Patent Application
20050152749
The present invention relates to the known field of off-shore drilling from an anchored support floating on the surface, and more particularly it relates to devices installed at sea bottom level for guiding drill strings.
More particularly, the invention relates to deflected drilling in deep water so as to reach points that are far away from vertically beneath the drilling equipment on the surface.
Once the depth of water becomes large, exploring and working production fields, in particular oil fields, is generally carried out from a floating support. In general, the floating support has anchor means for keeping it in position in spite of the effect of currents, winds, and swell.
During drilling operations, it also generally has means for handling drill strings, and guide equipment associated with safety systems installed on the sea bottom.
Drilling is usually carried out vertically beneath the drilling equipment, and then penetrates into the ground vertically over a height of several hundreds of meters. Thereafter, drilling is continued until the petroleum deposit referred to as the “reservoir”, either in a vertical direction or else with a progressively increasing angular deflection so as to reach points of said reservoir that are offset to a greater or lesser extent.
The stage of starting a well is generally performed by lowering from the surface a drilling bedplate that rests on the sea bottom and that is provided with guide lines going to the surface, after which a length of pipe referred to as “casing” is lowered, this pipe being of large diameter, generally 36 inches (″) (=0.914 meters (m)) having a total length of 50 m to 60 m. The casing is made up from unit lengths of pipe, each measuring about 12 m long, which unit lengths are assembled together by screw engagement on board the drilling platform, at derrick floor level. In order to withstand forces, each unit length of casing has, at each of its ends, a zone that is reinforced over a length of 0.5 m to 1 m, which reinforced zone is constituted by extra thickness corresponding to about half to twice the ordinary thickness of the wall of said casing, with said screw thread being machined in said thickness. Once assembled, said casing passes through said baseplate and is then simply put into the ground, which is generally quite loose, so driving can often be performed by merely jetting (i.e. by squirting water under pressure). The first length of casing serves to consolidate the walls of the well in its zone close to the sea bottom, and thus acts as a device for guiding a second length of casing which is smaller in diameter and generally has a total length of 150 m to 200 m, said second length of casing itself also being built up by assembling together 12 m unit lengths of pipe having reinforced end zones and presenting an outside diameter, including the reinforced threaded zones, that is significantly smaller than the inside diameter of the outer casing so as to enable it to slide freely during installation, and also so that cement slurry can be delivered under good conditions. The second casing is then either vibro-driven, or else it is driven by drilling if the ground requires drilling, and then the gap between said casings and the ground is cemented from the surface, as is the gap between said two casings. During these stages, the work is “open-hole” work and there is a risk of being exposed to ground instability, or indeed to unwanted ingress of water at shallow depth beneath the sea bottom (“shallow water flow”), which can severely disturb the stage of starting the well.
Depending on the nature of the ground, it may be necessary to consider using a third length of casing or even a fourth in order to reach a sufficient depth for initiating drilling proper.
Thus, the multiple lengths of casing present large gaps between each of said lengths and the next, and in addition, because each of said length of casing extends from sea bottom level down to its own bottom end, this implies that at sea bottom level and over the full height of the first length of casing and of the subsequently installed lengths, there exist radially two, three, or even four or more successive thicknesses of casing which are not useful in subsequent operations since during the main stages of drilling and operating the well, only one thickness of casing is needed to support downhole equipment and to seal the assembly. These multiple redundant layers of casing in the zone close to the sea bottom are made necessary by the way in which well drilling is started in prior art methods, and this redundancy represents a considerable quantity of steel, and thus a very high cost.
Patent GB-2 338 009 describes a way of installing multiple independent casing elements that are installed successively one inside another with small clearance. Said elements are installed in sequence, one after the other, and because of the small clearance, this makes it possible to minimize the maximum diameter of the hole that is to be drilled, both for the outermost casing element and for the intermediate casing element, thereby correspondingly reducing the quantity of drilling waste to be removed and the power requirements of the drilling equipment, and consequently reducing hourly operating costs.
U.S. Pat. No. 5,307,886 describes a system and a method of installation enabling multiple casing elements to be used with small clearance, and minimizing the space between said casing and the wall of the hole drilled in the ground.
A first problem on which the invention is based is to provide a guide device enabling a drill string and a drilling tool to be guided as deeply as possible into the subsoil at the bottom the sea so as to avoid such accidents of unwanted ingress of water that occur at shallow depths in the ground while casing is being installed.
