Natural Gas Hydrates in the Krishna-Godavari Basin Sediments under Marine Reservoir Conditions: Thermodynamics and Dissociation Kinetics using Thermal Stimulation

Abstract

The gas hydrate deposits of the Krishna-Godavari (KG) basin in India have a huge potential of fulfilling the energy needs of the country for several years to come. We present a detailed thermodynamic and kinetic study of methane hydrate formation and dissociation in the presence of an actual Krishna-Godavari (KG) basin marine sediment sample at varying concentrations, i.e., 10, 20, and 35 wt %, in an aqueous solution. This study revealed the possibility of dual induction during methane hydrate formation in the presence of pure water and 10 wt % KG basin sediment solution. As the sediment concentration increased, the inhibition effect during the methane hydrate formation became more pronounced. The heat of dissociation values were found to be decreasing with the increase in sediment concentration. The kinetic experiments depicted the stochastic nature during the hydrate formation. The methane gas consumption and the rate of methane hydrate formation were found to be high in the case of pure water, followed by 10, 20, and 35 wt % sediment solutions. However, the initial rate of methane hydrate formation among the sediment solutions was observed to be high in the case of the 20 wt % sediment solution. The water-to-hydrate (W-H) conversion and gas-to-hydrate (G-H) conversion were found to be reducing with an increase in sediment concentration due to the confining effect of the water–gas system. During kinetic dissociation, the stable temperature range before the hydrates actually started dissociating was found to be increasing with sediment concentration, and the maximum temperature up to which the hydrates remained stable was ∼6 °C. The rate of hydrate dissociation was high in the case of the pure water system and slightly decreased in the 10 wt % sediment solution; however, it was found to be almost similar in 20 and 35 wt % sediment solutions. This study will certainly add value toward a better understanding of the KG basin reservoir for future exploration of methane gas from the hydrate deposits.