EP0100230B1

EP0100230B1 - Earth boring apparatus

Info

Publication number: EP0100230B1
Application number: EP83304298A
Authority: EP
Inventors: Ben Wade Oakes Dickinson Iii; Robert Wayne Dickinson; Stanley O. Hutchison; Sherman C. May; Charles S. Mackey
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-07-26
Filing date: 1983-07-25
Publication date: 1988-12-28
Also published as: BR8303989A; BE897361A; FR2540968B1; GB2124278A; MX159238A; IT1163856B; IT8322246A0; GB2124278B; DE3326350A1; SE8304122L; EP0100230A2; IL69277A0; AU1696883A; DE3326350C2; SE8304122D0; DE3378778D1; KR840005515A; EP0100230A3; IT8322246A1; AU564613B2

Description

The present invention is directed to earth boring apparatus for the formation of a bore hole for use in the recovery or the enhancement of the recovery of oil from an oil-bearing formation, or for the recovery of mineral deposits or the like, or for drilling through an underground formation for some other purpose.
The present invention is concerned with earth boring apparatus which utilises pressurised fluid for forming a bore hole and comprises a guide pipe, a tube which extends from within and out of one end of the guide pipe, and a drill head at the outer end of the tube.
Patent Specification US-A-2 345 816 (Hays) discloses such a type of apparatus. In this known apparatus the tube is made of rubber and is clamped to a tubing string. To feed the tube through the pipe, downward pressure is exerted on the tubing string from the derrick floor. This apparatus also has a fixed configuration device employing a number of rollers forturning the tube so that it extends horizontally.
The present invention is characterised in that the guide pipe is adapted to be coupled at its other end to a source offluid under pressure, the inner end of the tube is open and in fluid communication with the guide pipe, a fluid seal is provided between the . tube and the guide pipe, and the tube is adapted to be fed through the pipe by the action on the drill head of the pressurised fluid used for forming the bore hole.
Preferably, apparatus according to the invention includes a tube bending device, characterised in thatthetube is of metal. This device, also known as a whipstock, is able to cause the tube to turn from the vertical to a generally horizontal direction in a radius of the order of 0.152 to 0.305m (6 to 12 inches) for a steel drilling tube having an outside diameter of the order of 31.8 to 38.1 mm (1.25to 1.5 inches) and a wall thickness of from 2.03 to 3.18 mm (0.08 to 0.125 inches). Due to the hoop stress caused by high pressure drilling fluid and the bending stress during movement through the device, the metal is plastically deformed but the tube does not collapse or break.
Preferably the tube bending device comprises a plurality of pivotally interconnected assemblies having a first configuration, which is generally longitudinal, and a second configuration which forms an arcuate tube bending guideway, each assembly including a plurality of rollers which define a part of the guideway.
Patent Specification US-A-1 660 999 (Mac-Donell) discloses earth bore apparatus which also utilises pressurised fluid for forming a bore hole and comprises a flexible tube with a drill head at one end for drilling horizontally or laterally. The drill head is carried at the lower end of a chain adapted to slide in and be guided by the channel of a guide member. As drilling progresses, the drill head is moved forward by lowering the chain in the guide.
Patent Specification US-A-3 934 659 (Tsiferov) discloses earth bore apparatus which comprises a rocket attached to a drill head provided with nozzles. Fuel in the rocket is ignited to produce gas issuing from the nozzles for breaking rock. The gas issuing from the nozzles is also used to suspend the rocket above the rock face.
In the accompanying drawings:

Figure 1 is a side elevational view,.partially in section, illustrating a drill string assembly with conventional surface apparatus, and an expanded, partially broken away well casing and radials;
Figure 2 is a schematic view, partially in section, of the assembly moving horizontally through a whipstock and turning to a vertical direction;
Figures 3 and 4 are side and end views, respectively, of a drillhead at one end of a tube;
Figure 5 is a sectional view illustrating the drillhead and a single opening;
Figure 6 is a sectional view taken along the line 6-6 of the same opening as in Figure 5, illustrating the oblique-oblique orientation of one of a number of multiple ports in the drillhead;
Figure 7 is a cross-sectional view of a casing including four radials and corresponding whipstocks, together with a central production string;
Figure 8 is a view of the apparatus of Figure 7 taken along the line 8-8;
Figure 9 is a detail in side elevation showing another tube bending device;
Figure 10 is a view looking toward the exit end of the guide way of the bending and straightening device of Figure 9;
Figure 11 is a detail in side elevation showing another tube bending and straightening device;
Figure 12 is a detail looking toward the exit end of the guide way of Figure 11;
Figure 13 is a detail in side elevation and in section showing means for establishing a sealed connection for introducing steam into the drilling tube;
Figure 14 is like Figure 13 but shows a connection after it is established for introducing steam;
Figure 15 is a schematic view in side elevation, illustrating apparatus disposed within an earth well, with the drilling tube extended in a lateral bore;
Figure 16 is a detail in side elevation, illustrating the tube bending device of Figure 15 and its mounting;
Figure 17 is a detail in section elevation, illustrating the bending device in side elevation and extended;
Figure 18 is a view looking toward the right hand side of Figure 17;
Figure 19 is a detail in section showing another tube bending device in side elevation;
Figure 20 is a view looking toward the right hand side of Figure 19;
Figure 21 is a detail in section showing sealing means between the well piping and the drilling tube;
Figure 22 is a side elevation, partly in section, showing a tube bending device in three sections;
Figure 23 is an elevation looking toward the right hand side of Figure 22;
Figure 24 is a side elevation like Figure 22, but showing the bending device in its operative configuration; and
Figure 25 is an enlarged detail in section showing adjustable means for straightening the drilling tube.

