GB2518438A

GB2518438A - Improved method and equipment for reinforcing a borehole

Info

Publication number: GB2518438A
Application number: GB1316894.3A
Authority: GB
Inventors: Zalpato Ibragimova; Steinar Wasa Tverlid
Original assignee: Statoil Petroleum ASA
Current assignee: Equinor Energy AS
Priority date: 2013-09-23
Filing date: 2013-09-23
Publication date: 2015-03-25
Anticipated expiration: 2033-09-23
Also published as: GB2518438B; GB201316894D0

Abstract

An epoxy polymer is arranged to be carried in drilling fluid 9 for reinforcing a borehole 1 during drilling of the borehole. The epoxy polymer is meltable, fusible, and/or curable. The epoxy may be dissolved and/or emulsified and/or dispersed in the drilling fluid along the surface of the borehole. A downhole treatment device 19 may be used to melt, fuse, and/or cure the epoxy thereby applying a liner of polymer at the surface 15 of the borehole. Curing may be performed by concentrating energy in a limited space in the vicinity of the surface. Energy beams such as lasers, microwaves, induction, or ultrasound may be used to intersect and cure the epoxy. The drilling fluid may contain particulate epoxy polymer material which may be solid metal particles coated in epoxy. The metal may be diamagnetic.

Description

Improved method and equipment for reinforcing a borehole

Technical field

The invention relates to drilling and reinforcing a borehole of a well.

Background

The construction of an oil or natural gas well requires a borehole of the well to be drilled and casing installed. The casing serves to strengthen the surface of the borehole and insures that no oil or natural gas seeps out of the well as it is brought to the surface, and further ensures that other fluids or gases do not seep into the formation through the borehole. In particular, the casing prevents losses of drilling fluid circulating down the borehole through a drill pipe string and a drill bit carried on the downhole end of the drill pipe string and further circulating upward to the top of the borehole through an annulus between the drill pipe string and the wall of the borehole.

The drilling fluid cools the drill bit, removes cuttings from the borehole and maintains hydrostatic pressure on pressurized subterranean formations. Usually, the surface or wall of the borehole is stabilized by running and cementing a tubular casing into the borehole, which means that drilling the borehole normally is a sequential process in which drilling the borehole and installing the casing alternate. The process is time-consuming, since the drill pipe string has to be removed from the borehole for installing of the casing.

It is known to use the tubular casing instead of the drill pipe string to direct and rotate the drill bit. In such a casing while drilling system, the casing is part of the drilling assembly and may be cemented in place where the appropriate depth is reached, and thereafter a length of the tubular casing is run through the cemented casing portion for further drilling the borehole. The casing while drilling process is unpredictable to some extent, since the casing quite easily may stick to the borehole, which makes the position of the casing shoe unpredictable, and some length of the casing may be lost with the result that the well may not reach desired depth (Nediljka Gaurina-Medimurec, "Casing Drilling Technology", Rudarsko-geolosko-naftni zbornik, Zagreb 2005, Vol. 17, pages 19 to 26).

From US 7,334,637 B2 it is known to form a temporary liner in a welibore by extruding a fusible polymer liner material, such as polyethylene or polypropylene from an assembly supported on the drill pipe string. An extruder extrudes the liner material onto the wall of the borehole while the liner material is fed from a reservoir at the surface level of the borehole through an additional piping running through the drill string. A heat source, for example a laser device, melts the fusible liner material extruded onto the wall of the borehole to produce the liner.

The liner produced according to US 7,334,637 B2 is a temporary liner intended to be replaced later on by a conventional tubular casing to be cemented in the borehole. The system requires an additional piping through the drill pipe. The fusible liner material must be capable of being extruded onto and adhered on the wall of the borehole.

Another method for stabilizing a wellbore during drilling in a sequential process is known from US patent 5,944,105. A downhole portion of the drill pipe string is provided with a plurality of nozzles through which fluid jets can be ejected. After having drilled the borehole into an unstable subterranean formation, fluid is pumped through the nozzles to enlarge the borehole by fluid jet erosion while moving the drill pipe string upwardly. After having enlarged the diameter of the borehole, a hardenable, permeable material, for example a hardenable organic resin, is ejected through the nozzles to till the enlarged portion of the borehole. The material is caused to harden by heat or a hardening agent, and thereafter the borehole is redrilled through the hardened material.

The known method does not allow a continuous lining of the formation while drilling.

