Technical Field

[0001] The present invention relates to composite pipes, in particular pipes for the oil and gas recovery industry, such as risers, casings and production tubing.

Background Art

[0002] The prevailing type of pipe sections that is used to form a string of pipe sections to be deployed into a subsurface well are pipe sections made from high strength steel alloys with high strength pressure sealing threaded connections. This pipe is used as flow conductor in extended reach long horizonal wells.

[0003] As wells get longer, the weight of the pipe is a limitation for further length deployment.

[0004] As wells get longer, also cost and availability of high strength steel alloy becomes an issue.

[0005] As wells are used for carbon gas injection, corrosion of steel material becomes an important consideration.

[0006] A composite material that includes carbon fibre is becoming an attractive alternative material to high alloy steel for use in fabrication of pipe sections and for completion equipment that is to be deployed in subsurface wells.

[0007] Carbon fibre combined with thermoplastics is a good composite material combination because it:

1. enables a cost-effective use of high strength carbon composite together with thermoplastic into a stiff and stable pipe structure,

2. the low weight and high strength of the final pipe section product allows deployment in longer wells,

3. carbon composite together with thermoplastic is in a positive cost development compared to steel alloys,

4. the manufacturing process of carbon composite together with thermoplastic lends itself to integrating cables and control line to the layered pipe structure, and

5. carbon composite together with thermoplastic is corrosion resistant. [0008] Thermoplastic Composite Pipe (TCP) products is already commercially available for flow of hydrocarbon in a three layered configurated. TCP is in use for pipe on the ocean floor, (www.strohm.eu). Such pipe products have been successfully qualified for flow of hydrocarbons according to DNV standards.

[0009] DNV-ST-F119 describes requirements for flexible thermoplastic composite pipes (TCPs) for offshore applications. This standard (ST) is intended to build trust and confidence in TCPs being safe and reliable for use in offshore service. Further, it has the objective of promoting continued innovation and technology development.

[0010] Latch and collet mechanism used to connect pipe spools is generally known in the industry, and the technique may be used in some applications when a threaded connection is not practical.

[0011] Examples of latch and collet mechanisms are Schlumberger's collet connectors, which are used to connect a BOP stack to a wellhead or to connect a Lower Marine Riser Package (LMRP) to a lower riser stack. An example of such a collet connector is shown in https://www.slb.com/drilling/rigs-and-equipment/pressure-con trol-equipment/collet- connectors/model-70-collet-connector.

[0012] WO2015/156678A1 describes a method for fastening coupling means to respective ends of pipes that are to be joined together, comprising a pair of mutually axially telescopic conical casings that are inserted, one on each pipe end, as the conical casing pair are mutually pushed together with the help of respective tightening bodies so that the radially outer casing squeezes the inner casing into a fastening against the surface of the pipe and joins the pipe ends together, so that a tight joining together is achieved between the ends of the pipes and it is characterized in that an inner conical casing is used which is divided into a number of sections of axially directed slits through the wall of the casing, said slits contribute to the inner casing being able to be forced radially inwards during the simultaneous closing of the slits and so that the inside of the inner conical casing is forced into a fastening against the surface of the pipe during the mutual pushing together of the casings. A coupling construction and an application of this are also described.

[0013] WO 8907220 Al describes an improved tubing connector assembly for coupling flexible tubing and forming a fluid tight seal is described. The tubing connector assembly includes a connector threadedly engaging a nut to full enclose a ferrule and a collet. Due to the surface interaction between the components of the invention, the ferrule and collet are axially compressed to grasp the tubing and obtain a very strong mechanical grip.

[0014] US 2015/275643 Al describes a propellant tool for use in a hydrocarbon bearing formation. The tool includes a tubular body having a connector on each end for connection with other tubular members within a tubular string. A coded marker is positioned on the tubular body and a propellant chamber is positioned on an outside surface of the tubular body. A propellant ignition mechanism positioned on the tubular body for igniting the propellant in the propellant chamber.

