The Hydratherm Hybrid Drilling Systems For Cheaper Heavy Oil Recovery
Authors: North J. , Knibb S.T. , Ali S.M. Farouq 
Published: March 2010

Abstract
Nearly 20 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 200 °CDATA[C to 1,100 °CDATA[C, producing thermal expansion and strength reduction of the rock-forming 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 should bring about exciting developments in heavy oil recovery, tar sand and oil shale exploitation, as well as having wider applications in mining, tunnelling and geothermal energy recovery ("HDR heat mining").

Introduction
When polycrystalline rock is heated rapidly, the outer surface expands first and thin flakes or chips are shed due to tensional stress. These are known as spalls, and the process as spallation. The process has been adapted as a drilling technique, and spallation drilling systems have been in common use for over 50 years in mining and quarry work. All have used air or oxygen and fuel, with water being used for cooling purposes only. Spallation systems offer a number of advantages over rotary drilling systems, not the least of which is that penetration rates in "hard" rocks can be extremely rapid. Because the burner (drill) head does not actually contact the rock face, wear on the equipment is kept to a minimum. As the drill string does not rotate, there is no torsional stress, further reducing wear and also the tendency of holes to wander off course. Flame jet spallation burners have already been developed to the extent whereby one was used to make a 335 m (1,100 ft.) hole at Conway, New Hampshire, USA(1). However, these apparently ideal drilling systems do not work in all rock types, but only in those which are able to sustain a rapid build-up of heat without undergoing partial melting. In practical terms, this ends to be those rocks which have a high quartz content. Some rocks are almost unspallable. It is primarily this limitation which has meant that spallation systems have not been adapted for soft rock drilling work in sedimentary basins. There are also considerable practical difficulties to supplying fuel and oxygen to a burner head operating at depth. The search for a solution to these problems has resulted in the drilling systems described in this paper.
It is known that low temperature spallation is more efficient than high temperature spallation in rocks with low brittle-to-ductile transformation temperatures (e.g., certain limestones)(2). Therefore, a means of controlling the thermal flux from the spallation head is essential if such rocks are to be cut. The chosen solution was to design a system that could supply water to the rock face whilst simultaneously delivering fuel and air to the burner head. This is done at ultra-high pressure so as to impose another destructive mechanism on the rock.