油气储层渗透率应力敏感性与启动压力梯度的关系

THE RELATIONSHIP BETWEEN STRESS - SENSITIVITY PERMEABILITY AND STARTING PRESSURE GRADIENT OF RESERVOIR

人们在进行油气储层渗透率应力敏感性实验研究时,得到的结论不统一。利用毛管模型及启动压力梯度理论,通过实验研究发现之所以会有不同的结论,是因为所取岩心的初始渗透率存在较大差异。经分析得到如下结论:由于启动压力梯度的存在,使得低渗、特低渗储层比中高渗储层具有更强的应力敏感性,当初始渗透率小于某一临界值时,渗透率越低对应力越敏感,大于此值后,渗透率降低只与有效应力有关,而与初始渗透率无关。在油气生产过程中,储层变形对低渗、特低渗油气藏生产的影响很强,加大了这类油气藏的开发难度。

There are different conclusions about the stress - sensitivity reservoir permeability. Some researchers think that the variation degree of permeability via effective stress is not related to the initial permeability, while others hold the contrast viewpoint. By means of stress - sensitive experiment, capillary model and starting pressure gradient theory, the reason that causes researchers hold different opinions is found: it is because the permeability values of cores which they studied are great different. By carefully analyzing, we draw the conclusion: because of starting pressure gradient, low - permeability reservoir is more stress sensitive than medium - high permeability, and when initial permeability is lower than a critical value, the lower the permeability is, the more stress - sensitive the reservoir is, and when permeability is greater than this value, regardless of the initial permeability, the reduction in permeability is a function of effective stress only. For tight reservoirs, reservoir deformation has great effect on oil and gas production, which increase the exploitation difficulties of this kind of reservoirs.