GB2593125A

GB2593125A - Method and apparatus

Info

Publication number: GB2593125A
Application number: GB1912211.8A
Authority: GB
Inventors: Docherty Euan
Original assignee: Fraserv Ltd
Current assignee: Fraserv Ltd
Priority date: 2019-08-26
Filing date: 2019-08-26
Publication date: 2021-09-22
Also published as: GB201912211D0

Abstract

A detection device 10 for detecting a departure path of an angled borehole relative to an existing lined wellbore and associated method. The device is adapted to form part of a cutting tool assembly and comprises a proximity sensor 4 for detecting the proximity of a tubular 13 in an existing wellbore and an inclination sensor 7 to detect inclination of the angled borehole relative to the existing wellbore. The proximity sensor may detect a magnetic field of said tubular using a magnetometer. The device may comprise a data storage means, central processing unit 6, power unit 2 and communication means. The device may have a non-magnetic mandrel body 3 that houses electric components. As an angled borehole (fig.6, 119) is cut relative to the existing borehole (fig.6, 11), the proximity of the tubular is detected using the proximity device located on a cutting tool assembly.

Description

METHOD and APPARATUS The present invention relates to a method and apparatus for detecting casing exit departure within an oil and gas well system, particularly, but not exclusively, for obtaining data and information on the departure point and path of a new borehole drilled from, and angled relative to, an existing wellbore.

Oil and gas wellbores are typically open holes or holes lined with metal tubulars, such as liners, casing or production tubing. Current downhole technology enables the drilling of multi-branch wells, in which one or more additional boreholes are drilled at an angle relative to a main wellbore. In order to create a new angled borehole, it is necessary to mill an exit in the existing metal tubular or casing lining the main wellbore, thereby allowing a window through which the drilling apparatus is run to create the angled borehole extending into an adjacent formation. Typically, the predetermined location and direction of the angled borehole is controlled with the use of a whipstock. The whipstock is a curved steel wedge having a face inclined at a predetermined angle to cause deviation of a milling and/or drilling assembly to create the new borehole angled relative to the main wellbore. Such a new borehole is commonly known within the oil and gas industry as a 'rat-hole' and is achieved using technology known as a 'whipstock casing exit system'.

These whipstock casing exit systems are routinely used globally to create rat-holes in oil and gas well systems.

Whipstock casing exit systems typically include a whipstock assembly for setting the direction of the rat-hole and a milling assembly for cutting the new rat-hole. Drill bits in a milling assembly have a tendency to take the path of least resistance when removing material such as metal tubulars, cement lining, and/or the formation itself This can lead to 'mill-walk', which is a deviation from the intended path of the rat-hole. Mill-walk can adversely affect the quality of the rat-hole resulting in problems such as: early exit from the main wellbore and a small window profile; crooked window profile, which may result in subsequent drilling assemblies being subject to adverse bending moments that can lead to damage or twist off; or tracking, where the milling assembly tracks the annulus of the existing wellbore. Thus, mill-walk is problematic and results in an ineffective rat-hole that must be remedied.

In a scenario where the new rat-hole has not departed from the existing wellbore path or failed to exit through the tubular or casing of the main wellbore as required, there are significant expense and time implications that may arise for subsequent drilling assemblies and operations. Therefore, a well operator must take corrective action to remedy the situation with a suitable drilling or milling assembly specifically designed to attain the correct departure angle. However, if an operator remains unaware of the issues encountered due to mill-walk or rat-hole tracking of the main wellbore, there is a high potential for damage with the associated time and financial cost, which may be as high as $100k-$500k per day or greater for deep water or extended reach drilling. Occasionally, subsequent operations following mill-walk have led to expensive measuring-whiledrilling (MWD) or logging-while-drilling (LWD) bottom hole assemblies (BHAs) becoming stuck across the casing exit and/or BHAs being lost in hole.

During a typical casing exit milling operation, the current indicator of a satisfactory rat-hole is the free passing occasionally with rotation, of the milling assembly from the whipstock kick off point to the bottom of the rat-hole. However, this free-passing simply confirms the milling assembly has successfully passed through the rat-hole on one or more occasions. It does not indicate if the rat-hole has followed the predetermined path or if the rat-hole has deviated and tracked the original wellbore.

