Abstract
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 cumulative gas production at Shenhu is ~509 m3 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 m3/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.
Highlights
Gas hydrates are crystalline substances composed of water and gas, in which a solid water lattice accommodates gas molecules in a cage-like structure [1]
Considering Equation (2), we suggest that much of the thermal energy injected is consumed for heating the hydrate reservoir if the temperature difference between the initial reservoir temperature and phase equilibrium temperature (ΔT, hereafter called reservoir temperature difference) is too large, which goes against effective hydrate exploitation by heat stimulation
The maximum of the temperature difference at Site SH2 in the Shenhu Area is 1.77 °C, we suggest that the initial temperature difference in the Shenhu hydrates is not a crucial factor influencing the hydrate exploitation by thermal stimulation
Summary
Gas hydrates are crystalline substances composed of water and gas, in which a solid water lattice accommodates gas molecules in a cage-like structure [1]. The hydrate saturation is high and up to ~48% of the pore space at the depth of 204 mbsf (meters below seafloor) at site of SH2, which greatly encouraged the enthusiasm of the scientists and the Chinese government Data from these cores were used to provide the first insight into the characteristics of the possible hydrate accumulations in the area [11,12], and can be used to evaluate the technical and economic feasibility of gas production from the hydrate accumulations by thermal stimulation. We discuss how the model applies to the Shenhu hydrate deposits on the northern continental slope of the SCS and numerically analyze the feasibility of hydrate exploitation by thermal stimulation in the fine-grained sediment
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