Ground source energy in crystalline bedrock-increased energy extraction using hydraulic fracturing in boreholes

The paper discusses the use of hydraulic fracturing to increase the yield in ground source heat pump systems in crystalline bedrock by creating a larger heat exchange area in the bedrock. It reports pilot tests using water-only hydraulic fracturing and hydraulic fracturing with the injection of sand. The use of sand as a propping agent appears to be more necessary in fractures with high counter pressures (>40 bars). The particle size of the sand should be adjusted to the counter pressure; for fractures with lower counter pressures a coarser sand is recommended.