Referring to Figure 1, the ground level 20 above a underground mineral bearing formation 22 is ilustrated on which a production rig 24 is disposed to the right and a coiled tubing rig 26 is disposed to the left. The function of the production rig 24 is to screw together sections of one or more guide tubes or pipes 30 and 32 at the site in a conventional manner. A drilling tube 34 is formed of a metal tube of the solid wall type which may, for example, have an outer diameter (OD) of approximately, 31.8 mm (1.25 in.), and is coiled on a spool and passed downwardly into the guide tube. When a sufficient length of the drilling tube 34 is in the guide pipe to reach the desired ultimate radial length, the drilling tube is severed and lowered down the guide pipe.
The lower portion of the drawing illustrates a pre-existing cemented-in well casing 28 in which are contained two different axially disposed guide pipe means, including the axially disposed guide pipes 30 and 32, terminating in whipstocks 30a and 32a, respectively, each whipstock having curved barrels or guideways. Disposed in each guide pipe is a drilling tube, the tube terminating in a drillhead 36. The drilling tube is formed of a relatively rigid metal material such as steel, and so has the advantage of moving in a substantially straight path through the formation. As illustrated, only the drilling tube 34, travelling in the guide pipe 30, is visible with the drillhead 36 at the forward end thereof. A suitable guide pipe is about 51 mm (2 in.) outside diameter in about 9.1 mm (30 ft.) sections.
The drilling tube 34 can be turned by bending and, upon turning through the whipstock 30a and drilling into the formation, becomes a radial or lateral tube or duct suitable for the injection of a hot fluid such as steam into the formation to heat up the viscous oil for removal. In the alternative, heat from the hot fluid causes the oil to flow back towards a casing containing a production pump as well as the radial, as better illustrated in Figures 7 and 8 described below.
In the illustrated embodiment, a fluid downcomer 38 (for example 31.8 mm (1.25 in.) outside diameter) projects centrally of the guide tubes 30 and 32 and is suitable for the injection of a foamed or foamable fluid or high viscosity fluid to assist the lifting of cuttings formed during operation of the drillhead 36, or during subsequent deposition of cement. Such cuttings flow back along the tube 34 and are lifted by foam to flow upwardly through axial spaces within the well casing 28. The tube 38 may also be used to conduct and deposit cement into the chamber 40 to fix the position of the radials and whipstocks upon completion of vertical bore hole drilling.
In a typical operation, the well casing 28 may be present from a pre-established injection well. A typical size in some areas of the United States for such casing is 140 mm (5.5 in.) in outer diameter, although larger casings may be used. Normally, the casing has been milled and the formation underreamed in a conventional manner to form the cavity 40 within which the whipstock 30a is disposed. An abrasive such as silica may be added to the drilling fluid supplied to the drillhead 36 or a separate drilling device, and directed against an existing well casing wall or cement formation to bore an opening through the casing or formation so that the drilling tube 34 and head 36 can move through the wall or formation to form a radial.
The general principle of forming a radial bore is now disclosed, although the detailed structure of the parts will be described more fully below in conjunction with the drawings. Briefly, the tube 34 is adapted to move within the guide pipe and provides an interior fluid passageway with an outward, open rearward end and a drillhead at its forward end. Single or multiple fluid exit ports are provided in the drillhead for the passage of drilling fluid from the fluid passageway of the tube into the adjacent formation. The interior of the guide pipe is in fluid communication with the rearward end of the interior passageway of the tube. Sealing means provides a seal between the tube and the guide pipe. High pressure fluid flowing through the fluid passageway of the tube applies pressure against the back of the drillhead to cause the tube to move in a forward direction. When the tube reaches the whipstock, combined stresses, including the hoop stress (or radial stress) caused by the high pressure fluid within the piston body, together with the bending stress in the whipstock, causes the tube, which is a normally rigid metal, to be stressed and deformed plastically in a physical metallurgical sense and to bend and turn into a radial, preferably horizontal, direction so as to be movable into the formation. The high pressure liquid issuing from the drillhead penetrates the formation and forms cuttings, which are turned into a slurry and passed back along the outside periphery of the tube into the cavity 40, wherein foam or other lifting fluid, which is passed downwardly through the downcomer 38, may be added to lift the slurry up to the surface of the formation through the axial space within the casing not otherwise occupied by the guide tubes. No fluid downcomer may be required and the fluid is directed into the surrounding formation under such force that the formation fractures, causing fissures into which the slurry can flow, whereby little, if any, cuttings are moved rearwardly along the radial bore and so lifting of such cuttings is not required.
A significant advantage of this system is that it is capable of drilling radial bores with a nonrotating drillhead, and that the bore hole is cased while drilling.
