Recent development in numerical simulation of enhanced geothermal reservoirs

Abstract

This paper briefly introduces the current state in computer modelling of geothermal reservoir system and then focuses on our research efforts in high performance simulation of enhanced geothermal reservoir system. A novel supercomputer simulation tool has been developing towards simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involving heterogeneously fractured geomaterials at different spatial and temporal scales. It is applied here to simulate and visualise the enhanced geothermal system (EGS), such as (1) visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e., the permeability) for the further numerical analysis and evaluation of the enhanced geothermal reservoir; (2) converting the available fractured rock image/fracture data as well as the reservoir geological geometry to suitable meshes/grids and further simulating the fluid flow in the complicated fractures involving the detailed description of fracture dimension and geometry by the lattice Boltzmann method and/or finite element method; (3) interacting fault system simulation to determine the relevant complicated rupture process for evaluating the geological setting and the in-situ reservoir properties; (4) coupled thermo-fluid flow analysis of a geothermal reservoir system for an optimised geothermal reservoir design and management. A few of application examples are presented to show its usefulness in simulating the enhanced geothermal reservoir system. KEY WORDS: numerical simulation, geothermal, EGS, microseismicity, finite element method, lattice Boltzmann method. INTRODUCTIONOver the past 30 years, a large amount of research and field testing on engineered geothermal system (EGS), also known as hot dry rock (HDR) and hot fractured rock (HFR) geothermal reservoirs, have been accomplished worldwide which include the reservoir construction, fluid circulation and heat extraction (e.g., Tester et al., 2006). A successful EGS reservoir depends on thermal-fluid flow at any given time which primarily determined by its mean temperature and pressure, the nature of the interconnected network of hydraulic stimulated joints and open fractures (including both stimulated and natural), the cumulative amount of fluid circulation (reservoir cooling) that has occurred and water loss (Rybach, 2010; Brown et al., 1999). The reservoir characteristics are complicated and functions of the applied reservoir pressure/stress that are controlling the nature and degree of interconnection within the network of fractures, therefore it is crucial to have good measures and understanding of such reservoir characteristics (i.e., permeability)

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