A METHOD AND A DEVICE FOR DEEP HOLE DRILLING

Abstract: A method and a device for drilling deep holes in the ground. The device comprises at least two axially adapted drilling bits (3a, 3b, 3c), an equal number of plates (4a, 4b, 4c) each having three shafts (5b, 5c) axially interconnecting the plates. Two of the shafts (5b, 5c) are moment rigidly attached to both plates (4a, 4b) while the third shaft (5a) is pivotably attached by joints (7, 11, 12) to both plates. The two first mentioned shafts (5b, 5c) are releasable from the upper plate (4b) by pulling in a locking pin (9, 10), which releases the telescopic heads (8) of the shafts from the plate (4b), the upper ends of said shaft being attached to the telescopic heads. At the release, the shafts are shortened telescopically by means of springs (14) and the drilling fluid is automatically shut off to the worn-out drilling bit (3a) and opened to the new drilling bit (3b). The remaining third shaft (5a) eccentrically interconnects the plates (4a, 4b) so that the lower worn-out drilling bit makes a semicircularly shaped evacuating pocket in the wall of the hole at the rotation. The third shaft (5a) is successively pivoted outwards until it forms an angle of e.g. 80<o> with the axle of the hole. An axle pin (11) having rectangular cross-section maintains the upper end of the third shaft (5a) by means of a sleeve (12) having a slit (13). The slit (13) has such a dimension that the narrowest cross-section of the axle pin at said angle can pass through the slit and release the third shaft (5a) from the second plate (4b). By this action, the worn-out drilling bit with three shafts and a plate is put in the semicircularly shaped evacuating pocket thus formed. During the time the evacuating pocket is formed, the cut material will sink down to the bottom of the drilling hole. The drilling can now continue downwards by means of the second drilling bit (3b) positioned thereabove after the drilling lining has been pushed down towards the bottom of the drilling hole.

Description: A METHOD AND A DEVICE FOR DEEP HOLE DRILLING FIELD OF INVENTION The invention relates to a method for drilling deep holes and a device for performing the method. The invention relates more specifically to a method and a device for exchanging a drill bit when it is worn-out without the need of lifting up the whole drilling rod to the ground position with all drawbacks pertaining thereto, which means that the exchange of drill bit can be done in situ down in the hole. PRIOR ART Drilling of deep holes into the earth crust is to-day of very large interest due to drilling after oil, nature gas and geoenergi. Deep hole drilling has after all been made since very long ago on-shore as well as off-shore. Drilling of deep holes will normally take place by sinking a drill with a drilling bit in the drilling hole in order to cut, i.e. decompose or crush, the material at the bottom of the hole. The crushed material, the so called drilling mud, will be washed up to the ground by a drilling fluid or wash water, which can be water, a mineral based oil or compressed air etc. As drilling proceeds downwards, the drilled hole will be lined with a steel tube. The drilling bit often consists of a roller type bit with e.g. three rollers having hard metal alloy tips evenly distributed on the surface. These rollers will be pressed with great force against the bottom of the hole and roll across the bottom, whereby the hard metal alloy tips are breaking or crushing the material at the bottom of the hole. This material can be of very variable hardness from primary rocks to unfixed species of stones as sandstone and even gravel and soil. Of course, the drill speed will be depending on the hardness of the ground. Another wellknown and used drilling technique is e.g. hammer drilling, whereby a pneumatically driven hammer is performing the material cutting in the drill hole. This drilling technique has its limitation in respect of how deep one can drill. At drilling with a roller type bit, the drilling bit of cource will be worn-out and must ordinarily be exchanged after drilling a certain distance. What will be worn in the drill bit is the bearings of the rollers and also the hard metal inserts. Therefore, bearings of the best quality and hard metal bits of highest structural strength and quality are used. In some applications the hard metal bits are replaced by dia ants, which makes the drilling bit more expensive. Moreover, the roller bearings are exposed to a very harch surrounding. At deep hole drilling the pressure of the liquid column into the hole will be very high and at the same time the hole is filled up with sludge cuttings. These facts entails that there will be extremely high demands as to leakages of the bearings, because if the sludge should come in between the bearings surfaces, they will be immediately destroyed. Though elaborate techniques are used to extend the life of the drilling bit it will with long time drilling sooner or later collapse. Then, as mentioned above, the drilling rod has to be taken up and the drilling bit will be changed at ground. The operation to wind up the drilling rod is a very time-consuming