Deep geothermal reservoirs are being targeted for renewable energy supply worldwide. However, while international research efforts are stepping up to the challenge of overcoming the low efficiency of heat recovery from depth to the surface, the showstopper remains the slow drilling speed provided by the conventional rotary system in deep hard rocks (> 4 km). Deep drilling requires long drilling times, often resulting in unacceptably high initial investment.
ORCHYD’s new drilling technology will increase hard rock drilling rates from the current range of 1-2m/h to up to 4-10 m/h. The novelty is to combine two, previously separate, mature technologies: High Pressure Water Jetting (HPWJ) and Percussive Drilling, in a system customised for hard rock geothermal reservoirs to depths of 6 km.
Planned experiments and solid-fluid coupled models designed to reveal the critical fragmentation mechanisms under in-situ stress conditions will be used to design, build and validate, with pilot drilling tests, the new system for field operations.
The hybrid development requires optimisation of: i) release of high stress concentrations on the hole bottom while drilling, ii) slotting circumferential relieving grooves on the hole bottom using HPWJ (up to 200 MPa), iii) in-hole production of the HPWJ using a down-hole pressure intensifier activated by the drilling vibrations, hence damping out harmful drilling system vibrations and iv) an advanced down-hole percussive rotating mud hammer for drilling to derive the maximum benefit from the modified bottom-hole stress regime.
ORCHYD ambition is to cut by 65% the drilling cost in hard rock sections. This will result in 30% reduction of the total cost of deep geothermal well construction. In addition, the new coupled Intensifier-HPWJ-Hammer system has the potential to drill and steer multi-lateral wells which greatly increase thermal connectivity, are cheaper, use far less water and are more controllable than conventional fracking stimulation.