Characterisation of Fracture Network Realisations for Geothermal Reservoir Flow Modelling

Abstract

Characterisation of fractured reservoirs is required for prediction of the economic viability of geothermal projects. However, accurate characterisation is often not possible mainly because of the uncertainties associated with fracture properties such as location, size, orientation and aperture. Modelling of fluid flow in geothermal reservoirs often requires explicit representation of the fracture network as only a minority of the fractures may be responsible for the majority of the flow. To account for the uncertainty, stochastic methods are used and multiple fracture network realisations are generated. Given the computation time associated with performing a fluid flow analysis, only a subset of these fracture network realisations can be analysed. We have investigated the use of fast-to-compute geometry based metrics to characterise individual fracture network realisations prior to selection of a sub-set for explicit fluid flow analyses, the goal being to select realisations that accurately represent both conservative and aggressive scenarios. To assess the success of the metrics, we used a fluid flow solver utilising a pipe network generator to represent the fracture networks as connected 1-dimensional flow elements. We find that the success of such metrics depends on the complexity of the fracture network.