各向异性应力边界条件下不同方向裂缝的变形特征

裂缝随地应力的变形规律对油气藏的高效开发具有重要的指导意义,目前中外对裂缝应力敏感变形特征的研究多集中在各向同性应力且方向与宏观压力梯度方向平行条件下的裂缝变形特征.但对各向异性应力不同方向裂缝的应力敏感特征研究较少.为此,建立各向异性应力条件下不同方向裂缝的变形计算模型,并研究流体压力、弹性参数、几何参数等对裂缝变形的影响及整个渗流介质渗透率张量的变化规律,最后通过物理模拟实验验证该模型的准确性.研究结果表明:裂缝性渗流介质加载各向异性应力时,与最大主应力方向夹角越小的裂缝渗透率越大;两组裂缝不对称分布时,随流体压力增大,裂缝系统渗透率主值变大,主值方向逐渐偏向应力敏感性强的那组裂缝,当两组裂缝正交分布时,只有主值大小会发生变化,最大主值方向始终平行于弹性模量较小的那组裂缝.

Deformation Characteristics of Fractures in Different Directions under Anisotropic Stress Boundary Conditions

The study of the deformation characteristics of fractures with in-situ stress has important guiding significance for the efficient development of oil and gas reservoirs. At present, domestic and foreign researches on the characteristics of fracture stress-sensitive deformation mostly focus on the characteristics of fracture deformation under the condition of isotropic stress and the direction parallel to the direction of macro pressure gradient. However, there are few studies on the stress sensitivity characteristics of fractures in different directions of anisotropic stress. Therefore, in this paper, a model for calculating the deformation of fractures in different directions under anisotropic stress is established. The influence of fluid pressure, elastic parameters, geometric parameters, etc. on fracture deformation and the variation law of permeability tensor of the entire seepage medium are studied. Finally, the accuracy of the model is verified by physical simulation experiments. Research indicates: When the anisotropic stress is loading on the fractured seepage medium, the smaller the angle with the direction of the maximum principal stress, the permeability of the fracture greater. When the two groups of fractures are asymmetrically distributed, as the fluid pressure increases, the main permeability value of the fracture system becomes larger, and the main value direction gradually deviates to the group of fractures with strong stress sensitivity. When the two groups of fractures are orthogonally distributed, only the main value will change, the direction of the maximum principal value is always parallel to the group of fractures with small elastic modulus.