From WO 2005/121 198 Al another sequential process for in-situ stabilizing the wall of a wellbore is known. After having drilled the borehole through a weak formation, the drill string is pulled up above the weak interval to be stabilized. A resin mixture is pumped through the drill string into the borehole to displace the drilling fluid from the drill string and the annulus between the drill string and the wall of the borehole and to squeeze the resin into the weak formation. After squeezing resin into the formation, the well is shut for several hours prior to cleaning set resin out of the wellbore and resuming drilling operation to deepen the well.

From US patent 6,311,773 B1 it is known to consolidate particulate solids in subterranean zones around a wellbore by causing a hardenable resin composition to flow between the particulate solids of the subterranean zone. By hardening the resin composition, the particulate solids will be consolidated into a hard, permeable pack.

Similar methods for consolidating the wall of a borehole are known, for example, from EF 0 879 935 A2, US 7,216,711 B2, US 7,264,052 B2, WO 03/102 086 A2, EP 0 542 397 A2 or US 4,428,426. These documents disclose resin-coated particles, for example sand grains or other proppants, for treating subterranean formations, in particular subterranean fractures.

Summary of the invention

An object of the invention is to provide a technique which allows reinforcement of a borehole of a well, in particular a well of petroleum and/or natural gas.

According to a first aspect of the invention there is provided equipment for drilling and reinforcing a borehole of a well comprising: a drill pipe string comprising a drill tool at its lowermost end; a drilling fluid circulation means for circulating drilling fluid through the drill pipe string and an annulus between the drill pipe string and the borehole; a downhole treatment device held on the drill pipe string for applying a liner of polymer material at the surface of the borehole, characterized in that the drilling fluid circulated through the annulus is a fluid system containing meltable, fusible and/or curable epoxy polymer dissolved and/or emulsified and/or dispersed therein and the treatment device is adapted to melt, fuse and/or cure the epoxy polymer contained in the drilling fluid in the vicinity of the surface (15) of the borehole (1).

Since the epoxy polymer for producing the liner of the borehole is contained in the drilling fluid (mud e.g. water based mud) anyway needed for drilling the borehole, no additional piping along the borehole or no downhole reservoir for polymer material is needed.

The amount of the epoxy polymer to be used will vary widely. The concentration of the epoxy polymer in the drilling fluid may be 0.5 to 10 %wt, for example 1 to 5 %wt, typically 2 to 5 %wt, e.g. about 1 %wt or 2 %wt.

A curing agent or hardener may be provided into the borehole to cause the deposited polymer to cure. Preferably the curing agent is delivered in a carrier, for example the drilling fluid. Conventional curing agents, which are well known in the art may be used.

Curing may be achieved by heating. The drilling fluid may be an aqueous carrier such as a water based drilling mud. Other additives such as surfactants, thickeners, diversion agents, pH buffers and catalysts may be included in the drilling fluid.

The treatment device is positioned at the drill pipe string downhole in the vicinity of the drill tool, which may be in the form of a simple drill bit, but also may include a roamer or a downhole assembly including a downhole drill motor. Due to the downhole pressure of the drilling fluid, some of the drilling fluid including epoxy polymer may be pressed into the pores of the formation and anchors the liner to the wall of the borehole. The epoxy polymer may be dissolved or emulsified within the drilling fluid, but in particular is in a particulate form, for example in the form of powder-like particles or granules, which adhere to each other when being melted, fused and/or cured by energy from the treatment device.

As used herein the term polymer refers to a compound which has a polydispersity index of greater than 1. As used herein the term polymer also encompasses mixtures of different types of epoxy polymers, e.g. which may comprise different repeat units and/or have different physical properties. As used herein the term "epoxy polymer" is intended to refer to a polymer that is formed from monomers comprising at least one epoxide group and which comprises at least one epoxide group.

The epoxy polymer may be cured, for example, by addition of a curing agent or hardener, heat and/or radiation.

The epoxy polymer may comprise particulates. The particulate epoxy polymer may consist of epoxy polymer only. Preferably, the particulate epoxy polymer comprises solid particles coated with meltable, fusible and/or curable epoxy polymer to mechanically strengthen the liner formed on the wall of the borehole. In a preferred embodiment, the solid particles are comprised of metal, in particular steel, to provide for ductility and toughness of the liner while the epoxy polymer will bind the composite together.

Preferably, the particles of the particulate epoxy polymer have a diameter of less than 1 mm, preferably of less than 0.3 mm, for example 0.1 mm, to improve anchoring in the formation and to reduce the porosity of the liner. A diameter of less than 0.3 mm is advantageous if the epoxy polymer is coated onto particulate metal cores.