According to a first aspect of the present invention, there is provided a method for detecting the departure path of an angled borehole relative to an existing wellbore lined with at least one tubular, the method comprising the steps of: providing a proximity detection device, wherein the proximity detection device is arranged to detect the proximity of the at least one tubular lining the existing wellbore; locating the proximity detection device on a cutting tool assembly, said cutting tool assembly adapted and arranged to cut out an angled borehole; cutting a borehole angled relative to the existing wellbore using said cutting tool assembly; and detecting the proximity of the at least one tubular using the proximity detection device located on the cutting tool assembly.

Thus, the method of the invention is advantageous, since it provides a means to detect whether the creation of a new angled borehole or rat-hole is following the predetermined path or if remedial action needs to be taken to rectify deviation from the anticipated departure point or path by the cutting tool assembly.

Optionally, the method includes providing a proximity detection device adapted to sense proximity of the at least one tubular.

Optionally, the method includes the step of detecting the magnetic field of the at least one tubular. Optionally, the method includes detecting the strength of the magnetic field of the at least one tubular to determine proximity of the tubular. Optionally, the proximity detection device measures at least one of: the direction, strength and/or relative change of the magnetic field as the cutting tool assembly cuts out the angled borehole. Optionally, the method includes the step of providing the proximity detection device with at least one proximity sensor. The proximity sensor may comprise a magnetometer.

Optionally, the method further includes the step of detecting inclination of the angled borehole. Optionally, the method comprises the step of detecting the path of the angled borehole created by the cutting tool.

Optionally, the proximity detection device further comprises an inclination device adapted to detect inclination of the cutting tool assembly relative to the existing wellbore.

Optionally, the method includes the step of providing the proximity detection device with at least one inclination sensor.

Optionally, the method includes the steps of cutting through the at least one tubular prior to cutting the angled borehole and detecting the path of travel of the cutting tool assembly through the at least one tubular using the proximity detection device.

The at least one tubular may be any tubular selected from the group comprising metal casing, liner, production tubing and the like. Optionally, the existing wellbore may be lined with at least two tubulars having different diameters. The at least two tubulars may be offset and thus not coaxial.

Optionally, the cutting tool assembly may comprise any kind of tool capable of cutting through the at least one tubular. Optionally, the cutting tool assembly comprises at least one drill bit or cutting tool. The cutting tool assembly may comprise a milling assembly including a cutting tool suitable for creating a hole in the at least one tubular and/or formation. The cutting tool assembly may comprise a drilling or milling assembly including at least one drill bit suitable for creating a hole in a tubular and/or formation.

Optionally, the method further includes the step of setting a whipstock in the at least one tubular to guide the cutting tool assembly in a predetermined location and orientation.

Optionally, the method includes detecting the proximity of the whipstock using the proximity detection device.

Optionally, the method may include the step of incorporating the proximity detection device as part of the cutting tool assembly.

Optionally, the method includes the step of embedding the proximity detection device within part of the cutting tool assembly. Thus, the proximity detection device may be accommodated within one or more chambers provided within the cutting tool assembly. The proximity detection device may be arranged to withstand temperatures and pressures experienced downhole. The chambers may be suitably sealed against well fluids.

Alternatively, the method may include the step of locating the proximity detection device within a subcomponent of a cutting tool assembly. Thus, the subcomponent may be arranged to interconnect with the cutting tool assembly. The method may comprise the step of incorporating the subcomponent containing the proximity detection device into the cutting tool assembly prior to cutting the angled borehole using said cutting tool assembly. Thus, the proximity detection device may be provided as a standalone sub forming part of the cutting tool assembly. The subcomponent may comprise a mandrel having a throughbore. The mandrel may comprise a non-magnetic material.

The method of the present invention is advantageous, since it provides confirmation of the path of the angled borehole or successful rat-hole departure with an independent device embedded within the cutting tool (or milling assembly) or as a standalone sub. The method provides a means to detect if the cutting tool assembly has departed the existing wellbore at the desired angle correctly while drilling the new rat-hole.

Optionally, the method includes the step of transmitting data from the proximity detection device to an operator. Optionally, the method includes the step of transmitting data from the proximity detection device to surface in real time. Alternatively, the method includes the step of transmitting data from the proximity detection device at predetermined time intervals.

