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The Krishna Godavari offshore basin to the east of India is a proven reserve, rich in natural gas hydrate. The impact of sediment characteristics on the hydrate formation has already been well established in open literature. In the present study, we have attempted to investigate the mineralogy of sediments collected from KG basin by elemental analysis (energy dispersive spectroscopy) and x-ray diffraction. Various physicochemical characteristics of the clayey sediments such as TDS, salinity, pH, conductivity and resistivity were analysed at various concentrations and compared together. Also, this paper highlights the rheological behavior of the sediment samples with concentrations of 20, 35 and 50 wt% at different experimental temperatures (278.15 K, 283.15 K and 288.15 K). Viscosity measurements were performed for a wide range of shear rates for all concentrations and comparative studies have been conducted on their exhibited behavior. The viscosity of sediment sample were found to be varying from 76.3 to 0.003 Pa s depending on the sediment concentration, temperature and shear rate. In addition, viscoelastic measurements were carried out at various angular frequencies for all the sediment samples. The work aims to characterise the sediments of KG basin and analyse the rheological behavior of sediment solution which has not yet been reported in open literature. This will provide vital information for possible methane recovery from KG basin hydrate reservoir by manipulating the host sediment behavior. • Analysis of physico-chemical properties of the KG basin sediment samples. • Mineralogy of KG basin sediment samples were analysed. • Rheological studies with different sediment concentrations at various temperatures. • Viscoelastic properties of KG basin sediment samples were analysed. [ABSTRACT FROM AUTHOR]

Natural gas hydrate is a potential source of methane which needs to be extracted from under the sea bed. For the economic recovery of methane from natural gas hydrates, production approaches such as depressurization, thermal stimulation, and inhibitor injection are being investigated. However, studies involving hydrate-bearing clayey sediments and recovery of methane from such reservoirs are rare. This work investigates in detail the potency of hydrate dissociation methods such as depressurization by constant rate gas release, thermal stimulation and the combination of two for energy recovery from hydrate bearing clayey sediments underlying a free gas zone. Pure water and two different mud samples containing 3 and 5 wt% of bentonite were used for methane hydrate formation and dissociation studies. Thermodynamic study of methane hydrate in the presence of bentonite clay was also conducted for the above two concentrations. No considerable effect of clay on the inhibition or promotion of methane hydrate formation was observed. Initially, methane hydrate formation has been investigated using pure water, 3 and 5 wt% bentonite mud at an initial hydrate formation pressure of 8 MPa and at a temperature of 278.15 K. Subsequently, methane hydrate dissociation experiments were carried out using depressurization, thermal stimulation and their combination. The effect of the rate of gas release on hydrate dissociation by depressurization was investigated using two different rates of 10 mL/min and 20 mL/min. Thermal stimulation experiments were carried out for ΔT = 15 K at the rate of 7.5 K/hr and the results on methane recovery were recorded. The detailed investigation shows that the combination of the two methods is more efficient for methane production than the standalone method in clayey hydrate reservoir. This study provides important insights into the hydrate production methodology from clayey hydrate reservoirs. [ABSTRACT FROM AUTHOR]