Distribution of Gas Hydrates indicators in the Magnolia field, Gulf of Mexico

Gas hydrates are a complex solid structure formed when molecules of light hydrocarbon, usually methane, are trapped in a cagelike structure of frozen water. To be formed, water and gas must exist in an area with high pressure and low temperature in the uppermost few hundred meters in marine sediments or in some permafrost zones onshore. This study investigated the occurrence and distribution of gas hydrate indicators in a reflection seismic dataset from the Magnolia deepwater oil field in the Gulf of Mexico, approximately 180 miles south of Cameron, Louisiana. The first step in this study was to establish the geothermal gradient in the sediments, determine the water bottom temperature, and estimate the gas composition. Common values cited in the literature for this area were used. Subsequently, the program CSMHyd, from the Colorado School of Mines, was used to determine the pressure-temperature stability curve for gas hydrates. The depth range in which hydrates can form, the Gas Hydrate Stability Zone (GHSZ), extends from the seafloor to the depth at which the stability and geothermal gradient curves intersect. The base of the GHSZ horizon was generated throughout the 3D seismic dataset using Petrel Seismic Interpretation software. Strong, reverse-polarity seismic reflections were interpreted to indicate accumulations of free gas trapped beneath the GHSZ, thereby suggesting hydrate presence above the base. The mapped gas indicators are consistent with the presence of gas hydrates as documented in other seismic studies and drilling in other areas within the Gulf. Petrel was used to map faults that might provide conduits for vertical gas migration and that serve to disrupt the continuity of the free gas features. Gas hydrates might be hazardous. Therefore, knowing where they are can prevent potential accidents during drilling operations. Also, gas hydrates may be produced as an energy source someday