| Summary: | Large amounts of natural gas hydrates have been found in sub-oceanic deposits and beneath permafrost regions. It has the potential to become a major hydrocarbon resource in the near future. Research is needed to evaluate the production possibilities of this new resource. CH4 hydrate dissociation and production is an endothermic process and a production challenge is the reservoir temperature reduction. CO2 is thermodynamically favoured over CH4 in the hydrate form and it has been suggested to use CO2 to prevent cooling by replacement of CH4 hydrates with CO2 hydrates. This technique has three advantages: sequestration of CO2, increased CH4 production and maintaining formation stability. The effect of CO2 injection on the CH4 production from a hydrate reservoir has been investigated by numerical simulations. A sensitivity analysis on the CH4 production has been performed by varying the injection pressure, temperature, reservoir properties, hydrate blockage models, intrinsic kinetic rates for CO2 hydrate formation and numerical parameters. The research has been performed by running numerical simulations using the kinetic simulator STARS from CMG. A 3D homogeneous class 2 hydrate reservoir was constructed with a production well completed in the hydrate zone and an injection well completed in the free water zone, injecting liquid CO2 in the free water zone below the CH4 hydrate zone. The injection and production well pressure were regulated to create CO2 hydrate forming and CH4 hydrate dissociation conditions in the reservoir. The simulation results have shown that when CO2 is injected, the cumulative CH4 production can increase with 50-60 %, while storing significant amounts of CO2 simultaneously. 2 % of the injected CO2 was produced at the production well. CO2 hydrates were formed directly under the CH4 hydrates, supplying the dissociating CH4 hydrates with a low grade heat source. No upward moving front of CO2 was observed. It is concluded that CO2 injection only increases CH4 production when the temperature of ...
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