Benefits of integrating seismic and gravity data in a subsalt environment: A case study at block BM-C-33, deepwater Campos Basin, offshore Brazil

Abstract Imaging subsalt layers is challenging in the BM-C-33 block in the Campos Basin’s ultradeep waters. This block is important because it has three significant gas and condensate discoveries in the presalt carbonate and volcanic reservoirs—Seat, Gávea, and Pão de Açucar. Understanding basement morphology is essential to better define the petroleum system in the area. To that end, we performed a 2D gravity modeling exercise along a northwest–southeast section using seismic interpretation as input to reduce the ambiguity of the modeling exercise. To achieve this, we fixed the main sedimentary horizons and their densities (calculated via well-log information) to better estimate the top of the basement morphology. This interpretation strategy better delineated the presalt sedimentary section and the complex structural framework with two asymmetric grabens bounded by a prominent horst, interpreted as a migration focusing high in the BM-C-33 area. In addition, our findings show that obtaining clear images remains challenging even after extensive processing of the seismic data set. We suggest that seismic node acquisition with ultralong offsets and multiazimuthal illumination and then carefully processing the data is required to accurately reveal the area’s prerift section and basement morphology under study.