procedure and will, at the same time, cause a lengthy drilling stop. In some case it can be very difficult and practically impossible to wind up the drilling rod, e.g. when the drilling hole has substantial bends. SUMMARY OF THE INVENTION The present invention intends to solve the problem of exchanging the drilling bit, so that this exchange can be done under ground without the need of winding up the drilling rod, whereby a long drilling stop will be avoided when a drilling bit has collapsed, and the drilling time will be considerably shortened. At the exchanging of the drilling bit under ground at the bottom of the hole, several problems will arise. Firstly the new drilling bit must be brought down adjacent the bottom of the hole. This problem is solved according to the invention, by having two or more drilling bits as an integral part of a drilling device at the bottom part of the drilling unit. Thus, when the first drilling bit is worn-out, there is another drilling bit positioned directly thereabove ready for use. The second problem, which the present invention specially is intended to solve, is where to position the worn-out drilling bit. The hole has a diameter which is as big as the drilling bit and there is no room for the exchange between the worn-out drilling bit and the new one positioned thereabove. It is previously wellknown per se that a drilling bit, which has been wedged in the hole, can not be disengaged, and for that reason has to be left in the hole. A new drilling bit can be assembled first after the drilling rod has been taken up to the ground. The drilling rod provided with a new bit is then sunk down again into the hole and the new drilling bit drills a side hole with a small angle near the original hole and proceeds downwards beside the old wedged drilling bit. Of course this technique can also be used in the drilling device of the present invention. However, it is very difficult to drill such a side hole. Besides, such a bending of the drill hole is a drawback. According to the present invention, a side hole is provided for the worn-out drilling bit, so that it is brought out of way and the drilling can continue downwards with the new drilling bit. Thus, according to the present invention, there is provided a method for drilling a hole in the ground, a drilling device being attached to a drilling rod driven by a drive means, the drilling device decomposing the ground below the drilling bit during the drilling, wherein the drilling device contains at least two drilling bits. When the first drilling bit is worn-out, said drilling bit is exchanged according to the present invention against the second drilling bit positioned thereabove, in situ at the bottom of the hole. The drilling device comprises a separating device having two steps. At the exchange of the first drilling bit, the first step of said releasing device is activated, whereby the worn-out drilling bit at continued rotation of the drilling device influences upon the side of the hole and opens an evacuating pocket. Preferably, the releasing device, for each exchangeable drilling bit consists of a plate and at least two shafts, which connect said plate with a corresponding second plate positioned thereabove, wherein the first shaft is releasable for activation of an eccentric device and the second shaft is pivotable and eccentrically connects the first plate with the other plate, so that the first plate with its released shaft/s/ is/are pivoting radially outwards to a predetermined angle, e.g. 80 , and then, when said shaft has achieved said angle, the shaft is released from its connection with said corresponding second plate positioned thereabove. Then, the first drilling bit with pertaining plate and shaft is placed into the evacuating pocket, thus formed. Suitably, each shaft is telescopic, so that the shaft will be shortened as to its length at the releasing from the corresponding connection with the second plate positioned thereabove. According to a preferred embodiment of the invention, the second shaft is connected to the second plate by an axle pin having essentially a rectangular cross-section and a sleeve with a slit having a width, which corresponds to the narrowest dimension of the axle pin. The shaft and the sleeve will be disengaged from the second plate and the axle pin, when the shaft has been pivoted radially outwards to said predetermined angle, by the fact that the axle pin can pass through said slit in said sleeve. The invention also relates to a drilling device for performing the method according to the invention. The drilling device is attached to a drilling rod and will be driven by a driving device and comprises at least two drilling bits adapted axially above each other. An eccentric device is adapted to take up a cone-shaped evacuating pocket in the side of the hole at activation with an activation device. A releasing device disengages the lowest drilling bit and put it into the cone-shaped evacuating pocket for further drilling with the second drilling bit positioned thereabove. Preferably, the eccentric device comprises an excentriccally adapted shaft, which radially and pivotably connects a first