Geological & Petrophysical Findings from Production Test Wells of Gas Hydrate Reservoirs at the Kuparuk State 7–11–12 Site in the Prudhoe Bay Unit on the Alaska North Slope

Abstract

Abstract As part of a long-term production test targeting gas hydrate reservoirs at the Kuparuk State 7–11–12 site in the Prudhoe Bay Unit on the Alaska North Slope, two production wells (PTW-1 and PTW-2) and one monitoring well (GDW) were drilled in 2023. This study advances reservoir characterization based on the earlier stratigraphic test well (STW) by integrating geological and petrophysical evaluations from the three new wells to refine initial reservoir conditions and reduce associated uncertainties. Well-to-well correlation established the structural and stratigraphic framework across the site, confirming good lateral continuity of the target sands and supporting the presence of a normal fault east of the STW at the B1 sand level. The observed B1 sand depths are consistent with the existing structural model characterized by a subtle structural high, with no major faulting near the production wells. Gas hydrate occurrences were identified in both B1 and D1 sands of the new wells. No distinct water-bearing intervals indicated by a sharp resistivity transition interpreted as a gas hydrate/water contact were observed in the B1 sand. To assess spatial heterogeneity in gas hydrate concentration, resistivity logs were compared with seismic impedance data, revealing significant positive correlations and demonstrating the utility of seismic impedance as an indicator of regional gas hydrate saturation trends. Reservoir properties in the B1 sand and its bounding units were evaluated using conditioned log data from the PTW-1 and GDW. The analysis focused on porosity, gas hydrate saturation, and intrinsic and effective permeability. A newly applied estimation method yielded lower permeability values than the conventional approaches. These estimates were validated using pressure core data from the GDW, providing a basis for refining log-based estimates in future updates. These integrated findings support continued refinement of the geological and reservoir models, enabling a more detailed understanding of reservoir behavior during production testing.