Sensitivity Analysis of Gas Production from Class 2 and Class 3 Hydrate Deposits

• Main Authors: Reagan, Matthew, Moridis, George, Zhang, Keni
• Language: unknown
• Published: 2009
• Subjects: 54; ANISOTROPY; EFFICIENCY; ENERGY SOURCES; GAS HYDRATES; GASES; HYDRATES; HYDROCARBONS; PERMAFROST; POROSITY; PRODUCTION; SEDIMENTS; SENSITIVITY ANALYSIS; WATER; WELL SPACING; Ice; permafrost
• Online Access: http://www.osti.gov/servlets/purl/960375; https://www.osti.gov/biblio/960375

Gas hydrates are solid crystalline compounds in which gas molecules are lodged within the lattices of an ice-like crystalline solid. The vast quantities of hydrocarbon gases trapped in hydrate formations in the permafrost and in deep ocean sediments may constitute a new and promising energy source. Class 2 hydrate deposits are characterized by a Hydrate-Bearing Layer (HBL) that is underlain by a saturated zone of mobile water. Class 3 hydrate deposits are characterized by an isolated Hydrate-Bearing Layer (HBL) that is not in contact with any hydrate-free zone of mobile fluids. Both classes of deposits have been shown to be good candidates for exploitation in earlier studies of gas production via vertical well designs - in this study we extend the analysis to include systems with varying porosity, anisotropy, well spacing, and the presence of permeable boundaries. For Class 2 deposits, the results show that production rate and efficiency depend strongly on formation porosity, have a mild dependence on formation anisotropy, and that tighter well spacing produces gas at higher rates over shorter time periods. For Class 3 deposits, production rates and efficiency also depend significantly on formation porosity, are impacted negatively by anisotropy, and production rates may be larger, over longer times, for well configurations that use a greater well spacing. Finally, we performed preliminary calculations to assess a worst-case scenario for permeable system boundaries, and found that the efficiency of depressurization-based production strategies are compromised by migration of fluids from outside the system.