Measuring the in Situ Hydrate Saturation from γ-Ray Transmissivity Changes during Local Dissociation

The worldwide abundance of gas hydrates in areas with engineering activities highlights the need for an accurate understanding of how much hydrate the soil contains, before any subsequent assessments are made. For the currently deployed gas hydrate saturation measurement, techniques are based on absolute measurements, derived from either the elastic properties of the formation, its nuclear magnetic resonance, or its electrical resistivity. None of those methods is wholly satisfactory, because of either the required reference measurements or a high dependence upon empirical correlations. This study explores the possibility to determine the hydrate saturation from relative measurements, by deriving its initial value from changes in γ transmissivity during the dissociation process of the contained hydrate. A customized testing apparatus was built, in which hydrate-bearing sand samples of up to 40% pore space saturation were first formed and then tested. The γ transmission from a 60Co source was measured by a...