Application of tubular silicone (PDMS) membranes for gas monitoring in CO2–CH4 hydrate exchange experiments

Abstract

The exchange of hydrate-bond CH4 with CO2 is one possible method for the production of CH4 from hydrate-bearing sediment which was investigated on different scales in the SUGAR project. Tubular polydimethylsiloxane (PDMS) membranes were utilized to monitor the spatial and temporal gas distribution in a large-scale experimental simulation on CO2–CH4 gas hydrate exchange.The suitability of PDMS membranes for the measurement of gaseous and dissolved CO2 and CH4 concentrations in pure and mixed gas systems was evaluated in lab-scale experiments. The results reveal a strong interacting mutual influence of CO2 and CH4 in CO2–CH4 mixed feed composition and in the presence of water. The competitive absorption between CO2 and H2O as well as membrane plasticization, which increases CH4 permeability and reduces CO2 permeability, makes a direct correlation of mixed systems to pure systems and a quantification of the gas concentration in the feed reservoir impossible.The successful run of five tubular PDMS membranes, employed in a large test reservoir during an experimental simulation of CO2-driven CH4 hydrate decomposition, demonstrates the high stability of the material in harsh conditions. Also, a time-resolved observation of the progressing CO2 front is possible and makes membrane incorporation a valuable addition to conventional ex situ gas measurements in reservoir tests of various dimensions. The monitoring technique can significantly contribute to a comprehensive process understanding with respect to the spatial distribution of hydrate formation, dissociation and reformation in the presence of CO2 and CH4.