METHOD FOR OVERBURDEN DRILLING, CASING SHOE AND CASING TUBE FOR THE METHOD, AND COUPLING ELEMENT FOR THE CASING TUBES

Abstract: When drilling in soil and simultaneous loading of casing tube it is desirable to be able to use casing tubes of plastic material such as PEH-plastic. This is made possible by a special design of a casing shoe (5) giving a strong joint between the casing shoe (5) and the casing tube (4). The casing shoe is made of metal and has a part (62) which is perforated of holes (63) filled with the plastic material. Tube couplings (12A, 12B) between the casing tubes can also be joined to the tubes (4A, 4B) in the same way as the casing shoe, i.e. that they are made of metal and each has one part (12A, 12B) perforated of holes (63A, 63B) filled with the plastic material.

Description: e , casing tube for the method, and coupling element for the casing tubes. The present invention refers to a method for overburden drilling with simultaneous loading of casing tube, a casing shoe and a casing tube for the method and a coupling element for casing tubes designed to be used with the method. When drilling in soil, a central pilot drill bit is used together with a reamer drill bit so arranged that it can be thrown out eccentrically in relation to the pilot drill bit and expand the hole drilled by it. Thereby the bore will be of a dimension enough to give place not only for the pilot drill bit with the reamer drill bit in its inner position but also for a casing tube brought down in the hole at the same time as the hole is drilled. The casing tube is driven downwards with the drill bit through a casing shoe welded to the end of the casing tube and influenced by the percussive drill hammer. The casing tubes usually consist of three meters in length of steel welded together as drilling and the tube is driven downwards to a suitabel extent. One problem when dealing with the casing tubes is their weight. One further problem is the possibility of corrosion, which in some cases causes the exchange of them to plastic tubes after the drilling, a circumstantial and laborious procedure. One object of the present invention is to eliminate the " exchange of casing tubes and one further object is to facilitate the handling of casing tubes during drilling. These and other objects are fulfilled by using casing tubes of plastic material from the beginning, which in turn according to the invention is made possible by a special design of the casing shoe and of coupling elements for the casing tubes giving a strong anchoring in the plastic material. Further advantageous design details appear from the claims and the detailed description. Still one further object of the present invention is to achieve a joint of the casing tubes of plastic material in a simple way. This can be done by joining metal elements to the ends of the casing tubes in the some way as the casing shoe, the metal elements supporting tube couplings, for example of the threaded type. The invention will now be described more in detail referring to the drawing t in which Fig.l shows schematic and partly broken through an example of a known design of the parts at the drill bit of a machinery for simoultaneous drilling and casing of the bore. Fig.2 and 3 shows partly in section the design of a casing shoe according to the invention in two embodiments, and Fig. 4 shows casing tubes with tube couplings according to the invention. The drill bit in Fig. 1 consists in a known manner of a pilot drill bit l, a reamer drill bit 2 and a guide 3 for a percussive drill hammer (not shown) . The drill bits 1 and 2 and the guide 3 can be rotated and axially influenced by the percussive drill hammer. A casing shoe 5 consists of an upper part 6 and a lower part 7, both cylindric. The inside diameters of parts 6 and 7 are alike and adapted to the outside diameter of the lower part of the guide 3. The outside diameter of the upper part 6 of the casing shoe is adapted to the inside diameter of the casing tube while the outside diameter of the lower part 7 is substantially the same as the outside diameter of the casing tube 4. The upper part 6 of the casing shoe is ended upwards with a shoulder 8, against which the guide 3 transfers the percussions of the hammer through a corresponding shoulder 10 of an enlarged part 11 of the guide 3. The casing tube 4 is pulled with the casing shoe when it is thrown downwards, the casing tube being welded together through a welding seam 9 at the upper end of the lower part 7. Fig. 2 shows a casing tube according to the invention partly in section. This is intended to be used instead of the casing shoe according to Fig. 1 in order to make possible casing with casing tube of plastic material or other materials which cannot be welded to a conventional casing shoe. The casing shoe 5 according to the invention has a lower part 7 which is essentially corresponding to this part of a conventional casing shoe. The upper part 6, however, is divided in one upper section 61 and one lower section 62, the upper section 61, as all of the upper parts of a conventional casing shoe, has an outside diameter adapted to the inside diameter of the casing tube 4 and an inside diameter equal to that of the lower part 7. The lower section 62 has essentially the same outside diameter as the upper section 61 but considerably less thickness. The lower section 62 is also perforated with holes 63, essentially with an even distribution. The holes 63 are circular in the drawing, but they can also be carried out with different shape and size, the thickness of the section 62 can also be varying and for example thicker around the circumference of the holes. The object of the holes is to cause a strong anchoring of the casing shoe on the casing tube 4 by way that it is connected thrugh the holes with an essentially tube shaped part 41 filling the space inside the inner surface of the lower section 62 to a substantially even inside diameter of the whole casing shoe. Another embodiment of the casing shoe 5 and the tube 4 is shown in Fig. 3. It corresponds to the embodiment of Fig. 2 except at the lower part 7 of the casing shoe, which is given a smaller outside diameter whereby a thin part 42 of the tube 4 surrounds it. The lower part 7 of the casing shoe is also shaped with a groove 72 at its lower part, in which plastic material 43 united to the thin part 42 is fitting. One more annular groove 71 is arranged, containig a packing ring 18, preferrably made of a material which expands in contact with water. The casing shoe according to the invention is preferrably joined to a suitable length of a casing tube to a well connected unit with a suitable heat treatment. During drilling the casing tube may be lengthened by way of a modified mirror welding or by joining w.ith some other conventional method. A suitable material for the casing tubes is PEH (high-density polyet n) . The connection of the lengths of casing tubes con also be done by means of equipping them at the ends with metal elements anchored at the tube end in the same way as the casing shoe. Accordingly, Fig. 4 shows two tubes 4A and 4B, each at the end connected with metal element 12A and 12B, respectively. For the sake of plainness a section of a part around a tube joint is shown on the right half of the drawing, while on the left half the tubes 4A and 4B are omitted in order to make the detailed design of the metal elements 12A and 12B clear. As with the casing shoe the metal elementes 12A and 12B are united to the actual tube by means of tube formed parts 62A and 62B, respectively, perforated by holes 63A and 63B, respectively, filled by the plastic material. Preferrably the tube formed parts 62A and 63B have a diameter which is in the middle between the inside and the outside diameter for the tubes 4A and 4B. They are designed with a thickness of material which is lowest at the outer end and increasing towards the end of the tube and the other parts of the metal element in order to achieve a good strength. The metal elements 12A and 12B may, for connection of the tube ends, be given a final shape with different types of tube couplings, for example of the bayonet type. One requirement when used as a casing tube for drilling is that both inside and outside surface at the joint is smooth and with no projections. As is shown in the embodiment in the figure each metal element has a part of even thickness 13A and 13B, respectively, closest to the end of the tube, after which follows a threaded part 14A and 14B, respectively. Thus, one of the metal elements 12A has an outer part with an even inside diameter and an externally threaded part 14A while the other metal element 12B has an outer part with an even outside diameter and an internally threaded part 14B. The threads 17 are preferrably of the trapezoid type. A packing 16 in the form- of an O-ring or the like may be arranged in a groove 15 between the part of even thickness 13A and the outside thread 14A for tightening against a part 19 outside the threaded part 14B. As the size, shape and distribution of the holes 63, 63A and 63B can be varied much within the scope of the invention, the number of holes and the sum of their areas can also be varied. In a preferred embodiment, however, the sum of the areas of the holed is at least equal to the cross section area of the casing tube 4. The invention is here described in connection with an embodi¬ ment but it shall only be restricted by the claims.

