Occurrence of gas hydrate in Oligocene Frio sand: Alaminos Canyon Block 818: Northern Gulf of Mexico

Abstract

A unique set of high-quality downhole shallow subsurface well log data combined with industry standard 3D seismic data from the Alaminos Canyon area has enabled the first detailed description of a concentrated gas hydrate accumulation within sand in the Gulf of Mexico. The gas hydrate occurs within very fine grained, immature volcaniclastic sands of the Oligocene Frio sand. Analysis of well data acquired from the Alaminos Canyon Block 818 #1 (''Tigershark'') well shows a total gas hydrate occurrence 13 m thick, with inferred gas hydrate saturation as high as 80% of sediment pore space. Average porosity in the reservoir is estimated from log data at approximately 42%. Permeability in the absence of gas hydrates, as revealed from the analysis of core samples retrieved from the well, ranges from 600 to 1500 millidarcies. The 3-D seismic data reveals a strong reflector consistent with significant increase in acoustic velocities that correlates with the top of the gas-hydrate-bearing sand. This reflector extends across an area of approximately 0.8 km 2 and delineates the minimal probable extent of the gas hydrate accumulation. The base of the inferred gas-hydrate zone also correlates well with a very strong seismic reflector that indicates transition into units of significantly reduced acoustic velocity. Seismic inversion analyses indicate uniformly high gas-hydrate saturations throughout the region where the Frio sand exists within the gas hydrate stability zone. Numerical modeling of the potential production of natural gas from the interpreted accumulation indicates serious challenges for depressurization-based production in settings with strong potential pressure support from extensive underlying aquifers.

Geologic controls on gas hydrate occurrence in the Mount Elbert prospect, Alaska North Slope

“…Overall, the available data suggests that gas hydrate in sand reservoirs typically leaves only small free (or mobile) water saturations (which varies with reservoir quality both laterally and vertically) with limited documented cases of intermediate saturation (ex. Collett et al, 2009;Dallimore and Collett, 2005;Boswell et al, 2009). Nonetheless, there are few detailed case studies to reference, and the Mount Elbert core data do suggest large, low S h (<20%; although not observed in log data, and not sufficient to create the seismic responses seen laterally) sections below the primary gas hydrate-bearing reservoirs, so this scenario clearly remains a possibility Inks et al, 2009;Behseresht et al, 2009).…”

Methane Flux and Authigenic Carbonate in Shallow Sediments Overlying Methane Hydrate Bearing Strata in Alaminos Canyon, Gulf of Mexico

“…The geology of the area is dominated by northeast-southwest trending salt-cored box folds of the Perdido fold belt which lie beneath a thick, mobile salt canopy [33,34].…”

“…Research by others has identified Block 818 in AC as a site of significant hydrocarbon flux and oil, gas, and gas hydrate accumulation [33][34][35][36][37][38][39] in a variety of turbidite deposits from sand sheets to amalgamated and leveed channel systems [36]. Boswell et al [34] used well data and 3-D seismic data to show evidence for significant, concentrated gas hydrate accumulation near the AC 818 #1 ("Tigershark") well.…”

“…Boswell et al [34] used well data and 3-D seismic data to show evidence for significant, concentrated gas hydrate accumulation near the AC 818 #1 ("Tigershark") well. Uplift of the Perdido fold belt has raised gas reservoirs in Oligocene Frio sands within the Lower Tertiary deepwater turbidite to shallow depths above the base of the gas hydrate stability (BGHS) zone.…”

“…Uplift of the Perdido fold belt has raised gas reservoirs in Oligocene Frio sands within the Lower Tertiary deepwater turbidite to shallow depths above the base of the gas hydrate stability (BGHS) zone. The Oligocene Frio sand is very fine-grained, immature volcaniclastic sand with a high porosity [34].…”