Crystallographic and geochemical properties of natural gas hydrates accumulated in the National Gas Hydrate Program Expedition 02 drilling sites in the Krishna-Godavari Basin off India

Abstract

Abstract This study presents the crystallographic and geochemical properties of different types of pore-space natural gas hydrate recovered by pressure core operations during the National Gas Hydrate Program (NGHP) Expedition 02 at three study areas in the Krishna-Godavari Basin off eastern India. The gas hydrate is structure I with hydration number n = 6.1–6.2, formed predominantly from microbial methane and small amounts of heavier hydrocarbons up to C3. Hydrate crystal lattice constants are nearly uniform regardless of sediment pore-space size. Ethane concentration varies with clay content and to some extent depth, and its measurement helps resolve the contributions of gases dissolved in pore water to hydrate formation. We also assess the disturbance of the core through drilling, using diffraction techniques and visual observation of hydrate-bearing sediments.