基于摩擦效应的砂岩裂缝密度定量预测

以挤压型盆地内低渗砂岩储层为研究目标,研究应力场与裂缝参数的关系,通过岩石力学实验与理论推导相结合的方法,建立一套基于考虑裂缝面摩擦耗能的裂缝密度定量预测方法。研究表明:岩石变形准则与能量转换法相结合是建立应力场和裂缝参数力学模型的有效途径,当岩石内部应力状态超过破裂条件后,裂缝密度随应变能密度的增加而增大;裂缝的形成除了要克服岩石内在的黏聚力外,还要克服围压与摩擦效应形成的阻力,可使用库仑-莫尔破裂准则进行岩石破裂判别,进而明确应力-应变与岩石产生裂缝密度的数学关系。所建立的模型应用于准西北缘低渗砂岩裂缝密度预测取得了良好的效果。

Quantitative prediction of fracture density based on friction effect

Aiming at low-permeability reservoirs in compressional basins, a new fracture density quantitative prediction method considering surface friction energy was developed using rock mechanic tests and theoretical derivation of relationships between the stress field and fracture parameters. The results show that the combination of rock deformation criteria with the energy conversion laws is an effective approach to establish the mechanical model of the stress field and fracture parameters. The fracture density increases with strain energy density, after the inner stress state exceeds failure conditions. In addition to breaking the inner cohesion in the sandstone, the formation of cracks has to overcome the resistance of the confining pressure and the frictional effect. The Coulomb-Moire criterion can be used to estimate rock rupture, and then to clarify the mathematic relation between the stress-strain and rock fracture density. The predictions of the established model are in good agreement with the observed fracture density of low permeability sandstone in the northwest margin of Junggar Basin.