Gas Production System From Methane Hydrates Layers by Hot Water Injection Using Dual Horizontal Well

Abstract The gas production system from methane hydrate layers by hot water injection using with dual horizontal wells have been investigated. In order to simulate gas production process in hot water chamber generated in methane hydrate layers, physical and numerical models have been presented. In this study, experiments and numerical simulations for the processe were carried out using two-dimensional scaled physical models to investigate fluids flow characteristics and the production performances. The thermal simulator, CMG's STARS, was used to simulate the experimental chamber growths of the physical and field models. The numerical simulations for the processes were also successfully carried out with a twocomponents (water and oil or methane hydrates), three-phases (water, methane hydrates and methane gas) and threedimensional numerical model matching with the physical model. The results from the history-matched numerical simulations were found to be in good agreement with those of the experiments on productions and chamber shapes by using the Intermediate3- Stone1 wettability model. The simulations of field productions using dual horizontal wells 500 m in length were carried out to evaluate cumulative gas production during three years hot water injection with 500ton/day that was varied from 5 × 106 to 9 × 106 m3. The production process was predicted to be economical, since convective heat transfer on the chamber boundary and gravity force on dissociated methane gas are expected. Introduction Recently, it has been confirmed by investigations that methane hydrate layers are reserved in sedimentation layers of depth more than several hundred meters from bottom of the sea floor, and it may be expected as the new natural gas resources. In-situ hydrates decomposition into water and gas will be required to produce methane gas economically from the layers, because methane hydrate is a kind of non mobile solid energy resources. In order to start decomposition of the methane hydrate, decompression or temperature rise out from its equilibrium zone is necessary, while heat should be supplied to dissociate it continuously. Thus, new production system to supply heat continuously into the methane hydrate layers and produce gas have been proposed. The depressurization, inhibitor injection and thermal recovery methods have been mainly investigated to produce gas. The gas production by the hot-water injection has an advantage compared with the depressurization (Kmath et al., 1991) and the inhibitor injection methods that the dissociation speed of methane hydrate and gas production rate may be relatively low due to low heat supply. On the other hand, the hot-water injection method using vertical wells needs drilling with high density into the layer (refer Masuda et al.), because the methane hydrates are formed in sand layers with very low permeability. In this paper, a new hot water injection method using dual horizontal wells has been proposed. The lower horizontal well is used for hot water injection and continuous gas production is carried out using upper horizontal well. experiments using with physical models, and numerical simulations have been presented in order to investigate production performances by the new thermal recovery system.

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