Different Types Of Naturally Occurring Fracture Networks

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It has been long recognized that the presence of naturally occurring fracture network can lead to unpredictable heterogeneity and anisotropy within many reservoirs. In past geophysicists acquired and processed P-wave reflection data at short offset, which automatically implied relatively small angular ray coverage. So seismic anisotropy, which is defined as directional dependence of elastic properties of earth remains unnoticed. But with the advance of methodologies, acquiring long offset and multi-component data become feasible and cost effective, anisotropy showed up. On a smaller scale, stresses in the Earth can cause rock to fracture in a consistent manner. If these fractures are aligned, the rock will be anisotropic with the fast direction parallel to the fractures and the slow direction perpendicular to them. In ideal cases, these observations can provide information on the state of stress in the Earth. Different types of anisotropy have resulted depending on the direction of fracture orientation. A set of parallel vertical cracks embedded in an isotropic background gives rise a transverse isotropic medium with horizontal symmetry axis. Similarly in sedimentary basins orthorhombic symmetry is commonly caused by parallel vertical fractures embedded within a VTI background medium. It may also arise due to two or three mutually orthogonal fracture sets, or due to two identical fracture systems criss-crossing with an arbitrary angle. Such sets of fractures

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