Optionally, the method includes the step of electrically connecting the proximity detection device to at least one communication cable and sending data from the proximity detection device via the at least one communication cable to a different location. Optionally, the method includes the step of transmitting data from the proximity detection device to a different location using mud pulse telemetry or wired drill pipe.

Alternatively, or additionally, the method may include providing an electronic storage means forming part of the proximity detection device. Optionally, the method includes the step of storing data within, and retrieving stored data from, the electronic storage means.

Optionally, the method includes the step of storing data in the electronic storage means and transmitting the data to surface via communications cables or at predetermined intervals. Optionally, the method includes the step of retrieving the proximity detection device and downloading data from the electronic storage means. Thus, the data may be retrieved when the cutting tool assembly is pulled to surface.

Optionally, the method includes the step of measuring the proximity of the at least one tubular using the proximity detection device. The method may include continuously measuring the proximity of the at least one tubular using the proximity detection device. The method may include the step of measuring the proximity of the at least one tubular at predetermined time intervals.

Optionally, the method includes the step of interpreting data from the proximity detection device to determine the path of the angled bore hole. Optionally, the method includes the step of providing the proximity detection device with an electronics pack comprising a processing means. The processing means may comprise a central processing unit Optionally, the proximity detecting device may be provided with a micro-processing unit (MPU) to interpret data relating to proximity detection and time intervals to thereby calculate the path of the angled borehole.

Optionally, the method includes the step of calculating the path of the angled borehole using at least some of the following data obtained by the proximity detection device: proximity measurements; inclination measurements; and time. Optionally, the method includes interpreting data obtained by the proximity detection device regarding proximity of the tubular relative to time, to calculate the path of the angled borehole.

Optionally, the method includes the step of continuing normal operations where data is interpreted to show the cutting tool assembly is following the predetermined path for the angled borehole. Thus, the method may subsequently include the step of continuing to drill the angled borehole along the predetermined path.

Optionally, the method includes the step of taking remedial action when data is interpreted showing deviation from the predetermined path of the angled borehole.

Therefore, if the data shows the casing exit window is incorrectly positioned or the rat-hole has not followed the predetermined path, the operator discovers the problems in a timely manner and can plan another required casing exit. Such information is useful to the operator, who will save time and costs by rectifying the problems at the earliest opportunity.

According to a second aspect of the invention, there is provided a detection device for detecting a departure path of an angled borehole relative to an existing wellbore lined with at least one tubular, wherein the detection device is adapted to form part of a cutting tool assembly, and wherein the detection device comprises at least one proximity sensor for detecting proximity of the at least one tubular within an existing wellbore and at least one inclination sensor adapted to detect inclination of the angled borehole relative to the existing wellbore.

Optionally, the proximity sensor comprises a sensor for detecting magnetic field and wherein the sensor is arranged to detect an adjacent tubular within the existing wellbore.

Optionally, the proximity sensor comprises a magnetometer.

Optionally, the proximity sensor and the inclination sensor are formed as part of a single sensor unit. Optionally, the sensors form part of an integral sensor unit.

Optionally, the detection device comprises a data storage means electrically coupled to the sensors. Optionally the data storage means is arranged to record and store data from the sensors.

Optionally, the detection device comprises a processing means electrically connected to the sensors, wherein the processing means is adapted for processing data attained by the sensors. The processing means may comprise a central processing unit. The processing means may comprise a printed circuit board (PCB).

Optionally, the detection device comprises a power source for providing power for the electronic components.

Optionally the detection device comprises a communication means electrically connected to the sensors and arranged for transmitting data to a remote location. The remote location may be surface and/or a location out of the wellbore. Optionally, the communication means may transfer data in real time. The communication means may comprise mud pulse telemetry or wired drill pipe.

Optionally, the detection device is a proximity detection device arranged to measure the proximity of one or more metallic components.

Optionally, the detection device comprises a sub-component of a cutting tool assembly.

Optionally, the detection device comprises a body for housing the electronic components. The body may comprise a non-magnetic mandrel.

Optionally, the sub-component has end connectors arranged to interconnect with end connectors of a milling assembly. The end connectors may be pin and/or box connectors adapted to interconnect with a complementary end connector.

Optionally, the detection device is adapted to be embedded within a cutting tool assembly. Optionally, the detection device may be embedded within a cutting tool assembly in a location close to the cutting tool.

According to a third aspect of the invention, there is provided a cutting tool assembly comprising the detection device according to the second aspect of the invention.

