GB2601547A

GB2601547A - Establishing a sidetrack in a well

Info

Publication number: GB2601547A
Application number: GB2019153.2A
Authority: GB
Inventors: Grindhaug Gaute; Weltzin Tore; Hovland Morten; Eidem Morten; Berge Frode; Mark Williams Stephen; Dahl Kristensen Brian
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2020-12-04
Filing date: 2020-12-04
Publication date: 2022-06-08
Also published as: GB202019153D0

Abstract

A system and method for use in establishing side branches extending laterally from a main well, comprising: a whipstock 2 comprising a body section 4 defining a surface that is axially inclined relative to a longitudinal axis when the whipstock is fixed within the main well, and a sacrificial layer 6 on said surface, the sacrificial layer being of a material that is soft relative to a material of the body section; and a mill 8 comprising a terminal part comprising cutting elements for cooperating with said sacrificial layer to cause said terminal part to be mechanically captured by the sacrificial layer as it passes across the whipstock, thereby inhibiting lateral movement of the mill so as to reduce the risk of the mill jumping and to avoid the need for a polish-run.

Description

ESTABLISHING A SIDETRACK IN A WELL

Technical Field

The present invention relates to establishing a sidetrack in a well such as a hydrocarbon reservoir producing well.

Background

For a variety of reasons it is often desirable to establish a sidetrack running away from a main hydrocarbon reservoir completed well. This can be achieved by running a so-called whipstock into the well and securing it at a location where a sidetrack is to be established. The whipstock has an angled surface such that it provides deflection of a milling tool to allow a window to be milled through the surrounding tubing. Thereafter a drilling Bottom Hole Assembly (BHA) is run into the well and is similarly deflected by the whipstock allowing the sidetrack to be drilled. Running of a whipstock and milling of a window is a relatively time-consuming process in an industry where time has enormous cost implications.

Summary

Aspects of the present invention provide a system and method for facilitating the establishment of a sidetrack, as set out in the appended claims.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings

Brief Description of the Drawinas

Figures la to lc illustrate an improved whipstock having a sacrificial layer for providing improved mill guidance with reduced vibrations; Figure 2 illustrates a whipstock with a sacrificial layer according to an embodiment; Figure 3 illustrates a whipstock according to an alternative embodiment; Figure 4 illustrates a whipstock according to a further embodiment; Figure 5 illustrates a mill being used to mill through a sacrificial layer and casing; Figure 6 illustrates a mill having an alternative terminal part with pointed triangular cutting elements; Figure 7 illustrates a mill according to an alternative embodiment having square cutting elements; Figure 8 illustrates a mill according to a further embodiment having cutting elements with a curved inner edge and Figure 9 illustrates a mill having multiple cutting elements.

Detailed Description

When establishing side branches it is important to minimise damage and wear to the milling tool, due to for example vibrations or unequal load balancing. One way to achieve this is illustrated in Figures la to 1c.

The whipstock 2 comprises a body section 4 of high strength steel. This may have a curved cross-section. It is proposed here to provide a layer of sacrificial material 6 on top of the whipstock body section 4. This might have a thickness in the region of 10-25% of the thickness of the whipstock body 4, and may be for example 5 cm or greater. The sacrificial layer 6 comprises material which is softer than that of the whipstock body 4.

This material might be, for example, aluminium, steel, a composite material (e.g. formed from glass fibre or carbon fibre), concrete, plastic, glass, wood, brass, copper, lead, epoxy, or any other material which is softer than the whipstock body 4. The basic principle of operation is that the mill 8 is held in place by the sacrificial material 6 as it passes over the whipstock 2 and this leads to reduced risk of the mill 8 jumping off the whipstock 2 too early, thereby reducing the risk of creating an undesirable "lip" on the bottom part of the window 10. This can avoid the need to do a so-called polish-run to remove the lip, which is currently needed in around 25% of all casing exit operations.

