Numerical Simulations of Depressurization-Induced Gas Production from the Gulf of Mexico, the Blue and Orange Walker Ridge 313 and the Green Canyon 955 Hydrate Deposits

In 2009, the U.S. Department of Energy, National Energy Technology Laboratory expedition in collaboration with the U.S. Geological Survey confirmed that gas hydrate occurs at high saturations within reservoir-quality sands in the Gulf of Mexico. A dataset of density and resistivity logs from the gas hydrate logging-while-drilling (LWD) expedition of the Joint Industry Project, Leg II were collected for the Walker Ridge 313 and Green Canyon 955 sites. The hydrate saturations were calculated from the resistivity logs using Archie’s Law with exponents of both n=1.5 and 2.5. From this interpretation and density log data vertical descriptions of hydrate saturation and porosity variability were developed to create geological models of the Blue and Orange Walker Ridge 313 and Green Canyon 955 deposits at different well interval locations. The set of seismic attenuation data from the pre-drill analysis and the LWD data provide approximate spatial-dimensional descriptions of the reservoir in the horizontal direction. Numerical simulations of gas production from the Gulf of Mexico hydrate reservoirs were conducted using the depressurization method at a constant bottomhole pressure. The results revealed that hydrate deposits can be easily destabilized due to their proximity to the base of hydrate stability. The predicted production rates display high (2.3-13.0 MMscf/day) values making the reservoirs potentially attractive targets for further exploration. The sustained high rates were maintained during first several years before the hydrate completely dissociated, releasing all of their stored methane. To evaluate longer production periods the spatial boundary conditions in the radial direction was increased. The results showed a broad development of secondary hydrate formation around a well at reservoir models with extended dimensions. The reasons of hydrate reformation occurrence are discussed. The obtained data emphasize the importance of the evaluation of reservoir spatial boundary conditions in prediction of its production potential.