Converted-wave elastic impedance and fluid identification factor in fractured reserviors

Abstract

Identification and prediction of fracture and its developmental zone is meaningful to reservoir exploration and development. According to solid mechanics ,fracture strata is anisotropic media . Previous formulation for S-wave elastic impedance neglects seismic anisotropic. In order to incorporate anisotropic , we use an approximation of converted PS-wave reflection coefficients to deduce converted wave elastic impedance in weakly anisotropic media for the first time. Through numerical simulation, the effect of Thomsen parameter, incident angle and azimuthal angle on the formulation are described in detail. At the same time, we analyze the precision of new approximation formulation and compare the hydrocarbon detection effect of PP wave and converted wave elastic impedance. The future work is to select the newest nonlinear inversion algorithm and realize elastic impedance inversion in anisotropic media.On the basis of sensitive fluid identification factor in isotropic media,we construct the new fluid identification factor in weakly anisotropic media, which is composed of PP wave and converted wave elastic impedance. The advantage of new fluid identification factor is to allow investigating AVO anomalies with the effect of anisotropic parameters .Then ,we can analyze the difference of fluid identification factor with azimuthal angle and anisotropic parameters in 3D space .Adding Thomsen parameter to the 25 formation models gived by Castagna and Smith, we analyze the identification effect. Numerical simulation results show that the new fluid factor can identify the gas sand and brine sand effectively.