Towards Efficient Ocean Bottom Seismic Acquisition in Pre-Salt Brazil

Summary The Brazilian Pre-Salt is undergoing rapid growth spurred by changes in local legislation, resulting in much increased demand for seismic data, especially Ocean Bottom Node data to characterize and monitor the complex carbonate reservoirs. This demand has led to a “traffic jam” of permit applications that will not allow surveys to be acquired where and when they are needed to influence business decisions. Increasing OBN seismic efficiency is one way to try to alleviate this congestion, by increasing the rate of node handling operations and the efficiency of source operations. We describe a model to estimate the duration and cost of such surveys, considering various scenarios for node deployment rates and number of seismic sources operating simultaneously. We identify the most efficient combinations that reduce idle time for the vessels. These include use of two autonomous source vessels or a single source vessel carrying quad and hexasource configurations. In all cases we use small volume seismic sources to reduce the acoustic energy output into the ocean. Field testing will be required to assess the ability of small sources (under 1000ci) to image the Pre-salt reservoirs, and the feasibility of deblending algorithms to preserve fidelity for 4D seismic monitoring.