Thermal hydrological modeling of the effect of fault zones intersecting primary porous media and the implications for enhancing Geothermal exploration potential at shallower depths

Abstract

For geothermal energy exploration, depth to required fluid temperature and potential extraction rates are important factors for economical viability. Local thermal anomalies found in boreholes might be associated with convective flow through faults. This research applies a finite element modeling method to investigate the effect of high permeability faults on large-scale convection in a sedimentary basin, roughly resembling the North Sea basin. An extensive literature review is included in an attempt to impose realistic permeability properties on basins and fault zones. Though frequently faults are considered to be ‘sealing’, this is only in the fault normal direction resulting from grain reduction in the core of the fault. The fracture network located at both sides of the core can, under certain conditions, become very permeable in the along fault direction. It was found that when faults are closely spaced, thermal convection originates even when the enveloping basin has too low conductive properties to start convecting itself. Significant temperature anomalies are produced that might indeed be utilized for geothermal exploration, where the high fault permeability can act as an extraction rate enhancer.