EP1340881A1

EP1340881A1 - Explosive window cutting apparatus and method

Info

Publication number: EP1340881A1
Application number: EP02075823A
Authority: EP
Inventors: Anthony Thomas Cole; Klisthenis Dimitriadis
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2002-03-01
Filing date: 2002-03-01
Publication date: 2003-09-03

Abstract

An improved method and apparatus are disclosed for initiating a side track from a cased wellbore by an explosive window cutting device in a one trip operation. The method involves inducing the explosive window cutting device (15) to cut a window in the well casing and subsequently locating a whipstock (12) in the wellbore adjacent to the window to guide a side track drilling device through the window, wherein the explosive window cutting device is located in a housing which is located underneath the whipstock, in which housing fragments of the well casing removed by magnets of the explosive window cutting device are stored.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method and apparatus for cutting a window in a casing of a cased well, and for subsequently drilling a sidetrack from the well by inserting a sidetrack drilling device into the window and actuating the drilling device to drill a sidetrack into the formation adjacent to the window.
Such a method and device are known from US patent No. 5,636,692. In the known device a whipstock is suspended from a window mill at the lower end of a drillstring and an explosive charge system is actuated to blast an opening into the well casing in the region between the whipstock and the window mill, whereupon the opening is reamed to the desired size of window by the milling device. A disadvantage of the known method is that the blast opening has an irregular shape and that the window subsequently cut by the milling device also has irregular contours which are difficult to seal of when a liner is inserted into the side track and needs to be sealingly secured inside the window to provide a sealed well branchpoint.
It is known from European patent No. 0846838 to cut a well-defined window into a well casing by means of one or more linear shaped explosive charges that are arranged in an endless pattern.
The charges are either arranged between a whipstock and a milling device from which the whipstock is suspended, such that the whipstock subsequently mills away the casing fragments cut away by the explosive charges, or the casing fragments are first removed from the wellbore by a magnet or harpoon carried by the window milling device, whereupon a whipstock and sidetrack drilling assembly is subsequently run into the wellbore to drill a sidetrack through the window cut into the well casing.
It is an object of the present invention to provide a method and apparatus for explosively cutting an accurately defined window and for subsequently drilling a sidetrack into the formation adjacent to the window in a single trip, without requiring the sidetrack drill to mill the casing fragments or requiring a cutting the window and removal of the casing fragments in a first run and insertion of the whipstock and sidetrack drilling device in a second run, which is a time consuming and expensive operation.

SUMMARY OF THE INVENTION

The apparatus for initiating a side track from a cased wellbore in accordance with the invention comprises an explosive window cutting device for cutting a window in the well casing and a whipstock for guiding a side track drilling device through the window, wherein the explosive window cutting device is located in a housing which is located underneath the whipstock, which housing is adapted to store fragments of the well casing removed by the explosive window cutting device.
The apparatus preferably comprises one or more ring shaped explosive charges which each surround one or more magnets for pulling the removed fragments of the well casing into the housing and the explosive charges and/or at least one of the magnets are mounted on a carrier body that is movably arranged in the housing.
The method according to the invention for initiating a side track from a cased wellbore comprises inducing an explosive window cutting device to cut a window in the well casing and subsequently locating a whipstock in the wellbore adjacent to the window to guide a side track drilling device through the window, wherein the explosive window cutting device is located in a housing which is located underneath the whipstock, in which housing fragments of the well casing removed by the explosive window cutting device are stored.
Preferably the explosive window cutting device and/or one or more magnets for pulling the removed casing fragments into the housing are mounted on a carrier body, which is movably arranged in the housing, which body presses the ring shaped explosive charges against the inner surface of the casing when the window is cut and which is retracted into the housing after the window has been cut to pull the removed fragments of the well casing into the housing.
Suitably, the explosive window cutting device and whipstock assembly is suspended from a drill string carrying a side track drill bit by means of a tool hanger which is mounted on top of the whipstock and which comprises a central opening which is wider than the outer diameter of a drill string but narrower than the outer diameter of a side track drill bit of the side track drilling device.
Preferably an assembly of expandable packers that are located above and below the housing is expanded when the explosive window-cutting device is actuated to isolate the wellbore in region of the housing from other parts of the wellbore during the explosion(s).
It is furthermore preferred that the assembly is equipped with axial and/or angular positioning sensors and that the window cutting device is positioned in a desired orientation in the wellbore by lowering the drill string to a predetermined depth into the wellbore and by subsequently rotating the drill string until the position sensors indicate that the window cutting device has a desired orientation for cutting the window and wherein after the window has been cut the drill string is lowered along a distance which corresponds to the distance between the centers of the whipstock and the housing whereupon the whipstock is locked within the casing such that the whipstock guides the side track drilling device into the window. In such case it is preferred that the whipstock is locked inside the casing by expanding the expandable packers.