plate adapted in connection with the first drilling bit with a second plate adapted in connection with the second drilling bit. Moreover, the activation device comprises at least another shaft, which connects the first plate with the second plate in a stable position and is releasable from the second plate by a releasing device. Said releasing device can comprise a telescopic head, which is adapted rigidly to connect the second shaft (shafts) to the second plate, said telescopic head being releasable from the plate by means of a remote-controllable locking device. The locking device can be remote-controllable from a distant position, e.g. the ground position, by radiowaves, microwaves, ultrasonic waved etc. When the telescopic head leaves its seat in step one, a channel and ventilation device is automatically affected in such a way, that the drilling fluid will be shut off to the worn-out drilling bit and is opened to the new drilling bit. According to a preferred embodiment of the invention the releasing device comprises a pin having essentially rectangular cross-section and a sleeve cooperating with the pin, which has a slit with a dimension corresponding to the smallest dimension of the pin, so that the pin can pass through the slit when it is positioned opposite to the smallest dimension of the pin. During the time when the evacuating pocket is provided, the cut material will sink to the bottom of the hole. Thus, when the drilling is shut off, the drilled hole must be sufficiently deep, so that the volume of the drilling hole below the drilling lining at least corresponds to the volume of the evacuating pocket. SHORT DESCRIPTION OF THE DRAWINGS The invention is described below in more details by means of a preferred exemplary embodiment of the invention with reference to the appended drawings. Fig. 1 is a perspective view of a drilling device according to the invention. Fig. 2 is a perspective view similar to Fig. 1 but with the drilling bit removed. Fig. 2a is a cross-sectional view taken according to line II-II in Fig. 2. Fig. 3 is a perspective view of a part of the drilling device according to Fig. 1 in a central position. Fig. 4 is a perspective view corresponding to Fig. 3 in a final position at the exchange of a drilling bit. Figs. 5 and 6 are perspective views showing the locking and trigging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In Fig. 1 the drilling device according to the invention is shown in perspective. The upper portion of the drilling device 1 is attached to a drilling rod 2. The drilling rod is driven by a driving device positioned at the ground level, e.g. a drilling platform or a ground-based station. Of cource, the driving device can also be positioned under ground in a cave, tunnel, etc. Three roller drilling bits or crowns 3a, 3b, 3c, positioned aligned below each other are connected to the rod 2. The lower crown 3a is initially performing the drilling work. The crowns are of ■ course of a wellknown construction and is not described in more details here, and the intention is that the present drilling device can also be used at other types of drilling devices, drilling bits and comparable arrangements for material cutting devices. Each bit 3a - 3c is arranged after the other with a transversal plate 4a - 4c and a damping device 6 (Fig. 2) placed between the "drilling edges" and nearest following plate. The plates are interconnected with three telescopic shafts 5a - 5c in the embodiment shown in Fig. 1. In the embodiment three shafts are shown, but it is easy to see that the number of shafts can vary depending on application and demand for structural strength. The plates are interconnected with the shafts and are maintained at a predetermined distance from each other by the drilling bits positioned therebetween and the damping devices. The damping device 6 is positioned on the upper side of the plate 4, as appears from the cross-sectional view II-II according to Fig. 2a. It has recesses for the three rollers of the drilling bit positioned thereabove. The operation of the damper is to damp the forces, which are excerted in the axial direction of the drilling rod and to transfer a rotation moment between the respective plates parallel with the telescoping shafts. As appears from Fig. 1 the drilling bits 3b and 3c are positioned within and protected by * the border of the cross plates 4 and the shafts 5 and are not worn during the drilling with the drilling bit 3a. The rotation moment from the drilling rod 2 is transferred by the plates 4 and the shafts 5 parallel with the drilling bits 3c and 3b to the drilling bit 3a. The drilling fluid flows from the drilling rod to channels built in the plates and thence inside one of the three telescopic shafts 5b, which interconnect the plates, and downwards to the drilling bit 3a having holes for this purpose. After that, the drilling fluid with the drilling mud flows up to the ground between the lining and the drilling rod 2. The drilling fluid is powered by a suitable pump device at the ground level. In Fig. 2 the drilling unit according to Fig. 1 is shown without drilling bits to show more clearly other details, among others the