Fracture density inversion based on azimuthal anisotropy and its application

The fracture prediction is an important area in petroleum geophysics. The shale gas reservoir with the vertical fractures can be equivalent to the transverse isotropy with the horizontal symmetry (HTI). In this paper, a new method of fracture density prediction was proposed based on the relationship between the fracture weakness parameters and the fracture density. Firstly, a new azimuthal AVO approximation equation and an azimuthal elastic impedance equation, which reflect the fracture density, were established. Then, an objective function for group-based sparse azimuth elastic impedance inversion was established with the Bayesian theory. On this basis, the stiffness matrix was solved by the damping least square method, and the shear modulus, normal and tangential weakness parameters were obtained. Finally, the relation between the fracture weakness parameters and the fracture density was used to predict the fracture density quantitatively. The reliability of fracture density estimation method was verified using the model and field tests.