GB2306985A

GB2306985A - Improvements in milling

Info

Publication number: GB2306985A
Application number: GB9522809A
Authority: GB
Inventors: Hector Filippus Alexand Susman; Kenneth Rodrick Stewart
Original assignee: LEDINGHAM CHALMERS TRUSTEE COM
Current assignee: LEDINGHAM CHALMERS TRUSTEE COM
Priority date: 1995-11-07
Filing date: 1995-11-07
Publication date: 1997-05-14
Anticipated expiration: 2015-11-07
Also published as: GB2306985B; GB9522809D0

Abstract

There is disclosed a milling tool and related method capable of milling/cutting of windows in oil/gas well casing. Problems exist with presently available milling equipment such as difficult of retrieval and speed of operation. The invention provides an improved milling tool (5) for milling a window(s) in a casing (10) comprising a drill bit (15), means for driving (20) the drill bit (15) and means (25) for positioning the drill bit (15) in contact with a selected portion of the casing (10) to be milled. In an advantageous embodiment the drill bit (15) has one or more cutting elements which element(s) is/are oriented substantially transversely with respect to the casing, in use; the means (25) for positioning comprise a transversely movable actuator strip movably positioned by a number of hydraulic pistons; the means for driving (20) the drill bit (15) drive the drill bit (15) along an axis oriented substantially longitudinally with respect to the casing, in use; and the means for driving (20) the drill bit (15) comprise a drilling motor (20).

Description

IMPROV15MI!NTS IN MILLING This invention relates to milling and in particular, though not exclusively, to a milling tool capable of milling/cutting of windows in oil/gas well casing.

Well casing is normally very tough, thick walled steel pipe which is placed inside a borehole of a well as a lining to secure the borehole and prevent the walls thereof from collapsing. Casing - sometimes referred to as casing tubing - may be seamless, spiral welded or seam welded and may, for example, be fabricated from various API grades of steel such as H40, J55, N80 or Pill. Sizes typically vary from around 4 inches (101.6 mm) OD to 30 inches (762 mm) OD, while weights typically range from around 11 lb/ft to 200 lb/ft (16.4 kg/m to 298 kg/m approximately) depending on diameter, thickness and grade. It has also been known to employ glass fibre reinforced plastic casing.

It is known that the cutting of windows in oil well casing, as required for side tracking, is a complicated process, normally requiring the use of a large number of tools not directly related to the cutting of the window itself, such as whipstocks, packers etc. The normal procedure is the setting of a cement plug on top of a packer above which a so-called "whipstock" is placed.

The whipstock basically consists of a hard metal wedge which guides a window milling drill bit gradually into the casing thus cutting a slot in the casing. As the slope of the whipstock is of a low value the pinching action on the drill bit is very severe therefore requiring extremely high torque and yet a low rate of progress is achieved due to the high friction losses of the drill bit against the whipstock which have to be subtracted from the total energy available for the cutting of the window. Furthermore when the window is cut the whipstock and packer require to be retrieved which is often a difficult and tedious process. To date the duration of an average window milling job is three to four days and often much longer.

It is an object of at least one aspect of the present invention to obviate or mitigate at least some of the aforementioned problems/disadvantages in the prior art.

It is a further object of one or more embodiments of at least one aspect of the present invention to provide a milling tool which may advantageously be positioned using coiled tubing with its inherently shorter positioning and retrieval times as against the use of conventional oil field tubing.

According to one aspect of the present invention there is provided a milling tool for milling a window(s) in a casing comprising a drill bit, means for driving the drill bit and means for positioning the drill bit in contact with a selected portion of the casing to be milled.

Preferably the drill bit has one or more cutting elements which element(s) is/are oriented substantially transversely with respect to the casing, in use.

Preferably the means for driving the drill bit drive the drill bit along an axis oriented substantially longitudinally with respect to the casing, in use.

Advantageously the means for driving the drill bit may comprise a drilling motor.

The drilling motor may comprise a stator and a rotor rotatably mounted in said stator, the stator being provided with a rod recess and an exhaust port, the rotor being provided with a rotor channel and at least one channel for conducting motive fluid from the rotor channel to a chamber between the rotor and the stator, and the rod recess being provided with a rod which, in use, forms a seal between the stator and the rotor.

The rotor may be provided with a seal for engagement with the stator.

The seal may be made from a material selected from the group consisting of plastics material, polyethylethylketone, metal, copper alloys and stainless steel.

The rod may be made from a material selected from the group consisting plastics, materials, polyethylethylketone, metal, copper alloys and stainless steel.

The stator may be provided with two rod recesses which are disposed opposite one another, two exhaust ports which are disposed opposite one another, each of the rod recesses being provided with a respective rod, the rotor having two seals which are disposed opposite one another.

The means for driving the drill bit may advantageously comprise two drilling motors, as hereinbefore described, arranged with their respective rotors connected together.

The drilling motors may be connected in parallel.

Alternatively the drilling motors may be connected in series.

The drilling motors may be arranged so that, in use, one drilling motor operates out of phase with the other.

