Surface Movement Induced by a Geothermal Well Doublet

Abstract

We investigated the impact of the exploitation of a typical geothermal well doublet on surface movement and fault (re)activation. When the pressure distribution is stationary, the largest effect should be expected from the progressive cooling of the reservoir, through the thermo-elastic coupling. The absolute value of the expected subsidence is low, but possibly measureable if circumstances are favorite. In that case the distribution of the subsidence can be used to obtain knowledge about the distribution of the cooled part of the reservoir. In addition, the shape of the subsidence pattern obtains information about the subsurface parameters like the elastic profile. In particular when horizontal displacements are available alongside vertical displacement, this information can be used in an inversion exercise to constrain the value of the elastic modulus. A proper monitoring strategy will help to optimize the information to be obtained. Fault reactivation is restricted to the injected temperature front. Stress paths in the fault plane depend on the location on the fault. Inside the reservoir, stress paths are critical and failure can be expected when the temperature front passes the fault. Above and below the reservoir the stress state returns to close-to-initial values when the temperature front has passed and no failure was observed. The risk for inducing seismic events that damage the producing reservoir is very low, although there is a small potential to induce felt events.