Key factors analyses for prediction of accurate gas production rate in hydrate reservoirs during model construction

Abstract

Numerical simulation is an important approach to evaluate the production potential of gas hydrate-bearing sediments (GHBS). Accurate prediction results provide vital bases for target selection, scheme design and risk prevention & control in the field practice. The factors in a specific model construction of the gas production simulation, including spatial discretization, simulation geometry and initial & boundary conditions, significantly affecting the prediction results, are analyzed in detail by using the TOUGH + HYDRATE software. The investigation shows that the very fine mesh division around the well is required during spatial discretization if we employ the homogeneous mesh size, and the alternative heterogeneous mesh division within a certain ratio of mesh size near the well is also acceptable. The mesh division in GHBS is mainly dependent on the production well type and that around the upper and lower interfaces of the reservoir is controlled by the formation permeability. Moreover, it is suggested that the thickness of burdens equal the hydrate burial depth or be determined through scoping computation trials within a planned production period, and the top and bottom thin layers be treated as Dirichlet boundaries. The determination of radial or horizontal dimensions depends on the number of wells (A single production well through scoping computation trials while multiple production wells through symmetry division). Finally, a concrete initialization process of the simulation system with or without free gas is suggested. The results of this study can provide an insight into the accurate gas recovery prediction.