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 as it has three significant gas and condensate discoveries in the pre-salt carbonate and volcanic reservoirs -- Seat, G൥a, and P⭠de A洣ar. 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 pre-salt 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 ultra-long offsets and multi-azimuthal illumination and then carefully processing the data is required to accurately reveal the area's pre-rift section and basement morphology under study.