Figure 2 illustrates apparatus for vertical hydraulic jet drilling. It utilises the tube and pipe assembly of Figure 1, in which the tube turns from a horizontal direction on the surface to a vertical direction by passage through a whipstock on the surface. This permits the guide pipe to extend along the ground rather than being supported vertically. The underground formation 42 includes an upper cavity 44 to facilitate drilling. A guide pipe 46 is supported at ground level by conventional means. The rearward end of the guide pipe 46 projects into a housing 48, which includes a source of high pressure drilling fluid, not shown, and also means for introducing a drilling tube 50 terminating in a drillhead 52. A chevron type drilling fluid seal 54 is provided. A curved whipstock 46d attached by a coupling 46c to the forward end of the main body of the guide pipe 46. The whipstock 46d includes a curved barrel adapted to bend or turn the tube 90° from a generally horizontal to a generally vertical direction.
In operation, the drilling tube 50 is urged forwardly away from the high pressure pump in the housing 48 to the left as shown in the drawing, past the seal 54, by the drilling fluid pressure applying force against the fluid pressure area of the rearward side of the drillhead. When the tube is forced through the whipstock 46d, bending forces are applied to cause the tube to conform generally to the curve of the whipstock, whereby the tube is caused to turn downwardly into the formation. A straightener portion 46e is provided at the forward end of the whipstock 46d.. It is inclined towards the vertical (for example at 5 to 10 degrees) in the same general direction as the forward movement of the tube. In this manner, the contact of the tube with the straightener at point A causes the tube to straighten into a generally vertical direction, rather than to continue its curve and curl backwardly into a spiral path. Drilling fluid is directed outwardly through one or more ports 52a of the drillhead 52 into the formation to provide a slurry through which the drill head readily moves under the force applied by the pressurised fluid.
The tube may be formed of steel or other metal of sufficient rigidity to travel in a straight line through the formation, but is capable of the above plastic deformation. For example, a suitable wall thickness for this purpose is 2.03 to 3.18 mm (0.080 to 0.125 in.) of 0.2482 to 0.4826 GN/m² (36,000 to 70,000 psi) or more yield steel for tubes ranging from 31.8 to 38.1 mm (1.25 to 1.5 inches) OD.
The principle of operation of the drilling tube guide assembly is more clearly illustrated in Figure 2. That is, the fluid seal 54 between the stationary guide pipe and movable drilling tube is provided so that the high pressure fluid emerging from housing 48 (for example at 6.895 to 68.95 MN/m² (1,000 to 10,000 psi) or higher) applies a high pressure force against the drillhead 52 to cause it to move forwardly at a relatively high speed. The pressurised drilling fluid presses against the seal 54 and the portion of the guide pipe upstream from that seal, which is in fluid communication with the entire length of the tube 50 to ensure that the major force is directed against the rearward side of the drill head to cause it to project forwardly. Although a minor portion of the pressure is lost due to the drilling fluid emerging through port or ports 52, the major portion of that force carries the drillhead and drilling tube forwardly.
Downstream of the seal 54, significant internal radial pressure (hoop pressure) causes the normally rigid drilling tube (for example formed of 2.03 to 3.16 mm (0.080 to 0.125 in.) wall thickness for steel tubing ranging from 31.8 to 38.1 mm (1.25 to 1.5 inches) outside diameter) to be highly stressed. This stress, together with the bending stresses created when the tube passes through the whipstock, causes the tube to be plastically deformed and turned or bent in a relatively short radius from a horizontal to a vertical direction.
Figure 2 shows vertical drilling without radial bores being formed. Since the pressure behind the seal 54 must be maintained for the above- described mode of propulsion and simultaneously jet cutting, the length of the. drilling tube downstream of the seal can be no greater than the initial length of the guide pipe upstream of the seal. One of the major advantages of the illustrated system is that no pre-existing casing is required, and it is unnecessary to drill a pre-existing hole for the tube.
Figures 3 and 4 illustrate a drillhead 56, which is mounted at the forward end of a drilling tube 58, suitably by welding. The forward end of the drillhead is generally rounded, hemispherical in shape with shaped generally forward directed ports 56a. In addition, elliptical ports 56b are provided for directing drilling fluid in a generally rearward direction to assist the fluidising of cuttings surrounding the piston body as it passes through the formation, to lubricate the cuttings and prevent binding with the formation and to assist movement of the formed cuttings in a rearward direction. Alternatively, all ports or a single port may be directed forward to maximise cutting.
Figures 5 and 6, illustrate the nose of the drillhead of Figures 3 and 4 in which one port 56a has a direction which is oblique in two different planes to the axis of the drillhead. In this manner, the jets cut the kerf or slot walls which would otherwise be formed forward of the drillhead by ports oblique in one direction only and cause possible drillhead resistance. By disposing the ports obliquely at least 10 to 30° off the axis in at least two different directions, the fluid jet shears the formation in such a manner that the drillhead functions progressively to shear off the kerfs in the cut formation as the drillhead passes.
