Gas hydrates have been attracted a great deal of attention because of their potential as an energy substitute and the climate implications. Drilling and sampling research on the hydrate deposit in the Shenhu Area on the northern continental slope of the Southern China Sea was a big breakthrough for hydrate investigation in China, but as a new potential energy source, how the gas can be effectively produced from hydrate deposits has become a hot research topic. Besides depressurization heat stimulation is regarded as another important means for producing hydrate-derived gas, however, the production efficiency and economic feasibility of producing gas by heat stimulation have not been clearly understood. In this paper, a simplified model for predicting gas production from hydrate deposits by heat stimulation is developed. The model ideally neglects the effects of heat convection and pressure regime in the sediments for simplicity. We compute the heat consumption efficiency and gas energy efficiency of gas production from hydrate deposits by heat stimulation, only considering effect of hydrate dissociation due to heat input. This model is for predicting the maximum production efficiency. By studying the hydrate reservoirs and significant parameters collected from drilling and sampling researches, we calculate the production potential of the Shenhu hydrate deposits and investigate the production efficiency and feasibility. Our research shows that the maximum amount of OPEN ACCESSEnergies 2011, 4 295 cumulative gas production at Shenhu is ~509 m 3 per meter in three years. The production potential is much lower than the industrial criterion for marine production. In our discussion the numerical simulations show that a practical potential of the gas production is merely 25 m 3 /m in 3 years and contribution of thermal stimulation is very small in joint-production schemes. We conclude that production cost is quite high and the economic value of producing gas from the hydrate through a vertical well is not attractive, even though the production by heat stimulation theoretically has a very high heat consumption rate and energy efficiency.Keywords: gas hydrate; heat stimulation; numerical analysis; Shenhu area Nomenclature:c p = heat capacity of sediment c g = heat capacity of gas c w = heat capacity of water P = system pressure ΔP=pressure difference in thermal production simulation Q = total heat consumption, T H Q Q Q = +Q T = heat consumption for raising sediment temperature Q H = heat consumption for decomposing hydrate Q C = net combustion heat of methane gas Q r =release rate of gas from hydrate deposit q g = gas flux q w = water flux R DH = heat consumption efficiency of hydrate dissociation R CH = energy efficiency of thermal hydrate exploitation r = distance to vertical well r d = dissociation radius r w = radius of vertical well, r w = 0.10 m r max = maximum radius of cylindrical domain simulated, r max = 10 m Δr = grid step in radius direction of cylindrical domain, Δr = 0.01 m S H = hydrate saturati...
[1] We develop a kinetic model for hydrate crystallization from methane gas venting through shallow sediments at Hydrate Ridge on the Cascadia margin of Oregon that predicts how pore water chlorinity, temperature, and crystallized hydrate evolve after the onset of steady venting. Predictions are compared to observations at Ocean Drilling Program Site 1249. In the preferred model, calculated gas hydrate saturation and chloride concentrations reach those observed at depths less than 20 m below seafloor (bsf) under the southern summit of Hydrate Ridge in~650 years, and the vertical water flux must be less than 50 kg/m 2 /yr. Hydrate accumulates more slowly between 20 m bsf and the base of the hydrate stability zone where there is no free gas, accumulating to observed levels of a few volume percent of hydrate in 10 5 to 10 6 years, depending on the water flux that is assumed through this zone. This dichotomy means that the presently observed gas venting must have been diverted to this area~650 years ago, or be episodic and infrequent. If the gas venting for the last 650 years has been as observed today, the latent heat of hydrate precipitation in the upper 20 m of sediments would have caused the temperature to increase~0.8°C at~20 m bsf and~0.2°C at~100 m bsf. This would have caused a~5 m rise in the elevation of the base of hydrate stability zone, and decreased the rate of hydrate crystallization from 1.
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