In a preferred embodiment, the treatment device comprises an energy radiating device which produces at least two distinct energy beams which are directed from different positions to a common spot in the limited space in the vicinity of the surface of the borehole where the energy beams intersect and focus the energy within said limited space. While the energy of a single energy beam does not suffice to fuse or cure the polymer in the bulk of the drilling fluid, the focused energy of the plurality of the energy beams is sufficient for producing the liner.

Particularly preferably the particulate polymer comprises a plurality of sets of particulates, e.g. 2 or 3 or 4 or more sets of particulates. By a set of particulates is meant a collection of particulates wherein at least 90 %wt and more preferably at least %wt of the particulates within the collection have an average diameter of ±20%, more preferably ±10% and still more preferably ±5% of the stated average. Particularly preferably the particulate polymer comprises a first set of particulates having a first average diameter and a second set of particulates having a second average diameter that is 7 to 15 times greater and more preferably 8 to 12 times greater than the first average diameter. Still more preferably the particulate polymer further comprises a third set of particulates having a third average diameter that is 1.5 to 5 times greater and more preferably 2 to 4 times greater than the tirst average diameter. Especially preferably the particulate polymer comprises a first set of particulates having an average diameter of 40 to 100 microns (e.g. 50 to 85 microns) and a second set of particulates having an average diameter of 700 to 1000 microns (e.g. 750 to 900 microns). Still more preferably the particulate polymer further comprises a third set of particulates having an average diameter of 120 to 300 microns (e.g. 150 to 250 microns). The particulate polymer may, for example, comprise: a first set of particulates having an average diameter of 50 to 85 microns, a second set of particulates having an average diameter of 750 to 900 microns and a third set of particulates having an average diameter of 150 to 250 microns.

When a plurality of sets of particulates is used, any of the sets may comprise particulates comprising a metal core and a polymer coating, particulates consisting of polymer or mixtures thereof. Preferably, however, the first set of particulates is particulates comprising a metal core and a polymer coating. More preferably the third set of particulates is particulates comprising a metal core and a polymer coating. Still more preferably the second set of particulates is particulates consisting of polymer.

The polymer may be selected or designed with at least one predetermined melting, fusing and/or curing temperature, so that the polymer may melt, fuse and/or cure above the predetermined temperature. As used herein, the term melting refers to the process by which the polymer changes into or becomes liquid. As used herein, the term fusing refers to the process by which the chains of one particulate polymer intermix and entangle with the chains of another particulate polymer. Typically fusing occurs after melting. As used herein, the term curing refers to the process by which polymer chains cross-link. The process of curing creates a 3-dimensional network of polymer chains which generally increases the hardness of the polymer. Typically curing occurs after melting and fusing.

The epoxy polymer used in the invention may be a homopolymer or a copolymer but is preferably a copolymer. The polymer may be crystalline, semi-crystalline or amorphous. Still more preferably the particulate polymer comprises a mixture of 2 or more (e.g. 2, 3 or 4) polymers. Preferably at least one polymer (e.g. 1 polymer) is crystalline. Preferably at least one polymer (e.g. 1 polymer) is amorphous.

Preferably at least one of the polymers used in the invention has a melting point of 40 to 200 °C, more preferably 50 to 150 °C and still more preferably 70 to 100 °C, e.g. when measured by melting point apparatus. Preferably at least one of the polymers used in the method of the invention has a glass transition temperature of 40 to 200 00, more preferably 50 to 150 °C and still more preferably 70 to 100 DC, e.g. when measured by a scanning caliometer. Preferably all of the polymers used in the method of the invention has a density of 100 to 2000 kg/m3, more preferably 300 to 1500 kg/m3 and still more preferably 1200 to 1300 kg/m3, e.g. when measured by a density meter.

Representative examples of suitable epoxy polymers include epoxy polymers of the bisphenol-A type, epoxy polymers of the bisphenol-S type, epoxy polymers of the bisphenol-F type, epoxy polymers of the phenol-novolak type, epoxy polymers of the cresol-novolak type, epoxidized products of numerous dicyclopentadiene-modified phenol resins, obtained by treating dicyclopentadiene with numerous phenols, epoxidized products of 2,2,6,6-tetra-methylbiphenol, aromatic epoxy polymers such as epoxy polymers with naphthalene basic structure and epoxy polymers with fluorene basic structure, aliphatic epoxy polymers such as neopentyl glycol diglycidyl ether and 1,6-hexane dial diglycidyl ether! alicyclic epoxy polymers such as 3,4- epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate and bis(3,4-epoxycyclohexyl)adipate, and epoxy polymers with a heterocycle such as triglycidyl isocyanurate.

