GB2316345A

GB2316345A - Preperforated coiled tubing

Info

Publication number: GB2316345A
Application number: GB9723195A
Authority: GB
Inventors: John R Martin
Original assignee: Quality Tubing Inc
Current assignee: Quality Tubing Inc
Priority date: 1994-06-30
Filing date: 1995-06-23
Publication date: 1998-02-25
Anticipated expiration: 2015-06-23
Also published as: GB2316024A; GB2316024B; GB9723195D0; GB2316345B; GB9723198D0

Abstract

A length of coiled tubing, comprising: a wall having an inner surface and an outer surface; a perforation adapted to selectively place the outer surface of the wall in fluid communication with the inner surface of the wall; and a plug 16 inserted into the perforation. The tube may be used for oil well lining.

Description

2316345 PREP'7RFORATED COILED TUBING 3 The invention relates to coiled

tubing and, in particular, to preperforated coiled tubing.

Conventionaldown-hole oil and gas drilling and production techniques require solid casings or liners which maintain the integrity of a well and contain certain drilling fluids. Referring to Figure 7A, when drilling is complete and the casing or liner 102.is in place, the casing or liner 102, or tubing (not shown), is used to produce hydrocarbons from the pay zone 100 to the surface 101. As a result, the casing 102 must be pierced at this location to allow hydrocarbons to Allow into and up the casing 102. This can be accomplished by lowering high energy shaped charges or bullets 104 into the well and firing them through the casing into the formation. However, piercing the casing in this manner contaminates, and sometimes damages, the formation.

Alternatively, referring to Figure 7B, the casing 102 may be preconditioned in certain areas to selectively allow production through the wall of the casing 102. According to one known type of preconditioning, holes 106 are drilled into the casing 102 before the casing is lowered into the well. Plugs 108 are then placed into the holes to prevent oil or gas from prematurely entering the casing. When the casing 102 is finally positioned in the well and hydrocarbons are to be produced from an area above the pay zone 100, the plugs 108 are removed from he holes 106 either by grinding or by dissolving with a chemical agent.

A disadvantage of conventional perforation methods is that it is necessary to drill a large number of holes in the round walls of the casing. This task is labor 2 intensive and very expensive. In addition, conventional plugging techniques are prone to undesired leakage.

In recent years, coiled tubing has been used in lieu of, or in addition to, conventional casings or liners during oil and gas drilling and production operations.

Referring to Figure 8, coiled tubing 110 comprises a long length of metal tubing on a spool 112. The tubing can be wound and unwound into the well, thus eliminating the need to piece together sections of straight pipe. In order to produce hydrocarbons from the well, coiled tubing must be pierced with bullets or shaped charges, as described above.

In accordance with the invention, a length of coiled tubing comprises a wall having an inner surface and an outer surface, a perforation adapted to selectively place the outer surface of the wall in fluid communication with the inner surface of the wall, and a plug inserted into the perforation. The perforation may comprise a doublecountersunk hole.

- 3 Particular embodliments af the invention are described in detail herein with reference to the 10 following drawings, in which:

f Figure 1 shows a sec--.,aon of pe= material according to ene c,2 'the invention; Figure 2 shcws a merocrat,-i pluc: and seal _in a on, strip according to one e-nbcd-.nen- c. he invention; Figure 3 shows the of perEcrations which occurs when the strip cif Figure 2 is for-mez into -ub;ng; Figures 4A through.C show a perfcra--ion formed in a strip af raw material according to another einbcd-Jment of the invention; Figures 5A and 53 show a tubing section f=med frorm the strim dem-icted in Figures 4A thrcugh 4C; Figure 6 shows a strip of raw -material according to another embodiiment of the invention; Figures 7A and 7B show a canventicnal dcwnhale casing cr liner; and 8 shows conventional coiled tubing.

As discussed above, downhole casings or straight tubing may be preconditioned in certain areas to allow production -t'n-- cugh the casing or tubing walls. In -fact, several means for preconditioning producticn tubing are known. To date, however, preconditicning -,ec,1n-4c:.,-,es have been insufficient and applicable only to casings or straight tubing already for-,-,ied from raw -matarial.