Optionally, the cutting tool assembly comprises a milling or drilling assembly.

Any aspect, feature or embodiment of the invention described herein may be combined with any other aspect, feature or embodiment of the invention where appropriate.

Further features and advantages of the first, second and third aspects of the present invention will become apparent from the claims and the following description.

Embodiments of the present invention will now be described by way of example only, with reference to the following diagrams, in which:-Fig 1 is a sectional schematic view of a detection device in the form of a subcomponent of a cutting tool assembly; Fig. 2 is a sectional schematic view of a whipstock set in casing and a milling window of an angled borehole; Fig. 3 is a sectional schematic view of a milling assembly milling the angled borehole of Figure 2; Fig. 4 is a sectional schematic view of the milling assembly of Figures 2 and 3 advancing the angled borehole, which is tracking the main wellbore; Fig. 5 is a sectional schematic view of a whipstock set in casing and an alternative milling window of an angled borehole; Fig. 6 is a sectional schematic view of the milling assembly milling the angled borehole of Figure 5; Figs. 7a and 7b are sectional schematic views of the milling assembly advancing the angled borehole of Figures 5 and 6 along the correct predetermined path; Fig. 8 is a sectional schematic view of the milling assembly departing the main wellbore early before contact with a whipstock and milling an angled borehole; and Fig. 9 is a sectional schematic view of the milling assembly advancing the angled borehole of Figure 8 that prematurely departed the main wellbore; Fig. 10 is a table listing method steps for milling an angled borehole; and Fig. 11 is a table listing method steps for remedial action once the proximity detection device has confirmed that the angled borehole has not followed the predetermined path. 25 According to a first embodiment of the invention, a detection device is shown generally at 10 in Figure 1. The detection device 10 is designed as a subcomponent of a drill string or milling assembly and comprises a cylindrical non-magnetic mandrel 3 having a throughbore. Each end of the mandrel 3 has standard drill pipe connectors 1, 5 (of box or pin type) and an inner diameter tailored to match the configuration of the milling assembly in which it is to be used. A power unit 2 and a central processing unit 6 are embedded within sidewalls of the mandrel 3 and electrically connected to one another. An outer portion of the sidewall of the mandrel 3 is cut away to provide slots for accommodating sensors in the form of a magnetometer 4 and an inclination device 7. The magnetometer 4 is a miniaturised microelectromechanical system (MEMS) magnetometer which is used to detect magnetic field strength. The magnetometer 4 and inclination device 7, are each electrically connected to the power unit 2 and central processing unit 6.

The internal chambers and slots of the mandrel 3 are sealed against well and drilling fluids and the detection device 10 is designed to withstand the temperatures and pressures experienced in each particular downhole application.

According to other embodiments, alternative proximity and/or inclination sensors may be used. Several sensors 4, 7 may be used for redundancy or to improve accuracy of measurements.

For example, the magnetometer 4 can include any instrument that measures magnetism, such as the magnetism of a magnetic material, or the direction, strength and relative change of a magnetic field at a particular location. Vector magnetometers measure one or more components of the magnetic field electronically. Using three orthogonal magnetometers, both azimuth and dip (inclination) can be measured. The square root of the sum of the squares of the components allows the total magnetic field strength (also called total magnetic intensity TM!) to be calculated using Pythagoras's Theorem. Such data can provide useful information on the proximity of adjacent tubulars or casing 12, 13 lining a main wellbore 16 and the inclination of the detection device 10 within a cutting tool assembly. This data in interpreted to indicate the direction, location and inclination of the path of the angled borehole.

An alternative sensor for incorporation into the detection device 10 is a 10-axis miniaturised microelectromechanical system (MEMS) inertial measurement system (IMU).

One example of another sensor that may be used as part of the detection device 10 is the VectorNav VN-100. The VectorNav VN-100 is a compact solid state miniaturised microelectromechanical system (MEMS) based sensor module, which uses an on-board algorithm to calculate tilt and heading angles at a rate of 200 times a second. It uses an accelerometer to sense the combination of linear motion plus gravity. The VN-100 is advantageous compared with other digital inclinometers due to its use of 3-axis gyro to calculate changes in orientation at a fast rate. The MEMS based 3-axis gyro measures how fast an object is rotating in three-dimensional space and enables a better measurement of tilt in the presence of dynamic motion. The VN-100 incorporates different inertial sensors including a 3-axis accelerometer, 3-axis gyroscope, 3-axis magnetometer and a barometric pressure sensor. The VN-100 achieves high performance by filtering out common error sources such as sensitivity to supply voltage variations and temperature dependent hysteresis.

