FIELD OF INVENTION

This invention refers to apparatus for directional earth drilling, particularly to a continuous wedging tool for directional diamond drilling. It is employed in geological prospecting for efficient and accurate steering of the borehole path at great depths in order to reach a specific zone and/or target in the ore body or other objects of interest.

PRIOR ART

A directional drilling tool that steers the borehole path in exploration diamond drilling is known [BG Patent 27473]. It consists of a stator concentrically embracing a bearing seated rotor with a retrievable core barrel in it. The rotor includes an upper and lower shafts connected by a spline assembly. The upper shaft ends up with a tool joint to connect to a drill string while to the lower shaft a core bit is attached. On the rotor there are two bearing assemblies - an upper one and a lower one formed around upper and lower rims with a tooth below the upper bearing assembly.

Said stator includes an upper and lower wedge members connected through channels and slits to a slide block in-between, on the front side of said slide block rollers are mounted. An upper spring is fitted between the upper bearing assembly and the upper wedge member, whereas a lower spring is placed between the pawl and the spline assembly. Onto the inner side of the upper wedge member there is a protuberance board with a groove where the thooth fits.

A disadvantage of the known directional drilling tool is that there is a risk of loss of orientation as well as deviation from the desired trajectory of the borehole since the operator has no information whether the tool is brought into working position, i.e. whether the rotor is released from the stator. Applying rotating forces to the rotor before being released can lead to a mechanical failure and/or breakage of the drill string. All the aforementioned shortcomings call for repeating unsuccessful borehole deviation cycles and increase the non-productive time and the risk of failures and breakdowns. All these reduce drilling efficiency.

SUMMARY OF THE INVENTION

The main objective of the present invention is to provide a continuous wedging tool for directional diamond drilling which is easy to operate and maintain, does not need additional drill rig equipment, ensures quick, accurate and reliable borehole steering at great depths in the desired direction.

The assignment is solved by creating a continuous wedging tool for directional diamond chilling comprising a composite stator assembly with a bearing seated composite rotor assembly in it, the lower end of said composite rotor assembly being attached to a suitable drill bit.

Said stator assembly consists of an upper wedge member, a lower wedge member, and a slide block in-between, said slide block having a forehead provided with suitable fixing elements. The upper-inner side of the upper wedge member is provided with an inner protuberance board with a locking groove.

Said rotor assembly consists of a solid upper shaft and a hollow lower shaft, of any suitable design, connected by spline assembly. Upper and lower rims are formed in the respective upper and lower shafts and upper and lower bearing assemblies are fitted around said rims. Under the upper bearing assembly a locking pawl is provided. The upper shaft ends up with a tool joint to connect to a drill string equipped with an orienting device. A drill bit is attached to the lower end of said lower shaft.

The continuous wedging tool for directional diamond drilling includes also a lower spring member placed between the locking pawl and the spline assembly and an upper spring member located between said upper bearing assembly and said upper wedge member.

The upper shaft is solid with an upper and lower longitudinal bores ending respectively in upper and lower side apertures for letting the drilling fluid through. A nozzle is provided in the lower longitudinal bore. A spline stuffing box is provided at the upper end of said spline assembly, and an upper stuffing box is provided above the upper bearing assembly.

The continuous wedging tool for directional diamond drilling may also comprise a spring housing surrounding said upper spring member. Said spring housing is positioned between said upper stuffing box and said upper wedge member connecting them in a known way.

The continuous wedging tool for directional diamond drilling may further comprise a wedge housing that covers said slide block, said wedge housing being placed between said upper and lower wedge members. Said wedge housing is provided with a window positioned centrally against the forehead of said slide block.

The lower and upper spring members can be spiral power springs.

The fixing elements may be a plurality of roller members pivotally attached to said slide block forehead. Said roller- members may have a conical shape. Said fixing elements may be metal bars, preferably tungsten carbide, hard facing or the like.

Said spline stuffing box may include an 0-ring, pad packing or other sealing means. The nozzle can be replaceable.

The advantage of the continuous wedging tool for directional diamond drilling according to the invention is that there is a signaling system that allows the operator to find out that the tool has been brought into a working position and the drilling can commence. This attains a better targeting of the borehole and allows drilling at great depths. It is easy to operate, reliable and requires no additional drill rig equipment. It curtails the drilling time as there is no need to carry out additional tripping operations and deviation cycles for correcting the trajectory of the borehole. This makes the continuous wedging tool for directional diamond drilling according to the invention more efficient in comparison with the known tools.

The spring housing around the upper spring forestalls the risk of plugging the space between the elements of the upper spring with cuttings thus decreasing the force with which the upper wedge presses the slide block, and decreasing the lateral force acting on the drill bit.

The wedge housing prevents the risk of jamming and blocking the slide block with cuttings which helps to increase the accuracy of deviation. Furthermore, the spring housing and the wedge housing prevent unwanted lateral bending of the continuous wedging tool for directional diamond drilling which additionally increases the accuracy of the borehole trajectory steering.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side view of a continuous wedging tool for directional diamond drilling in non-working position;

Fig. 2 is a schematic longitudinal section of a continuous wedging tool for directional diamond drilling in non-working position;

Fig. 3 is a side view of the lower part of a continuous wedging tool for directional diamond drilling in working position;

Fig. 4 is a cross section of A - A from Fig. 2;

Fig. 5 is a cross section of B - B from Fig. 2;

Fig. 6 is an enlarged view of part C from fig. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figures 1 to 6 feature a preferred embodiment of the continuous wedging tool for directional diamond drilling according to the invention. On fig. 1 it is shown in non- working position inside borehole 33. The continuous wedging tool for directional diamond drilling comprises a composite stator assembly 1 with a bearing seated composite rotor assembly 2 in it. A drill bit 3 is attached to the lower end of said composite rotor assembly 2.