damping device already described. It appears that one of the shafts 5a is attached to the lower plate 4a with a pin 7. The same shaft is fastened to the upper plate with a pivotable coupling, which will be described in more details below. Each one of the two other shafts 5b and 5c are moment rigidly fastened to the lower plate 4a and is releasably connected to the upper plate 4b by a telescopic head 8, as more clearly appears from Figs. 3 and 4. Each telescopic head is retained in one position with a locking pin 9, which is controlled by a piston positioned in a cap 10. By this device the locking pin 9 will be retracted and the telescopic head 8 dreleased from the plate 4b. According to the present invention, the locking device with an impulsing receiver is hermetically enclosed in the plate 27 in Fig. 5. Accordingly, in order to release the telescopic head 21 from the plate 27 there is provided an activation by an impuls to an impuls receiver, which triggers a spring activated punching pin, which then liberates the gas which is enclosed in the capsule. The gas provided with overpressure is conducted in channels according to Fig. 5 to the other side of the piston 23, that means where the locking pin 22 prevents the telescopic head 21 from leaving the plate 27. At the same time as the pressure will be liberated around the piston, the spring 24 also pushes on the piston 23, when the counter-pressure has sunk sufficiently. The telescopic head 21 is influenced upon both by the external fluid pressure and the telescoping springs, which however is operating in the opposite direction in relation to the fluid pressure, whereby the pressure at the locking pin 22 decreases and has a more favourable situation to leave its hole in the telescopic head 21. The special packing at the outlet of the channel 25 to the locking pin 22 is then made free and the fluid pressure reaches the end of the locking pin 22. At that time, all forces cooperates towards the locking pin 22 and in one direction. When the locking pin 22 has passed the channel 26 the fluid will be directed in around the telescopic head 21, which then imply a pressure equlization at either side of the locking profile 28. The locking pin 22 has left its hole, the telescopic head 21 has left its seat, and the springs of the telescoping shafts 5b and 5c can push their housings into each other and the shafts are shortened all but the shaft 5a. The entire device, which holds the telescopic head in position, and an impulsing receiver designed for releasing the telescopic head, are hermetically enclosed into the plate 4. The impulsing receiver can be remote-controllable in a number of different ways, as by radiowaves, microwaves, ultrasonic waves or any other form of impulses propagating inside the drilling rod filled with liquid or evacuated. Also other impuls paths and impulsing forms can be useful on special occations, but for the time being the above mentioned solution is preferred. The capsule with a locking pin provided with a piston can be driven pneumatically, hydraulically or else mechanically, which can be arranged in a suitable way. As mentioned before, the drilling fluid is automatically shut off to the worn-out drilling bit 3a at the first step of the release. The automatics are that the telescopic head influences upon a mechanism, which holds a flap in a channel for drilling fluid in such a way that the fluid is directed to the drilling bit presently used. At the exchanging, when the telescope head is leaving its seat and due to the contracting movements of the telescope shafts, the mechanism changes the position of the flap, so that the drilling fluid is switched off to the worn-out drilling bit and opens to the new one. By this appears that each drilling bit in a drilling device has at least one shaft provided with a channel, and a plate with a channel and valve device designed therefor. When a worn-out drilling bit 3a is to be changed, it will take place according to the invention in the following way. Firstly, the rotation of the drilling device is stopped and possibly the drilling hole is washed free from cuttings. Then, an impulse signal is sent to the impulse receiver positioned in the plate 4b, which activates the two capsules with its locking pins, each releasing the corresponding telescopic head 8 and shaft 5b or 5c. The drilling bit 3a and the plate 4 thereof is now only connected to the plate 4b by the shaft 5a. Each shaft 5 is provided with a spring 14, which shortens the telescopic shafts. Thence, the drilling device is firstly put in a slow rotation. The worn-out drilling bit 3a, the plate 4a and the shafts 5b and 5c are now eccentrically hung up by the shaft 5a. This will further bring about that, due to the rotation, said elements are affected by the acceleration forces and are forced outwards towards the wall of the drilled hole. The shafts 5b and 5c are not any longer preventing such a movement. The shaft 5a is pivotably attached to both the plate 4a and the plate 4b and does not prevent such a movement outwards. The worn-out drilling device will now wear at the drilling wall and will take up a cone-shaped slit in the wall. This process is