Thrust Fault and Sub-Thrust Imaging in the Taranaki Basin with Least-Squares Tilted Orthorhombic Q-RTM

Summary The Taranaki Basin is one of New Zealand’s largest basins. Initially forming as a Cretaceous rift basin, it has over 400 exploration and production wells. Early basin history is characterized by extensional fault blocks, and as basin evolution continued, thrusting and inversion associated with the convergent active margin set up trapping mechanisms for petroleum accumulations. Recent fault blocks within shallow Plio-Pleistocene sediments exhibit strong azimuthal anisotropy. Without considering this effect, seismic imaging in the area suffers structural discontinuity and fault misplacement. Below these fault blocks, it is challenging to image the thrust system and sub-thrust structures due to poor illumination from strong velocity variation around the thrust. To overcome these challenges, we focused on two major aspects. First, we built a tilted orthorhombic (TORT) velocity model to handle the strong azimuthal anisotropy in the overburden. At the time, we only had access to narrow-azimuth (NAZ) data, thus we derived the TORT parameters through scanning based on stack and gather responses. Second, we applied least-squares (LS) TORT Q-RTM to honor azimuthal anisotropy and compensate for poor illumination from the complex velocity. We observed significant imaging uplifts compared with the vintage data that subsequently provided an improved geological interpretation.