Development Of A Method For Fracture Detection Using An Elliptical Model For P-wave Amplitude

Underground strata with high angle fractures can be approximated by transverse anisotropic media with horizontal symmetry axes, i.e., HTI media. For seismic waves propagating in the HTI media, their amplitude attenuation changes with the angle between the observational direction and the anisotropic direction of the media. Therefore, seismic survey using an observation system covering waves propagating in all directions can reveal the directional attenuation pattern of seismic wave amplitude, which can in turn be used to estimate the density and orientation of fractures developed in the underground rocks. These estimated fracture parameters are useful for petroleum exploration.The method for the inversion of fracture information, including its direction and density, is based on an elliptical model of seismic P-wave amplitudes. The main achievements of the work are as follows:(1) First, the fundamental theory of the elliptical amplitude inversion was developed on the P-wave amplitude distribution model for HTI weak anisotropic medium. Then an inversion algorithm and software was developed for the extraction of anisotropy information of the medium from seismic data. Finally parameters of fractures in the rocks, including directions and density, can be evaluated using the anisotropy information.(2) A method for modeling of elastic waves in three-dimensional HTI media was developed using a high-order staggered grid finite difference scheme and a PML boundary condition. Computer software based on the methods was developed using C on Linux. A simulation of amplitude ellipse fracture detection(AEFD) using the software demonstrates that the elliptical amplitude inversion method is effective.(3) The elliptical amplitude inversion method is further developed into a new phase capable of extracting anisotropic amplitude of instantaneous frequencies using a wavelet transformation approach.(4) A 3-D seismic data was processed using the software developed in this paper. The maps of fracture parameters resulted from the processing demonstrated that the software is useful for fracture detection.