Figures 7 and 8 illustrate a combination injection well and production well. There, a pre-existing well casing 90 is provided, and four guide tubes 92, 94, 96 and 98 ending in whipstocks 92a, 94a, 96a and 98a, respectively, are placed circumferentially within the casing. Whipstocks 92a and 96a extend parallel to each other in opposite directions. Similarly, whipstocks 94a and 98a extend parallel to each other in opposite directions and perpendicular to the directions of the whipstocks 92a and 96a. Drilling tubes 100, 102, 104 and 106 are directed downwardly through the guide tubes 92, 94, 96 and 98, respectively, and turn through their respective whipstocks to form horizontal or radial portions 100a, 102a, 104a and 106a, respectively. Thus radials project every 90 degrees in a horizontal direction into the formation.
Centrally of the well casing 90 is a production tubing or pipe 110 of a conventional size and shape, including a conventional sucker rod pump assembly with a sucker rod 112 and a schematically illustrated piston valve 114 in Figure 8. At the bottom of the tubing 110 is a conventional slotted cylindrical portion 110a, which is permeable to oil flow but which filters out particulate matter, much as a wire-wrapped screen sand filter.
In use of the system shown in Figures 7 and 8 and after the radials (100a, 102a 104a, 106a) are in place and the bottom of the production tubing 110 is in place in a sump at the bottom of the casing 90, a hot fluid such as steam flows through the radials and out of the drillheads to heat the adjacent oil bearing formation to allow the oil to flow downwardly and laterally and into a sump 116. There, the oil is pumped to the surface in a conventional manner by the sucker rod pump assembly. Heat energy is used effectively since some of the heat from the downwardly flowing steam is utilised to maintain the upwardly flowing oil at a temperature such that the oil is maintained as a fluid as it is delivered to the top of the well.
Referring again to Figure 8, the apparatus may be used for "steam soaking" in the following manner. After formation of the radials 100a, 102a, 104a and 106a, they may be cut from their corresponding whipstocks, and the whipstocks withdrawn to the surface for possible re-use. Then steam is passed down well casing 90 to permeate into the formation. A pump is placed in the sump as illustrated, and the oil, which has been heated by the steam to flow into the sump, is pumped to the surface.
The force applied to the drillhead may be sufficient to cause the drilling tube to move at a rate faster than the jets can effectively fluidise the formation which the drillhead contacts. Means may then be provided in the form of a restraint line for controlling the maximum rate of movement of the piston body. Such a line may also serve to monitor the speed with which the drillhead progresses into the formation.
Apparatus of the foregoing type may be utilised for the injection of a hot fluid or steam through the radials which are for heating the underground formation for production at either the same casing as the one from which the radials project, or at a remote casing.
When drilling iscomplete, the well is sealed as illustrated in Figures 13 and 14 or by some other means. For example, the well may be sealed by passing cement intd the area surrounding the drilling tube through the fluid downcomer or guide tube. If the openings in the drillhead are of insufficient size to pass the necessary volume of steam or other fluid, an abrasive may be included in the drilling fluid to erode out the openings to the desired size for fluid injection, or the openings may be enlarged by the action of a suitable solvent. The drillhead may be completely severed using an explosive charge.
Two further tube bending device are illustrated in Figures 9 to 12. In both instances the dimensions and configurations are such that the well must be of sufficient diameter to permit their introduction. In Figure 9 a housing 151 encloses a portion of a tube bending device 152. The bending device comprises a rigid body which is formed by spaced side plates 154 that are secured together by connecting walls. Two series of rollers or sheaves 156 and 157 are journalled between the side walls 154, and are positioned to form a curved guide way 158. This guide way 158 is dimensioned to be compatible with movement of the drilling tube there through. The arrangment is such that when the drilling head and tube are forced through the guide way by hydraulic pressure, the tube is at all times in contact with a plurality of sheaves 156 and 157, and is bent to the desired radius. A tube straightening means 159 is disposed at the exit end of the guide way 158, and consists of a cruciform-like body 161, which is attached to the side plates 154. The body 161 carries four sheaves, namely upper and lower sheaves 162, and opposed side sheaves 163. These sheaves are so formed that their peripheral surfaces embrace substantially the entire circumference of the drilling tube.
When the drilling tube is caused to pass through the guide way 158, the bending is accompanied by some change in its cross-sectional configuration. More specifically as the tube reaches the end of the guide way it has a cross-section which is oval rather than circular. Straighttening of such a tube is sometimes more effective if it includes some reforming of the tube to a circular configuration. To accomplish this, the sheaves 163 are so formed that they apply force to the exiting drilling tube to somewhat reform the tube to a circular cross-section while simultaneously applying an unbending force. In connection with the straightening action, the sheaves 162 and 163 also co-operate with the adjacent ones of the sheaves 156 and 157.
In another construction the cruciform type of straightening means shown in Figures 9 and 10 is not used. Thus as shown in Figures 11 and 12, the straightening means in such event employs only the two upper and lower sheaves 162.
