低渗透油藏非线性微观渗流机理

Study on non-linear flow mecbanism in low permeability porous medium

针对目前很多学者对低渗透油藏微观渗流机理方面的认识仍存在分歧及未认识到非线性渗流根本原因的现状,从低渗透油藏多孔介质特征、微尺度流动效应和边界层理论等方面,阐述了低渗透油藏非线性微观渗流产生的机理。结果表明,低渗透油藏孔喉细微、孔喉比大、孔道半径在微米级别、比表面大及微小孔道比例显著增加是低渗透油藏渗流规律不同于中高渗透油藏的客观物理条件;微尺度流动效应是低渗透油藏存在启动压力梯度和非线性渗流的根本原因,同时吸附边界层的存在加剧了微尺度效应,使得启动压力梯度和渗流横截面积随驱替压力梯度增加而增加,参与渗流的流体随驱动压力的增加而变稠。

At present, there are still many divergences on the mechanism of micro-flow in low permeability porous medium, and most of scholars don't recognize the fundamental causes of non-linear flow. The mechanism of non-linear flow in low permeability reservoirs is elaborated from the characteristics of the low permeability porous medium, micro-scale flow effects and boundary layer theory. The features, such as small pores and throats, large ratio of pores and throats, the average pore radius of the micron level, large surface area, and signifieant increase in micro-channels leading to the seepage in low permeability reservoirs, are all different from that in high permeability reservoirs. The micro-scale flow effect is the fundamental causes of non-linear flow and the presence of start-up pressure gradient, while the existence of adsorption layer intensifies the micro-scale effect, as well as the increment of start-up pressure gradient corresponding to the rise of seepage cross-sectional area, and the fluid participated in the seepage process will be densified in accordance with the rise of the driving pressure.