Specific examples of suitable epoxy polymers include diglycidylether compounds of mononuclear divalent phenols such as resorcinol and hydroquinone; diglycidylether compounds of multinuclear divalent phenols such as 4,4'-isopropylidene diphenol (bisphenol A) and 4,4-methylene diphenol (bisphenol F); glycidylether compounds with alcohol such as butyl alcohol or higher alcohols; diglycidylether compounds of diols such as ethyleneglycol, propyleneglycol, butanediol and hexanediol; glycidylether compounds with mononuclear monovalent phenol compounds such as phenol, metacresol, paracresol and orthocresol; glycidylester compounds with monovalent carboxylic acids such as neodecanoic acid; diglycidylester compounds of aliphatic, aromatic or alicyclic dibasic acids such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, suberic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid and cyclohexane dicarboxylic acid; glycidyl amine compounds such as 1,3-bis(N,N-diglycidyl aminomethyl) benzene and 1,3-bis(N,N-diglycidyl aminomethyl)cyclohexane.

More preferably the epoxy polymer is selected from 4,4'-isopropylidene diphenol diglycidylether (a bisphenol A-type epoxy polymer), 4,4'-methylene diphenol diglycidylether (a bisphenol F-type epoxy polymer) or a mixture thereof. An epoxy polymer based on 4,4-isopropylidene diphenol diglycidylether (a bisphenol A-type epoxy polymer) is particularly preferred. Adhesion happens due to molecular attraction of contacts between substances for melting and hardening in liquid form. The active component is typically Bisphenol A and the curing agents for epoxy resins may be polyamines, aminoamides and/or phenolic compounds.

The epoxy polymer preferably may comprise a mixture of different types of polymers.

The blending of different types of epoxy polymer is often beneficial to achieve the desired melting, fusing and/or curing profile. Suitable polymers for use in the methods of the present invention are commercially available, e.g. from Akzo Nobel. For example, an epoxy polymer with the active component 4,4'-isopropylidene diphenol (bisphenol A) available from Akzo Nobel under the trade name Resicoat® may be used! for example having a real density 1-1.9 g/cm3, bulk density 300-1000 kg/rn3, and softening point of >50°C. For example, the Resicoat® product code HNHO7R available from Akzo Nobel may be used.

In another embodiment, the energy source, e.g. an energy output port of the treatment device is positioned near the surface of the borehole and directs its energy beams directly onto the surface. An energy shielding or an energy reflector concentrates the energy to the limited space in which the liner is to be produced and protects the bulk of the drilling fluid outside said limited space from radiated energy.

The energy source of the treatment device can be of any type that allows directed radiation of energy onto the surface of the borehole. Preferably, the energy source is a laser device or an induction heating device or a microwave radiating device or a super-sonic energy radiating device. The type of the energy source may be chosen depending on the polymer and/or in case of particulate material comprising a core, e.g. a metal core, in dependence of the material of the core, as it known in the art.

The liner may be continuously produced on the wall of the borehole. The thickness can be controlled by controlling the concentration of the polymer within the drilling fluid, the axial of the speed of the drill pipe string and the circulating velocity of the drilling fluid along the wall of the borehole. Depending on the porosity of the formation, the epoxy polymer may migrate into the formation to seal and/or improve anchoring of the liner at the formation. Basically, it is sufficient to compact the epoxy polymer contained in the drilling fluid starting from the average concentration of the polymer in the drilling fluid, but preferably the treatment device is adapted to specifically raise the concentration of the epoxy polymer in the vicinity of the wall and in particular in the vicinity of the limited space, in which the treatment device concentrates energy for curing, fusing and/or curing the epoxy polymer.

In a preferred embodiment, additional pressure is exerted onto particulate epoxy polymer by magnetic forces produced by at least one magnet of the treatment device.

The particulate epoxy polymer comprises solid particles of a diamagnetic material, for example copper, which is repelled within the magnetic field produced by the treatment device onto the surface of the borehole. The magnetic repellent force pushes the particles towards and into the formation where the particles concentrate for forming the liner.

