Anisotropic Permeable Zones Identification and Seismic Discrimination of Stress and Fracture Induced Anisotropy

Abstract:

Anisotropic permeability is a measure of the ability of a fractured reservoir to allow fluid to pass through it. Fractures in a reservoir rock not only provide space to accumulate fluid but also provide channels for fluid migration. Therefore, identifying anisotropic permeable zones in fractured reservoirs using seismic attributes is very important for oil and gas exploration and production in petroleum industry.

Azimuthal AVO or AVOZ inversion method is wildly used to solve the strength of anisotropy from pre-stack P-wave seismic data, which indirectly reflect the degree of fracture developed in a reservoir rock. However, seismic anisotropic response is also attributed to subsurface principle stresses. So, it is uncertain to predict the subsurface anisotropy is caused by fractures or stress.

We extended AVOZ inversion method in frequency domain and derived frequency-dependent AVOZ or AVOZF inversion formula. The AVOZF inversion algorithm utilizes both azimuth and frequency information to calculate the anisotropic dispersion gradient term related to the fluid saturated fractures from pre-stack P-wave seismic data, which can be used to identify anisotropic permeable zones of reservoir. Combining AVOZF inversion method with AVOZ inversion method offers key information to discriminate stress and fracture induced anisotropy.

The application demonstrates AVOZF inversion method combine with AVOZ inversion method provides robust workflow for anisotropic permeable zones identification and seismic discrimination of stress and fracture induced anisotropy, which improves the accuracy of oil and gas exploration in anisotropic media and reduce drilling risk.