1. - Referring to Figure i, a flat sheet (11stripll) 10 s.kelm raw ma- s used to -aria!, praferablv s-eel, - r)rrduce tubing. Round perforations 12 are formed in the s't::.i.p 10 using any suitable such as drilling or, preerably, punch,-;na. D- m. ill,ng in tIl-e flat is much easier and less expensive than drilling llin the raundfl c-,.ce the tubing has been formed. Punching -;S even mcre but previcusly was not, used because it can only be done in the flat. The perforations are then plug,ed in a manner described in detaill belonw.

Once the mer..Ocrat-cns are formed and plugged, several of the strips are welded together, preferably at a bias of 450, to lLcr-.,i a strip having a desired lengzh. Tu---,.rig is fcr-,.,ied from the composite strip by running the strip tk-hrcuc:,h a tube -7f cciled tubing is desired, the tubing is then, coilled onto a spool. The process of coiled tubing from a composite strip is described in detail in U.S. Patents Nos. 4,863,091 and 5,191,911, the disclosures of which are hereby incorporated by reference.

Because the tubing may cone in countless sizes and thicknesses, the strip 10 may be of any possible dimension. In the preferred embodimient, the diam-1-,," oF 7.-33 Mid 88.9 m t the tubing is between approximat-ely 2.375 and 3 5 1, and v 3 81 nn) the wall thickness is between apprcx-J:?.ately 0.150'1 0.210 5.33 mm), d-i.nens-icns cf the strip io are deter-mined accordingly. perforations 12 nay also appear in numerous sizes and patterns, demending I-Ipcn the application for which the tubing will ultimately be usec. In the preferred eT.bcdinent", the perforations, 12 are _(9.53 rm) having a diameter of 0.37-:)Z,,-rick are positioned such tI,,1; 5t Che resultant tubing comprises approximately (40.32 mmi) 0.25 in2.4o per-one foot of tubing.

Referring to Figu--e 2, the preferred perforation is a double-countersunk hole formed in the strip 10. To c -- _m this hole, a circular hole 20 is munched into the Strim 10. A. 22 is than drille,' into the firstcounzersink 22. hcle 20, the f,-rs- ccu-"ers;nk the hole 20.

c---c,,-lar hale 20 is munc. n-c t.-ircuc'n th-R StrIp R4.45 runj 10, which has a thick-ass of 0.175,v. Circular 0. Ccu- tars -ir...c 2,4 has a d-;lfe-tgr cf f12.83 nn) (2. mm) ().=05" and extends to a dePth cf ()-095"below the cuter surface 26 of the. s--iD 10, while ccun-tarsin'c22 has a (9.53 mm)- 0.76 mm) of 0. 3-75.. jana extends- Q--030,'ond countersink k3.18 mm ' 2 4 e., to a depth c f 0. 125 Z below the outer surface 26) Referring again to F.igure 1, re-."tcvable plugs 14 are placed within the perforations 12 in the strip 10.

The plugs 14 preferably fit into the perfcrations 12 in a sh of manner which ma-f-tains the s-mooth c.

ylindrical fini 23 the tubing. In other words, the plugs!4 should not surface c- -the The plugs i'r shouid- also be of jO The preferrea; p!,-gs are also discussed; in -.ore dezail Also claced within each perfora--icn 12 is a seal ing (not s"cwn in Fligure 1), w.i-ic", _in with the cluc 11, creates a the tub- created the 3:1 be--ween the surfaces c, i -c, 10. The sealing element may assume many forms, including, but not limited to, fabric washers, chemical compounds, flexible rings, and polytetrafluoroethylene (PTFE). It is also possible to use a pressureresponsive seal, one whose sealing characteristics improve as pressure is increased. Regardless of the type of sealing element used, the perforated tubing must be able to withstand extremely high internal and external pressures, as well as repeated coiling and uncoilling stresses. In io the preferred embodiment, the plugged and sealed perforations must be able to withstand a minimum-pressure of 2000 psi, and at least eight co 11 ing/uncoi ling cycles.

Referring again to Figure 2, the preferred plug 16 and sealing element 18 are placed within the perforation.

The preferred plug 16 is a hollow-head, closed-end button rivet, such as the I'Klik-Fast11 rivet produced by Marson Corporation (Model No. ABS4CLD). Other embodiment_s may include plugs designed specifically for perforated tubing systems, such as the 1IEZ-Trip11 manufactured by Stirling Design International. The preferred sealing element 18 is a rubber 0-ring, available from any manufacturer of commercial sealing rings.

