Experimental and numerical investigation of hydrate-guest molecule exchange kinetics

Abstract

The 2012 Iġnik Sikumi #1 Field Trial in Alaska was designed to test at field scale a methane hydrate production methodology that involves injecting carbon dioxide (CO2) in situ to exchange with methane (CH4) within a hydrate structure, thus releasing the methane for production. Since the completion of the field trial, experimental and numerical investigations have sought to better understand observations in terms of CH4 production and changes to the hydrate bearing formation. Collectively, these insights may lead to more effective strategies for producing CH4 from naturally occurring hydrates. This study presents results from a laboratory experiment performed at conditions experienced during the field trial (8.27 MPa and 275.15 K) to collect data relating to the CH4 molecular exchange process. The experiment intentionally isolated the kinetic guest molecule exchange process from additional hydrate formation and mechanical changes to the hydrate bearing sand. Data were used to inform development of numerical models that were then used to fit key hydrate parameters (bound water saturation, kinetic formation constant, kinetic exchange constant, and preferential exchange weighting factors) and analyze experimental results. Results were in agreement with observations of preferential CO2/CH4 guest molecule exchange at Iġnik Sikumi #1 and from previous experimental studies while providing quantitative estimates of changing hydrate compositions. Additionally, simulations confirmed hydrate behavior and composition profiles otherwise indirectly evidenced by experimental results.