If the drilling fluid contains particulate epoxy polymer comprising solid particles having a particle density higher than the density of the drilling fluid including particulate material other than the particulate epoxy polymer, the concentration of the epoxy polymer in the vicinity of the wall of the borehole can be raised by a centrifugal separator coaxially arranged with the drill pipe string. The centrifugal separator centrifugates the higher density particulate polymer towards the wall of the borehole while the drilling fluid flows axially along the annulus. The centrifugal induces a whirl in the drilling fluid around the drill string a certain distance before and in the limited space curing position. Preferably, the solid particles of the particulate polymer have a density which is higher than the density of formation particles contained in the drilling fluid and also higher than the density of the rest of the drilling fluid. Due to the centrifugal action the particles with the highest density. e.g. the particulate polymer will be separated onto the wall of the borehole to produce the layer while lighter components of the drilling fluid will remain in a radially inner portion of the annulus.

In a preferred embodiment, the centrifugal separator is in the form of a helical vane coaxially stationary surrounding the drill pipe string. In another embodiment, the centrifugal separator can be in the form of a motor-driven impeller coaxially rotating with respect to the drill pipe string. The impeller has a fan wheel which produces the whirl in the drilling fluid to centrifugate the particles onto the wall of the borehole.

The idea of concentrating particulate polymer at the wall of the borehole by means of centrifugating the drilling fluid in the annulus can also be carried out with a treatment device not being adapted to concentrate the energy in a limited space near the wall of the borehole. The aspect of the centrifugal separator thus can be used with an equipment the treatment device of which heats the drilling fluid within the total radial depth of the annulus.

According to a second aspect of the invention, there is provided a method of reinforcing a borehole (1) of a well comprising the steps of: circulating a drilling fluid (9) containing a meltable, fusible and/or curable epoxy polymer dissolved and/or emulsified and/or dispersed therein along the surface (15) of the borehole (1); and melting, fusing and/or curing the epoxy polymer in the vicinity of the surface (15) of the borehole (1).

The method is preferably performed while drilling the borehole. The melting, fusing and/or curing step may be performed by concentrating energy melting, fusing and/or curing the polymer in a limited space in the vicinity of the surface. The concentrating step is preferably performed while drilling of the borehole (1) is continued. The concentrating step is performed to produce a lining or liner at the surface of the borehole. The liner advantageously acts to provide support and strength to the borehole wall.

According to a third aspect there is provided apparatus for performing the method of the second aspect. The apparatus may comprise further features as defined in relation to the first or second aspect above. The equipment of the first aspect may be used to perform the method of the second aspect.

According to a fourth aspect of the invention, there is provided a borehole lining produced from said melting, fusing, and/or curing of the epoxy polymer by performing the method of the second aspect.

According to a fourth aspect of the invention, there is provided an epoxy polymer arranged to be carried in drilling fluid for reinforcing a borehole during drilling of the borehole, the epoxy polymer being meltable, fusible and/or curable in the vicinity of the surface of the borehole, e.g. by concentrated energy in a limited space in said vicinity.

The epoxy polymer may be as defined above.

Descrirtion and drawings There will now be described, by way of example only, embodiments of the invention with reference to the accompanying drawings of which: Fig. 1 is a schematic section through a borehole of a well with a first embodiment of an equipment for drilling and reinforcing the borehole; Fig. 2 is a section through the borehole of the well with anothei embodiment of the equipment for drilling and reinforcing the borehole; Fig. 3 is a cross-section of a particle contained in the drilling fluid used with the equipment while dulling; Fig. 4 is a sketch of an improvement of the equipment to be used with the equipment of Figs. 1 or 2; and Fig. 5 and Fig. 6 are sketches of alternatives to the improvement of Fig. 4.

Fig. 1 shows a section through the downhole end of a borehole 1 of a well intended to puoduce oil and/or natural gas from a formation 2. The bouehole 1 is drilled by a dulling equipment 3 comprising a drill pipe string 5 having at its lowermost end a drill bit 7. The drill pipe string 5 can be constructed in form of a coiled tubing, and the drill bit 7 may include a roameu and a downhole drill motor. Drilling fluid 9 (mud) is circulated from the top of the borehole 1 down to the drill bit 7 through the dull pipe stung 5 (auuow 11) and back to the top of the borehole 1 through an annulus 13 radially between the drill pipe string 5 and the surface 15 or wall of the borehole 1 (arrow 12). The drilling fluid lubricates the drill bit 7 and conveys chips the dull bit 7 has produced from the fournation to the top of the bouehole 1. As it is known in the art, the drilling fluid also provides for a counterbalance to formation fluid pressure to prevent uncontrolled flow of fluids from the formation 2 into the borehole 1 or vice versa.

