PNNL

Abstract

The subject simulator STOMP-HYDT-KE is latest in the series of numerical simulators developed by the Pacific Northwest National Laboratory (PNNL) for investigating production technologies for natural gas hydrates. The first simulator in this series, STOMP-HYD, was capable of simulating four production technologies: 1) depressurization, 2) thermal stimulation, 3) inhibitor injection and 4) CO2 exchange. This simulator assumed equilibrium conditions between the mobile and hydrate components of the hydrate formers, CH4 and CO2. Experiments conducted at the Korea Institute of Geoscience and Mineral Resources (KIGAM), however, demonstrated that guest molecule exchange was a kinetic process, with respect to the time scales for flow through geologic media. The second simulator in the series, STOMP-HYD-KE, extended the capabilities of STOMP-HYD, by solving separate conservation equations for the mobile and hydrate components of the hydrate formers, CH4 and CO2. Hydrate formers transitioned between mobile and hydrate forms via hydrate formation, dissociation, and exchange; where, all three mechanisms were controlled via kinetic rates. The STOMP-HYDT-KE simulator extends the capabilities of its predecessor by including a third hydrate former, N2. As with the two other hydrate formers, CH4 and CO2, the mobile and hydrate components of N2 are solved separately. In its full capability configuration, the STOMP-HYDT-KE solves nine conservation equations at each grid cell: 1) energy, 2) water mass, 3) mobile CH4 mass, 4) hydrate CH4 mass, 3) mobile CO2 mass, 4) hydrate CO2 mass, 3) mobile N2 mass, 4) hydrate N2 mass, and 9) inhibitor mass. The modular design of the simulator allows for one or two of the hydrate formers and/or the inhibitor to be eliminated from the solution. The transition between STOMP-HYD-KE and STOMP-HYDT-KE involved two significant changes in the code: 1) equation of state module and 2) ternary hydrate equilibria. This report documents the incremental changes that were made to develop the STOMP-HYDT-KE simulator from the STOMP-HYD-KE simulator and demonstrates the simulator application via a series of benchmarking problems.