| P-wave seismic anisotropy is of growing concern to the exploration industry. The transmissional effects through dipping anisotropic strata, such as shales, cause substantial depth and lateral positioning errors when imaging subsurface targets. Using anisotropic physical models the limitations of conventional isotropic migration routines were determined to be significant. In addition, these models were used to validate both anisotropic depth migration routines and an anisotropic, numerical raytracer.; In order to include anisotropy in these processes, one must be able to quantify the anisotropy using two parameters, ϵ and δ. These parameters were determined from headwave velocity measurements on anisotropic strata, in the parallel-, perpendicular- and 45°-to-bedding directions. This new method was developed using refraction seismic techniques to measure the necessary velocities in the Wapiabi Formation shales, the Brazeau Group interbedded sandstones and shales, the Cardium Formation sandstones and the Palliser Formation limestones. The Wapiabi Formation and Brazeau Group rocks were determined to be anisotropic with ϵ = 0.23 ± 0.05, δ = –0.05 ± 0.07 and ϵ = 0.11 ± 0.04, δ = 0.42 ± 0.06, respectively. The sandstones and limestones of the Cardium and Palliser formations were both determined to be isotropic, in these studies.; In a complementary experiment, a new procedure using vertical seismic profiling (VSP) techniques was developed to measure the anisotropic headwave velocities. Using a multi-offset source configuration on an appropriately dipping, uniform panel of anisotropic strata, the required velocities were measured directly and modelled. In this study, the geologic model was modelled using an anisotropic raytracer, developed for the experiment. The anisotropy was successfully modelled using anisotropic parameters based on the refraction seismic results.; With a firm idea of the anisotropic parameters from the aforementioned studies, these parameters were then used in the anisotropic depth migration of a real dataset from the Alberta Foothills. The final anisotropic section demonstrated several improvements over the isotropic section. This anisotropic section is considered to be more accurate, in terms of depth and lateral position of reflectors, and thus a more complete solution than the isotropic result.; In conclusion, seismic velocity anisotropy can seriously affect the imaging of subsurface play targets and every effort should be made to take these effects into account using anisotropic processing routines. |
