Modeling Subsurface Gas Release in Tropical and Shallow Waters: Comparison with Field Experiments off Brazil's Northeast Coast

ABSTRACT

Despite the fast growth of underwater oil and gas exploration in low latitude regions, very few experimental data acquisition and modeling studies involving gas release in tropical and shallow waters are found in literature. In this article, a dataset of geophysical and gas release measurements obtained from an in situ experiment conducted off the northeastern Brazilian coast are used as a baseline for evaluating the GASOCEAN blowout model. Hydrological and hydrodynamic data were collected for distinct seafloor gas plume releases (3000 to 9000 L/hr) during neap/spring tides of summer/dry and winter/wet periods. Simulation results indicate that the gas plume is horizontally displaced by the horizontal current as it rises through seawater column. The extreme situation provided a critical radius (maximum horizontal displacement) from the gas release source of 35.2 m. The comparison between the measured and the calculated data showed that the model satisfactorily represented the main features of the gas release, such as the displacement (11.6–35.2 m), diameter (1.2–2.8 m), and ascending time (1.1–1.6 min) of the plumes. Although the mean plume widths have the same order of magnitude between the measurements and the calculations, improvements may enhance the model's performance during the earlier plume development.

Key Words:

• underwater gas blowout
• tropical shallow water
• northeastern Brazilian coast
• mathematical modeling
• GASOCEAN model

ACKNOWLEDGMENTS

This research was supported by the Brazilian National Research Council (CNPq) under the project grants 550197/2005-2 (CTPetro 16/2005) and 558143/2009-1 (CTHidro/CTInfra 38/2009). The authors are also thankful to everyone who was engaged in the sea campaigns.