Publications

The complex overburden in the Sisi-Nubi area, located offshore Kalimantan in the Mahakam deltaic system, consists of a series of narrow and rectilinear channels in which gas has accumulated. The gas-filled channels are characterized as having a lower velocity compared to the surrounding sediment velocity. Reprocessing and reimaging the existing legacy data with Q prestack Kirchhoff depth migration performed in 2011 and 2014 did not accurately model the sharp velocity contrasts in the shallow overburden, which led to image distortion in the deeper reservoir level and resulted in less confidence interpretation and a high level of uncertainty in the amplitude variation with offset analysis. In the area with ultra-shallow-water depths (ranging from 60 to 100m), the conventional reflection tomography workflow utilized in the legacy reprocessing workflow did not adequately resolve the complexities of the shallow overburden due to the weak shallow seismic reflections and large reflection angle range that goes beyond critical angle. To resolve the near-surface model complexity, the 3D prestack depth migration project integrates full-waveform inversion in the velocity model building to delineate the velocity variation in the shallow overburden; this improves the reservoir imaging below the shallow gas anomalies.