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为了明确低渗致密气藏发生滑脱效应的压力界限,测试了低渗致密岩样的视渗透率在不同孔隙压力下的变化规律。测试前采用平移法求得了岩样的有效应力系数。测试实验表明,当孔隙压力从地层压力下降到临界压力时,气体流动开始发生滑脱效应,发生滑脱效应的临界压力随着渗透率的增加而降低。得出了定量表征滑脱效应压力界限的公式。当地层压力大于临界压力时,不存在滑脱效应,实验室得出的克氏渗透率小于储层的真实渗透率;当地层压力小于临界压力时,实验室进行气体测量渗透率时应该采用回压阀,此时用回压测得的克氏渗透率值以及求得的滑脱因子更加准确。
In order to clarify the pressure limit of slippage effect in low permeability tight gas reservoirs, the change law of apparent permeability of low permeability tight rock samples under different pore pressures was tested. Before the test, the effective stress coefficient of the rock sample was obtained by the translation method. The experimental results show that when the pore pressure drops from the formation pressure to the critical pressure, the gas flow begins to slip, and the critical pressure of the slip effect decreases with the increase of the permeability. The formula that quantitatively characterizes the pressure limit of slippage effect is obtained. When the formation pressure is greater than the critical pressure, there is no slippage effect, and the laboratory derived Kjeldahl permeability is less than the true permeability of the reservoir. When the formation pressure is less than the critical pressure, the laboratory should use the back pressure Valve, at which point the Krefelv’s permeability measured with back pressure and the derived slip factor are more accurate.