The rubber O-ring 18 is placed within countersink 22, while the rivet 16 is inserted from the outer surface 26, through countersinks 22 and 24, and through the hole 20. When the rivet is properly installed, the button-end 30 overlaps the hole 20 and presses firmly against the "inner" surface 28 of the strip 10. In addition, the body 32 of the rivet 16 fills the hole 20, while the rivet head 34 fits into countersink 24. Countersink 24 is formed deep enough so that the rivet head 34 does not extend significantly beyond the outer surface 26. Furthermore, -he O-ring 18 and the rivet!6 are forced or bound together in such a way that they cooperatively form a fluid-tight seal between the cuter surface 26 and the inner surface 28 of the strip 10. The head 34 and body 32 of the rivet 16 contain a hollow channel 36, the purpose of which is described hereinbelow.

Referring to Figure 3, when a strip of perforated -- -f orm, material is milled to form a tube 40, tube, ing stresses act u-non the perforations. As a result, the shanes of the holes 20 and the countersinks 22 and 24 are altered. As the strip bends, the circular holes and countersinks elongate, and they begin to taper from the outer surface 26 to the inner surface 28 of the tubing 0 the 40. If a rigid plug were used, this defor-mation of hole would cause the plug to leak. This is why, in t he prior art, perforations were always drilled in the round after the tubing had been formed. The plug and sealing element of the invention solve this problem by providing a flexible yet durable seal. Thus, the properties of the plug and sealing element must be sufficient to allow each to assume the shape of the distorted perforation. The rivet 16 is preferably made from a malleable metal, such as an aluminum or magnesium alloy. The O-ring IS is preferably made from an elastic material, such as rubber. Other embodiments of the plug and sealing element may be necessary to withstand the tube-forming process. For example, a rivet which does not extend beyond the inner surface of the tubing may be needed to prevent damage during some tube-milling processes. The 0-ring may need to be constructed of a more heat-resistant material.

When the tubing is coiled onto or uncoiled from a spool, coiling stresses, similar to the tube-forming stresses, act upon the perforations, plugs, and sealing elements. However, unlike the tube- forming stresses, which act upon the perforations around the longitudinal the - %-resses occur along the axis ol ubing, the coiling st longitudinal axis of the tubing, i.e., in the direction of coiling around the spool. As a result, the coiling forces cause additional deformation of the perforations. Because of the malleable and flexible qualities of the plug and sealing element of the invention, the plugged perforation more readily withstands these coiling forces.

In some embodiments, the rivet 16 and O-ring 18 may be inserted into the perforation after the tube is formed from the strip. For example, the rivet and O-ring may be forced into the distorted hole. Alternatively, the distorted hole may be milled to restore the hole to a generally circular shape, and the rivet and O-ring may be inserted therein.

In other embodiments, the preferred hole 20 and countersinks 22 and 24 may be formed in the tubing 40 is instead of in the strip 10. In this case, the hole 20 is not subjected to the tube-forrting stresses which occur when the tube is formed from the strip, and thus undergoes no deformation. The rivet 16 and 0-ring 18 are claced into the undeformed perforation in the tube. In those embodiments concerning the production of coiled tubing, the perforation may be formed and plugged after forming the tubing from the strip, but prior to coiling it onto the spool. However, the plug mus-L still be able to withstand repeated coiling and uncoiling stresses.

Referring to Figures 4A-4C and SA-5B, an alternative perforation 25 is formed in the strip 10 in such a way that it has generally circular shape in the resultant tubing. As discussed above, when the strip 10 is curved to produce a section of tubing, tube-forming stresses alter the shape of the perforation 25. In particular, stress forces (.F,) on the outer surface 26 of the strip cause expansion of the perforation 25, while forces (F,) on the inner surface 28 cause compression of -he cerforation. The amplitudes and directions of the tube-for-ming stresses will depend upon several factors, including, but not limited to, the ty-p.e of material from which the strip 10 is produced, the thickness of the strip 10, and the diameter of the tubing 40 produced from the striz 10.

The structure of the perforation 23 must be sufficient to compensate for the tube-for-ming stresses expected to occur during formation of the corresponding section of tubing. To produce a generally circular double-countersunk perforation in the section of tubing (Figure SA), bevels B! through 35 are formed in the strip 10. As shown in Figure 4A, bevels B1, B3 and 35,- which represent the sidewalls of the hole and the countersinks (20, 22 and 24 in Figure SA), taper outwardly from the outer surface 26 to the inner surface 28 of the strip 10.