An important feature of this approach is a new mill design, an embodiment of which is illustrated in Figures la to 1c. The end 12 of the mill 8 has a frustoconical recess formed at its centre. Whilst the shape shown in the drawings shows the lowermost edge 16 of the mill 8 having flat terminations, these may be further tapered into a much narrower end. As the mill 8 enters the sacrificial layer 6 the end 12 of the mill 8 is captured within and rotates through the sacrificial layer 6. The mill profile, by being captured by the sacrificial layer can reduce vibrations and wear by increased stability in all directions during the milling process. The result of this is increased mill life and better window quality. Also, the mill time may be decreased, as, normally, the speed of milling is limited by the risk of early "jump-off". Since the mill 8 is held by the sacrificial layer 6 and the mill profile, the milling speed can be increased without negatively affecting the window quality.

The approach is also of potential value during low side exit since the "forced" position of the mill 8 on the whipstock 2 will prevent gravity from pulling the mill 8 off the whipstock 2 too early. The approach could potentially open the opportunity for new features such as drilling a short side branch using the mill 8 instead of a separate BHA (Bottom Hole Assembly).

Figures 2 to 4 show plan views of different whipstocks 2. Figure 2 shows a whipstock 2 with a body section 4 and a sacrificial layer 6, which covers substantially the whole of the body section 4. The sacrificial layer 6 has been welded or glued to the body section 4, or is held by a profile in the body section 4. The whipstock 2 is in general tapered, so that a greater circumference at the bottom of the casing is covered compared to the top. For example, half the circumference of the casing may be occupied by the whipstock at one end, while a third of the circumference of the casing is covered at the other end. The sacrificial layer 6 follows this tapered shape.

Figure 3 shows an alternative embodiment of the whipstock 2, wherein the sacrificial layer 6 is a strip of material at the centre of the body section 4. This may be preferential in order to save material and to provide a substantially constant weight/resistance from the sacrificial layer. The body section 4 comprises a rectangular slot 19, in which sacrificial layer 6 is received.

Figure 4 shows an embodiment similar to that of Figure 2, but the sacrificial layer 6 is attached to the body section 4 by bolts 17.

Figures 5 to 8 show cross sectional views of mills 8 having different cutting elements 22.

Figure 5 shows a mill 8 milling through a sacrificial layer 6, while milling a window 10 in a casing 20. The terminal part 18 of the mill 8, comprises cutting elements 22 located around an outer circumference of the mill 8. The cutting elements 22 have a width that is less than the thickness of the sacrificial layer 6, so that, in operation, the mill 8 is held by the sacrificial layer 6. The cutting elements 22 in Figure 5 have a slanted inner edge 24 and a flat lower edge 16. In Figure 6, the cutting elements 22 have a triangular cross section, with a slanted inner edge 24 and a pointed end. In Figure 7, the cutting elements 22 have a square cross sectional shape. Figure 8 illustrates an embodiment with cutting elements 22 having a curved inner edge 24.

Figures 9 shows a front view of a mill 8 having eight cutting elements 22 in the terminal part 18 of the mill 8. The openings 26 in the terminal part 18 between cutting elements 22 allow fluid and cuttings from the milling process to pass back over and behind the mill 8. The cutting elements 22 can have a flat lower edge 16.

In general, embodiments described herein provide a system for use in establishing side branches extending laterally from a main well used for the production of hydrocarbons.

The system comprises a whipstock comprising a body section (e.g. high strength steel wedge for guiding the mill) defining a surface that is axially inclined within the main well in use, and a sacrificial layer on said surface, the sacrificial layer being of a material that is soft relative to a material of the body section. The system further comprises a bottom hole assembly (BHA) for coupling to a drill pipe and comprising a mill, the mill comprising a cutting element for cooperating with said sacrificial layer to cause a terminal part of the cutting element to be mechanically captured by the sacrificial layer as it passes across the whipstock, thereby inhibiting lateral movement of the BHA.

The lateral thickness of said sacrificial layer is preferably greater than a lateral thickness of said terminal part of said cutting element (e.g. the sacrificial layer is thicker than the width of the cutting elements of the mill), in order to ensure a good holding interaction between the mill and the whipstock. For example, the sacrificial layer can have a thickness in the range of 5 cm to 10 cm.

