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Geo-Drill enables cost-effective DTH technology

Fri, 24 July, 2020

The Down The Hole hammer commonly referred to as DTH drilling, is a  tool that has a piston that is powered by either compressed air or high pressure fluids. Although pneumatic drilling tools have been used in drilling applications since the late 1800’s when Simon Ingersoll created the first pneumatic drill patenting in 1871, it wasn’t until the 1960’s that air hammers really started to develop, primarily due to increase in compressor technology. Widely used for deep drilling in hard rocks, the DTH hammer concentrates percussive energy, at the base of the wellbore, imposing high stress points that break the rock into small chips that can be carried out of the wellbore, either by the exhaust air (pneumatic hammers) or by the exhaust fluid. The nature of the fluid ranges from water, through to complex mixtures of polymers and sometimes, suspended colloids of hydratable clays, although very rarely used with hammers. Whether using air or fluid, it requires the drilled cuttings (chips) to be carried up and out of the wellbore.

Air vs Water DTH hammers

As the name suggests, air-powered DTH hammers use compressed air to power the pneumatic tool. Air hammers, however, are less effective at larger depths (>4,000m) due to the difficulty of removing cuttings and overcoming the ingress of fluids and hydrostatic heads. Additional disadvantages include inability to use drilling fluids to control wellbore stability by means of hydrostatic control and the risk of blowouts when high-pressure fluids or gases enter the wellbore (can be life threatening when drilling through hydrocarbon zones)!

On the contrary, water powered DTH hammers are energy efficient, compared to air hammers, with deeper drilling capabilities making them ideal for drilling application in hard and stable rocks. Despite these advantages, currently most water (fluid) hammers suffer from limitations due to the need for ‘potable’ water to avoid wear and damage to the percussion system and when drilling deeper most fluid hammers suffer poor performance, as the volumes of water required to ensure proper cleaning of the hole are too great for the piston to cycle effectively. The use of fluid additives such as Polyanionic Cellulose (PAC) Polymers, which flow easily when pumped, but gel quickly when pumping stops and suspend cuttings, can help, there are still performance issues with the hammer.

Geo-Drill: Holistic and cost–effective DTH technology

The air and water-hammer systems have successfully been used for geothermal drilling over the past several years. However, challenges associated with cuttings transport/removal can lead to increased tripping times due to reduced lifetime of drilling components.

Geo-Drill enabled DTH hammer provides the benefits high rates of penetration (ROP), as well as the ability to use drilling fluids for improved cuttings transport and wellbore stability. The use of a fluidic oscillator rather than the conventional valve allows much less strict tolerances in the percussion mechanism, thereby enabling usage of drilling fluids that have higher solids content. Unlike the traditional fluid hammers, DTH hammers are driven by bi-stable fluidic oscillators, and offer the following advantages:

  • Very high reliability due to few moving mechanical parts. The probability of failure due to wear of such moving, mechanical parts is thereby reduced;
  • Independence from environmental influences. The bi-stable fluidic switch can be used autonomously of shocks, vibrations, accelerations and temperature. It is also functional under high pressures and flows, overcoming numerous issues associated with conventional air/fluid hammers.

The Geo-Drill technology, therefore, promises progress beyond the state-of-the art by providing a robust DTH fluid hammer design:

  • Powered by bi-stable fluidic oscillator which has been optimised with advanced simulation studies;
  • High-performance coatings to improve the lifetime for operation in the aggressive environments of geothermal drilling.