Synthesising Uniform Gas Hydrate in Natural Porous Media under Partially Saturated and Fully Water Saturated Conditions

The majority of laboratory techniques used to measure the geophysical properties of sediment hosted gas hydrates assume a uniform distribution of hydrate in the pore space in order for results to be interpreted correctly. Of the several methods for hydrate synthesis in the laboratory, the technique thought to produce the most homogeneous specimens is the partial water saturation method. There is also a method thought by some to produce homogeneous hydrate in water saturated sediments - the excess water method. X-ray CT scanning has shown that at low (10%) and high (60%) initial starting water saturations, hydrate formation is indeed relatively uniform across a sand specimen, when formed under partially saturated conditions. However, at water saturations between 30-40%, hydrate formation is no longer evenly distributed across the same sand core when using this method. Until recently, the excess water method had not been investigated with X-ray imaging, and so actual hydrate distribution within a sediment is unknown when formed in these conditions. In an effort to identify a reliable method that will result in uniform methane hydrate formation in sediment cores, several different procedures were investigated using the partial water saturation method: 1. Using an additive to the pore water in the form of salt or a biological initiator; 2. Mixing kaolinite into the sand pack and 3. Freezing of the moist sand before pressurization with methane. Additionally, hydrate was formed in fully water saturated conditions by use of the excess water method. In each experiment, X-ray CT scanning was utilized in order to observe the distribution of the hydrate inside the sand, and determine the effectiveness of each technique at producing a uniform hydrate bearing sediment.