Another problem is to reduce the amount of handling and assembly performed on board the drilling platform of unit lengths of pipe serving to make up said lengths of casing, thereby reducing the difficulty, the duration, and therefore the cost of installing casing, particularly in ultra-great depths, i.e. in depths of 2000 m to 3000 m, or even more. Since such handling is performed in successive independent sequences, and even when the time spent specifically in burying the first length of casing in the ground, and then the second length of casing, etc. remains acceptable, the intermediate handling consisting in raising gripping tools to the surface and then lowering the following length of casing then represents a considerable amount of time and thus a considerable cost of not using the extremely expensive drilling equipment, particularly when the depth of water is 2000 m, 3000 m, or even 4000 m to 5000 m, or more. In addition, the stages of cementing the gap between two lengths of casing requires a very large amount of time, thereby increasing the cost of the operation.
Another problem is to greatly reduce the quantity of steel needed for making such casing by minimizing redundancy and also the clearance between successive lengths of said casing.
Furthermore, when drilling a plurality of deflected wells, it is possible to set up an array of wells in an umbrella shape, all stemming from a single position for the floating support on the surface, thus making it possible throughout working of the field to group together all of the surface equipment in the same location. Such installations are referred to as dry tree units (DTUS) because the wellheads are dry since they are brought together at the surface out of the water. This makes working much easier since it is possible to access any one of the wells from DTU in order to perform all of the maintenance and inspection operations required on wells, and this can continue throughout the lifetime of the installation which can be as much as 20 years to 25 years or even longer.
Such deflected drilling is possible only if the reservoirs are at great depth, for example 2000 m to 2500 m, since it is essential to have a borehole with a vertical length of several hundreds of meters in the sea bottom prior to initiating deflection of the well, and given that the radii of curvature used in deflected wells are of the order of 500 m to 1000 m.
Patents EP 0 952 300 and EP 0 952 301 describe methods and devices for drilling deflected wells by taking advantage of the depth of water in order to begin drilling as far away as possible from vertically below the drilling equipment, and in order to rest on the sea bottom in a manner that is substantially tangential to the horizontal.
In those patents, the guide devices installed on the sea bottom penetrate into the ground and enable the borehole to be started in the sea bottom while it is inclined at a given angle relative to the vertical. The guide device is connected to the drilling equipment by a pipe known as a drilling riser which guides the drill string that passes therealong and which serves to raise drilling mud and debris.
The guide element installed on the sea bottom must make it possible to comply with large radii of curvature of 500 m to 1000 m, and consequently it must be of large dimensions, while nevertheless remaining very strong in order to be able to accommodate the considerable forces generated by the drill string which is also constrained to follow the same radius of curvature, thereby giving rise to very high levels of friction and to a risk of the assembly becoming destabilized during drilling.
In addition, that guide element of considerable size and mass needs itself to be pre-installed in ultra-great depth, i.e. in depths of water of 1000 m to 2500 m, or even more.
More precisely, in EP 0 952 301, the guide device includes a pipe element referred to as a “conductor” which is the borehole guide tube deployed from a floating support via the drilling riser down to a structure referred to as a “skid” resting on the sea bottom. Said skid structure holds and guides the conductor tube horizontally a certain height above the sea bottom. The conductor then takes up a curve towards the sea bottom under the effect of its own weight. While it is being deployed, the conductor co-operates with drilling tools so as to become partially buried in the sea bottom. Putting such a guide device into place, and in particular putting the conductor into place from the floating support represents a considerable operational constraint. In addition, the guide device provides no control over the curvature of the conductor. Furthermore, in order to ensure that the radius of curvature is large, and in particular greater than 5000 m, it is necessary for the conductor to be deployed tangentially to the horizontal over several tens of meters beyond the bearing point which guides it on the skid structure.
Finally, those patents do not describe any means for ensuring that said conductor is put into place with a large radius of curvature as is necessary for the drill string, and above all to allow the casing elements to operate with a minimum amount of lateral friction inside the pipe.
For a radius of 600 m, if the well head is 2 m above the ground, the conductor will reach the ground 50 m further away, which means that there is a free and unsupported cantilevered-out portion of conductor that is 50 m long, which is not acceptable since there is a danger of the conductor breaking or kinking because of local curvature that is too sharp since it is not under control. In addition, the cantilevered-out portion can be harmful to proper operation during drilling operations and also throughout the lifetime of the well which might exceed 25 years.
