Local grid refinement for multi-scale geothermal reservoir simulation with TOUGH2

摘要

Thermodynamic conditions of geothermal reservoir fluids, such as pressures,temperatures, phase compositions, and concentrations of dissolved solids and non-condensable gases, may show strong spatial variability in the vicinity of production and injection wells. Large spatial variations also can occur near reservoir heterogeneities, such as faults and lithologic contacts. In numerical simulation of flow and transport, fine gridding is required to accurately represent steep changes in fluid conditions. This can necessitate prohibitively large numbers of grid blocks in conventional finite difference discretization, where finer gridding must be applied globally with reference to a global system of coordinates. The objective of the work presented in this report was to develop a more economical alternative, in which fine gridding is applied only to regions in which large gradients in thermodynamic conditions need to be resolved. We have implemented a scheme for two dimensional local grid refinement into the general-purpose geothermal reservoir simulator TOUGH2. We discuss the concept and applications to production from and injection into fractured two-phase reservoirs. The accuracy and economy of local grid refinement are demonstrated by comparison to simulations using conventional high resolution grids.