Abstract
Natural Gas Hydrate is a potential and clean energy resource which is widely distributed in the ocean and permafrost. Depressurization is a promising method to produce gas from hydrate deposits. Class 2 hydrate accumulations are composed of hydrate-bearing layers overlying a zone of mobile water, and the presence of bottom-water will influence the pressure drop propagation and dissociation of hydrate-bearing layers. This study aims to propose an optimal strategy for gas production from Class 2 hydrate deposits by depressurization with considering the effect of the thickness and location of the production intervals by numerical simulation methods. The results show that the dissociation of hydrates is mainly determined by two mechanisms, which are the pressure drop propagation and heat transfer from the upper and lower strata, respectively. The thicker the production layers, the greater the average gas production rate. When the production intervals include the bottom-water layers, the gas production rate significantly increases. However, with the increase of the thickness of bottom-water included in the production intervals, the increment of cumulative gas production decreases and the cumulative water production increases. When the intrinsic permeability is up to 1000mD, the production zone should not contain the bottom-water layers. It is recommended that the completion production intervals should contain all the hydrate-bearing layers and the upper half of the bottom-water layers when the intrinsic permeability is between 1 and 100 mD.
Published Version
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