Using x-ray computed tomography to estimate hydrate saturation in sediment cores from Green Canyon 955, northern Gulf of Mexico

Quantifying the amount of gas hydrate in a reservoir provides valuable insight on gas hydrates' potential as a resource and their contribution to the global carbon cycle. We develop a new method to estimate hydrate saturation from density-sensitive x-ray computed tomography (XCT) scans of pressure cores from the northern Gulf of Mexico (Green Canyon Block 955). Although several studies have used XCT to quantify gas hydrate in the fractures of fine-grained sediments, our study is one of the few to use XCT for coarse-grained (sand and silt) reservoirs. We calibrate our new method with grain density and quantitative degassing measurements from the same intervals. This paper uses the density difference between gas hydrate (0.924 g/cm(3)) and pore-water brine (1.035 g/cm(3)) and assumes these changes linearly affect the XCT measurements allowing for estimates of hydrate saturation. Overall, the XCT calculations agree with the hydrate saturation from quantitative degassing. For example, in core H005-3FB-3, quantitative degassing indicated a hydrate saturation of 88% +/- 3.5%, whereas the XCT calculations yielded a saturation of 90% +/- 4.8%. These results are encouraging because they suggest that XCT analysis has the potential to nondestructively estimate hydrate saturation.

Automated summary

This study develops a new method to estimate hydrate saturation in reservoirs using density-sensitive XCT scans and verifies its accuracy with quantitative degassing measurements. The results show that XCT analysis has the potential to nondestructively estimate hydrate saturation.