oa 2.5D Forward Modeling – a Cost Effective Solution that Runs on Small Computing Systems

Full wave elastic forward modeling from full 3D depth models to produce 3D – 3C shot records is extremely compute intensive. A methodology has been developed that enables geophysicists to utilize an extremely complex geologic model in the X direction, but that is consistent in the Y direction to produce 3D – 3C full wave elastic forward modeling results. This methodology can be successfully used to test the viability of recording parameters in thrust belt environments that exhibit extremely complex structures in the dip direction but relatively stable structures in the strike direction. Many other geologic situations involving fracture systems can be effectively modelled using this technology. The method is capable of taking into account the quasianisotropic and velocity dispersion effects of thin beds. Also, for the case of TTI anisotropy (or tilted fracturing, or some combination of tilted fracture systems) 2.5 D modeling allows us to simulate both “fast” and ‘slow” shear waves and also simulates the effects of wave coupled refraction. In addition, Q parameters for P and S waves can be defined to accurately simulate polarization effects for both surface waves and volume waves. The accuracy of the method is such that geophysicists can predict the azimuthal AVO and velocity effects of fracture systems and test the effectiveness of full elastic inversions and various seismic methods that are available to measure azimuthal variations of seismic parameters. The mathematical derivation of the process will be discussed and examples of the usage of 2.5 D forward modeling in exploration will be illustrated.