Research On Fractured Reservoir Prediction With Azimuthal Seismic Data

The nearly vertical orientation of the fractured formation is a HTI medium, i.e.,the axis of symmetry in the horizontal direction transversely isotropic medium. HTImedium seismic wave velocity and reflection amplitude varies with the azimuth andangle of incidence changes, and reflects azimuthal anisotropy. Based on the inversionof seismic azimuth gathers a variety of the azimuth amplitude of properties andanisotropy gradient can be applied to the fracture orientation, density anddevelopment with forecasts.HTI medium elastic matrix is the bridge of connecting to the fracture parametersand the seismic response. In summarizing a variety of the build the elastic matrixtheory of anisotropic media, and combinated the equivalent media theory andThomsen theory can obtain new elastic matrix construction method in HTI mediaobservation system coordinate system. To get HTI media accurate reflectioncoefficient when P-wave incidents, according to HTI medium elastic matrix and waveequation derivation the HTI medium Christoffel equation and used to study the HTImedium phase velocity and polarization direction and then combined with HTImedium boundary conditions to derive the HTI medium elastic wavethree-dimensional reflection transmission equation. Azimuth seismic responsecharacteristics of the crack formation can be studied through the equation.Elastic parameters with fractured medium the azimuth variation can be detectedthe formation fracture development, Young’s modulus is the ratio of elastic mediumstress and strain in the elastic deformation, based on petrophysical analysisthe largeamount of difference in the Young’s modulus of the largest and fracture strike thancrack tendency. By inversion of seismic azimuth gathers different orientations ofYoung’s modulus, the Young’s modulus can fit a ellipse, ellipse longitudinal directionsfracture strike and elliptic rate may indicate a fracture density. The HTI medium AVOgradient varies with azimuth change and toward the largest difference in crackorientation and crack. Individually for each azimuth gathers for AVO analysis can not guarantee that all AVO intercept that is self-excited since closing reflection coefficientconsistent and did not eliminate the impact of seismic wave reflection coefficient.Proposed two-step inversion azimuthal AVO gradient in order to overcome thedeficiencies of conventional AVO analysis, the first step is not to consider the impactof the wavelet and get pure P-wave seismic data and the azimuthal AVO gradientrecords, the second step based on the the least reflective layer assumptions bysimulated annealing the law constantly the iterative inversion wavelets and accuratesubsurface interface position, the method can reduce the wavelet matrix dimensionand decreases the wavelet matrix condition number, and to obtain a good state ofinversion equation. According to the azimuthal AVO gradient ellipse analysis canpredict fracture density and the actual work area the fracture strike priori informationcan solve azimuthal AVO gradient predict fracture orientation90degrees ofuncertainty.Fracture parameters can affect the anisotropic size, the anisotropic gradient canreflect the anisotropy strength. Downton linearized Ruger reflection coefficientapproximation formula and obtain anisotropic gradient characterization of thereflection coefficient formula, anisotropic gradient inversion method by the two-stepmethod for characterize subsurface fractures anisotropy strength, combined with theactual work area the cracks toward priori information can solve the problems theanisotropic gradient predicted crack toward90degrees of uncertainty.Based on actual data, through the Young’s modulus extraction and applicationprocess to verify the correctness of the method of the paper.