EVALUATION OF TWO NORTH SLOPE, ALASKA, DEPOSITS FOR A POTENTIAL LONG TERM TEST OF GAS PRODUCTION FROM HYDRATES

As part of the effort to investigate the technical feasibility of gas production from hydrate deposits, a long‑term field test (lasting 18‑24 months) is under consideration in a project led by the U.S. Department of Energy. We evaluate two candidate depoits: the D‑Unit accumulation at the Mount Elbert site, and the C‑Unit deposit at the PBU‑L106 site, both in North Slope, Alaska. Both deposits are bounded by impermeable shale top and bottom boundaries (Class 3), and are characterized by high intrinsic permeabilities, high porosity, high hydrate saturation, and a hydrostatic pressure distribution. The D‑unit deposit involves a single layer, is shallower, and is characterized by a lower pressure and temperature than the deeper, warmer (and thicker deposit at the PBU‑L106 site, which is composed of two hydrate‑bearing strata separated by a shale interlayer. We investigate by means of numerical simulation involving fine grids the production potential of these two deposits using both vertical and horizontal wells. We also explore the sensitivity of production to key parameters such as the hydrate saturation, the formation permeability and porosity, the system heterogeneity, the boundary permeability, and the initial temperature. The results indicate that the PBU‑L106 deposit has a distinct advantage as a candidate for the long‑term production test. At either site, production from horizontal wells may be orders of magnitude larger than that from vertical ones. Additionally, production increases with the formation permeability and porosity, with the temperature of the deposit, with heterogeneity along the vertical axis (layered systems) and with a decreasing permeability of the boundaries. The effect of the hydrate saturation on production is not monotonic, i.e., it appears to be optimal at medium levels (about 50%) and depends on the time frame of production.