Another problem of the present invention is thus to provide a guide device in an application to drilling in a manner that is deflected in the depth of the water, that can reliably be installed with a large radius of curvature, i.e. in which it is possible to ensure that the radius of curvature is greater than 500 m, in particular, and which is easy to build and put into place.
In a first aspect providing a solution to the problem of guiding the drill string and the drilling tool as deeply as possible, the present invention provides a guide device for an off-shore drilling installation comprising at least one drilling riser extending from a floating support to said guide device on the sea bottom, said drilling being performable from said floating support using a drill string fitted at its end with drilling tools passing through said drilling riser and said guide device, said guide device being characterized in that it comprises a telescopic guide pipe comprising coaxial telescopic guide elements about an axis XX′ and of decreasing diameters, the elements being preassembled one in another in such a manner that said telescopic pipe elements are suitable for sliding in the direction of said axis XX′ one inside another, the smallest-diameter, innermost telescopic pipe element being fitted at its end with breakup means for breaking up the ground suitable for enabling said telescopic guide pipe to be progressively buried in the ground by sliding said telescopic pipe elements outwards, thereby enabling a drilling tool at the end of said drill string to be guided more deeply in the ground.
It will be understood that the guide pipe is buried progressively in the ground from a retracted initial position in which the smallest-diameter innermost telescopic pipe element is retracted inside the larger-diameter telescopic pipe elements. All of the telescopic pipe elements are thus positioned inside an outermost telescopic pipe element of largest diameter. The progressive burying of said breakup means takes place by progressively sliding the smaller-diameter elements out from the larger-diameter elements, and thus initially by sliding out the smallest-diameter innermost telescopic pipe element, and then progressively sliding out telescopic pipe elements of increasing diameters until all of the telescopic pipe elements are fully deployed in outward extension.
By proceeding in this way with a conventional vertical borehole, a single guide device is lowered from the surface instead of the two or three devices of the prior art, which represents a considerable saving in time when drilling in deep water, for example in depths of 2000 m, 3000 m, or even more, since those elements need to be lowered in succession. In addition, if the ground is unstable, or indeed if shallow water flow occurs, since the casing is continuous over its entire length, the risk of collapse is considerably reduced, or even completely eliminated. Finally, the operations of cementing the device of the invention are reduced to a minimum since it is no longer necessary to perform cementing after each length of casing has been put into place in the preceding length, as is the case with the lengths of casing in the prior art. Cementing is performed once only, after the telescopic device has been fully deployed.
In a preferred embodiment, said smallest-diameter innermost pipe element presents a diameter substantially equal to the diameter of said drilling riser.
In a particular embodiment, said means for breaking up the ground are constituted by a multiply-perforated capsule enabling water or mud to be jetted into the ground by being injected under very high pressure.
More particularly, said telescopic guide pipe has at least three coaxial telescopic pipe elements.
Still more particularly, each of said telescopic coaxial pipe elements presents a length of 50 m to 300 m, preferably of 100 m to 200 m, said deployed guide pipe presenting a length of 150 m to 600 m, and preferably of 200 m to 300 m. The guide device of the invention is initially prefabricated on land, then put into the retracted configuration by inserting the pipes one inside another so as to reduce total length to a minimum, and then put in the water and fitted with buoyancy elements, after which it is towed to the site so as to be on the axis of the drilling derrick, where it is finally upended in such a manner that the top portion of said telescopic pipe can be taken hold of by the handling tool installed at the end of the drill string handled by the derrick, with the assembly then being lowered in a single operation in a vertical configuration to the guide baseplate resting on the sea bottom.
Since prefabrication takes place on land, with each of said telescopic pipe elements being built up by assembling successive unit lengths of pipe, said unit lengths are merely welded together end to end in conventional manner, like when making pipe lines. There is thus no need to reinforce the ends of each 12 m unit length since there is no thread to be machined therein, so the assembly presents optimum diameter that is greatly reduced compared to the prior art.
The term “retracted telescopic guide pipe” is used to mean that the various preassembled telescopic pipe elements are arranged in such a manner that the smaller-diameter elements are inside the larger-diameter elements.
