.

Xifeng extra-low permeability reservoir is of high content of wax and high ratio of oil to gas,and its formation saturation pressure difference is also little.The quick reduction of the production pressure difference in near borehole zone in production process results in the escape of dissolved gas,which causes the increase of the heat exchange capacity among different fluids,the decrease of temperature,and furthermore causes the serious reservoir organic scale plugging due to the precipitation of heavy components in near borehole zone.The seepage features of the two phase of oil-water and the single phase of oil and water in Xifeng extra-low permeability reservoir are studied at different temperature in laboratory based on seepage mechanics and boundary theory,and the results show that,the decrease of temperature and pressure can cause the increase of the adsorption of the heavy components in crude oil in the surface of reservoir void and the thickening of fluid boundary layer,which furthermore causes that the threshold pressure gradient of the oil seepage and the water seepage and oil-water mobility ratio increase,oil-water two-phase area becomes narrow and the wettability of cores changes from water wet to oil wet,which will cause the decrease of oil displacement efficiency and oil well productivity.