The Reinga Basin is a relatively unexplored sedimentary basin located to the northwest of Northland; it is regarded as the northern continuation of the Northland Basin. The Reinga Basin is bounded to the west by the compressional West Norfolk and Wanganella Ridges. To the northeast, the basin is bounded by Reinga Ridge and the Vening-Meinesz Fracture Zone. In 2008-2009, New Zealand Petroleum and Minerals, jointly with CGG Veritas, acquired two 2-D multi-channel petroleum speculation seismic surveys, Stratus-2D and Reinga-09, within the Reinga Basin. To date, no bottom-simulating reflections (BSRs) indicating the presence of gas hydrates have been conclusively identified in either survey. However, several areas of anomalously high amplitude and unresolved polarity have been identified within the probable gas hydrate stability zone (GHSZ). Prestack inversion on prestack Kirchhoff time-migrated CMP gathers using the Hampson-Russell Suite has been undertaken on these anomalous amplitude areas to determine the nature of these strong reflections. Due to the lack of well control in the Reinga Basin, background velocity models required for the prestack inversion were calculated using several methods; (1) travel-time inversion, (2) stacking velocities, and (3) stacking velocity pseudo-wells. Prestack inversion results from a portion of the STRATUS-2D seismic suggest that most areas of anomalous amplitude are associated with igneous intrusions. P-wave impedance inversions suggest that two of the anomalies may be caused by the presence of shallow (100-200 ms below seafloor), stratigraphically controlled free gas migrating updip along an unconformity.
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Inversion of shallow amplitude anomalies in multi-channel seismic reflection data from the Reinga Basin
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