A drilling motor as hereinbefore described is disclosed in PCT/GB95/00069 (W095/19488) HARRIS & SUSMAN, the content of which is incorporated herein by reference.

The means for positioning may comprise a hydraulically operated setting mechanism.

The means for positioning may moveably position the drill bit in contact with a selected portion of the casing to be milled, in use, by means of the setting mechanism controllably pushing against the casing.

The means for positioning may also include orientation means for controllably rotating the milling tool within the casing, in use.

The orientation means may comprise an orientation tool, as known and available in the art.

According to a second aspect of the present invention, there is provided a method of milling a window in a casing comprising the steps of: providing a milling tool comprising a drill bit, means for driving the drill bit and means for positioning the drill bit in contact with a selected portion of the casing to be milled; placing the milling tool within the casing; positioning the drill bit in contact with the selected portion; and driving the drill bit so as to form a window in the casing.

Advantageously the drill bit is positioned and driven so as to mill the casing in a substantially transverse direction with respect thereto.

The method may comprise the further step of continuing to drive the drill bit and moving the milling tool in a substantially longitudinally direction with respect to the casing thereby further forming the window by either pushing or pulling on the tool.

Advantageously the milling tool is conveyed within the casing by means of coiled tubing.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawing, which is: Fig 1 a schematic sectional side view of an embodiment of a milling tool according to the present invention positioned within a casing.

Referring to Fig 1 there is illustrated an embodiment of a milling tool, generally designated 5, according to the present invention within a tubular casing 10 of an oil/gas well.

The milling tool 5 which is intended for milling a window(s) in the casing 10 comprises a drill bit 15, means for driving the drill bit 15 and means for positioning the drill bit 15 in contact with a selected portion of the casing 10 to be milled.

The drill bit 15 has one or more cutting elements which element(s) is/are oriented substantially transversely with respect to the casing 10.

The means for driving the drill bit 15 drive the drill bit 15 along an axis oriented substantially longitudinally with respect to the casing 10 in use.

In this embodiment, the means for driving the drill bit 15 comprise a drilling motor 20.

It is envisaged that the drilling motor 20 in this embodiment is of the type disclosed in PCT/GB95/00069 (WO95/19488) HARRIS & SUSMAN, the content of which is incorporated herein by reference. However, it should be appreciated that the drilling motor 20 may alternatively be a Moineau motor.

The means for positioning comprise a hydraulically operated setting mechanism 25. The means for positioning moveably position the drill bit 15 in contact with a selected portion of the casing 10 to be milled, in use, by means of the setting mechanism 25 controllably pushing against another portion of the casing 10.

In this embodiment, the setting mechanism 25 comprises a transversely moveable actuator strip 30 which is moveably positioned by a number of hydraulic pistons 35 which are operated by hydraulic fluid required for the normal operation of the drill motor 20.

The means for positioning also includes orientation means (not shown) for controllably rotating the milling tool within the casing, in use. The orientation means may comprise an orientation tool of the type known in the art.

The setting mechanism 25, therefore, controls the radial movement of the milling tool 5 within the casing 10, while the orientation means controls the rotational position of the milling tool 5 in a transverse plane of the casing 10.

In use, a window can be milled in a selected portion of the casing 10 by: placing the milling tool 5 within the casing 10; positioning the drill bit 15 in contact with the selected portion; and driving the drill bit 15 so as to drill through and form a window in the casing 10.

In this embodiment the milling tool 5 is conveniently conveyed down the inside of the tubular casing 10 by means of coiled tubing (not shown) so that the drill bit 15 is substantially at the level of the selected portion. The milling tool 5 is then rotationally positioned within the casing 10 by the orientation means so that cutting element(s) of the drill bit 15 substantially face the selected portion. The drill bit 15 is then brought into contact with the casing by the action of the setting mechanism 25. Subsequent driving of the drill bit 15 by the drilling motor 20 causes a window to be formed in the selected portion of the casing 10.

After the drill bit 15 has penetrated through the wall of the casing 10, longitudinal pulling or pushing of the milling tool 5 with simultaneous driving of the drill bit 15 causes the window in the casing 10 to be further formed.

The embodiment of the present invention hereinbefore described is given by way of example only, and is not meant to limit the scope of the invention in any way.

It should particularly be appreciated that advantageously, but not exclusively, the present invention consists of an orientation tool followed by a modified drill motor and a specially shaped window milling drill bit. The drill motor may be modified by the inclusion of a hydraulically operated setting mechanism. The aforesaid mechanism pushes the drill motor housing and thus also the drill bit in a radial direction but allows longitudinal movement of the motor housing in such a way as to allow a slot to be milled in the casing after the drill bit having perforated the casing through the radial force exerted on it by the setting tool. The setting tool may consist of a radially moveable actuator strip operated advantageously, but not exclusively, by a number of small hydraulic pistons which are operated by the pressure of the fluid required for the normal operation of the drill motor.Alternatively, a longitudinally moving piston may have its axial movement translated into a radial movement by a cam mechanism operating the radially moveable actuator strip in such a fashion as to move the motor housing in a radial direction with the earlier mentioned result of cutting a radial slot in the casing.