Likewise, bevels B2 and B4 taper inwardly from the outer surface 26 to the inner surface 28. The angle to which each bevel is cut depends upon the characteristics of the raw material and the tube-fotming stresses that will occur. During formation of the tube 40, the tube-forming stresses act an the bevels such that bevels BI, B3 and B5 are parallel to each other and perpendicular to "--he surfaces of the tubing section 40, and bevels B2.and B4 are parallel to each other and the surfaces of the tube 40.

The bevels 31 through BS are also formed such that they are variably rounded and oblong in shape. Figure 4C (not to scale) depicts the perforation as viewed from the inner surface 28 of the strip 10, showing -he varied geometry between the bevels. Bevel B5 lies closest to the outer surface 26, where the outer stress forces (F.) cause the greatest expansion of the perforation. Therefore, bevel BS is the most oblong of the bevels.

As the bevels approach the middle, but not necessarily the center, of the strip iO, the bevel shape is increasingly circular. At some point within the strip 10, again depending upon the characteristics of the raw material and the anticipated tube-for-ming stresses, the bevel shape is substantially circular. From this point, the bevels become increasingly oblong as they approach the inner surface 28 of the strip 10. More important, however, is the offset the bevels lying in the inner part of the strip have with respect to the bevels lying in the outer part of the strip. This offset ensures that the perforation tends to a generally circular shape as the inner stress forces compress the inner bevels, while the outer stress forces (Fa) expand the outer bevels.

After the tube 40 is formed from end-welded strips 10, the perforation 25 comprises a hole 20 and countersinks 22 and 24 which are substantially is cylindrical (Figures 5A and 5B). The perforation 25 is then sealed and plugged, as described above, and the tube can be spooled to form coiled tubing.

Referring to Figure 6, another embodiment of the flat strip 30 of raw material has nonuniform thickness throughout the length of the strip 30. There may also be inconsistencies in other characteristics of the material from which the strip 30 is formed, e.g., varying steel hardness or composition throughout the strip 30. In this case, each of the perforations 32a and 32b is uniquely formed according to the characteristics of the strip 30 at the area in which the perforation is located. Because of the inconsistencies in the strip 30, the tube-forming stresses on perforation 32a will differ from those on 32b, and the shapes of the punched perforations will vary accordingly. As a result, regardless of characteristic inconsistencies in the strip 30, the perforations 32a and 32b each will have generally circular shape after the strip 30 is milled into tubing.

Referring again to Figure 2, when the perforations must be opened to produce hydrocarbons from a well, the - 11 rivet 16 is easily removed from the tubing by one of two methods. According to one method, the rivet 16 is dissolved by a chemical solution, such as an acid. For an aluminum or magnesium rivet, a solution of approximately 15% hydrochloric acid (HCI) is pumped into the tubing along its inner surface 28. When the solution reaches the rivet 16, the acid quickly dissolves '"he metal alloy, thereby opening the plugged perforation. Hydrocarbons from the well then enter the tubing for production at the surface.

Another removal method provides for grinding or milling the rivet to open the perforaticn. As described above, a hollow channel 36 runs through the head 34 and the body 32 of the rivet 16. The hollow channel 36 extends beyond the interior surface 28 of the tubing, and is closed by the button-end 30 of the rivet 16. In order to open the perforation, a downhole gauge reamer (not shown) is run internally through the tubing. When the reamer reaches the rivet 16, the cutting action of the reamer mills away the button-end 30, thereby exposing the hollow channel 36 and opening the perforation. Hydrocarbons from the well then flow into the tubing through the perforation for production at the surface.

1 12

Claims

A length of coiled tubing, comprising: a wall having an inner surface and an outer surface; a perforation adapted to selectively place the outer surface of the wall in fluid communication with the inner surface of the wall; and a plug inserted into the perforation.
2. The length of coiled tubing according to claim 1, wherein the perforation comprises a double-countersunk hole.
3. The length of coiled tubing according to claim 1 or claim 2, further comprising a sealing element inserted into is the perforation, said sealing element and said plug forming fluid- tight seal between the inner surface and the outer surface of the wall.
4. The length of coiled tubing according to claim 1, further comprising a pressure-responsive seal.
5. The length of coiled tubing according to claim 4, wherein said seal responds to pressures internal and external to said coiled tubing.