Alternatively, or additionally, the detection device 10 may include a heading reference system. Attitude Heading Reference Systems (AHRS) are a 3-axis inertial measurement system (IMU) combined with a 3-axis magnetic sensor and an on-board processor that creates a virtual 3-axis sensor capable of measuring heading (yaw), pitch and roll angles of an object moving in 3-dimensional space.

An advanced detection device 10 using one or more of the referenced sensors with associated processing capabilities is able to log the casing 12, 13 profile to interpret the path of the angled borehole with confidence. Thus, the detection device 10 enables mapping of the length and orientation of a casing exit profile relative to the main wellbore 16.

According to the present embodiment, a multilateral well system is to be constructed from the main wellbore 16 that is lined with two sets of non-concentric casing 12, 13 having different sizes. The multiple lateral additional branches are to be drilled from the main wellbore 16 to access new rock formations containing reservoirs of oil and gas. A well operator plans a casing exit operation to make a casing exit in the host casing 12, 13 at the predetermined location in order to create an angled borehole or rat-hole. The operation is achieved using a casing exit system comprising a whipstock assembly and a milling bottom hole assembly (BHA) containing the detection device 10, the make-up and operation of which is described in detail below. Data received from the detection device will give the well operator confirmation that the milling bottom hole assembly (BHA) has made full contact with the whipstock scoop and that rat-hole departure has been achieved in the predetermined location relative to the main wellbore 16. Alternatively, the data received will alert the operator to a rat-hole that deviates from the intended path and enable the operator to take timely remedial action to remedy incorrect casing exit departure.

The casing exit system contains a milling bottom hole assembly (BHA) 17 and a whipstock assembly. The milling BHA 17 contains the following components: an upper watermelon mill with a smooth outer diameter (OD), a flex joint, a lower watermelon mill and a starter mill. Each of the mills comprise cutting tools or drill bits for removal of material downhole. The whipstock assembly contains a whipstock 14 and an anchor device.

The upper watermelon mill ensures the inner diameter (ID) of the casing exit aperture is full gauge to accept the OD of subsequent drill and completion assemblies. The upper watermelon mill with smooth OD is usually run to the bottom of the casing exit aperture. The flex joint is designed to allow some flexibility of the milling BHA 17 between the upper and lower watermelon mills, but is not run in all systems. The lower watermelon mill with a rough OD ensures the ID of the casing exit aperture is full gauge to accept the OD of subsequent drill and completion assemblies and is typically run into the rat-hole.

The starter mill is designed to mill the casing exit in conjunction with the whipstock 14 and the starter mill transports the whipstock assembly to the setting depth via a transit or shear bolt. The whipstock 14 provides a fixed slope to push the starter mill and the watermelon mills into the casing. The anchor device rotationally and axially locks the whipstock 14 at the required depth within the host casing 12, 13 and it may also provide hydraulic isolation.

Prior to commencement of casing exit and rat-hole drilling operations, the milling BHA and whipstock BHA are made up and interconnected. The milling assembly 17 including the starter mill, the watermelon mills, flex joints and other tubulars are connected together using standard drill pipe connectors. Above the milling BHA 17, an orientation device is located. The orientation device may include a measuring-while-drilling (MWD) device or a universal borehole orientation (UBHO) device to allow correct orientation of the whipstock 14 scoop at setting depth. The detection device 10 is made up as a subcomponent of the milling assembly 17 and connected to adjacent components by means of the pin and/or box end connectors 1, 5 in a location close to a leading end of the milling assembly 17. The whipstock BHA incorporating the whipstock, an anchor, a packer and other components to permit disconnect or debris management is connected to the starter mill of the milling BHA 17 via a transit or shear bolt.

The casing exit system is deployed downhole through the main wellbore 16 and the host casing 12, 13. The whipstock and milling BHA 17 is run to the required setting depth within the inner casing 13 having a 5 foot, 5 inch (1.65m) diameter. The inner casing 13 is located within an outer casing 12 having a 7 foot (2.13m) diameter and the outer casing 12 is non-concentric and situated within a borehole 11. The present operation to exit the casing 12, 13 requires the milling assembly 17 to cut through two off-centre casing 12, 13 sizes making rat-hole departure even more difficult to predict or attain with confidence.

