Permeability Evolution of Gas Hydrate-Bearing Pressure Core Sediment Recovered from the Alaska North Slope HYDRATE 02 Geo Data Well

Quantifying petrophysical properties of gas hydrate-bearing sediments is essential for evaluating natural gas production efficiency from gas hydrate. In 2022, pressure cores were recovered from the HYDRATE 02 Geo Data Well, (GDW) on the North Slope, in support of the JOGMEC-DOE-USGS Collaborative Gas Hydrate R&D Project in Alaska. Pressure core sampling of the B1 sands, where in situ hydrate saturation and pore structures were preserved by maintaining temperature and pressure within hydrate stability conditions, enabled evaluation of permeability evolution during gas hydrate dissociation under controlled laboratory conditions. Here, we integrate analyses using the Pressure Core Analysis and Transfer System (PCATS) scanning on-site in Alaska, laboratory Pressure-core Nondestructive Analysis Tools (PNATs) measurements, and permeability testing with the Transparent Acrylic Cell Triaxial Testing system (TACTT). Results show that effective permeabilities (hydrate-bearing sediment) are typically one to two orders of magnitude lower than intrinsic permeabilities (hydrate-free sediment) under the same effective stress condition, consistent with previously reported pressure-core studies. Furthermore, increasing effective stress induces porosity reduction and permeability loss, consistent with consolidation expected during reservoir depressurization. Core samples from within the primary sand reservoir were typically clean sand beds with high gas hydrate saturation. Detailed evaluation of one sample revealed intervals of lower gas hydrate saturation of two types: (1) fine-grained laminae and (2) clean sand beds that were undersaturated despite favorable hydrate-formation conditions. The relationship between median grain size (D50) and intrinsic permeability demonstrates that the coarse-grained portion of the B1 sands follow a steeper in the log–log relationship trend than that observed in available global gas hydrate data sets. Permeability in hydrate-bearing sands appears to be strongly controlled by both hydrate saturation and subtle reservoir matrix textural variability, and the associated permeability reduction observed in GDW samples during depressurization likely also occurred during a long-term production test associated with the production well HYDRATE P1 (PTW-1). Integrating pressure-core measurements, grain-size regressions, and log interpretation provides valuable inputs for reservoir simulation, improving the understanding of gas production behavior at the Alaska North Slope extended-duration gas production test site.