In a second aspect, serving to solve the problem of putting a guide device into place in an application to drilling a borehole that is deflected in the depth of the water, the present invention provides a guide device that is useful in an off-shore drilling installation, an installation in which at least one drilling riser extends from a floating support to a said guide device at the sea bottom, said drilling riser deflecting progressively from a substantially vertical position at said floating support to a position that is substantially horizontal or tangential to the horizontal at the sea bottom, said drilling being performable from said floating support via said drilling riser and said guide device in such a manner that the borehole in the sea bottom is begun at a given angle of inclination α relative to the horizontal that preferably lies in the range 5° to 60°, and more preferably in the range 25° to 45°, said guide device being characterized in that it comprises a said telescopic guide pipe in a buried position in which said telescopic guide pipe in the retraced position or the outer telescopic pipe element when said telescopic pipe is deployed, comprises in succession:
The curvature of the telescopic guide pipe is thus determined by controlled burying of the guide pipe. Because of the considerable length of said guide pipe in the retracted position, each of the retracted segments can take up the same curvature without generating significant levels of force within the assembly.
The means for burying the retracted telescopic guide pipe make it possible, by burying the pipe, to obtain pipe curvature having a large radius of curvature that is of a desired and controlled value, given that the radius of curvature depends on the characteristics and the arrangement of said burying means.
It will be understood that said inclined linear portion extends tangentially from said curved portion and it is the angle of inclination of said linear portion which determines said starting angle a of the borehole.
It will also be understood that the term “horizontal at the sea bottom” means a position that is substantially horizontal as a function of the relief of the sea bottom.
In a particular embodiment, said guide pipe presents a length of 100 m to 600 m, preferably of 250 m to 450 m, with a said given angle of inclination α of the guide pipe lying in the range about 10° to 60°, and preferably in the range 25° to 45°. The desired curvature for the guide pipe then corresponds to an increase in inclination of about 1° per 10 m portion of the length of the guide pipe, giving a radius of curvature of about 560 m.
In a preferred embodiment, said front end of the retracted telescopic guide pipe is engaged in a baseplate carrying a load resting on a front soleplate such that said baseplate maintains said front end of said guide pipe substantially horizontal on the sea bottom while it is being towed. Said baseplate prevents the front end of said retracted telescopic guide pipe becoming buried, and also prevents it from turning about a substantially horizontal axis perpendicular to the towing axis.
The present invention also provides a method of making a guide device of the invention, the method being characterized in that the following steps are performed:
The present invention also provides an off-shore drilling installation comprising a drilling riser extending from a floating support to a guide device of the invention to which said drilling riser is connected.
For drilling that is deflected in the depth of water, said drilling riser deflects progressively from a substantially vertical position at said floating support to a position that is substantially horizontal or tangential to the horizontal at the sea bottom, drilling being performable from said floating support via said drilling riser and said guide device in such a manner that a borehole begins in the sea bottom at a given angle of inclination a relative to the horizontal, preferably lying in the range 10° to 80°.
The present invention also provides a method of making a drilling installation of the invention, characterized in that the following steps are performed:
Finally, the present invention provides a method of drilling with the help of a drilling installation of the invention, the method being characterized in that drilling operations are performed and a borehole is constructed by deploying drill strings co-operating with drilling tools and columns of tubing via a said drilling riser and a said guide device buried in the sea bottom.
More precisely, it will be understood that the drill string serves initially to deploy the drilling tools, and subsequently to deploy the tube elements known as “casing” which constitute the borehole as drilling progresses and successive elements are put into place in the sea bottom.
Other characteristics and advantages of the present invention appear in the light of the following description of various embodiments given with reference to the accompanying figures, in which:
To clarify explanation, clearance between adjacent elements of the telescopic pipe has been exaggerated to a considerable extent in the figures so as to make it easier to understand how the sliding, guiding, and sealing means operate.
As shown in
In a preferred variant of the invention, the drilling platform 1 is replaced merely by a surface vessel, preferably with dynamic positioning, and the guide device 3 once upended is then suspended from a cable connected to a winch installed on board the vessel. The guide device is then lowered by cable as a simple pendulum, preferably without using guide lines, and is then inserted into the drilling baseplate. Penetration is started by jetting, with hydraulic power being delivered by the surface vessel and conveyed to the bottom, e.g. by means of a flexible hose. When jetting is no longer effective, the surface vessel ceases that operation, and the operation of installing the guide is subsequently terminated by the drilling platform once it reached the site, vertically over the well that is to be drilled. By proceeding in this way, the cost of putting casing into place is greatly reduced since the daily cost of a surface vessel represents a small fraction of the cost of a drilling platform capable of drilling in water at depths of 3000 m, 4000 m, or even more. In addition, the necessary drilling equipment can be of lower power and thus of reduced cost since it does not need to handle the telescopic guide device of the invention, nor even individual conventional casing elements as in the prior art.
