Publications

An area offshore northwest Java including a major and complex gas reservoir was surveyed using an ocean bottom cable (OBC) acquisition. The survey consisted of orthogonal shot and receiver lines, featuring an ultra-sparse 400 m line interval for both shots and receivers. This sparse layout resulted in a large common offset vector (COV), lack of fold, and poor illumination, leading to a pronounced acquisition footprint. The presence of gas clouds in the shallow section introduced strong kinematic distortions and amplitude loss due to spatial velocity variations and absorption effects, severe attenuation affected penetration of the deeper layers. Velocity heterogeneity within the carbonate layer and gas clouds in the overburden further complicated velocity model building in this extremely shallow water environment (7-20 m). Well planning using vintage seismic data proved challenging for this field, as the imaging did not clearly capture gas generation and migration pathways.

We demonstrate how an advanced workflow can overcome challenges associated with imaging beneath gas clouds and heterogeneous carbonate layers using a sparsely acquired OBC dataset. Key elements of the workflow include Visco-acoustic Time-lag Full Waveform Inversion (Q-TLFWI) and Least Squares Q-Pre-Stack Depth Migration (LS-QPSDM), along with high-fidelity 5D interpolation. Q-TLFWI was applied to obtain reliable velocity and Q updates, which were critical for addressing kinematic distortion and amplitude loss. To further address illumination issues caused by velocity heterogeneity and sparse acquisition and amplitude loss due to absorption effects, LS-QPSDM was applied to improve the imaging of targeted regions. Additionally, 5D interpolation was applied to minimize the impact of the large COV spacing and further enhance signal-to-noise ratio (S/N) and detailed structural clarity. The workflow resulted in an improved image, facilitating better interpretation of the carbonate build-up reservoirs and provided a clearer geological understanding of the gas generation and migration systems.