Figures 13 and 14 illustrate the introduction of drilling fluids such as steam into the drilling head after formation of the bore hole.
This may be necessary if the sliding seal suitable for feeding the drilling tube is not sufficiently tight to fully contain steam injection into the drilling tube for heating the underground formation. This is the purpose of the steam seal now described.
The figures show a guide pipe 166 together with a threaded coupling 167 between sections of the guide pipe. The drilling tube 168 passes through a seal 164. The upper end of the drilling tube 168 is provided with a threaded collar portion 171. The lower end of the upper section of the guide pipe 166, is also provided with an internally threaded portion 172. The threads of the coupling 167 are made the same as the threads of the collar 171 and portion 172. More specifically the threads for coupling the two sections of the guide pipe may be left-handed, and the threads of the portions 171 and 172 are also made left-handed. Assuming that hydraulic pressure has been applied to the guide pipe to force the drilling tube 168 and its attached drilling head laterally into the mineral bearing formation and steam or other treatment fluid is now desired to be introduced into the drilling tube, the coupling 167 is disengaged by turning the upper part of the guide pipe 166 clockwise, after which it is lifted and turned counterclockwise to engage the threaded portions 171 and 172. This provides a sealed metal to metal coupling. The parts are then in the condition shown in Figure 14. Steam or other treatment fluid can now be introduced through the guide pipe and through the drilling tube 168, and from thence into the mineral bearing formation.
Figures 13 and 14 also show an annular portion 173 at the inlet to the portion 171, which is formed to provide a downwardly convergent entrant opening. This improves the flow characteristics of the arrangement in that it provides a transition from the larger internal diameter of the pipe 166 to the smaller internal diameter of the tube 168. The portion 173 is dimensioned to form a stop when the threaded portions 171 and 172 are engaged.
Figure 15 schematically shows an earth well 210 which extends down to a mineral bearing formation 211. The well is provided with a casing 212, which extends down to a cavity 213 that is adjacent to the formation 211. The pipe extending into the well comprises a pipe string 214 within which a drilling tube 215 is normally disposed. As shown in Figure 21, a seal 216 is mounted within the pipe string 214, and forms seal between the pipe string and the drilling tube 215. The upper open end of the drilling tube 215 is above the seal 216, when the drilling tube is fully extended as shown in Figure 15. Before the drilling tube is extended it is within the pipe string 214, with its drilling head 217 located below the seal 216. The structure 221 serves to carry a tube bending device 222. While the seal 216 may be incorporated in a coupling between any sections of the pipe string 214, it is preferably incorporated in the coupling adjacent to the upper end of the bending device 222. Pipe 249 is a fluid downcomer.
Figure 15 also schematically shows a production rig 224 of the mobile type, and a reel carrying truck 225 which carries a supply of the drilling tube 215.
An extensible whipstock or bending means is shown in Figures 16 to 18. It comprises the structure 221, which carries bending assemblies 226 and 227. Structure 221 is in the form of a pipe section having one side cut away as indicated at 228. Assembly 226 comprises a rigid mounting made of rigid side plates 229 attached to a back plate (not shown), and a top plate 231. This assembly is securred to the structure 221 as indicated at 232. The assembly 227 similarly includes a rigid mounting formed by the connected side plates 233, which have a pivotal connection 234 with the lower end of the assembly 226. The upper assembly 226 carries two series of rollers or sheaves 236 and 237. They are disposed to form a guideway 238, dimensioned to receive the drilling tube 215. The lower assembly 227 is similarly provided with two series of rollers or sheaves 239 and 240. They are positioned to form the guideway 242.
The bending device described above is extended from a first longitudinal configuration to a second arcuate configuration shown in Figure 17, by swinging the lower assembly 227 outwardly and upwardly. The guideway formed by each assembly becomes a segment of the entire guideway formed when the lower assembly is swung to the position in Figure 17.
Suitable power means is provided for moving the lower assembly 227 to the extended position shown in Figure 17. This comprises a hydraulic actuator 244 of the cylinder-piston type, having its operating rod pivotally connected at 246 with the side walls 233 of the assembly 227. When hydraulic liquid under pressure is applied to the actuator 244, it moves the lower assembly 227 from the position shown in Figure 16, to that shown in Figure 17. Continued application of hydraulic pressure to the actuator 244, or hydraulic loading, serves to retain the assembly in the position shown in Figure 17, during passage of a drilling tube through the assembly, and during subsequent drilling operations. Assuming that the actuator is of the single acting type, the control valve for admitting or venting hydraulic fluid may be closed after actuation to lock the assembly 226 in the extended position. Figure 15 shows a tube 247 extending to the top of the well for the hydraulic operation of the actuator 244.