The portion 3a of said guide device is fitted at its front end with a sealing sliding ring 32a for providing low friction guidance of the portion 3b and it is secured at its rear end to the drilling riser in a catenary configuration 2.
The portion 3c of said guide device is fitted at its front end with a capsule 35 that is pierced by multiple orifices, or indeed it is fitted with a series of nozzles making it possible merely by injecting water or mud under very high pressure to break up cohesion of the ground and thus enable the well to be started merely by jetting, and at its rear end it has a non-sealing sliding ring 33c.
Complementary sliding rings 34 are advantageously installed at optionally regular intervals, respectively between the portions 3a & 3b and 3b & 3c so that when the portions of the guide device are highly curved, as shown in
The drilling tool 36 is secured to the bottom end of the drill string 38 and is actuated from the derrick installed on the surface on the floating support. Said drilling tool 36 is constituted by a turbine 361 actuated by fluid under pressure, in general drilling mud delivered by the drill string 38, actuating a tool carrier 362 having cutting tools 363 secured to the front face thereof and having a drum carrying retractable cutting tools 364 shown in the retracted position in
Thus, at the beginning of the driving-drilling operation, the drilling tool 36 secured to the end of the drill string 38 is lowered from the surface so as to reach the position shown in
Once the jetting effect is no longer sufficient to cause the front section to advance, jetting is stopped and the drilling tool 36 is moved forwards by pushing down the appropriate length of drill string 38 from the surface. A centering collar 37a secured to the turbine 361 slides freely inside the portion 3c of the guide device; said collar allows drilling mud and debris to pass freely in both directions from upstream to downstream. At the end of the advance stage, the collar 37a comes into abutment against a string 37b secured to the portion 3c of the guide device, inside it. The collar 37a and the ring 37b present complementary threaded portions (not shown) so that merely by turning the drill string from the surface, it is possible to secure the turbine body 361 mechanically to the portion 3c of the telescopic guide device, as shown in
In order to make it easier for the tool 36 to advance inside the riser and then the portion 3c of the telescopic guide device 3, said riser and said guide portion are substantially identical in section, and centralizers 38a are advantageously installed that are secured to the drill spring and that slide freely in said riser. Since such centralizers are known to the person skilled in the art of drilling boreholes, they are not described in greater detail herein.
In
In the final position, the drill string is operated from the surface to turn in the unscrewing direction so as to release the turbine body 361 from the ring 37b and thus from the portion 3c of the telescopic guide device 3.
After changing tool, drilling is subsequently performed in conventional manner, after taking care to close the orifice 31 by means of a valve (not shown) so that the drilling mud can be recovered at the surface for recycling in the drilling process.
In order to prevent the various portions 3b and 3c being rotated during screwing and unscrewing of the turbine body to the front end of the portion 3c, said portions 3a, 3b, and 3c may advantageously be in the form of square or hexagonal section tubes. If they are in the form of circular tubes, indexing is advantageously included in the sliding bearings 33.
The telescopic guide pipe 3a, 3b, and 3c is described above in an application associated with vertical drilling, however it is also applicable to deflected drilling, as shown in
FIGS. 7 to 19 show the telescopic guide pipe 3 in the context of a deflected borehole, i.e. both in an inclined and curved position, and also in a retracted position, i.e. a position in which the various telescopic pipe elements 3a, 3b, and 3c are nested with the smaller elements inside the larger elements. That is why in the description below, when reference is made to said guide pipe, it is a telescopic guide pipe in the retracted position that is being referred to, i.e. one in which the smaller-diameter telescopic pipe elements are slid into the outermost telescopic pipe element. When reference is made to elements co-operating with said telescopic guide pipe, then reference is being made to the element co-operating with the outermost telescopic pipe element 3a as shown in FIGS. 1 to 5.
Said drilling riser 2 deflects progressively from a substantially vertical position 2a at said floating support 1 to a position 2b that is substantially horizontal or tangential to the horizontal at the sea bottom, with drilling being operated from said floating support 1 via said drilling riser 2 and the retracted telescopic guide device 3 in such a manner that the borehole begins in the sea bottom at a given angle of inclination α relative to the horizontal, preferably lying in the range 10° to 80°.
