Modeling of Carbon Dioxide Replacement in Methane Hydrate Structure

Methane hydrate reservoirs as an unconventional resource of natural gas can secure demand of energy in the world for many years. Efficient production prom this resources is the subject of concern. CO2-Methane replacement is a novel method for production from naturally occurring methane hydrate deposits such that methane production and CO2 storage take occur simultaneously.

 In this study a new kinetic model is proposed for CO2-Methane replacement in hydrate structure. This kinetic model is developed based on the mechanism proposed for replacement in the hydrate structure in the presence of excess water in a slurry phase of methane hydrate. According to this mechanism partial breakage of methane hydrate cages, methane-CO2 substitution and formation of CO2 hydrate proceed simultaneously. Methane hydrate dissociation and CO2 hydrate formation kinetic parameters are evaluated experimentally and fitted on polynomials as function of pressure and temperature.

Evaluation of the effects of pressure and temperature on the replacement efficiency show that higher replacement efficiency is obtained at higher temperatures and lower pressures. It means that replacement kinetic is controlled by methane hydrate dissociation step. Since, higher temperature and lower pressure favor dissociation of methane hydrate. At 278.15 K the replacement efficiency decreased from 15.78 to 8.80 as total pressure increased from 55 bar to 65 bar, at 280.15 K it decreased from 26.98 to 15.91 by decreasing total pressure from 60 bar to 70 bar. At same pressure 60 bar for 280.15 K and 278.15 K the replacement efficiency is 20.96 and 11.59 respectively.