Identifying and quantifying gas hydrate by joint analysis of P-wave velocity and resistivity

Gas hydrate residing in pore spaces and fractures are two representative distributions in general sediment settings. Morphology of hydrate distribution is essential for assessing its resource potential, understanding its formation, and determining optimum strategies for exploitation. Based on theoretical modeling, we find that in the case of identical hydrate concentration, fracture-filling gas hydrate-bearing sediments (GHBS) generally exhibit higher resistivity but lower P-wave velocity than those of pore-filling GHBS. As a result, the cross plot of these two properties are strikingly different between two types of GHBS. By comparing the cross plot of field measurements to the theoretical cross plot, we hypothesize that the gas hydrate morphology can be identified, and hydrate saturations can also be estimated. We test and verify the hypothesis using well log data from the second gas hydrate expedition in China. The results show that gas hydrate morphologies are successfully identified by this method, and the estimated hydrate saturations generally conform to the pore-water freshening measurements.