Session 3 - Oral 5
GPSFLOW/Hydrate: A new numerical simulator for modeling subsurface multiphase flow behavior of hydrate-bearing geologic systems
Bingbo Xu a, Keni Zhang b,
a Institute of Groundwater and Earth Science, Jinan University, Guangzhou 510632, China
b Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract: Numerical simulation is one of the most important means for designing natural gas hydrate (NGH) extraction schemes, evaluating gas production, and comprehending the sensitivity of field parameters. Currently, NGH-related numerical modeling studies are dependent on a very limited number of simulators, such as CMG-STARS, TOUGH+Hydrate, MH21, and STOMP-HYD. However, most of these simulators were developed many years ago and without taking advantages of the recent development in gas hydrate research and advances in computing techniques. In this study, we develop an efficient gas-hydrate simulator based on a General Purpose Subsurface Flow simulation program (GPSFLOW). GPSFLOW is a hybrid parallel computing integral finite-deference code developed with C++ by using object-oriented programing.
The new development extends the GPSFLOW for solving mass balance equations of the multiphase and multicomponent flow in hydrate-bearing subsurface reservoirs under ambient conditions. The simulator allows having heat and up to 6 mass components, i.e., water, three gases (CH4, CO2, N2), water-soluble inhibitors, and sand. Especially, sand is treated as an independent non-Newtonian flow phase and modeled as a Bingham fluid. The mass components are partitioned among five possible phases (gas phase, aqueous phase, hydrate phase, ice phase, and non-Newtonian fluid phase). CH4 or binary/trinary gas hydrate dissociation or formation, phase changes, and the corresponding thermal effects are fully described, as are the effects of inhibitors by incorporating the most recent literature. The thermodynamic properties of gas mixtures are solved from the cubic equation of state together with direct use of the NIST database for pure CO2 properties. In computing, the simulator uses a domain decomposition technology to realize hybrid parallel computing of distributed memory (MPI) and shared memory (OpenMP), together with multiple GPU computing. The new code can describe all possible hydrate formation and dissociation mechanisms, such as depressurization, thermal stimulation, salting-out effects, inhibitor-induced effects, and flow behaviors including sand, which have been verified by either analytical solutions or by other simulation codes.
Accounting for CO2 and N2 as multi-component gases in the new code can better understand the guest molecule exchange behaviors which will be helpful in the development of the promising technology for natural gas production and CO2 sequestration. In addition, the capability for sand flow simulation of the new simulator provides an efficient tool in tackling the challenging sand production problems as faced in Japan’s Nankai Trough, China’s Shenhu, and other trial production.Keywords:
Natural gas hydrate; Numerical simulator; Multi-component and multi-phase fluids; Sand production