In 2023, the International Renewable Energy Agency and the International Geothermal Association released a report underscoring the pivotal role of geothermal energy in the transition to a CO2-neutral energy system. In Europe, where over 50% of energy demand is driven by seasonal heating, geothermal systems are crucial for the heat transition. However, uncertainty in well productivity and high upfront costs for well construction present significant financial risks, slowing market adoption. Multi-lateral wells are a proven method for addressing reservoir heterogeneity and enhancing productivity, but the challenge lies in making their construction cost-effective for geothermal operators. One of the factors that would improve cost-efficiency would be increase of Rate of Penetration (ROP).
Directional Steel Shot Drilling (DSSD) technology uses high pressure jets containing steel shot particles, which are retrieved at surface after they have been supporting hole making. The steel shot particles are injected downstream of the mud pump in the drill pipe and circulated down into the bottom hole assembly. The steering sub converts the steel shot particle concentration into pulsed concentration synchronized with the rotation of the drill bit, a polycrystalline diamond compact (PDC) bit with modified nozzle positions and configuration. When the jets in the bit rotate across the hole bottom, there will be more particles and more erosion on one side of the hole bottom than the other. Next to the advanced and effective directional control method of the DSSD technology, the erosive action of the accelerated steel shots enhance the rate of penetration (ROP) up to a factor of three in hard rock making drilling much more cost-effective.
Mechanical specific energy (MSE) is widely used to quantify drilling efficiency and maximize ROP in oil and gas wells drilling. MSE is affected by the level of downhole torque and the effect of weight on bit (WOB). MSE is a well-known concept to quantify the cutting efficiency of the rock: Energy = Power * Time; Power = Torque * RPM.
Without Weight on Bit (WOB) there is no torque on the bit and no ROP. However, with DSSD there is ROP, even without WOB. And the torque is provided by jetting the steel shots.
As part of the European GEOTHERMICA project ‘DEPLOI the HEAT,’ the DSSD system's operational performance is being evaluated in collaboration with various partners. The research includes large-scale component testing, factory acceptance testing, a field trial, and a pilot in a live well. Large-scale tests have demonstrated that with low WOB, the ROP in concrete, limestone, and granite can be tripled compared to conventional PDC bits, potentially reducing overall drilling costs by significantly cutting drilling time. The tests also showed that excellent borehole wall quality and effective hole cleaning could be achieved in the laterals.
This paper presents ROP improvement with DSSD, in combining the MSE to the drilling strength (DS) and amount of energy used for hole making.