The sacrificial layer may comprises a single curved metal sheet, for example of aluminium. However, the sacrificial layer may be formed of any material which is less hard than the material of the whipstock. The sacrificial layer may cover substantially the whole body section of said whipstock. Alternatively, the sacrificial layer may comprise a strip (e.g. a rectangular strip) of said material, which covers less than 60% of said body section of said whipstock. For example, the sacrificial layer may be a rectangular (or curved rectangular) strip having a width in the range of 10 cm to 50 cm and run along the entire length of the whipstock (typically 4 m to 6 m).

The whipstock typically comprises some attachment means for attaching said sacrificial layer to said body section. For example, the sacrificial layer may be attached by glue (e.g. an epoxy), welding, heat fixing, or with screws or bolts (or any combination of these means). Alternatively, the surficial layer may be formed as an integral part of the whiptock by machining. The whipstock may also comprise a guiding structure, such as a slot, in said body section for receiving said sacrificial layer, so that the sacrificial layer is held in place at least in part by the shape of the body section.

The cutting element may define a substantially frustoconical space at a terminal end of said mill. The terminal part of said cutting element may comprise one or more cutting elements, and each cutting element can have a cross sectional shape being one of a triangle, a rectangle, a trapezium, and a rectangle with an inner curved edge.

Also described herein is a method of establishing a side branch extending laterally from a main well using the milling system as described herein. The method comprises securing the whipstock at a location within a liner of the main well adjacent to where the side branch is to be established, and lowering the BHA on a drill pipe into the main well to a location above said whipstock. The method further comprises lowering the BHA while operating the mill such that the BHA is deflected laterally by the whipstock whilst the cutting elements of the terminal part mill through the sacrificial layer being captured by the sacrificial layer as it does so, the mill further milling through the liner and into the formation to establish the side branch.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. It will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

Claims 1. A system for use in establishing side branches extending laterally from a main well used for the production of hydrocarbons, said main well having a longitudinal axis, the system comprising: a whipstock comprising a body section defining a surface that is axially inclined relative to said longitudinal axis when the whipstock is fixed within the main well in use, and a sacrificial layer on said surface, the sacrificial layer being of a material that is soft relative to a material of the body section; and a mill comprising a terminal part comprising cutting elements for cooperating with said sacrificial layer to cause said terminal part to be mechanically captured by the sacrificial layer as it passes across the whipstock, thereby inhibiting lateral movement of the mill.
2. A system according to claim 1, wherein a lateral thickness of said sacrificial layer is greater than a lateral thickness of said terminal part.
3. A system according to claim 1, wherein said sacrificial layer has a thickness in the range of 5 cm to 10 cm.
4. A system according to claim 1, 2 or 2, wherein said terminal part defines a substantially frustoconical space in said mill.
5. A system according to any one of the preceding claims, wherein each cutting element has a cross sectional shape being one of a triangle, a rectangle, a trapezium, and a rectangle with an inner curved edge.
6. A system according to any one of the preceding claims, wherein said sacrificial layer comprises a single curved metal sheet.
7. A system according to any one of the preceding claims, wherein said material of said sacrificial layer comprises one of aluminium, steel, brass, copper or lead.
8. A system according to any one of the preceding claims, wherein said sacrificial layer covers substantially a whole of said body section of said whipstock.
9. A system according to any one of claims 1 to 7, wherein said sacrificial layer comprises a strip of said material, which covers less than 60% of said body section of said whipstock.
10. A system according to any one of the preceding claims, wherein said whipstock further comprises attachment means for attaching said sacrificial layer to said body section.
11. A system according to claim 10, wherein said attachment means comprises one or more of a glue, a weld, a heat fixing, screws, and bolts.
12. A system according to any one of the preceding claims, wherein said attachment means comprises a guiding structure, such as a slot, in said body section for receiving said sacrificial layer.
13. A method of establishing a side branch extending laterally from a main well used for the production of hydrocarbons, using the system of any one of claims 1 to 12, the method comprising: securing the whipstock at a location within a liner of the main well adjacent to where the side branch is to be established; lowering the mill into the main well to a location above said whipstock; and further lowering the mill while rotating the mill such that the mill is deflected laterally by the whipstock whilst the cutting elements of the terminal part mill through the sacrificial layer being captured by the sacrificial layer as it does so, the mill further milling through the liner and into the formation to establish the side branch.