schematically shown in Fig. 3, which shows the worn-out drilling bit directly after release of the shafts 5b and 5c. From the same Fig. 3 it also appears how the free ends of the shafts 5b and 5c will cut into the other side of the drilling wall and scratch and wear material out therefrom. However, the most useful work will be performed by the worn-out drilling bit itself. While the drilling device continues to rotate, the cone-shaped slit will be progressively bigger and the shaft 5a will make a wider angle with the plate 4b. The rotation speed must from time to time during the process be slowly increased, so that the centripetal force will increase and thus the material cutting of the worn-out drilling bit 3a in the now semicircularly shaped evacuating pocket. The joint between the shaft 5a and the plate 4b consists of an axle pin 11 obliquely positioned in a predetermined angle and fixed in the plate 4b and by the sleeve 12 provided with a slit. The oblique axle pin 11 has a plane cross-section, as appears from Figs. 3 and 4, and the sleeve 12 has a cylindric cross-section and is provided with a slit 13, having a dimension corresponding to the smallest portion of the pin. The releasing of the sleeve from and the pin takes place when the narrowest part of the pin is aligned with the slit. At the starting position the slit 13 of the sleeve 12 is positioned in its highest position. As the shaft 5a is angled outwards from the vertical line of the driving rod during the continuous rotation thereof, the slit of the sleeve is displaced forwards the norrowest portion of the axle pin. At the predetermined angle of the inclination of the axle pin, the slit 13 of the sleeve 12 is positioned opposite the narrowest part of the axle pin. Since the width of the slit 13 is equally large as the narrowest part of the axle pin, the sleeve 12 will leave the axle pin 11, which is shown in Fig. 4. The diameter of the pocket can be further increased in the following way. For the sleeve to leave the axle pin 11, the sleeve slit 12 must overcome a certain frictional drag in the slit 13 which is attained by means of an increased rotation speed. During the period, when the rotation speed is slowly increased, the accelerating force will lengthen the telescopic shaft 5a, which is provided with a double-acting spring. The worn-out drilling bit 3a is wearing material essentially in the radial direction, increasing the diameter of the pocket, whereby a ring-shaped slit will be formed. When the accelerating forces are as large as the friction drag, the sleeve 12 slips over the axle pin 11. Until this moment the turning moment for the rotary movement has been transferred by the axle pin 11 to the sleeve 12 of the shaft 5a and to the plate 4a and the worn drilling bit 3a for influencing on the side of the hole. The semicircular shaped evacuating pocket thus taken up has now at least achieved a sufficient dimension to be able to accomodate the worn-out drilling bit 3a with plate 4a and pertaining shaft 5. As the sleeve 12 is released from the axle pin 11, the moment transferring by this joint is discontinued and the drilling bit 3a follows the tangential direction to the circular path of the rotary movement. The'evacuating pocket will now fulfil its task to enclose and to keep the drilling bit 3a, the plate 4a and the telescopic shafts 5 for ever. When the rotation of the drilling rod has stopped, the drilling lining is pressed to the bottom of the drilled hole, whereby the evacuating pocket will be sealed. The new drilling bit 3b is at its right place in the drilling device and the drilling can start again in an unlimited prolongation. Above there has been mentioned that the springs 14 are pulling together the telescopic shafts and thus the telescopic heads of the shafts 5b and 5c will be out of the way. Shaft 5a is still elongated during the entire process due to the gravitation and due to the accelerating forces. When then the sleeve 12 passes over the axle pin 11, the spring 14 is contracted also in said shaft 5a for shortening it for its final keeping. In Fig. 1, a drilling device having three drilling bits has been shown, but according to the invention it is realized that the drilling unit can operate with at least two drilling bits and the upper limit for the number of bits only depends on the application. Accordingly there is no difficulty in putting together for example six drilling bits in a line. In Fig. 2, there is shown a channel system 15 for the drilling fluid and it is realized that it is only one example of such a channel system. In Fig. 4, a shaft 5b is shown which can be provided with a spring 16, which facilitates the removal of the locking pin 9 and the release of the telescopic head 8 from the plate 4b. Instead of springs, a pneumatical and hydraulical force transformer can be used between the two parts of the telescope legs. The drilling device according to the present invention can as well be adapted to other drilling methods, such as turbo drilling etc. The invention is not limited to the embodiments disclosed hereinabove but can be modified in many respects within the scope of the invention as defined by the appended claims.

