METHOD AND APPARATUS FOR MILLING A WINDOW IN CASING

Abstract

A process is described for milling a window in the casing (2) of an oil or gas producing well, for example in order to drill a lateral well branching off from the main well. A wireline milling tool is first used, in a relatively low cost operation, to create a small window (14) or notch in the casing (2). Provided a small window (14) or notch can be created successfully, an expensive heavy duty coil tubing milling operation can then be conducted to create the full window, some 4-6 feet in length. Previous attempts to create a full window using wireline tools have encountered difficulties due to there being no circulating drilling fluid to remove metal swarf and due to the need for the tool to be supported by casing during the milling operation, when the integrity of the casing is being compromised by drilling the window. The proposed wireline tool has an actuator (4) with relatively small stroke length and a relatively small container (8) to manage the swarf produced by the milling process. (FIG. 2).

Claims

1. A method of milling a window in the casing of an oil or gas well, the method comprising: running a first milling tool into the well to a milling site using wireline, the first milling tool including a facility to grip the casing; gripping the casing with the milling tool gripping facility, milling away a portion of the material of the casing at the milling site and then withdrawing the milling tool; running a second milling tool into the well to the milling site, using coiled tubing or jointed drill pipe; using the second milling tool, milling away further material from the casing at the milling site until a window of a required dimension has been milled through the casing.

2. The method according to claim 1, wherein a whipstock is run into the well prior to running in the first milling tool, and the first milling tool is run in to a location adjacent the whipstock.

3. The method according to claim 1, wherein the full thickness of the casing is not penetrated by the first milling tool or the first milling tool mills a window in the casing having a length selected from 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18 inches.

4. The method according to claim 1, wherein the first milling tool comprises an extendable actuator arm on the end of which is a milling head, and the actuator arm extends from approximately 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 inches.

5. The method according to claim 1, wherein the first milling tool mills away approximately 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 in.sup.3 of casing steel.

6. The method according to claim 1, wherein fluid is circulated during milling to remove milled swarf.

7. A wireline milling tool comprising: a tool body including a mechanism for gripping casing to anchor the tool; a milling head and a rotary drive; an actuator arm for transmitting drive to the milling head, the actuator arm being selectively extendable up to 24 inches.

8. The wireline milling tool according to claim 7, further comprising a container for collecting swarf milled away by the tool, the container having a volume of approximately 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 in.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:

[0029] FIG. 1 is a schematic view of a wireline milling tool in situ in a casing, with a whipstock in place; and

[0030] FIG. 2 is a view similar to FIG. 1 showing the tool in the process of milling a small window in the casing.

DETAILED DESCRIPTION

[0031] Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

[0032] FIG. 1 shows a milling tool in accordance with the invention. The drawing is not to scale, and the aspect ratios of the various components may have been shown incorrectly for the sake of clarity. The terms “proximal” and “distal” are used to describe the location of features of the tool, and these terms are used with respect to the entrance to the well, i.e. the surface.

[0033] The tool comprises a tool body 1 which is shown anchored in casing 2 by means of retractable gripping elements 3. At the distal end of the tool is an actuator arm 4 mounted to the tool body 1 via a linkage, represented generally at 5, which allows the arm to be angled. At the distal end of the actuator arm is a milling head 6 which rotates with the arm 4. Within the tool body and the actuator arm is an internal shaft (not shown) which rotates the milling head 6. The details of the actuator arm 4, including telescopic construction allowing it and the drive shaft to extend whilst rotating the milling head are omitted for clarity, as are the hydraulic actuators internal to the arm. However, the general construction of these features would be well known one of ordinary skill in this field. Unlike coil tubing milling tools, the milling head 6 and arm 4 are designed such that cut swarf is fed back through the arm 4 and collected within the tool body 1.

[0034] In the tool body 1 are located a mechanism 7 for engaging and disengaging the gripping elements 3, a collection area 8 for cuttings, a CPU 9 for controlling the functioning of the various elements of the tool, a power unit 10 including an electrically powered hydraulic pump (not shown) for supplying hydraulics to drive some of the tool elements (not shown), and a cable head 11 for connecting with a cable 12 on which the tool is run into the well and which supplies it with electrical power.

[0035] The milling tool is unusual in that the capacity of the actuator arm to move the milling head along the casing is very small in comparison to known coil tubing milling tools and also in comparison to previous unsuccessful designs for wireline milling tools. The maximum stroke length is in this example 24 inches. This would normally be sufficient to mill a small window in the casing with a length of about 18 inches. Depending upon the tool design, stroke length may vary from approximately 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, up to 24 inches or more. Given different stroke lengths, the small window may also vary from 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, to 18 inches or more. Alternatively, the tool may simply mill a notch or cutaway extending a substantial distance through the casing but not actually penetrating the full thickness of the casing.

