A novel method of acquiring geothermal energy from unconsolidated sandstone reservoir by multi-directional wells deep borehole heat exchanger

摘要

The clogging problem during injection seriously limits the development and utilization of geothermal resources in unconsolidated sandstone area. Deep borehole heat exchanger can circumvent the problem of clogging, and however, high drilling and completion costs restrict its application. To reduce the drilling and completion costs and shorten the payback period, here a multi-directional wells deep borehole heat exchanger (MDWDBHE) system is proposed by sharing the vertical well and drilling directional wells at the lower part of vertical well with high extracted thermal output per meter well depth. The research result shows that for vertical well without directional well, the dynamic payback period is 18.55 years, while for MDWDBHE having 3 and 4 directional wells with the deflection point depth of 2000 m, the dynamic payback period is respectively 7.70 and 7.51 years, indicating that MDWDBHE can be popularized on a large scale just like the shallow ground source heat pump.