特低渗透储层岩石渗透率应力敏感新机制

A New Mechanism for the Permeability Stress-sensitivity of Reservoir Rock with Ultra-low Permeability

地层岩石多孔介质的渗透率应力敏感性一直是石油工业与岩土工程建设等领域持续研究的一个热点课题。在低渗透岩石渗透率应力敏感性实验研究的基础上,提出了毛管束-孔隙网络渗流模型的多孔介质渗透率应力敏感新机制,该模型充分考虑了多孔介质孔隙之间相互连通的复杂性、渗流迂曲度以及不同类型和大小的孔隙对多孔介质渗透率贡献率的差异。有效应力作用下,低渗岩石中作为主要渗流通道的较大孔喉首先被压缩变小,流体渗流阻力和孔隙迂曲度均同时增大,这是导致有效应力加载初期岩石渗透率急剧减小的主要原因。同时渗透率越小的岩心,其中所发育的较大孔喉越少,该部分孔喉闭合后对岩心渗透率的影响越大,因此渗透率越小的岩石应力敏感性越强。与相关学者的研究成果对比表明,本文提出的新模型能够更好地解释低渗透岩石应力敏感性较强的内在原因。

The permeability stress-sensitivity of formation rock is one of the most important research subjects in the petroleum industry and geotechnical industry. A capillary tube-pore network flow model is presented in order to explain permeability stress-sensitivity based on permeability stress-sensitivity experiments. The new model fully considers the complex connectivity among pore throats, pore structure tortuosity, different types and sizes of pore throats, and their different contribution ratios to the rock permeability. When effective stress is loaded on the low permeability rock samples, the larger pore throats, as the main flow channel, are firstly compressed smaller. Therefore, both fluid flow resistance and pore tortuosity simultaneously increase; it is the main reason that the rock permeability dramatically declines in the initial period for increasing effective stress. Since there are less large pore throats in the rock with lower permeability, those larger pore throats compressed smaller could have a greater impact on the rock permeability. Therefore, the smaller the rock initial permeability is, the stronger its stress-sensitivity is. Comparing with the experimental results for pore structure deformation, the new model is very reasonable for explaining the permeability stress-sensitivity of low permeability rock.