This invention relates to a drilling device. More particularly, it relates to a drilling device within which conventional, screwed-together drill pipes have been replaced by a continuous drill string of hoses, and with power and communication transmission via cables onto an electric drilling motor disposed down within the borehole, and directly behind the drill bit.

Technology for economical and environmentally correct utilization of renewable energy will become important in the future. Utilization of geothermal energy is a renewable resource which, upon use of proper technology, may provide large amounts of energy centrally relative to the point of consumption.

According to known techniques, geothermal heat is recovered today substantially by virtue of drilling with a rotating drill string and drill pipes screwed together section by section.

In order to exploit geothermal energy efficiently, a hole length in the order of 3000 m must be drilled down into the Earth's crust. The drilling must allow for directional control in order to achieve an optimum positioning of the hole relative to geological formations.

When using a rotating drill string and steel pipes screwed together, the weight of the drill string becomes several hundred tonnes. This requires large structures on the surface to be able to handle the forces on the drill string, and storage space for drill pipes.

When using known technology, signals for directional control of the drill string are transmitted by virtue of pressure pulses in the fluid being pumped down at the centre of the drill string. Such equipment is very expensive and complicated, simultaneously offering low capacity with respect to signal transmission.

The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art.

The object is achieved in accordance with the invention and by virtue of the features disclosed in the following description and claims.

A drilling device is provided, wherein the conventional rotating drill string has been replaced by three or more flexible hoses coiled onto hose drums. This reduces the weight of the drill string to a minimum as compared to the current technique. By so doing, extensive and large hoisting equipment, and also handling of drill pipes, may be avoided. The space requirement and noise from surface equipment are reduced substantially. This provides for significant economic and environmental benefits.

A hoisting wire connected to a winch is disposed at the centre of the borehole, and in such a manner that a drilling motor and hoses may be hoisted up and lowered down into the borehole. Cables for transmission of electric power and signal transmission are disposed together with the hoisting wire. Weight on the drill bit is provided by virtue of drill collars placed immediately behind the drilling equipment.

When using a continuous cable, cost-effective drilling and real-time communication between the surface and the bottom of the borehole are achieved, whereby data from the drilling process may be monitored continuously and actions may be initiated should unforeseen situations arise down within the borehole.

A smaller hoisting tower on the surface is used for assembly of a drilling machine with equipment, and for lowering casings into the borehole when required.

In the following description, an example of a preferred embodiment is referred to and is depicted in the accompanying drawings, where:

Fig. 1 shows the drilling device with associated equipment placed on the

surface;

Fig. 2 shows a detail of the feeding head for hoses and hose drums;

Fig. 3 shows an assembly of an electric drilling motor with associated

equipment; Fig. 4 shows a detail of hoses and a hoisting wire with associated cables in the borehole;

Fig. 5 shows the feeding head for hoses;

Fig. 6 shows a section through the feeding head;

Fig. 7 shows a hydraulic pump with a valve for operation of the feeding head;

Fig. 8 shows an electric drilling motor with a gear;

Fig. 9 shows a section through the drilling motor and the gear;

Fig. 10 shows a rolling anchor for preventing rotation of the drilling motor and the drill string.

In the drawings, reference numeral 1 denotes a derrick structure above a base structure 2. A winch 13, a snatch block 14 and a hoisting wire 3 are connected to the derrick structure 1 for allowing the drilling machinery 7 and the hoses 5 for transport of drilling mud, which is pumped down by means of a mud pump 11, to be hoisted up and lowered.

The return mud flows in the interstice between the hoses 5 and the borehole wall 37 so as to transport out cuttings broken loose by the drill bit 18. Outbound mud is recovered via the connection 17 on the feeding head 16.

The hoses 5 are coiled onto hose drums 4 and are conveyed into the borehole through the feeding head 16. The feeding head 16 consists of two main parts 26, 35. The guiding of the hoses 5 takes place in the interstice 27. In order to allow the hoses to be squeezed together so as to close the outlet when subjected to an undesired overpressure from the borehole, the piston part 26 is arranged in such a way that hydraulic fluid pressure from the pump 29 may, via the valve 28 and the pipes 30, move the piston part 26 along the main axis 15. Thereby, a desired closing function is achieved when subjected to an overpressure that may arise in the borehole when drilling into pressurized gas pockets.

Drilling machinery 7 and casings 10 are handled by means of a lift truck 9 on a surface ground 12.

The drilling machinery 7 is assembled from several elements. Lowermost there is a drill bit 18 of a known design. Behind the drill bit there is a stabilizer 19, behind which there is a drilling motor and gear 20 followed by a directional control 21. The intermediate sub 22 interconnects the directional control unit 21 and the rolling anchor 23, which prevents rotation of the drilling machinery 7. The rolling anchor consists of a number of rollers which are forced against the borehole wall. The drilling motor and gear 20 consists of an electric motor 23 connected to a planetary gear 33, which increases the torque and transmits rotation to an output shaft with a threaded connection 31. Power and communication to the electric motor and directional control 21 are transmitted via the hoisting wire with integrated electricity and fibre communication 3.