When the bending device is to be salvaged, following application of steam or other treatment fluid through the radially extending drilling tube 215, the pipe string 214, together with the housing structure 221, can be pulled upwardly to force retraction of assembly 227 and crushing and breaking off of the extended portion of the drill tube. In the event the actuator 244 is of the double acting type, it can be used as power means to retract assembly 227 with crushing or buckling of the drilling tube. Tubing 215 may be severed explosively or otherwise prior to whipstock collapse.
As shown in Figure 17 the series of rollers or sheaves 236, 237 and 239, 240 carried by the assemblies 226 and 227 provide a continuous curved guideway 238, 242 through which the drilling tube 215 is caused to pass, to apply the desired bend. The sheaves of each assembly may engage either the inner or outer walls of the bent tube. The tube bend usually will be through 90°, although this may vary depending upon particular requirements. By way of example bending radii can be of the order of 0.152 to 0.305 m (6 to 12 inches), for steel pipe ranging from 31.8 to 38.1 mm (1.25 to 1.5 inches) outside diameter, and a wall thickness of the order of 2.03 to 3.18 mm (0.080 to 0.125 inches). The metal of the tubing may, for example, have a yield point ranging from 0.2482 to 0.4826 GN/m² (36,000 to 70,000 pounds per square inch) or more.
One would normally expect the tubing to buckle or break upon bending to such relatively short radii. However, the fact that the tubing does not buckle or break is attributed in part to the presence of a liquid at relatively high pressure within the tube, while the tube is in transit through the bending device. This imposes hoop stress in the metal walls in conjuniction with stresses applied during bending.
Referring to Figure 17, the sheaves 239a, 239b, 239c and 239d, and the opposed sheaves 240a, 240b and 240d, are arranged to form a straight guideway. The purpose of these sheaves is to form straightening means whereby the drilling tube leaving these sheaves is relatively straight. The sheaves 239d and 240d are large in diameter and have peripheral grooves such that they embrace substantial the entire circumference of the tube. Thus this arrangement serves to apply straightening forces to the tubing as it leaves the guideway. In addition to straightening the tube by applying unbending forces, the sheaves 239d and 240d may have reforming surfaces to reform the tube from an oval to a more circular section.
For the purpose of strengthening the structure 221 against side thrust, its upper end is shown attached to a template extension 221 a, which may be a pipe section which extends for a substantial distance into the well casing 212.
The manner in which the extendible whipstock is used in practice, is as follows. Assuming that the well has been drilled by conventional means, and that the cavity 213 has been formed adjacent to the mineral bearing formation 211, sections of the drill string 214 are assembled with the lowermost coupling attached to a member 251 of the tube bending device. An adequate length of the drilling tube is provided with the hydraulic jet- type drilling head 217 attached to the end. This is then assembled within the drill string with the drillhead at or slightly below the seal 216. An adequate length of drilling tube is one which has a length sufficient to extend laterally for the required distance, plus a further length sufficient to ensure that the upper open end of the tube is well above the seal 216, when the tube is extended as shown in Figure 15. The assembly of the drill string 214, together with the attached housing 221 and bending device 222, is now lowered into the well, at which time the bending device is in a retracted or longitudinal configuration. When the bending device has reached a level corresponding to the mineral bearing formation, the upper end of the pipe 214 is connected to a source of hydraulic liquid (for example, water) at a relatively high available pressure, which may range, for example, from 6.815 to 68.15 MN/m² (1,000 to 10,000 psi) or more. In an alternative and preferred method, the drill string, including the whipstock but not the drillhead and drill tube, is first lowered to the desired final location. Then the drillhead and drill tube are lowered. Assuming now that one desires to make a lateral bore into the mineral bearing formation, the bending device 222 is extended as shown in Figure 15 to its second configuration, by applying hydraulic pressure to the actuator 244, and the high pressure hydraulic liquid is introduced into the upper end of the pipe string 214. The hydraulic liquid flows into and through the drilling tube 215, and by virtue of the fluid pressure areas afforded by the drilling tube together with the drillhead 217, the tube is driven downwardly through the seal 216, the bending device 222, and then laterally against the formation as set out above. The jet drilling head 217 penetrates the formation to form a laterally extending bore as shown, for example, in Figure 15. At the conclusion of this operation, and assuming that the mineral bearing formation is to be treated with steam or other fluids, application of hydraulic pressure to pipe string 214 is discontinued, a steam seal is formed, and this string connected at the surface of the well with a source of the treating fluid. Thus the apparatus may then serve over an extended period of time as means for introducing treating fluid well into the mineral bearing formation.