A description of the various method steps for milling a casing exit and creating the rat-hole are outlined in Figure 10. The whipstock 14 is run to the correct setting depth within the inner casing 13, which is determined by the MWD/UBHO above the milling BHA 17.

The whipstock 14 is oriented and an anchor or packer is set in the correct location such that an inclined face of the whipstock 14 sets the correct angle for the predetermined path of the rat-hole. The starter mill of the milling assembly 17 is disengaged from the whipstock 14 to separate the milling BHA 17 and the whipstock BHA. The milling BHA 17 follows an angled path set by the angled face of the whipstock 14. The milling assembly 17 is operated to mill a casing exit window 15, by cutting out a portion of the casing 12, 13 as shown in Figure 2. Continued operation of the milling assembly 17 cuts an angled rat-hole 19 in the formation shown in section in Figure 3 and the casing exit window 15 or aperture is cleaned up using the watermelon mills.

According to the present embodiment, throughout the milling operation, the magnetometer 4 of the detection device 10 is measuring magnetic field data allowing calculation of the proximity of the metal whipstock 14 face, and the casing 12, 13 lining the wellbore 16. In addition, the inclination device 7 is measuring inclination of the milling assembly 17 to supplement data obtained by the magnetometer 4. The magnetometer 4 and inclination device 7 are powered by the power unit 2, and the data received from the sensors 4, 7 is electrically communicated to the central processing unit 6 where the data is processed and stored.

The detection device 10 in the present embodiment is electrically connected to surface via communications cables in the form of mud pulse telemetry or wired drill pipe and the detection device 10 sends a signal containing the electronic data to surface. The data may be continuously communicated 'live' or in real time throughout the milling operation. In this scenario, 'live' data received during the milling operation enables an accurate plot of casing exit departure once the milling operation commences. Alternatively, the data may be sent in packets or bytes of information at certain time intervals. At surface, the data is interpreted by the operator to plot the angle of inclination, the location of the casing exit window 15, the path of the rat-hole 19 and the proximity to the surrounding metal components such as the whipstock 14 and the casing 12, 13.

According to another embodiment, no real-time or 'live' signal is transmitted to surface during the milling operations. Instead, the detection device 10 gathers data from the sensors 4, 7, which is recorded and stored by the central processing unit 6 in the electronics pack. The information and stored data is retrieved and downloaded when the milling BHA 17 is pulled out of the hole (POOH). The downloaded data is then analysed at surface.

According to either embodiment, the data is interpreted to determine whether or not the casing exit window 15 is correctly positioned and the rat-hole is successfully following the predetermined path.

The embodiment depicted by Figures 2 to 4, shows the detection device 10 has identified that the rat-hole 19 has tracked the existing wellbore 16 path.

As shown in Figure 3, the rat-hole 19 is tracking the existing borehole 11 such that the desired departure angle has not been achieved. Factors which may adversely affect the quality of the casing exit window 15 or result in rat-hole tracking of the main wellbore 16 are: washout portions of the original borehole 11; formations with a low or very high compressive strength; bad or no cement in the annulus between the outer casing 12 and the borehole 11; damaged host casing 12, 13; crooked wellbore 16 path; and adverse bending moments between the assemblies and downhole equipment.

Milling of the rat-hole 19 continues as the milling assembly 17 is further advanced. As shown in Figure 4, the magnetometer 4 within the detection device 10 measures the magnetic field strength of the casing 12, 13, which may be interpreted to confirm the actual location of the casing 12, 13 relative to the milling assembly 17 in which the detection device 10 is located, as depicted schematically by reference numeral 18. The inclination device 7 within the detection device 10 provides additional data confirming the actual inclination of the angled path of the rat-hole 19 created by the milling assembly 17.

