An integrated thermal system, named "Gas to Wire System", for gas production from methane hydrate (MH) layers and generating electricity has been presented based on a balance of waste heat of power plant and dissociations heat of MH including heating the MH layer with hot water. Firstly, gas production by the depressurization method was discussed based on the heat balance between MH dissociation heat and latent heat generated by decreasing of MH equilibrium temperature. The ideal initial MH saturation, showing the maximum one to get 100% gas recover-factor, was obtained as around 16%, even if 6 MPa depressurization is applied for a MH layer. Thus, the depressurization method may be applied for MH layers with low MH saturation less than 20%. The gas production system by injecting hot water from the plant and MH layers using a pair of dual-horizontal wells were modeled and simulated numerically. In the MH reservoir, a dissociated region flowing hot water between dual-horizontal wells, namely hot water chamber, was generated to produce gas continuously. Numerical simulations on MH gas production by hot water injection into a MH layer at Eastern Nankai Trough have been carried out by STARS TM with a pair of dual-horizontal wells 500m in length drilled in the methane hydrate layer of 20 m in layer thickness. Furthermore, a gas production scheme, which uses flow direction changes with four pairs of dual-horizontal wells in radial arrangement in a MH layer with area of 1 km 2 located at Eastern Nankai Trough, has been presented, and its production performance was evaluated by the numerical simulation as the cumulative gas production for 15 years is 1.3×10 8 std-m 3 . Finally, total heat balance of the MH gas production system has been investigated, and the waste heat of power generating plant can provide enough heat to increasing MH layer temperature and MH dissociation.
For sustainable development of Southeast Asian countries, the use of regional biomass waste for power generation must be promoted. In our Vietnam‐Japan joint project contributing to the sustainable development goals (SDGs), a shrimp farm in Ben Tre (Mekong Delta area) was selected as a demonstration site for an energy circulation system that includes a solid oxide fuel cell (SOFC). We found that sludge accumulated during intensive‐shrimp culture can be used as a source of methanogenic bacteria to decompose lignocellulosic and starch‐based biomass. Bagasse and coconut pomace are mixed with the shrimp pond water containing organic matter and minerals, then supplied to a digester with seed sludge (shrimp pond sludge) to produce biogas, which converted to electricity using the SOFC system. The green electricity is used for shrimp culture, main industry of this region. Based on this concept, a pilot plant with 1 kW SOFC system was constructed at the shrimp farm in Ben Tre. So far, stable biogas production necessary for the continuous operation of the 1 kW SOFC was achieved by the daily supply of 6 kg of bagasse and 8 kg of coconut pomace (dry basis), and power generation efficiency of 53.1% (LHV: lower heating value) was achieved.
A gas production system from methane hydrate (MH) sediment layers by combination method with hot water injection and bottom hole pressure control at production well using radial horizontal wells has been proposed.Firstly, gas production characteristics by the depressurization method with bottom hole pressure control have been evaluated by numerical simulations of cylindrical homogeneous MH layer model. The cumulative production gas amount or MH recovery ratio were limited with the pressure reduction from MH equilibrium pressure, because the sediment pressure must be suppressed to keep mechanical stability of sediment layers under the sea bottom. Furthermore, effects of numerical bock modeling and averaging physical properties of MH layers have been discussed as those numerical simulation errors against the original deposit model show a safety side results to evaluate economic issues in gas amount and production rate.By applying the present production system with combining hot water injection and bottom hole pressure control, the numerical simulation results showed that dissociated region including two wells filled with hot water, named as hot water chamber, is expanded outer ward from the area center of MH layer with continuous gas production. The simulations on gas production by injecting 85°C hot water into the MH layer with 1km×1km and 20m in thickness by using four pairs of dual horizontal wells 500m in length were carried out. It was found that 2MPa pressure reduction from MH equilibrium pressure made the gas production 2.2 times compared with the case of hot water injection only without pressure reduction control.
Numerical simulations on consolidation effects have been carried out for gas production from offshore methane hydrates (MH) layers and subsidence at seafloor. MH dissociation is affected by not only MH equilibrium line but also consolidation (mechanical compaction) depended on depressurization in the MH reservoir. Firstly, to confirm present model on consolidation with effective stress, the history matching on gas production and consolidation has been done to the experimental results using with synthetic sand MH core presented by Sakamoto et al. (2009). In addition, the comparisons of numerical simulation results of present and Kurihara et al. (2009) were carried out to check applicability of present models for gas production from MH reservoir in field scale by depressurization method. The delays of pressure propagation in the MH reservoir and elapsed time at peak gas production rate were predicted by considering consolidation effects by depressurization method. Finally, seabed subsidence during gas production from MH reservoirs was numerically simulated. The maximum seabed subsidence has been predicted to be roughly 0.5 to 2 m after 50 days of gas production from MH reservoirs that elastic modulus is 400 to 100 MPa at MH saturation = 0.
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