Seismic Depth Imaging in Anisotropic Media East Coast of Canada Case Study

Li Lu

Our ultimate goal of seismic data processing is to produce seismic images with correct lateral and vertical positions, and with amplitude proportional to the reflection coefficients in the subsurface. A good migrated image depends strongly on the accuracy of the velocity model.

Prestack depth migration (PSDM) is a powerful tool not only for imaging but also for velocity model building. The main techniques used for migration velocity analysis include vertical updating and tomography analysis , including anisotropy parameters estimation.

To achieve the goal of accurately positioning the seismic events in subsurface, the velocity anisotropy should be accounted for. If the presence of velocity anisotropy is important, then ignoring it will significantly degrade the final image accuracy.

This thesis examines a frontier exploration survey acquired off the East Coast of Canada by Statoil Canada Ltd. and processed by CGG. Kirchhoff isotropic PSDM and tilted transverse isotropy (TTI) PSDM were conducted with the goals of good imaging and good velocity estimation. Structural interpretation and Amplitude Versus Offset (AVO) analysis for this survey demonstrate the benefits of TTI PSDM, whose subsurface images significantly reduced the exploration risk compared with isotropic PSDM.

Estimation of reliable anisotropy parameters is challenging, especially for the survey studied in this thesis where no well information is available. This thesis presents a practical production method for building five parameter fields needed for TTI PSDM: pwave velocity, Thomsen's anisotropy parameters and the angles describing the symmetry axis of the anisotropy. This method includes 1D joint inversion (Huang, 2007) to estimate anisotropy parameter and high resolution tomography (Hu, 2011) to obtain accurate velocity models.