Behavior of gas production from Type III hydrate reservoirs

A large number of studies are underway to evaluate the possible role of gas hydrates as a potential energy resource. One class of such studies involves the development and use of mathematical models to (i) estimate the rate of gas production from hydrate reservoirs under different operating conditions, and (ii) better understand the role of different parameters in hydrate decomposition. A number of researchers (e.g., Masuda et al., 1997, Moridis, 2003, Hong and Pooladi-Darvish, 2005 and Sun and Mohanty, 2006) have already studied gas production from hydrate reservoirs that had an underlying free-gas phase (Type I). Similarly, hydrate reservoirs that totally lie within the hydrate stability zone and are located between impermeable layers on top and bottom (Type III) have received significant attention (e.g., Moridis and Reagan, 2007, Konno et al., 2010, Anderson et al., 2011 and Moridis et al., 2011).In this study, a numerical simulation approach is used to investigate gas production from Type III hydrate reservoirs. A number of mechanistic and sensitivity studies have been conducted to better understand the factors controlling the rate of gas production. It is shown that the ability to decompose hydrates at a significant rate not only depends on the rate of heat transfer (as in Type I reservoirs), but also on the ability of the formation to allow fluid flow (this is a much less important factor for Type I reservoirs). In this work, the interaction between fluid flow and heat transfer is explored, and conditions that would allow significant gas production rate are illustrated. The challenges in the numerical modeling of Type III hydrate reservoirs are also discussed.

► Numerical study of gas production from Type III hydrate reservoir by depressurization.
► Initial p/T conditions and permeability strongly affect the production rate.
► Decomposition “finger” on top/bottom of hydrate layer causes this rate to increase.
► Importance of heat transfer perpendicular to fluid flow requires 2-/3-D modeling.
► Competition between heat flow and fluid flow may influence hydrate decomposition.