The declining conventional hydrocarbon resource and increase in energy demand has encouraged the development of unconventional gas resources. One specific type of unconventional gas is the natural gas hydrate. The substantial size of the hydrate resource is a motivating factor in its development. In the early phases of development of hydrate reservoirs data is limited and a large number of sensitivity studies are required. Efficient and accurate analytical models are suitable for such sensitivity studies. One of such solutions is presented in this work.
An analytical solution is developed to model rate of gas generation and hydrate recovery when gas is produced from an inclined hydrate-capped gas reservoir where the geothermal gradient is accounted for. As a result of the difference in temperature within the hydrate column, the size of the decomposing area increases with continued production.
Development of the analytical model of this work is based on a material balance equation that is combined with the solution for the temperature of the decomposed zone and hydrate equilibrium curve. The three equations are solved simultaneously for the gas generation rate. To validate the assumptions made in the development of the analytical model, a numerical simulator was used. The effects of different reservoir parameters on the reservoir performance were investigated by performing sensitivity analysis. The sensitivity results show how a steeper reservoir that extends closer to the base of permafrost leads to less recovery, or how a thicker hydrate cap could maintain the reservoir pressure for a longer time.
The model developed in this study can be used as an approximate engineering tool to evaluate the role of hydrates in improving the productivity and extending the life of tilted hydrate-capped gas reservoirs.