The construction illustrated in Figures 19 and 20 has another form of tube straightening means. In place of the tube straightening rollers or sheaves 239d and 240d there is a cruciform-type of straightening means 251. It comprises a body 252 on which are mounted opposed rollers or sheaves 253 and 254, together with laterally disposed rollers or sheaves 256 and 257. The grooves in the peripheries of these sheaves are proportional whereby they embrace substantially the entire circumference of the tube. Although the drilling tube is not collapsed during bending, there is a plastic deformation of the metal walls, whereby when the tube leaves the guideway, its configuration in cross-section is slightly oval, rather than circular. The rollers 256 and 257 may be set whereby when the tube passes between them, side pressure is applied to the tube side walls to somwhat reform the cross-sectional shape to near circular. This aides straightening of the tube, whereby, together with the action %of sheaves 239a to 239c and 240a, 240b, that portion of the tube extending from the straightening means to the formation, is sufficiently straight to transmit the desired thrust of the drilling head into the formation, without further straightening.
Figures 22 to 25 illustrate a plurality of sheaves that form the arcuate guideway of the bending device. However the bending device is formed by three assemblies, instead of the two assemblies of Figures 16 and 17. Also an adjustable straightening means is provided. The housing 261 is similar to the housing structure 221 of Figure 16. The tube bending device comprises three assemblies 262, 263 and 264, each of which forms a segment of an arcuate guideway. The assembly 262 comprises rigid side walls 266 that are rigidly secured together in spaced relationship, and are fixed to the upper portion of housing 261. The edges of the sidewalls are shown connected by closure or cover plates 266a and 266b. The assembly 263 likewise comprises spaced connected walls 267, the upper ends of which have a pivotal connection 268 with the side walls 266 of assembly 262. The walls 267 are also shown connected by closure or cover plates 267a and 267b. The assembly 264 also comprises spaced conniected walls 269 that have a pivotal connection 271 with the lower ends of the walls 267, and which have closure or cover plates 269a and 269b.
Figures 22 and 23 show the assemblies 263 and 264 retracted within the housing structure 261 in a longitudinal configuration. A power means for extending the assemblies to the arcuate configu- rate shown in Figure 24 comprises a hydraulic actuator 272 that is pivotally anchored at 273 to the housing 261 and has an operating rod 274 pivotally connected at 276 to the side walls of the assembly 264. The side walls of the assemblies 262 and 263 have their adjacent ends 276 and 277 formed whereby they come into abutting engagement when the bending device is fully extended. The opposed ends 278 and 279 of the side walls of the assemblies 263 and 264 are similarly formed. In place of the power actuator 272, the assembly 264 may be connected to a pull cable extending to the top of the well.
When actuator 272 is actuated by hydraulic pressure, the assemblies 262, 263 and 264 are pivoted to the limiting position shown in Figure 24, with the ends 276 and 277, and 278 and 279 in abutting engagement.
Each of the assemblies 262, 263 and 264 has a plurality of rotatable sheaves that are disposed in such a manner as to form, when the assemblies are in their operative position, a continuous tube bending guideway which progressively bends the drilling tube as the tube is driven through the guideway. The complete guideway is arcuate, with the assemblies 262, 263 and 264 forming segments of the arc. The sheaves for the assembly 262 are designated 281 and 282; for the assembly 263 they are designated 283 and 284; and are designated 286 and 287 for the assembly 264. The sheaves 286a, 286b, 286c, 286d and 286e, and_,)287a, 287c and 287e co-operate to straighten the drill tube before it leaves the assembly 264. The sheave 287c is adjustable to adjust the straightening force that it applies. It is rotatably carried by a structure 288, which in turn is pivotally connected to a pin or shaft 289 that is carried by the side walls of assembly 264. The positioning of the sheave 287c can be adjusted relative to the sheaves 286b, 286c and 286d by adjustment of a screw 291. To enhance the straightening action, the sheaves 286b, 286c and 286d are disposed with a line joining their centers arched upwardly (Figures 24 and 25). The sheave 287e is not essential for the straightening action and may be omitted. The adjustment feature of the sheave 287c is also applicable to the constructions of Figures 9, 11, and 16.
As in Figures 16 and 17, sheaves 286e and 287e are of such size and with grooves such that they substantially embrace the circummference of the drilling tube. They are intended to somewhat reformm the tube to a more nearly circular form.
The tube straightening means of Figures 22 to 25 when extended functions in substantially the same manner as the construction of Figures 16 to 20. However, when retracted, it is more compact since the assemblies 262, 263 and 264 have a straight longitudinal configuration. Also when the actuator 272 is energised to extend the assemblies to the arcuate or operative configuration, the assembly 264 is the first to be swung outwardly because of the locations of the pivotal connections 271 and 272, and is followed by the assembly 263.
When the drilling tube is being driven through the bending means and into the adjacent formation, water should be introduced into the assent blies 262, 263 and 264. Thus a small duct may divert some water from above the seal to the assembly 262. It may discharge into assembly 262 or it may connect with ducts 294, 295 and 296 in the side walls of the assemblies. The latter ducts are so located that they are in communication when the assemblies are extended. The duct 296 may discharge sprays of water through nozzles 297. Introduction of water tends to flush out and prevent clogging of the guideway or jamming of the sheaves due to entrance of foreign material (for example, sand or small rocks).
The closures or cover plates for the assemblies 262, 263 and 264 may be used to keep out rocks or other debris. In some instances they may be perforated.

