Permeability of methane hydrate-bearing sandy silts in the deep-water Gulf of Mexico (Green Canyon Block 955)

Abstract

Permeability is one of the most crucial properties governing fluid flowinmethane hydrate reservoirs. This paper presents a comprehensive permeability analysis of hydrate-bearing sandy silt pressure-cored from Green Canyon Block 955 (GC 955) in the deep-water Gulf ofMexico.We developed an experimental protocol to systematically characterize the transport and petrophysical properties in pressure cores. The in situ effective permeability ranges from0.1md (1.0 × 10-16m2) to 2.4md(2.4 × 10-15m2) in these natural sandy silts cores with hydrate occupying 83%-93% of the pore space. When hydrate dissociates from these cores, the measured intrinsic permeability (k0) is 0.3 md (3.0 × 10-16m2) to 9.3 md (9.3 × 10-15m2); these results are affected by finesmigration during hydrate dissociation.We analyzed samples reconstituted from these sandy silts and found k0 to range from -12 md (-1.2 ×10-14m2) to -41 md (-4.1 ×10-14m2). The water relative permeabilities (krw) of GC 955 pressure cores are large relative to other natural pressure cores from offshore Japan, offshore India, and onshore Alaska. These krw values are also higher than predicted by current conceptual relative permeability models where hydrate fills the pores or coats the grains of the sediments. This fundamental conundrum requires further study. Our work provides essential parameters to reservoir simulation models seeking to predict hydrate formation in geological systems, evaluate the gas production potential, and explore the best way to produce this energy resource in sandy silt reservoirs.