Claims: Claims 1. A method for overburden drilling with simultaneous loading of casing tube at which a percussive drill hammer is arranged to influence a casing shoe connected with the casing tube at its lower end, characterized in that the casing tubes used are of plastic material and that the casing shoe is made of metal perforated of holes filled with the plastic material. 2. A method according to claim 1, characterized in that the casing shoe is equipped with a perforated part which is relatively thin and cylindrical and that a casing tube surrounding the perforated part is connected with a tube- formed part of the same material through the holes in the perforated part. 3. Casing shoe for casing tubes with a lower, cylindrical part (7) with an outside diameter substantially corresponding to that of the casing tube and an upper cylindrical part (6) with an outside diameter substantially corresponding to the inside diameter of the casing tube, characterized in that the upper cylindrical part (6) to at least one part is perforated by holes (63) and has a bigger inside diameter then the rest of the casing shoe. . Casing shoe according to claim 3, characterized in that the upper cylindrical part (6) is surrounded by the end of a casing tube (4) of plastic material, that the inner surface of the perforated part is filled out to the same inside diameter as the rest of the casing shoe of the same material (41) as that of the casing tube and that this is connected with the casing tube through the holes. 5. Casing shoe according to one of the claims 3 and 4, charac erized in that the sum of the .areas of the holes (63) is at least equal to the cross section area of the casing tube (4) . 6. Tube (4, 4A, 4B) of plastic material, for instance for casing of bores, characterized in that it in at least one end is connected to a metal element (5, 12A, 12B) which for anchoring in the tube includes one substantially tube formed part (62, 62A, 62B) perforated of holes (63, 63A, 63B) filled by the plastic material. 7. Tube according to claim 6, characterized in that the metal element constitutes a casing shoe (5) . 8. Tube according to claim 7, characterized in that the metal element includes a tube coupling device (13A, 14A, 13B, 14B, 15, 16, 17, 19). 9. Metal element (12A, 12B) intended for a strong joint with a tube (4A, 4B) of plastic material, characterized in that it includes a tube coupling and at least one substan¬ tially tube formed part (62A, 62B) perforated of holes (63A,63B) for joining together with the tube thereby that the material of the tube surrounds the tube formed part filling the holes. 10. Metal element according to claim 9, characterized in that the tube formed part (62A, 62B) is of thickest material at the end facing the tube coupling and is tapering off to the other end.

Inventors: EDMAN KNUT OESTEN, EDMAN, KNUT, OESTEN
Applicants: EDMAN KNUT OESTEN, EDMAN, KNUT, OESTEN
Application year: 1993
Main classification: E21B7
IPC codes: E21B7, E21B10, E21B17, F16L15, F16L47