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由于地质成因的不同,岩石渗透率往往具有不同程度的大小和方向性差异,即呈各向异性的特点。目前,岩石渗透率方向性特征的理论和试验研究仍然不足,缺乏岩石渗透率各向异性量化评估。基于国内CCUS场地储层砂岩,沿正交方向钻取岩芯试件若干,完成瞬态法覆压渗透率测试。试验结果表明,特低渗砂岩正交方向渗透率随围压(上覆岩层压力)加载呈幂律函数递减,当围压加载至20 MPa以后,正交方向渗透率差异性逐步降低,即渗透率由各向异性逐步向各向同性过渡,且储层砂岩竖向渗透率压力敏感系数普遍低于水平侧向。通过建立一种空间坐标系下渗透率计算模型,将岩石内部渗流规律等效为空间正交方向渗透率模型,并借用统计学标准差定义提出渗透率各向异性系数?k,将不同岩性储层岩石渗透率不均匀性作归一化处理,定量地描述了覆压试验过程中试件渗透率各向异性的变化规律。
Due to the different geological causes, rock permeability often has different degrees of size and direction of the difference, that was anisotropic. At present, theoretical and experimental studies on directional characteristics of rock permeability are still inadequate, and there is a lack of quantitative evaluation of rock permeability anisotropy. Based on the sandstones in the domestic CCUS site, a number of core samples were drilled along the orthogonal direction to complete the transient method of compressive permeability test. The experimental results show that the permeability in the orthogonal direction of the ultra-low permeability sandstone decreases with the increase of the confining pressure (overburden pressure) as a power-law function. After the confining pressure is applied to 20 MPa, the permeability difference in the orthogonal direction gradually decreases, that is, the permeability The rate from anisotropy to isotropic transition gradually, and the vertical permeability of reservoir sandstone pressure sensitivity coefficient is generally lower than horizontal. By establishing a model of permeability calculation in the space coordinate system, the seepage law in the rock is equivalent to the permeability model in the orthogonal direction of space, and the anisotropy coefficient of permeability? K is proposed by the definition of statistical standard deviation. The heterogeneity of reservoir rock permeability is normalized, and the variation regularity of anisotropy of permeability of specimen in the process of overburden test is quantitatively described.