Characterizing Fracture Properties in Geothermal Reservoirs using Electrical Resistivity Measurements with Conductive Fluid Injection

Abstract

This paper discusses a method of characterizing fracture connectivity in geothermal reservoirs using conductive fluid injection and electrical resistivity measurements. A ‘library’ of discrete fractal fracture networks with different spatial fractal dimensions was generated. For each of the networks, the time history of electric potential difference between well pairs was calculated as a conductive fluid was injected into the reservoir. The conductive fluid travels along fracture paths from the injector towards the producers causing the electric potential difference to drop. The changes in electric potential are related to the connectivity of the fracture network. One of the fracture networks was used as a hypothetical geothermal reservoir and inverse modelling was used to match the time-history of the electric potential to other fracture networks. For comparison, inverse analysis was also used to match tracer return curves alone and the study showed that locations of connected areas were estimated better using the electric potential approach. Thermal return curves for the reservoir were calculated and the results showed promising possibilities for using electric potential measurements to predict thermal breakthrough.