Numerical Modeling of Hydraulic Stimulation in HDR Reservoirs by 2D Distinct Element Method

Abstract

Hot Dry Rock geothermal reservoirs are considerably different from conventional geothermal reservoirs which exist only in the geologically privileged regions. In fact, HDR reservoirs are artificially created reservoirs which can be considered at any accessible depth of the Earth’s crust with a suitable volume of hot dry rock. One of the main characteristics of HDR reservoirs is enough permeable paths to allow water flow in the region between injection and production boreholes. Hydraulic stimulation is a technique employed to create these permeable paths in such regions.

It is important to know the shape, size and permeability of the fractured zone created by stimulation in order to assess the feasibility of the project and to determine the optimum relative locations of the injection and production boreholes. Improving permeability allows the system to reduce its hydraulic resistance. This operational hydraulic parameter called impedance is related the pressure required to force water through the reservoir. Another parameter called the water loss rate is the difference between the rates of water injected and produced.

Since stimulation experiments conducted at great depths are very expensive, numerical modeling can play a significant role. In this paper, the hydraulic and mechanical response of jointed rock mass in an HDR reservoir is considered under the high pressure hydraulic injections using a distinct element code. The code is capable of considering the Hydro-Mechanical coupling. A parametric study on different joint specifications is carried out to illustrate the variation of impedance and water loss rate.