Experimental Studies On Physical Parameters Of Simulated Natural Gas Hydrate Bearing Sediments And Thermal Stimulation Exploitation

As a 21st century strategic energy resources, natural gas hydrate (NGH) has great development potential and application prospects. The properties and mining methods have attracted national attention. Through experiments, analysis and calculation technology, the relationship between physical parameters and NGH saturation, the law of dissociation and dissociation-front movement in porous media by thermal stimulation were discussed in this paper.The experiment devices were designed to simulate submarine in-situ hydrate sediments. Experiments with different hydrate saturations were conducted and the results showed that, when Hydrate formation, the pressure dropped, the temperature increased slightly, and the resistivity first decreased and then increased significantly. The functional relation between NGH bearing sediments resistivity and NGH saturation could be obtained by equal NGH bearing sediments resistance to the pore water, rocks skeleton, and hydrate resistance in parallel. Regressed the Archie formula and pointed out that NGH illiquidity and cementing effect made saturation exponent n values on the high side. Permeability experiments showed that the reservoir permeability decreased with hydrate formation in porous media and NGH made pore-network structure changed. For hydrate saturations less than 30%, the experimental values of permeability agreed better with its theoretical estimates for the grain coating model, and the value of N=3 compared better with the Masuda's permeability model. However as hydrate saturation exceeded above 30%, the experimental results were in better agreement with the pore filling tendency of hydrate, and the value of N=9 fit better.NGH thermal stimulation experiment showed that, the gas production could be divided into three stages: free gas output, NGH dissociation, free gas output; Water production rate fluctuated in the water injection rate. Higher injection temperature and rate could increase decomposition rate but decrease energy efficiency; in the same conditions of injection temperature and rate, the energy efficiency decreased during the hot-brine injection period because of heat-loss.Temperature could monitor dissociation-front better than resistivity and the moving rate could be drawn by multiple regression method. According to the energy conservation, the quantity of injection heat equal to the sum of hydrates decomposition and the heat-loss of each part. The energy distribution could be calculated, which used in NGH decomposition account for 39.48%.