A normal window milling procedure would, typically, consist of positioning at the required depth the milling drill bit by the advantageous but not exclusive means of coiled tubing, thereafter the earlier mentioned positioning tool will orientate the motor housing and thus the actuator strip in the opposite direction of the required window to be milled. When pumping action is commenced the pressure rise before the actuator pistons will cause the actuator strip to travel outwards thus exerting a radial force onto the milling drill bit.

After a prerequisite period the drill bit will radially cut through the casing wall. When a radial slot has been cut in the casing wall axial force can now be exerted on the coiled tubing causing the whole assembly to move in a longitudinal direction and in so doing cutting a slot in the direction of the axial force. It is expected that cutting rates in the order of four feet per hour may be expected.

Unique features of the disclosed embodiment of the present invention include: - initial radial only penetration of the casing wall to initiate the window milling process; - the hydraulic means by which the window milling drill bit is forced radially onto the casing wall to penetrate same in order to start the window milling process; - the longitudinal movement of the milling bit after radial penetration of the casing wall; - the specific shape of the crown of the window milling drill bit as shown in Fig 1; - comprises an attachment to an existing drilling motor.

Claims

1. A milling tool for milling a window(s) in a casing comprising a drill bit, means for driving the drill bit and means for positioning the drill bit in contact with a selected portion of the casing to be milled.

2. A milling tool as claimed in claim 1, wherein the drill bit has one or more cutting elements which element(s) is/are oriented substantially transversely with respect to the casing, in use.

3. A milling tool as claimed in claim 2, wherein the means for driving the drill bit drive the drill bit along an axis oriented substantially longitudinally with respect to the casing, in use.

4. A milling tool as claimed in any of claims 1 to 3, wherein the means for driving the drill bit comprises a drilling motor.

5. A milling tool as claimed in claim 4, wherein the drilling motor comprises a stator and a rotor rotatably mounted in said stator, the stator being provided with a rod recess and an exhaust port, the rotor being provided with a rotor channel and at least one channel for conducting motive fluid from the rotor channel to a chamber between the rotor and the stator, and the rod recess being provided with a rod which, in use, forms a seal between the stator and the rotor.

6. A milling tool as claimed in claim 5, wherein the rotor is provided with a seal for engagement with the stator.

7. A milling tool as claimed in claim 6, wherein the seal is made from a material selected from the group consisting of plastics material, polyethylethylketone, metal, copper alloys and stainless steel.

8. A milling tool as claimed in any of claims 5 to 7, wherein the rod is made from a material selected from the group consisting plastics, materials, polyethylethylketone, metal, copper alloys and stainless steel.

9. A milling tool as claimed in claimed in any of claims 5 to 8, wherein the stator is provided with two rod recesses which are disposed opposite one another, two exhaust ports which are disposed opposite one another, each of the rod recesses being provided with a respective rod, the rotor having two seals which are disposed opposite one another.

10. A milling tool as claimed in claimed in any preceding claim, wherein the means for driving the drill bit comprises two drilling motors arranged with their respective rotors connected together.

11. A milling tool as claimed in claim 10, wherein the drilling motors are connected in parallel.

12. A milling tool as claimed in claim 10, wherein the drilling motors are connected in series.

13. A milling tool as claimed in any of claims 10 to 12, wherein the drilling motors are arranged so that, in use, one drilling motor operates out of phase with the other.

14. A milling tool as claimed in claimed in any preceding claim, wherein the means for positioning comprises a hydraulically operated setting mechanism.

15. A milling tool as claimed in claim 14, wherein the means for positioning moveably position the drill bit in contact with a selected portion of the casing to be milled, in use, by means of the setting mechanism controllably pushing against the casing.

16. A milling tool as claimed in claim 14 or claim 15, wherein the means for positioning also include orientation means for controllably rotating the milling tool within the casing, in use.

17. A milling tool as claimed in claim 16, wherein the orientation means comprises an orientation tool.

18. A method of milling a window in a casing comprising the steps of: providing a milling tool comprising a drill bit, means for driving the drill bit and means for positioning the drill bit in contact with a selected portion of the casing to be milled; placing the milling tool within the casing; positioning the drill bit in contact with the selected portion; and driving the drill bit so as to form a window in the casing.

19. A method as claimed in claim 18, wherein the drill bit is positioned and driven so as to mill the casing in a substantially transverse direction with respect thereto.

20. A method as claimed in claim 18 or claim 19, wherein said method comprises the further step of continuing to drive the drill bit and moving the milling tool in a substantially longitudinally direction with respect to the casing thereby further forming the window by either pushing or pulling on the tool.

21. A method as claimed in any of claims 18 to 20, wherein the milling tool is conveyed within the casing by means of coiled tubing.

22. A milling tool for milling a window(s) in a casing substantially as hereinbefore described with reference to the accompanying drawings.

23. A method of milling a window in a casing substantially as hereinbefore described with reference to the accompanying drawings.