| Abstract |
Realistic numerical modeling of unconventional geothermal reservoir types such as “supercritical” resources in volcanic areas or Enhanced Geothermal Systems (EGS) in deep, crystalline fractured rocks of non-volcanic areas is currently impossible with the official releases versions of standard geothermal reservoir modeling tools such as the TOUGH family of codes. Temperatures of supercritical resources in the immediate vicinity of a magma body exceed the codes' limit of 350°C and the complex geometry of irregularly fractured EGS reservoirs cannot adequately be represented in TOUGH. Most other simulation tools require rather coarse spatial discretization on an often orthogonal grid, which prevents the resolution of features such as faults or complex geometries of geological units. In addition, almost all tools impose rather strict limits on the user’s flexibility to develop and use own constitutive relationships for rock or fluid properties. In this contribution, we introduce to the geothermal community the Complex Systems Modeling Platform, CSMP++, a highly modular simulation platform, co-developed by ETH Zurich, Montanuniversität Leoben, and Heriot-Watt University. CSMP++ uses unstructured meshes to represent complex, realistic geometries. Pre- and postprocessing is done with external tools. Realistic geologic models can be constructed in CAD programs or standard geologic modeling tools such as GOCAD and can be converted to CSMP++ readable computational meshes using industry-standard meshing tools. Fractures can be represented as lower dimensional elements (lines in a 2D model or surfaces in a 3D model) and a broad variety of element types allows representing complex, “geologically realistic” geometries. Finite element, finite volume and control volume finite element methods can be employed for solving coupled sets of diffusion-type (e.g. heat conduction) and advection-type (e.g. fluid convection) partial differential equations to employ the best suited methods for the various conservation laws governing geothermal systems. CSMP++ has equation of state modules for pure water and saltwater providing the full phase relations and fluid properties (enthalpy, density, viscosity etc.) as a functions temperature, pressure, and composition to magmatic conditions, i.e., 1000°C, 500 MPa, and 0 to 100% NaCl. CSMP++ is a C++ code library the modular structure of which allows users to write their own modules for material properties (e.g. permeability as a function of temperature, fluid pressure, etc.) or to incorporate additional partial differential equations to be added to the simulation. Different constitutive relations can be applied in user-defined subregions of the model. The user is also free to define and output any variable of interest, which can be analyzed by a variety of postprocessing tools, e.g. the powerful Paraview visualization program. We present examples of recent applications, i.e., the simulation of the natural life cycle of high enthalpy systems and the first simulations of the “supercritical” hydrology near magmatic intrusions such as that encountered in the IDDP-1 well at Krafla in Iceland (Scott et al., 2015). The ability to now include the actual heat source and increasingly realistic representations of the geologic structure as well as physical parameters will allow significantly improved methods of resource and sustainability assessment. Furthermore, we expect that our new simulation techniques will provide a virtual test bed to explore scenarios for supercritical resource exploitation prior to expensive drilling. |