Constraining Gas Hydrate Occurrence in the Northern Gulf of Mexico Continental Slope: Fine-Scale Analysis of Grain Size in Hydrate-Bearing Sediments

Authors: Alexandra Hangsterfer, Neal Driscoll and Miriam Kastner

Venue: 6th International Conference on Gas Hydrates, Fairmont Hotel, Vancouver, Canada, July 6-10, 2008. http://www.icgh.org/ [external site].

Abstract: Within the subseafloor, methane hydrates form within the gas hydrate stability zone (GHSZ). Two areas within the Gulf of Mexico (GOM) were investigated in this study: Keathley Canyon and Atwater Valley. The GOM contains an underlying petroleum system and deeply buried, yet dynamic salt deposits. Salt tectonics and fluid expulsion upward through the sediment column lead to the formation of fractures, through which high salinity brines migrate into the GHSZ, destabilizing gas hydrates. Originating from the thermal and biogenic degradation of organic matter, thermogenic and biogenic hydrocarbons also migrate to the seafloor along the GOM’s northern slope. Gas hydrate occurrence can be controlled by either primary permeability, forming in coarse-grained sediment layers, or by secondary permeability, forming in areas where hydrofracture and faulting generate conduits through which hydrocarbon-saturated fluids flow. The goal of this study is to determine the relationship between grain-size, permeability, and gas hydrate distribution. Grain-size analyses were performed on cores taken from Keathley Canyon and Atwater Valley in the GOM, on sections of cores that both contained and lacked gas hydrate. The initial results indicate that gas hydrate occurrence in Keathley Canyon and Atwater Valley is constrained by secondary permeability, being structurally controlled by hydrofractures and faulting that act as conduits through which methane-rich fluids flow.

Related NETL Project
This presentation is related to the NETL project DE-FC26-01NT41330, “Characterizing Natural Gas Hydrates in the Deep Water Gulf of Mexico: Applications for Safe Exploration and Production Activities”. This project is conducting a range of tool development, data analysis, laboratory studies and field investigations designed to improve understanding of the occurrence and distribution of naturally-occurring methane hydrate in the deepwater Gulf of Mexico. The project is primarily focused on determining industry's current capabilities for remote detection and characterization of hydrates for the purpose of predicting how natural gas hydrates affect the safety of deepwater oil and gas E&P operations. In addition, the project is providing data that can be used in the study of hydrate impacts on global climate, and will aid greatly in the assessment of hydrate as a potential future resource.

Project Contacts
NETL – Richard (Rick) Baker (richard.baker@netl.doe.gov or 304-285-2714) Chevron Technology Petroleum Company – Emrys Jones (emry@chevron.com or 281 566-2269)