Nearly twenty years of research and field testing has resulted in the development of Hydratherm ™'s hybrid drilling system, which uses ultra-high pressure (UHP) drilling fluid jets and / or a variable thermal spallation gas jet. The gas jet subjects the host rock to pulsed heat fluxes at temperatures ranging from 20 °C to 1,100 °C, producing thermal expansion and strength reduction of the rockforming minerals. The UHP jets then quench, cut and erode the rock momentarily after heating. The combined mechanisms enable ultra-fast rock penetration (20–50 m/hr in hard rock) by means of spallation, erosion, fracturing, chipping and cutting.
This technology has exciting applications in heavy oil recovery.
The Hydratherm system can be employed for drilling oil, gas or geothermal wells. It may also be adapted for mining, boring, tunnelling or the cutting of chambers and will operate at great depth. Together with other Hydratherm technologies, it can be employed in heavy oil recovery. These include faster and cheaper well drilling and the economical thermal treatment of heavy oil reservoirs, especially those at great depths. The latter is achieved by the creation of deep fractures and cavities in hot dry rock (HDR) to produce supercritical (> 380 °C) steam at critical pressure (3,204 psi) for injection into the shallower oilbearing formations above. Employing similar techniques, the drilling system may also be used for the economical production of geothermal steam as a source of energy. Other applications include subterranean incineration or storage of hazardous wastes, subterranean storage of volatile liquids or water, large-scale tunnelling, microtunnelling, conventional mining and quarrying.
This paper describes the drilling technology and how it can be used for developing heavy oil reserovirs.
The system comprises a hybrid rotary head drilling system in which a supersonic thermal gas jet is superimposed upon multiple pulsed or continuous ultrahigh pressure (UHP) hydrojets. The latter deliver a special surfactant solution to the rock surface which acts as both cutting medium and drilling fluid. The gas jet (the "Hypertherm" system) or the UHP hydrojets (the "Hyperjet" system) may be used independently or simultaneously (the "Hyperdrill" system). In the latter case a combination of thermal gas jet heat flux spallation and UHP hydrojet erosion/cutting are used to penetrate the host rock. Figure 1 shows the drilling assembly.
The hot thermopulsing gas jet induces intense thermal stress at the rock face. Spallation occurs and this, together with the action of the superimposed pulsed UHP hydrojets, produces small rock chips which are blown out of the well by exiting combustion gases. The cutting and erosive actions of the hydrojets are assisted by the thermal reduction of rock strength that takes place due to the heat flux delivered to the rock surface by the spallation gas jet. The heat fluxes are delivered intermittently, imposing a variable temperature field, whilst the actions of the spallation gas jet and multiple hydrojets combine in such as way as to produce cyclic heating and quenching. This maximizes the thermal shock effects at the surface of the host rock.