The controlled burying means 34, 51-53, 71-73, 8-9, and 13 shown in FIGS. 7 to 19 enable said retracted telescopic guide pipe 3 to be buried in the sea bottom when said retracted telescopic guide pipe 3 is subjected to traction T along the sea bottom from its front end 31:
In a first preferred embodiment of the invention, said controlled burying means comprise:
It will be understood that in the first preferred embodiment of the invention as described above with reference to
By exerting traction on the towing cable 10, the assembly pulls the anchor which begins to become buried (25), thereby entraining (24) the rear end 33 of the guide pipe. The circular shape of the guide pipe brakes penetration only moderately, whereas the soleplates 52, 53 distributed along the pipe oppose penetration with a force that is proportional to their area. Since the front soleplate 51 is of large dimensions, the front of the guide device remains on the sea bottom and the deadweight 6 stabilizes the assembly in such a manner that the axis of the guide device remains substantially horizontal, i.e. parallel to the sea bottom 4.
One method of making a guide device of this type consists in applying traction to the front end 31 of said retracted telescopic guide pipe 3 until said intermediate soleplates 52, 53 are buried in the ground at ever increasing depth on approaching the rear end 33 of the guide pipe so as to obtain the desired radius of curvature R, preferably greater than 500 m, and more preferably lying in the range 500 m to 1000 m.
In another preferred embodiment of the invention, shown in
These deflectors 71, 72, and 73 serve to control the curvature of the retracted telescopic guide pipes as buried in the sea bottom since, once said deflectors are in a horizontal position, as shown in
The guide device preferably comprises a plurality of deflectors 71, 72, and 73 distributed along the outer pipe element of said telescopic guide pipe, said deflectors being inclined at angles α1, α2, and α3 that become smaller for deflectors 71-73 closer to said front end 31.
The guide pipe is thus fitted with a plurality of deflectors 71-73 secured to the guide pipe and oriented at angles α1-α3 relative to the axis XX′ thereof. The deflector 71-73 is, for example, a simple plane metal sheet, preferably a reinforced sheet, and preferably disposed symmetrically about the vertical and horizontal axial planes XX′, YY′, and XX′, ZZ′ of the guide pipe, being welded to the guide pipe of the guide device as shown in
A multitude of optionally identical deflectors 71-73 are advantageously disposed along the guide device, each deflector presenting a respective angle α1-α3 that becomes smaller for deflectors closer to the front end 31, as shown in
One method of making a guide device in this second embodiment consists in applying traction T to the front end 31 of said retracted telescopic guide pipe 3 until said deflectors 71, 72, 73 are buried in the ground in horizontal positions so as to obtain said desired radius of curvature which is preferably greater than 500 m, and more preferably lies in the range 500 m to 1000 m.
Said secondary pipes 8 are preferably connected via their ends 81, 82 to the front and rear ends 31, 33 of said outer pipe element of said telescopic guide pipe, and they communicate with said front and rear ends 31 and 33 so as to make it possible to feed them using a single feed pipe 19 feeding said front end 31 of said telescopic guide pipe 3.
A method of implementing a guide device of the above type comprises the following steps:
In another preferred version of the invention shown in
More precisely, the guide device comprises:
The ordinary portion of the guide pipe is free to move vertically through the central opening 22 of the structure 20, as shown in
The guide device preferably comprises:
These flexible connections 171, 172, and 173 are constituted, for example, by cables or chains connected first to the external structure 20 at 26 and secondly to the guide pipe at 27. These connection points 26-27 are shown in
A method of implementing a guide device of the above type consists essentially in applying traction T to the front end 31 of the outer pipe element of said telescopic guide pipe 3 and to said rigid outer structure 20 secured to said guide pipe until said connection(s) 171-173 prevents at least said rear portion 33 of said retracted telescopic guide pipe from becoming buried any deeper, so as to obtain the desired radius of curvature R which is preferably greater than 500 m, and more preferably lies in the range 500 m to 1000 m.
All of these controlled burying means 51-53, 71-73, 13, 20, 171-173 of the invention described with reference to the various above embodiments can be implemented either individually or in combination, since the nature of the ground can sometimes make extremely powerful means necessary if the ground is very cohesive.
The outer structure 20 is preferably continuous along the guide pipe and represents an additional mass of 25 to 75 tons. Jetting is performed using pressurized water raised at the surface to pressures lying in the range 20 bars to 100 bars and applied to the secondary pipes 8.
By way of example, with a telescopic guide device, the portions 3a, 3b, and 3c have respective diameters of 21″ (0.55 m), 18″ (0.45 m), and 16″ (0.40 m), and each of them has a length lying in the range 100 m to 150 m.
By way of example, for a guide device for drilling vertically as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 02/07537 | Jun 2002 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR03/01867 | 6/18/2003 | WO |