To protect the wall 15 of the borehole 1 and to continuously and simultaneously apply a liner 17 to the wall 15 for reinforcing and sealing the surface of the formation, a treatment device 19 is attached to the drill pipe string 5 adjacent to the drill bit 7. The treatment device 19 fuses and/or cures epoxy polymer which is contained in the drilling fluid 9 in a dissolved and/or emulsified and/or dispeused form and which circulates together with the drilling fluid 9 in the annulus 13 along the wall 15 of the borehole 1.

Under the pressure of the drilling fluid 9 the epoxy polymer enters to a certain degree into the pores, cracks, passageways and/or spaces in the formation 2 and helps to anchor the liner 17 produced on the wall 15 to the formation 2.

The liner 17 is preferably continuously produced on the wall 15 by the treatment device 19 as explained in more detail below. The thickness of the liner 17 is controlled by controlling the density of the polymer material within the drilling fluid 9, the axial speed of the drill pipe string 5 carrying the treatment device 19 and the circulating velocity of the drilling fluid 9 within the annulus 13.

The epoxy polymer preferably is in a particulate form with a particle size of less than 1 mm, preferably less than 0.3 mm, for example 0.1 mm. The material should withstand well fluids and drilling fluids. It is essential that the epoxy polymer is capable of fusing and/or curing above a threshold temperature either by melting above the threshold temperature or by being initiated to cure above the threshold temperature. The polymer can be a one-component system or a two-component system. Of course, instead of a temperature threshold other epoxy polymer systems may be used relying on another initializing process, for example on the basis of UV-light energy supply.

The treatment device 19 comprises a plurality of laser devices 21, here three laser devices 21 * which are staggered in axial direction of the drill pipe string 5 and each of which produces a plurality of laser beams 23 distributed around the drill pipe string 5.

Groups of laser beams 23 with at least one laser beam 23 of each of the laser devices 21 are directed onto the wall 15 of the borehole such that the laser beams 23 of each group intersect in a limited space 25 in the vicinity of the wall 15 of the borehole 1.

Thus, the groups of laser beams 23 are focused to said limited space and provide energy spots of a raised energy level within the limited space 25 as compared to the rest of the annulus 13 where the bulk of the epoxy polymer circulates with the drilling fluid 9. In this way, the epoxy polymer is melted, fused and/or cured to form the liner 17 in the space 25. The bulk of the polymer may not be influenced.

The treatment device 19 and thus the laser beams 23 rotate together with the drill pipe string 5. In case of a non-rotating drill pipe string, the treatment device 19 is rotated by a downhole motor relatively to the drill pipe string 5. Axially on both sides of the treatment device 19 centralizers 27 are provided to guide the treatment device 19 concentrically with the borehole 1.

During drilling the borehole 1, the drilling fluid 9 continuously circulates through the drill pipe string 5 and the annulus 13 past the treatment device 19. The continuously rotating laser devices 21 are focused to a "hot spot" within the limited space 25 so as to heat the polymer material contained in the drilling fluid 9 above the threshold temperature of the epoxy polymer and melts, fuses and/or initiates curing of the polymer material in the vicinity of the wall 15 to continuously build up the liner 17 simultaneously with the feed motion of the drill bit?.

In the following, other embodiments of the invention will be described. Components having a similar purpose or function as described with respect to Fig. 1 will be assigned the same reference numeral with a letter added for distinction. Reference is made to

the above description of Fig. 1.

Fig. 2 shows a drilling equipment la which differs from that of Fig. 1 by the treatment device 19a. Contrary to the plurality of laser devices 21 of Fig. 1, the treatment device 19a comprises a plurality of energy radiating devices 29 each having an energy output port 31 positioned in the vicinity of the wall isa of the borehole la, and a shielding or reflector 33 which shields the bulk of polymer material outside the limited space 25a against the energy radiated into the limited space 25a in the vicinity of the wall 15a.

Thus, the epoxy polymer present in the space 25a will be fused and/or cured to form the liner 17a. The shielding/reflector 33 is shown in the form a plate; of course, other forms may be used, for example tubes which radially extend beyond the energy output pod 31 towards the wall isa.

Both in Fig. 1 and Fig. 2, a plurality of energy beams or energy devices are provided around the drill pipe string. As being obvious for a man skilled in the art, only one group of energy beams or only one energy output pod is sufficient.

Instead of laser devices as shown in Fig. 1, microwave devices or induction heating devices or ultrasound devices may be used. The same applies to the embodiment of Fig. 2.

