By Shaun Dunn, Sonardyne International
Brazil’s presalt reservoirs lie in more than 2,000 m water depth, plus another 3,000 m beneath the seabed, making seismic imaging particularly challenging. A new approach to acquiring 4D seismic data, promising more efficient and cost-effective surveillance of complex presalt fields, is being tested offshore Brazil.
Traditional seismic surveys using ocean-bottom nodes (OBNs), while providing high-quality seismic data, are often expensive and logistically complex, involving the large-scale deployment and recovery of nodes using remotely operated vehicles (ROVs). These factors can limit the frequency and economic viability of frequent 4D seismic campaigns, which are essential for understanding reservoir dynamics over time.
This is particularly challenging for monitoring large presalt carbonate fields where production by alternating water and gas injection generates subtle and complex 4D signals that are difficult to measure. These signals require on-demand monitoring with sufficient fidelity and repeatability to overcome the high levels of survey noise prevalent in conventional node-based surveys.
The "On-Demand Ocean Bottom Node" (OD OBN) program is addressing these challenges by providing a disruptive approach to time-lapse seismic data acquisition. At its core is a long-term OBN system that can remain on the seabed for several years, capturing seismic data that can be recorded and harvested on-demand using autonomous underwater vehicles (AUVs), without the need for repeated deployment and retrieval cycles.
Launched in 2018, the research and development program is a collaboration between partners Shell, Petrobras, SENAI CIMATEC and Sonardyne, supported under the Research Development and Innovation funding clause of the Brazilian National Agency for Petroleum, Natural Gas and Biofuels (ANP).