DESCRIPTION OF THE DRAWING

The invention will be described in more detail and by way of example with reference to the accompanying drawing in which Fig. 1 provides a schematic longitudinal sectional view of an explosive window cutting and sidetrack drilling apparatus according to the invention.
Fig. 1 depicts a wellbore 1 in which a steel well casing 2 is secured to the surrounding formation 3 by means of an annular body of cement 4.
An apparatus 5 for explosively cutting a window 6 in the well casing 2 and for subsequently drilling a sidetrack 7 into the formation 3 adjacent to the window 6 is suspended in the wellbore 1 from a drillstring 8 which carries at its lower end a sidetrack drill bit 9.
The upper end 10 of the apparatus 8 has an opening 11 which is wider than the drill string 8 but narrower than the sidetrack drill bit 9 such that said upper end 10 forms a hanger for suspending the apparatus from the drill string 8 when the assembly is lowered into the well.
The apparatus 5 further comprises a whipstock 12, a housing 13 that is mounted below the whipstock 12 and a wireless orientation sensing and control device 14. The apparatus 5 also comprises an explosive window-cutting device 15 comprising one or more linear charges 16 and one or more magnets 17 that are mounted on a carrier arm 18. The arm 18 pushes the charges 17 against the casing 2 when the charges 17 are fired to cut one or more fragments from the casing 2 such that a well defined window 20A is cut in the casing, and which arm is retracted after cutting the window 20A to pull the casing fragments 20B into the housing 13 by means of the magnets 17.
Expandable packers 21, 22 are mounted above and below the housing 13 to seal off wellbore in the region of the explosive window cutter 15 when the linear charges 16 are fired.
After cutting the window 20A the packers 21,22 are retracted and the apparatus 5 is lowered into the wellbore 1 over a selected distance by further lowering the drillstring 8 into the wellbore 1 along a distance that corresponds to the distance between the center of the housing 13 and the center of the whipstock 12.
When the orientation sensing and control device 14 indicates that the sidetrack bit 9 is oriented adjacent to the window 20A the packers 21 and 22 are expanded again to secure the whipstock 12 inside the casing 2. Subsequently the drill bit 9 is actuated to drill the sidetrack 7 and the drill string 8 and bit 9 are gradually lowered though the opening 11 to drill the sidetrack 7.

Claims

An apparatus for initiating a side track from a cased wellbore, the apparatus comprising an explosive window cutting device for cutting a window in the well casing and a whipstock for guiding a side track drilling device through the window, wherein the explosive window cutting device is located in a housing which is located underneath the whipstock, which housing is adapted to store fragments of the well casing removed by the explosive window cutting device.
The apparatus of claim 1, wherein the housing comprises one or more magnets for pulling removed steel casing fragments into the housing.
The apparatus of claim 2, wherein the explosive device comprises one or more ring shaped explosive charges which each surround one or more magnets.
The apparatus of claim 3, wherein the explosive device and/or at least one of the magnets are mounted on a carrier body, which is movably arranged in the housing.
The apparatus of claim 1, wherein the apparatus comprises at its upper end a tool hanger comprising a central opening which is wider than the outer diameter of a drill string but narrower than the outer diameter of a side track drill bit of the side track drilling device.
The apparatus of claim 5, wherein expandable packers are located above and below the housing for isolating the wellbore in region of the housing from other parts of the wellbore when the explosive window-cutting device is actuated.
The apparatus of claim 1, wherein the apparatus is equipped with axial and/or angular positioning sensors and with means for orienting the window cutting device in a desired orientation in the wellbore and for subsequently lowering and orienting and locking the whipstock such that the whipstock guides the side track drilling device into the window.
A method for initiating a side track from a cased wellbore by inducing an explosive window cutting device to cut a window in the well casing and subsequently locating a whipstock in the wellbore adjacent to the window to guide a side track drilling device through the window, wherein the explosive window cutting device is located in a housing which is located underneath the whipstock, in which housing fragments of the well casing removed by the explosive window cutting device are stored.
The method of claim 8, wherein one or more magnets pull removed steel casing fragments into the housing.
The method of claim 9, wherein the explosive window-cutting device comprises a plurality of ring shaped explosive charges that are successively actuated to break adjacent fragments from the casing which fragments have an outer contour that forms the window.
The method of claim 10, wherein the explosive device and/or at least one of the magnets are mounted on a carrier body, which is movably arranged in the housing, which body presses the ring shaped explosive charges against the inner surface of the casing when the window is cut and which is retracted into the housing after the window has been cut to pull the removed fragments of the well casing into the housing.
The method of claim 8, wherein the explosive window cutting device and whipstock assembly is suspended from a drill string carrying a side track drill bit by means of a tool hanger which is mounted on top of the whipstock and which comprises a central opening that is wider than the outer diameter of a drill string but narrower than the outer diameter of a side track drill bit of the side track drilling device.
The method of claim 8, wherein expandable packers that are located above and below the housing are expanded when the explosive window cutting device is actuated to isolate the wellbore in region of the housing from other parts of the wellbore during the explosion(s).
The method of claim 12, wherein the assembly is equipped with axial and/or angular positioning sensors and the window cutting device is positioned in a desired orientation in the wellbore by lowering the drill string to a predetermined depth into the wellbore and by subsequently rotating the drill string until the position sensors indicate that the window cutting device has a desired orientation for cutting the window and wherein after the window has been cut the drill string is lowered along a distance which corresponds to the distance between the centers of the whipstock and the housing whereupon the whipstock is locked within the casing such that the whipstock guides the side track drilling device into the window.
The method of claim 13 and 14, wherein the whipstock is locked within the casing by expanding the expandable packers.