Experimental Research On Gas Production From Natural Gas Hydrate By Depressurization

Natural gas hydrate can be an important potential energy resource for the future. The technology for exploiting natural gas hydrate has became a hotspot in energy academic community. In this paper formation and dissociation of methane hydrate in subsea sediments have been studied under simulated HSZ (hydrate stability zone) conditions. The process of hydrate formation and dissociation is analyzed to reveal the impact of hydrate saturation ,back pressure, sand-pack permeability on system temperature, pressure, gas production rate and gas yield, and study the law of reservoir electric resistivity variation and experimental test the minimum driving force (drawdown pressure) for hydrate dissociation. Experimental results show that by way of interval water injection, nearly all the gas is converted into hydrate,and only water and hydrate reserve. Hydrate saturation, back pressure, pore property of sand-pack have impact on hydrate dissociation and gas output: the bigger the hydrate saturation, the higher the economic value; the back pressure is proposed at about 2MPa~3MPa. The high pressure will lead to small gas production, and the low pressure will lead to hydrate formed in second order in wellbore and immediate vicinity of wellbore and cause some impair because of dissociation endothermic reaction; the better the penetrability of porous medium, the easier the gas output. Experimental studied the law of reservoir electric resistivity variation during hydrate dissociation, which shows that salinity and connectivity of pore fluid reciprocally influence the reservoir electric resistivity, and this reveals the mechanism of hydrate dissociation in porous medium. Experimental test the minimum driving force (drawdown pressure) for hydrate dissociation, which is useful to the sand face pressure design.