The meltable, fusible and/or curable epoxy polymer preferably is in a particulate form consisting of particles with a size of less than about 1 mm, preferably of less than 0.3 mm and more preferably of about Ui mm. The particles may consist completely of polymer material, but preferably have a structure as shown in Fig. 3 as a section through particle 35. The particle 35 has a core 37 of solid material like mineral material, e.g. sand or preferably a metal. The core 37 is entirely coated by a layer 39 of the polymer. By melting, fusing and/or curing the coating 39 during production of the liner, the particles 35 are combined to an integral layer by fusing or curing the coatings 39 together! while the core 37 provides for ductility and toughness, in particular when the cores 37 consist of steel.

S

Fig. 4 shows a sketch of an improvement which may be added to the embodiments of Figs. 1 or 2. The particles 35b, which have the structure as shown in Fig. 3 have a core consisting of a diamagnetic metal, for example copper, which, brought in a magnetic field, is repelled by a magnet. In order to produce repellent forces acting on such particles 35b, the treatment device 19 as explained in Fig. 1 or the treatment device 19a of Fig. 2 comprises at least one magnet 41, the magnetic field of which is directed so as to force the diamagnetic particles 35b towards the wall 1 Sb of the borehole. The magnet 41 is positioned downhole of the limited space 25b at which energy indicated at 43 melts, fuses and/or cures the polymer material ot the particles 35b to form the liner 17b. The magnet 41 concentrates the particles 35b in the vicinity of the wall 15b and exerts some radial pressure onto the particles 35b before and while forming the liner 1 7b.

Fig. 5 shows an embodiment which allows raising the concentration of particulate epoxy polymer in the vicinity of the wall 15c of the borehole lc. The particulate polymer comprises solid particles as shown in Fig. 3 at 35 having a solid core in particular of a metal like steel with the core being coated with meltable, fusible and/or curable epoxy polymer. The solid particles have an overall density which is higher than the density of any other particles, for example formation particles contained in the drilling fluid and also higher than the density of the rest of the drilling fluid. By engineering the solid particles of the particulate polymer material in this way, the particulate material can be concentrated at the wall 15c of the borehole ic by producing a drilling fluid whirl within the annulus 13c around the drill pipe string Sc at a certain distance before and within the curing position defined by the treatment device 19c within the limited space 25c.

As shown in Fig. 5, a centrifugal separator 45 is provided coaxially with the drill pipe string Sc upstream in the tlow direction 12c of the drilling fluid 9c. The centrifugal separator 45 is in the form of a helical vane 47 coaxially fixed to the drill pipe string Sc to impart a whirl movement (arrow 49) to the drilling fluid 9c flowing uphole in the annulus 14c. As indicated in Fig. 5, the concentration of the particulate epoxy polymer within the whirl fluid flowing uphole in the direction 12c rises towards the fusing and/or curing position in the limited space 25c.

Fig. 6 shows a variant of the centrifugal separator 45d in the form of a fan wheel 51 which is arranged coaxial to the drill pipe string Sd. A motor 53 rotates the fan wheel 51 to produce a centrifugating whirl of drilling fluid within the annulus 13d. Again the particulate polymer contained in the drilling fluid is concentrated some distance before and within the curing position at the limited space 25d.

The treatment device 1 9c or 1 9d, respectively, makes use of the energy concentrating idea the embodiments of Figs. 1 and 2 are based on. Since the centrifugal separators 45, 45d of the embodiments shown in Figs. 5 and 6 provide for a concentration of the polymer material in the vicinity of the wall of the borehole, it is preferred but not necessary that the energy produced by the treatment devices is radially confined or concentrated at the vicinity of the wall. The limited space may be extended radially up to the drill pipe string since the centrifugal action lowers the concentration of particulate polymer in the vicinity of the drill pipe string. The same applies to the embodiment shown in Fig. 4.

Various improvements and modifications may be made without departing from the scope of the invention herein described.

