Prediction Of Fracture Medium Parameters Based On Seismic Anisotropy

The recognition degree of fracture distribution and fracture types,and the cognition degree of fracture density and fracture weakness parameters are of great significance to earthquake prediction,oil and gas exploration and mineral development,etc.Effective prediction of fracture medium parameters can provide certain theoretical support for oil and gas resources development to increase production and avoid mine disasters.Among anisotropic media,Orthotropic Anisotropy(OA)media not only considers the anisotropy caused by periodic thin layers,but also considers the vertical fracture anisotropy,which is close to the actual underground reservoir,and is one of the commonly used models for inversion of anisotropic parameters or fracture parameters.Particle Swarm Optimization,PSO)is a stochastic algorithm based on particle swarm,which is a commonly used nonlinear inversion method with simple calculation process and few control parameters.However,a single PSO algorithm is easy to fall into local minima in the optimization process,and its global search ability is poor.In this paper,PSO algorithm is combined with simulated annealing(SA),and SA algorithm is added to PSO algorithm.By adjusting the temperature,the global optimal position of PSO algorithm is modified,and PSO algorithm and SA algorithm are mixed and optimized.This PSO-SA algorithm based on simulated annealing has the advantages of stronger global optimization ability,overcoming premature phenomenon and not falling into local minimum easily.Anisotropic AVO inversion is based on the approximate equation of reflection coefficient of anisotropic media.Based on the approximate equation of reflection coefficient of OA media,this paper establishes the inversion objective function of anisotropic parameters of OA media,uses PSO-SA algorithm to realize pre-stack AVO inversion of OA media,obtains anisotropic parameters of OA media,and effectively predicts fracture filler types through the correlation between anisotropic parameters and fracture weakness and other parameters.Further,According to the relationship between fracture weakness,fracture density and ODHSR(orthogonal differential horizontal stress ratio)factor,the fracture density and ODHSR factor of medium are predicted,and finally the fracture-related parameters such as fracture weakness,fracture density and odhsr factor can be predicted by inversion of anisotropic parameters of OA medium.In this paper,several sets of theoretical models are established,and some models of Marmouusi 2 are improved.The inversion method is calculated by using various models.The inversion process is stable,the error of inversion results is small,and the predicted results are consistent with the actual prior model,which proves the correctness and effectiveness of the inversion method.The research results will provide theoretical support for AVO inversion of seismic wave anisotropy,and provide more theoretical basis for identification of fractured reservoirs and in-situ stress analysis of reservoirs.