低渗透储层应力敏感系数统一模型

低渗透储层应力敏感性的研究虽已引起中外学者的关注,但目前仍未形成统一认识。为了更准确地描述低渗透储层的应力敏感性,通过保持围压不变、改变流体压力的实验方法,研究了低渗透储层渗透率随有效应力的变化规律及其影响因素。在此基础上,按照岩石压缩系数的定义方法,提出了渗透率应力敏感系数的概念,在综合考虑孔隙结构、有效压力及滞后效应等参数的基础上,结合分形理论,建立了应力敏感系数的统一模型。结果表明,渗透率随有效压力的增加呈阶梯状减小,且与孔隙结构及有效应力加压方式有关;渗透率应力敏感系数可以定量表征储层渗透率随有效应力变化的敏感程度,其值越大说明储层敏感性越强;所建模型考虑了岩石内部孔隙结构、外部有效应力变化及滞后效应等多种因素的综合影响,可以全面表征储层的应力敏感性,并预测不同孔隙结构岩石的渗透率随有效应力变化的规律。

Universal model of stress sensitive coefficient for low permeability reservoir

The study on stress sensitivity in low permeability reservoir has attracted more and more attentions of researchers home and abroad,but,there is so far no common understanding on it.To describe the stress sensitivity of low permeability more accurately,the relationship between permeability and effective pressure and its effect factors are studied by laboratory experiments with variable fluid pressures,while keeping confining pressure steady.On this base,a stress sensitive coefficient is presented according to the definition method of rock compressibility,and combined with fractal theory,a universal model of stress sensitive coefficient is built after taking into account of the effect of pore structure,effective stress and hysteresis effect.The results show that the permeability decreases in step shape with the rise of effective stress,and it is related to pore structure and effective stress loading way.The stress sensitive coefficient of permeability can characterize the rock sensitivity quantitatively:the larger the value,the stronger the stress sensitivity.The model built in this paper,taking into account of the effect of pore structure,the effective stress changes and hysteresis effect,can characterize the stress sensitivity in general,and it can forecast the permeability change laws with the change of effective stress,so,it has a wide adaptability.This result has important significance to the further study of stress sensitivity in low permeability reservoir.