Claims

CLAIMS: 1. A method of reinforcing a borehole (1) of a well comprising the steps of: circulating a drilling fluid (9) containing a meltable, fusible and/or curable epoxy polymer dissolved and/or emulsified and/or dispersed therein along the surface (15) of the borehole (1); and melting, fusing and/or curing the epoxy polymer in the vicinity of the surface (1 5) of the borehole (1).
2. A method according to claim 1, performed while drilling the borehole.
3. A method according to claim 1 or 2, wherein the melting, fusing and/or curing step is performed by concentrating energy melting, fusing and/or curing the polymer in a limited space in the vicinity of the surface.
4. A method according to claim 3, wherein the step of concentrating energy for melting, fusing and/or curing the polymer in the vicinity of the surface (15) of the borehole (1) comprises the step of simultaneously directing at least two energy beams (23) to the limited space (25) such that the energy beams (23) intersect within a limited space (25).
5. A method according to claim 3, wherein the step of concentrating energy for melting, fusing and/or curing the epoxy polymer in the vicinity of the surface (isa) of the borehole (la) comprises the step of outputting the energy in the vicinity of the limited space while shielding and/or reflecting the energy at the side of the limited space remote of the surface (isa) of the borehole (la).
6. A method according to any preceding claim, wherein the drilling fluid (9) contains particulate epoxy polymer material comprising solid particles (37), in particular solid metal particles coated with meltable, fusible and/or curable epoxy polymer.
7. A method according to claim 6, wherein the solid metal particles (37) consist of a diamagnetic metal and the method further comprises the step of magnetically accelerating the particles towards the surface (1 Sb) of the borehole.
8. A method according to claim 6, when dependent upon claim 3, wherein the step of circulating the drilling fluid comprises producing upstream of the limited space (25c, d) of concentrated energy a whirl of drilling fluid coaxial with the borehole (lc. d) for centrifugating particulate polymer material towards the surface (15c, d) of the borehole (lc,d).
9. A method according to any of claims 6 to 8, wherein the particles have an outer diameter of less than 1 mm, in particular less than 0.3 mm.
10. Equipment for drilling and reinforcing a borehole of a well comprising: a drill pipe string (5) comprising a drill tool (7) at its lowermost end; a drilling fluid circulation (11, 12) means for circulating drilling fluid (9) through the drill pipe string (5) and an annulus (13) between the drill pipe string (5) and the borehole (1); a downhole treatment device (19) held on the drill pipe string (5) for applying a liner (17) of polymer material at the surface (15) of the borehole (1), characterized in that the drilling fluid (9) circulated through the annulus (13) is a fluid system containing meltable, fusible and/or curable epoxy polymer dissolved and/or emulsified and/or dispersed therein and the treatment device (19) is adapted to melt, fuse and/or cure the epoxy polymer contained in the drilling fluid in the vicinity of the surface (15) of the borehole (1).
11. Equipment according to claim 10, wherein the treatment device (19) is an energy radiating device to concentrate energy for melting, fusing and/or curing the epoxy polymer in a limited space in the vicinity of the surface, the device producing at least two energy beams (23) which intersect in the limited space (25) in the vicinity of the surface (1 5) of the borehole (1).
12. Equipment according to claim 11, wherein the energy radiating device comprises at least two laser light devices (21) or microwave devices or induction heating devices or ultrasound devices providing intersecting energy beams (23).
13. Equipment according to claim 10, wherein the treatment device (19a) has at least one energy output port (31) positioned in the vicinity of the surface (iSa) of the borehole (1)a.
14. Equipment according to claim 11, wherein the energy output port (31) has associated thereto an energy shielding (33) and/or an energy reflector to focus the energy to the surface (15a) of the borehole (la).
15. Equipment according to any of claims 10 to 114, wherein the drilling fluid (9) contains particulate epoxy polymer.
16. Equipment according to claim 15, wherein the particulate polymer comprises solid particles (37) coated with meltable, fusible and/or curable epoxy polymer.
17. Equipment according to claim 16, wherein the solid particles (37) are comprised of metal.
18. Equipment according to any one of claims 10 to 15. wherein the drilling fluid (9) contains particulate epoxy polymer comprising solid particles (37) of a diamagnetic metal coated with fusible and/or curable polymer material, and wherein the treatment device (19) comprises magnetic accelerating means (41) for radially accelerating the particulate epoxy polymer towards the surface (15b) of the borehole.
19. Equipment according to any one of claims 10 to 18, wherein the dulling fluid contains particulate epoxy polymer comprising solid particles having a particle density higher than the density of the drilling fluid including particulate material other than the particulate epoxy polymer and wherein the downhole treatment device (19c, d) comprises a centrifugal separator (45; 45a) coaxial with the drill pipe string (Sc, d) adapted to centrifugate the higher density particulate polymer of the drilling fluid circulating in the annulus (13c, d) radially outwards towards the surface (15c, d) of the borehole (ic, d).
20. Equipment according to claim 12, wherein the centrifugal separator comprises coaxial to the drill pipe string (Sc, d) a stationary helical vane (45) or a motor-driven fan wheel (51).
21. A borehole lining produced from said melting, fusing, and/or curing of the epoxy polymer by performing the method of any of claims ito 9.
22. An epoxy polymer arranged to be carried in drilling fluid for reinforcing a borehole during drilling of the borehole, the epoxy polymer being meltable, fusible and/or curable in the vicinity of the surface of the borehole.