Comparison of Gas Production From Gas Hydrate Reservoirs Using Vertical and Horizontal Wells

Methane hydrates may contain significant amounts of hydrocarbons both in the permafrost and in oceans due to favorable settings of pressure and temperature. This simulation-based work is aimed to estimate and compare natural gas production from hydrate-bearing reservoirs on the Alaskan North Slope using horizontal and vertical wells in hydrate bearing reservoirs. It has been established that high amounts of gas can be obtained from hydrate reservoirs using depressurization technique and vertical wells [1]. In this paper, numerical studies are conducted on similar reservoirs using horizontal and vertical wells in the hydrate bearing layers using CMG STARS. CMG STARS (Steam, Thermal, and Advanced Processes Reservoir Simulator) is a three-phase multi-component thermal and steam additive simulator, developed by the Computer Modeling Group Limited (CMG). This paper also examines the feasibility of hydraulic fracturing in the permafrost methane hydrate reservoirs.

The geologic settings of the hydrate reservoirs are obtained from the USGS-NETL Methane Hydrate Code Comparison project [2].  For comparison of performance of both the wells, various values of porosity, intrinsic permeabilities, reservoir temperature, hydrate saturation and free water saturation will be used in the simulations and results will be compared. In the base reservoir model, a hydrate layer is bound by two shale layers, above and below. The vertical well simulation will be carried out using a cylindrical domain and the horizontal well simulation will be carried out using a rectangular Cartesian domain. Average pressure and temperature are 12°C and 9 MPa in the hydrate bearing layer. The production will be adjusted to the volume of hydrate present in each of the reservoirs. It is predicted that the horizontal well will produce gas more instantaneously than the vertical well.

1.       Sloan, E.D., and C. Koh, Clathrate Hydrates of Nautral Gases. 3rd Edition, Boca Raton, FL: Taylor and Francis, Inc., 2008

2.       Wilder, J., et al. An International Effort to Compare Gas Hydrate Reservoir Simulators. In Proceedings of the 6th International Conferenceon Gas Hydrates. 2008. Vancouver, British Columbia, Canada.