The stator assembly 1 consists of an upper wedge member 4 and a lower wedge member 5, with a slide block 6 in-between, said slide block 6 having a forehead 7. Conical rollers 8 are freely attached to said forehead 7. Onto the inner side of the upper end of the upper wedge member 4 there is a protuberance board 9 with a locking groove 10 (shown in figs. 2 and 4).

The rotor assembly 2 consists of a solid upper shaft 11 and a hollow lower shaft 12 connected by spline assembly 13. An upper rim 14 is formed in the upper shaft 11 with an upper thrust bearing assembly 15 around it and a locking pawl 16 below it.

The upper shaft 11 ends up with a tool joint 17 to connect to a drill string equipped with an orienting device (not shown). On the lower shaft 12 a lower rim 18 is formed with a lower bearing assembly 19 around it.

A lower spiral spring member 20 is provided between the locking pawl 16 and the spline assembly 13 and an upper spiral spring member 21 is positioned between the upper thrust bearing assembly 15 and the upper end of the upper wedge member 4. In the upper shaft 11 are provided upper and lower longitudinal bores 22 and 23 ending respectively in side apertures 24 and 25 for letting the drilling fluid through (fig. 6). A replaceable nozzle 26 is provided in the lower longitudinal bore 23 of the upper shaft 11. A spline stuffing box 27 with an 0-ring 32 is provided at the upper end of the spline assembly 13. Above the upper thrust bearing assembly 15 there is an upper stuffing box 28. The continuous wedging tool for directional diamond drilling comprises also a spring housing 29 surrounding the upper spring member 21. The spring housing 29 is positioned between the upper stuffing box 28 and the upper wedge member 4. It is connected to them by known means .

The continuous wedging tool for directional diamond drilling includes also a wedge housing 30 that embraces the slide block 6 and is situated between the upper and lower wedge members 4 and 5. The wedge housing 30 is provided with a window 31, which corresponds to the size of the forehead 7 of the slide block 6 and is positioned centrally against said forehead 7.

The operation of the continuous wedging tool for directional diamond drilling according to the invention is described in detail further down referring to figs. 1 to 6. The continuous wedging tool for directional diamond drilling is assembled on the ground in a way that the locking pawl 16 is blocked in the locking groove 10 (fig. 5), thus preventing rotation of the rotor regarding the stator. Fixing the rotor 2 to the stator 1 allows the continuous wedging tool for directional diamond drilling to be oriented to the tool-face angle, which ensures the steering of the borehole trajectory. Assembled in this way the continuous wedging according to the invention is run down in the borehole.

When it reaches just above the borehole bottom, it is oriented by known orientation means. Then the circulation of the drilling fluid begins and the continuous wedging tool for directional diamond drilling, which is secured against rotation goes further down until the drill bit 3 touches the bottom hole. The drilling fluid passes successively through the upper longitudinal bore 22, the upper side aperture 24, the lower side aperture 25, the lower longitudinal bore 23, and then flows through the nozzle 26 which serves to control the circulating pressure. By increasing the axial load the upper shaft 11 causes compression of the upper spring member 21, which in turn exerts pressure on the upper wedge member 4. Under the applied spring force Fl (fig. 3) the upper wedge member 4 presses and pushes sideways the slide block 6 with force F2 and the forehead 7 protrudes out through the window 31 of the wedge housing 30.

The force F2 of slide block 6 makes the edges of the fixing elements 8 penetrate into the borehole wall 33, thus securing the stator 1 against rotation, but allowing its longitudinal motion.

Under the applied axial load the upper shaft 11 of the rotor 2 moves downwards at a distance equal to the stroke h of the spline assembly 13, wherein the locking pawl 16 comes out of the locking groove 10 formed in the protuberance board 9 of the upper wedge member 4 and unlocks the rotor 2. Thus the lower and the upper side apertures 25 and 24 which connect the upper and the lower longitudinal bores 23 and 22, pass successively through the spline stuffing box 27. As a result the flow of the passing through drilling fluid is restricted (fig. 6).

This causes a temporary increase in the circulation pressure of the drilling fluid, which is recorded on the ground by a pressure measuring device (not shown). This indicates to the operator that the continuous wedging tool for directional diamond drilling is set in position and the required axial load and torque can be applied.

As a result of the lateral force F2, a lateral force F3 with an opposite direction occurs in the drill bit 3. As the stator 1 is secured against rotation, said force F3 has a constant direction hence the drilling continues along a curve, which is part of a circle with a certain radius in the plane of orientation.

After the cycle of directional drilling has ended, the rotation is brought to a halt, the circulation of the drilling fluid is terminated and the axial load is removed. Under the forces exerted by the upper and lower springs 20 and 21, the upper shaft 11 is moved upward at a distance equal to the stroke h of the spline assembly 13, wherein the upper wedge member 4 and the lower wedge member 5 are spaced apart, and the slide block 6 is retracted in starting position. In this position the continuous wedging tool for directional diamond drilling is pulled out of the borehole.

In core drilling the same mode of operation is applied. The drill bit 3 is assembled with a core barrel . and run in hole. The core sample formed during drilling is collected in the core barrel and retrieved on the ground.