Comparison between Pressure Core and Remolded Tetrahydrofuran-Hydrate-Bearing Core Testing Using Sediments Recovered from the Alaska North Slope

Pressure core testing has offered valuable insights into understanding the fundamental geomechanical and hydraulic properties of natural hydrate deposits. Yet, this technology is not always available, and the pressurized samples are complex to analyze. On the other hand, there have been numerous laboratory tests of natural sediments with synthetic hydrates using tetrahydrofuran (THF) to provide complementary geomechanical and petrophysical data. However, a direct comparison of these properties of methane-hydrate-bearing cores to THF-hydrate-bearing specimens does not exist. This study focuses on testing hydrate-bearing reservoir samples collected from the B1 sand in the Alaska North Slope as part of the JOGMEC-DOE-USGS Collaborative Gas Hydrate R&D Project, using the pressure core and a series of synthesized THF-hydrate-bearing samples. The results show that hydrate-free remolded samples, constructed using a water pluviation technique and under similar compression, consolidation, permeability, stiffness (i.e., wave velocities), and lateral stress distributions as the intact core (i.e., posthydrate dissociation of the pressure core), yield similar results. For hydrate-bearing sediments, effective permeability derived from consolidation data increases almost linearly with the effective porosity in the semilog plot for both the pressure core and remolded with THF-hydrate samples. However, the permeability of the THF-hydrate-bearing sediments is about an order of magnitude higher than that of the pressure core when both have identical effective porosities. We have concluded that remolded samples prepared via water pluviation with THF hydrate can provide meaningful geomechanical properties complementary to pressure core testing, however, with higher permeability than pressure core measurements.