Claims: CLAIMS 1. A method for drilling a hole in the ground, comprising a drilling device attached to a drilling rod driven by a driving means for decomposing the ground below the drilling device for the drilling, c h a r a c t e r i z e d in that the drilling device comprises at least two drilling bits and when the first drilling bit is worn-out, exchanging said first drilling bit against a second drilling bit positioned thereabove in situ at the bottom of the drilling hole. 2. A method according to claim 1, c h a r a c t e r i z e d in that the drilling device comprises a releasable device, releasable in two steps, whereby at the exchange of the first drilling bit, an eccentric device is activated in a first step, whereby the worn-out drilling bit at continued rotation of the drilling device influences upon the side of the drilling hole and makes a semicircularly shaped evacuating pocket in said side, whereupon the worn-out drilling bit is put in said pocket in a second step out of the way for continued drilling by means of the drilling bit positioned thereabove. 3. A method according to claim 2, c h a r a c t e r i z e d in that the releasable device for each exchangeable drilling bit comprises a first plate and at least two shafts, which connect said first plate with a corresponding second plate positioned thereabove, releasing said first shaft from said second plate for activation of the eccentric device, said second shaft being pivotable and eccentrically connecting said first plate with the corresponding second plate positioned thereabove so that said shaft and said first plate at the rotation of said drilling device is pivoted radially outwards to a predetermined angle, e.g. about 80 , and that, when " said second shaft has achieved said angle, said second shaft being released from its connection with the corresponding second plate positioned thereabove and said first drilling bit and the corresponding first plate and shaft is put in the semicircular evacuating pocket thus formed. 4. A method according to claim 3, c h a r a c t e r i z e d in that each shaft is telescopic and is pulled to a shortened length at the release from the corresponding second plate positioned thereabove. 5. A method according to claims 3 or 4, c h a r a c t e r i z e d in that the second shaft is connected to said second plate by means of an axle pin having essentially a rectangular cross-section, and a sleeve having a slit with a width corresponding to the smallest dimension of the axle pin, and that, when the shaft has been pivoted radially outwards to said predetermined angle, said shaft and said sleeve are released from said second plate and said axle pin by passing said axle pin through said slit of the sleeve. 6. A drilling device for performing the method according to claim 1 for drilling a hole in the ground, said drilling device being attached to a drilling rod and driven by a driving means, c h a r a c t e r i z e d by a) at least two drilling bits (3a, 3b, 3c) adapted above each aother and axially aligned in relation to each other; b) an eccentric device (5a) adapted to make a semicircularly shaped evacuating pocket in the side of said hole; c) an activation device (8, 9, 10, 5b, 5c) in order to activate said eccentric device; d) a releasing device (11, 12) for releasing the lowermost drilling bit and putting it in said formed semicircularly shaped evacuating pocket for continued drilling with the second drilling bit positioned thereabove; e) a switching device for shutting off the supply of drilling fluid to the worn-out drilling bit and opening the supply of drilling fluid to the new drilling bit. * 7. A drilling device according to claim 6, c h a r a c t e r i z e d in that said eccentric device comprises an eccentrically adapted shaft (5a), which radially pivotably connects a first plate (41) adapted in connection with said first drilling bit (3a) with a second plate (4b) adapted in connection with said second drilling bit (3b), and that the activating device comprises at least a second shaft (5b, 5c), which connects said first plate (4a) with said second plate (4b) in a stable position and which is releasable from said second plate by means of a releasing device (8, 9, 10). 8. A drilling device according to claim 7, c h a r a c t e r i z e d in that the releasing device comprises a telescopic head (8) adapted to rigidly attached said second shaft (shafts) (5b, 5c) to said second plate (4b), said telescopic head (8) being releasable from said plate (4b) by means of a remote controllable locking device (9, 10). 9. A drilling device according to claim 8, c h a r a c t e r i z e d in that the locking device is remote controllable from a remote position, e.g. the ground position, by means of radiowaves, microwaves, ultrasonic waves etc. 10. A drilling device according to any one of claims 6 to 9, c h a r a c t e r i z e d in that the releasing device further comprises an axle pin having essentially rectangular cross-section and a sleeve cooperating with said axle pin having a slit with a dimension corresponding to the narrowest dimension of the axle pin so that the axle pin can pass through said slit when it is positioned opposite to the narrowest dimension of the axle pin.

Inventors: DANIELSSON PER, DANIELSSON, PER
Applicants: DANIELSSON PER, DANIELSSON, PER
Application year: 1986
Main classification: E21B10
IPC codes: E21B7, E21B10, E21B23