[0015] WO 2021/066971 Al describes a downhole connection assemblies include a connector to receive a conductor and pin at opposite ends. The connector includes a first electrical collet, a separate second electrical collet and a sleeve. The first collet includes a first recess in a first end to receive the conductor and a second recess in a second end to receive the pin. The second collet is positioned around the pin and separated from the first collet. The sleeve is positioned around the pin, first collet and the second collet. Downhole cables include a center electrical conductor, a first insulator positioned around the center conductor, a second insulator positioned around the first insulator, and a pressure tube surrounding the second insulator. The cable further includes one or more slots extending axially along a length of the second insulator, or one or more slots extending axially along an inner diameter of the pressure tube

Summary of invention

[0016] The present invention has as an objective to combine the advantages of composite pipes with the advantages of latch and collet mechanisms. This is achieved according to the invention by the features of subsequent claim 1. A novel method of connecting two pipe sections is defined by subsequent claim 9.

Brief description of drawings

Figures 1-9 shows schematically the manufacturing process of the composite pipe sections of the invention,

Figures 10-18 shows sequentially the assembly of a pipe string using pipe sections according to the invention, and

Figures 19-21 shows an alternative embodiment with cabling through the connection.

Detailed description of the invention

[0017] It should be noted that in the appended drawings, the thickness of layers, collet segments, threads and other parts is greatly exaggerated for visibility. Likewise, the extent of movement of the collet segments is greatly exaggerated. [0018] First the manufacturing process will be explained, referring to figures 1-9, which shows schematically the manufacturing in main steps.

[0019] In figure 1 the three first layers 2-4 of the pipe section 5 is built on a mandrel 1. The layers may be an inner layer 2 of carbon fibre in a matrix, a plastic filler 3 and an outer layer 4 of carbon fibre in a matrix. These layers make up the body of the pipe section. The invention is, however, not limited to any specific layer composition, as this may vary according to the requirements for the pipe sections.

[0020] Then, as shown in figure 2, a template in the form of a temporary spacer ring 6 is placed around the mandrel at the upper end of the pipe section 5 layers 2-4. After this an outer layer 7 of carbon fibre in a matrix is wound. The layer 7 extends along the whole length of the pipe section 5, over the spacer ring 6 and a short distance beyond the spacer ring 6 as shown in figure 3 by reference number 8. In the part 8, the layer 7 will have a greater thickness than the rest of the layer 7 and extend inwards to the surface of the mandrel 1, forming a lug, which purpose will become evident later.

[0021] Then an outer plastic layer 9 is applied, as shown in figure 4. By this layer is also formed a hang-off shoulder 10, which purpose will be evident from the following description.

[0022] Then the inner mandrel 1 is removed, as shown in figure 5.

[0023] Next an important step of the manufacturing will be performed. The outer plastic layer 9 and the carbon fibre layer 7 will be slit lengthwise along the length of the spacer ring 6 and along the thicker portion 8. The purpose is to create a collet as shown in the cross section of figure 6, where twelve collet segments lla-lll are shown. This is done by making twelve cuts 12a- 121 with an appropriate cutting tool. The width of each cut may, e.g., be 4,7 mm, which will provide sufficient freedom of action for the collet segments lla-lll.

[0024] Figure 7 shows the result in longitudinal section, showing two diametrically opposite collet segments Ila and 11g. In a further step a set of threads 13 are formed between the collet lla-lll and the shoulder 10. The threads are preferably quarter-turn threads, i.e., threads that require only a ¹ /4 turn of the parts to screw these along the full length of the threads.

[0025] Next the spacer ring 6 is removed. To facilitate this, the collet segments lla-lll have to be bent outwards to let the spacer ring 6 pass. The result is as shown schematically in figure 8 where the collet segments lla-lll now extend freely from the end of the multiple layered part of the pipe section 5. At the end of the multiple layered part of the pipe section 5 is an inward shoulder 14 created by the three innermost layers 2-4. At their outer ends, the collet segments lla-lll have gripping sections or lugs 17a- 171 formed by the thicker portion 8. These may be slightly chamfered at the upper inside end.

[0026] It should be understood that at the opposite end of the pipe section 5 is a similar end, comprising a collet lla-lll, shoulder 10 and threads 14. This end may be formed at the same time as the first end or alternatively they may be formed one after the other.