Claims

1. Earth boring apparatus which utilises pressurised fluid for forming a bore hole and comprises a guide pipe, (30, 32; 46; 92, 96, 98; 166; 214), a tube (50; 58; 100, 102, 104, 106; 168; 215) which extends from within and out of one end of the guide pipe, and a drill head (36; 52; 56; 217) at the outer end of the tube, characterised in that the guide pipe is adapted to be coupled at its other end to a source (48) of fluid under pressure, the inner end of the tube is open and in fluid communication with the guide pipe, a fluid seal (54,164,216) is provided between the tube and the guide pipe, and the tube is adapted to be fed through the pipe by the action on the drill head of the pressurised fluid used for forming the bore hole.

2. Apparatus as claimed in Claim 1, characterised in that the fluid seal is an annular seal (54; 164; 216) which is secured inside the pipe and the tube extends through the seal.

3. Apparatus as claimed in either preceding claim, characterised in that the drillhead (56) has a plurality of ports (56a) at least one of which extends in a direction which is oblique in two different planes to the drill head longitudinal axis.

4. Apparatus as claimed in any preceding claim, characterised in that the drill head (56) has a plurality of ports (56b) at least one of which is for directing fluid in a direction opposite to that of intended feeding of the tube.

5. Apparatus as claimed in any preceding claim, and which includes a tube bending device (30a, 32a; 46d; 92a, 94a, 96a, 98a; 152; 222), characterised in that the tube is of metal.

6. Apparatus as claimed in Claim 5, characterised in that the tube bending device comprises a plurality of pivotally interconnected assemblies (226, 227; 262, 263, 264) having a first configuration, which is generally longitudinal, and a second configuration which forms an arcuate tube bending guideway (158; 238, 242), each assembly including a plurality of rollers (157, 162, 163; 236, 237, 239, 240, 253, 254, 256, 257; 281, 282, 283, 284, 286, 287) which define a part of the guideway.

7. Apparatus as claimed in Claim 6, characterised in that the asemblies are interconnected in series and are connected to powered means (244; 272, 274) for changing their configuration.

8. Apparatus as claimed in Claim 5, 6 or 7, characterised in that the tube bending device includes means (159,161,162,163; 239, 240; 251, 253, 254; 286a to e, 287 a to e, 288, 289, 291) for straightening the tube after having been bent.

9. Apparatus as claimed in Claim 8, characterised in that the means for straightening the tube includes a roller (287c) mounted so as to be adjustable along the path of movement of the tube.

10. Apparatus as claimed in any one of Claims 5 to 9, characterised in that the tube bending device includes means for re-shaping the tube cross-section after having been bent.

11. Apparatus as claimed in any preceding claim, characterised in that a restraint is provided for controlling the rate of feed of the tube through the pipe.