[0036] The collection area 8 for cuttings is relatively small compared with previous attempted designs for wireline milling tools, since the tool is designed to mill away only a relatively small amount of metal. In this example, which is designed for milling a window in 5 inch casing, the collection region has a total volume of 50 in.sup.3. Depending upon the casing size and window length, different volumes of cuttings may be generated from approximately 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 in.sup.3 of casing steel, or more. If larger casing is to be catered for, a larger capacity would likely be necessary.

[0037] A whipstock tray 13 is shown in the casing distal of the milling tool.

[0038] FIG. 2 shows the same tool with its actuator arm 4 in its fully extended state and having milled an inclined cutaway portion 15 of the casing 2 ending in a small window 14 in the casing 2. Cuttings 16 are shown in the collection area 8.

[0039] Stroker tools and milling heads are, of course, both currently available technology. With some development, it may be possible create a suitable tool by adapting an existing high force stroker tool in combination with a rotational device for cutting the window.

[0040] The operation of milling a casing window using the wireline milling tool will now be described.

[0041] The operation would normally be performed through existing production tubing, although this is not essential. A whipstock is first run through the production tubing and out of the end of the tubing. Alternatively, it may be possible to set a whipstock within the tubing and mill a window through tubing and casing. The whipstock comprises a packer or other anchor, with a shallow inclined tray portion made of a hard material. This is shown at 13 in FIGS. 1 and 2. The purpose of the whipstock is to divert the direction of the milling head and to help provide the necessary reaction force to allow it to bear against the casing 2 opposite the whipstock tray 13; the material of the whipstock tray being chosen such that it is not itself milled away to a substantial degree.

[0042] The milling tool is then run into the tubing on wireline. The tool may free fall into the tubing or, if the well is substantially deviated from vertical, it may be pumped down. Unlike delivery using coil tubing or drill string, the surface equipment needed for this operation is not substantial, and the operation could be performed from a production platform or from a vessel. It is not necessary to employ a costly drilling rig.

[0043] Wireline includes an electric power cable which, directly or indirectly, powers the various functions of the milling tool.

[0044] Once the milling tool has passed along the tubing to the region of the well where a casing window is required the gripping elements 3 are extended by means of an actuating mechanism 7 whose details are not shown but are conventional. The mechanism is powered hydraulically from the power unit 10, which includes an electric hydraulic pump powered from the wireline supply.

[0045] The tool can be installed in the casing relatively near to the point where the casing window is to be started (e.g. adjacent the proximal end of the whipstock or whipstock tray), since it is only intended at this stage to mill away a small amount of the casing. The casing will therefore retain most of its strength, even very near the portion to be milled. The tool may be installed, for example, 6 inches from the start (proximal end) of the window to be milled.

[0046] Once installed in position, the milling head is rotated by a drive shaft and linkages (not shown) extending from an electric motor (not shown) in the power unit 10 and through the tool body 1 and the actuator arm 4.

[0047] A hydraulic mechanism (not shown) in the actuator arm 4 then extends the arm 4 distally of the tool body 4. The drive shaft (not shown) includes a telescopically extendable portion which allows it to extend whilst continuing to rotate the milling head 6. If all goes well, as the milling head 6 advances the whipstock tray 13 forces it into engagement with the casing wall and the steel of the casing 2 is milled away. The forces involved are considerable, for example as much as 3,000 lbs force, making this a challenging operation.

[0048] The linkage 5, as well as linkages (not shown) in the drive shaft, allow the angle of the actuator arm 4 with the axis of the casing to change to accommodate the milling head 6 progressing along the whipstock tray 13.

[0049] The arm is extended a total of 24 inches to mill a small window in the casing with a length of about 18 inches . Once this is achieved, the actuator arm 4 and the gripping elements 3 are retracted. The tool is then withdrawn.

[0050] Provided this operation has been performed successfully, a drilling rig, e.g. with coil tubing equipment, may then be brought up and a conventional milling tool deployed using coil tubing (or drill pipe) to mill the full size 4-6 feet window. The fact that a small window has already been created considerably increases the chances for a successful milling operation with the coil tubing tool. When running the milling tool on coil tubing or drill pipe, fluid may be circulated in a conventional way to remove the swarf from the milling process and bring it up to the surface. The milling tool run on coil tubing or drill pipe is not shown in the drawings, since such devices are well known.

[0051] In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as a additional embodiments of the present invention.

[0052] Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.