[0027] Before shipping, the ends of the pipe section 5 are conveniently equipped with a protective cap 15, as shown in figure 9. The cap has inside threads 15a that fit the threads 13 of the pipe section 5. The cap 15 of the uppermost end of the pipe section 5 is removed when the pipe section 5 has been secured in a rotary table 16. The pipe section 5 will rest on the shoulder 10 in the rotary table 16.

[0028] Next the assembly of a pipe string from several pipe sections 5 will be explained, referring to figures 10-23. In these figures some of the layers of the pipe section have not been detailed.

[0029] Figure 10 shows a longitudinal section of the upper end of a pipe section with the collet segments lla-lll exposed. The collet segments have slightly different shape at their upper ends, as the gripping parts 17a-17l are chamfered to the extent that they have a triangular shape. Figure 11 shows a view without a section through the collet segments lla-lll and layer 7.

[0030] In the first step of the assembly, a connection sleeve 18, as shown in figure 12, is inserted into the upper end of the pipe section 5. The sleeve 18 has depression in the form of a ring-shaped groove 19 around its circumference at the middle of its length. The insertion of the sleeve 18 forces the collet segments apart, as shown in figure 13. A gasket 20 has been placed on the shoulder 14 before the sleeve 18 is inserted.

[0031] When the connection sleeve 18 has been pushed fully against the shoulder 14 and compressed the gasket 20, the gripping parts 17a-17l of the collet segments lla-lll enters the groove 19 and firmly rains the sleeve 18, as shown in figure 14.

[0032] In the next step, as shown in figure 15, thin key plates 21a-2 II are inserted into each of the slits 12a-12l between the collet segments lla-lll (only two shown in the figures). The key plates 21a-211 are conveniently attached to each other by a flexible connection, such as a key ring-type installation too, so that they cannot be accidentally dropped. The key plates 21a-2 II may be simple rectangular pieces, as shown in figure 15, or they may have an extension that fits into the groove 19 of the connection sleeve 18.

[0033] As also shown in figure 15, a locking sleeve 22 with inner threads 23 has been screwed onto the threads 13 of the pipe section 5. [0034] Next, as shown in figure 16, a second gasket 20' is placed on top of the connecting sleeve 18 and a second pipe section 5' is pushed onto the connecting sleeve 18.

[0035] As shown in figure 17, the two pipe sections 5 and 5' are firmly connected. A filler part 23 may be placed outside the collets and key plates to fill the gap between these and the locking sleeve 22. If a single locking sleeve is used, the filler part 23 will conveniently have threads on its outer surface so that the locking sleeve can be threaded over this part. If two locking sleeves are used, the filler part may be smooth, as shown in the figures. The filler part is conveniently made up of two half cylindrical parts.

[0036] Figure 18 show the completed connection with locking sleeves 22 preventing the collet segments from accidentally moving outward. The locking sleeve(s) 22 may be made wholly or partly of a thermoplastic material, or it may be made of steel.

[0037] Figure 19 shows an embodiment of the pipe section and connection where a set of cables 24 have been embedded in the pipe section 5 during manufacturing. The cables 24 have wet mate connectors 25 at the internal shoulder 14 of the pipe section 5. The connection sleeve 18 also has cables 26 therein. If the connecting sleeve 18 is made of steel, the cables 26 may be placed in a longitudinal groove. It is however preferred that the connection sleeve 18 is made of a composite material, similar to the pipe section 5. In that case the cables may be embedded in the composite material. At the end surfaces of the connection sleeve 18 the cables 26 are coupled to wet mate connectors 27. In all other aspects, the pipe section 5, connection sleeve 18 and associated parts are identical to the previously described embodiment.

[0038] As shown in figure 20, the connection sleeve 18 has been completely connected to the first pipe section 5, and the wet mate connectors 25, 27 have been properly connected. A second pipe section 5', which also comprises cables 24' with wet mate connectors 25', is about to be coupled to the connection sleeve 18.

[0039] As shown in figure 21, the two pipe sections 5, 5' have been connected through the connection sleeve 18 and the cables 24, 24' have been properly coupled. This way power and/or signals can be conducted along the pipeline. This will ensure power to equipment in the well and communication between equipment, such as sensors, in the well and the surface.