低渗油藏束缚水下油相启动压力梯度分析

低渗油藏流体渗流具有一定的启动压力梯度,但目前对启动压力梯度的确定方法不一,且主要考虑的是单相流体（如单相油）的启动压力梯度.文中则通过室内物理模拟实验测试单相水、单相油以及束缚水下的油相流动启动压力梯度.结果表明：通过驱替实验数据回归得到的最小启动压力梯度比直接测得的要小得多,更贴近现场实际;最小启动压力梯度与渗透率呈较好的幂函数负相关关系,即随着渗透率增加,启动压力梯度逐渐减小;渗透率相同时,单相油的启动压力梯度要大于单相水,而束缚水下的油相启动压力梯度要明显大于单相油和单相水.对油井产能来说,在注采井距确定和油藏数值模拟中,应考虑束缚水下的油相启动压力而非单相油.研究结果对低渗—特低渗油藏渗流理论研究具有重要意义.

Analysis on starting pressure gradient of oil phase at irreducible water in low permeability oil reservoirs

It is known that there is certain starting pressure gradient in low permeability oil reservoirs, but there are still some different opinions on the determining methods and the starting pressure gradient of single phase fluid, such as oil phase, is mainly considered. This paper tests the starting pressure gradient of water, oil and oil at irreducible water in lab. The results show that the minimum starting pressure gradient determined by regression is lower than that directly tested, and it is more close to that of reality; the minimum and quasi starting pressure gradient are both functional to the permeability, with the increase of permeability, the starting pressure gradient is decreased; for the same permeability cores, the starting pressure gradient of single phase oil is larger than that of single phase water, while the starting pressure gradient of oil phase at irreducible water is larger than that of the above two, which affects the production more, so the starting pressure gradient should be considered in both determination of well distance and reservoir simulation. The results provide references for studying the flow laws of low and ultra-low permeability oil reservoirs.