In this case, data from the detection device 10 shows the rat-hole 19 has tracked the main wellbore 16. Since the operator has the benefit of this data at surface, the operator must take corrective action taken prior to running the drilling assembly in hole. The drilling assembly includes measuring-while drilling (MWD) or logging-while-drilling (LWD) devices, which may include nuclear material. Thus, it is important to avoid these MWD/LWD devices being lost or stuck in hole, which is an increased risk where the rat-hole 19 has tracked the wellbore 16. In addition, running these MWD/LWD devices into a rat-hole that has tracked an existing wellbore 16, will adversely affect the data obtained by the MWD/LWD devices. Thus, the present invention is advantageous since the early information on rat-hole 19 tracking of the existing wellbore 16 enables an operator to save time and money by immediately taking corrective action and eliminates the problems of damage to drilling assemblies caused by running the drilling assemblies into rat-holes 19 that track the main wellbore 16.

The table of Figure 11, shows the next steps taken by an operator where rat-hole 19 tracking of the main wellbore 16 has been identified. A suitable BHA is run in hole and another milling operation is undertaken to attain the correct rat-hole departure path. The BHA is pulled from the hole and if correct rat-hole departure is confirmed, the drilling assembly is run in hole to complete the operation. The table shows that in this scaenario, an additional 24 hours is typically required to address and obtain accurate rat-hole 19 departure.

The present method and apparatus saves time and costs in this scenario. If an operator remained ignorant of the rat-hole 19 tracking the existing wellbore 16 path, subsequent drilling operations would be adversely affected and additional time, typically, an extra 48 hours, would be required to remedy the situation. The additional time includes extra rig time and additional service costs. Furthermore, the MWD/LWD BHA may be damaged or lost in hole, which would add significant time and cost to the drilling programme.

A number of different embodiments of the invention are described. In order to minimise repetition, similar features of the different embodiments are numbered with a common two-digit reference numeral and are differentiated by a third digit placed before the two common digits. Such features are structured similarly, operate similarly, and/or have similar functions unless otherwise indicated.

Figures 5 to 7b, show an example of an angled rat-hole 119 drilled at the correct angle. The equipment and operational procedure is similar to the example previously described and is shown in the table of Figure 10. As shown in the table of Figure 10, the correct orientation of the casing exit window 115 and rat-hole 119 that is milled accurately following the predetermined path without any operational issues is achieved within 41 hours.

During the milling phase of the operation, the detection device 10 logs proximity of the whipstock using the magnetometer 4 and inclination using the inclination device 7.

Throughout the milling operation, the detection device 10 within the milling assembly 17 continues to log the inclination using the inclination device 7. Thus, the angle x in Figure 7a can be determined. The location of the existing host casing 12, 13 is also determined by identifying magnetic field strength depicted by reference numeral 118 relative to the milling assembly 17 using the magnetometer 4 as shown in Figure 7b. This data is interpreted as confirmation of correct casing exit aperture profile and rat-hole 119 departure following the predetermined path.

Data received and interpreted from the detection device 10 informs the operator that the milling operation has been successful. This knowledge allows the operator to progress with drilling the rat-hole 119 and continuing subsequent drilling operations with confidence. The milling assembly 17 is pulled out of the main wellbore 16 and a drilling BHA is run in hole (RIH). The expensive drilling and logging tools are RIH with the drilling BHA with minimal to zero risk of damage or loss due to the successful departure of the rat-hole 119.

A further embodiment is shown in Figures 8 and 9. Again the assembly, equipment set-up and operational steps are similar to those previously described with reference to earlier embodiments. Figures 8 and 9 show an example of early casing exit departure and consequently a deviation from the predetermined path of the rat-hole 219.

One factor that can influence early casing exit departure is the weight applied to the milling assembly 17 to allow the blades of the cutting tool to remove steel from the casing 12, 13. The applied weight will vary depending on the location of the milling assembly 17, the type of steel casing 12, 13, the strength of the formation, the presence or type of cement in the annulus and several other operational factors. Inappropriate weighting of the milling assembly 17 or applying weight to the milling BHA 17 at the wrong time can lead to early casing 12, 13 exit and premature departure of the rat-hole 219.

During the milling phase, the starter mill has departed prior to contact with the inclined face of the whipstock 14. Thus, the milling BHA 17 has not followed the predetermined path for the angled rat-hole 219. Data gathered by the inclination device 7 and the magnetometer 4 of the detection device 10, confirm the location of the whipstock 14 and casing 12, 13 within the existing wellbore 16. Such data is interpreted to reveal an early departure and casing 12, 13 exit. The extent of actual dog leg severity sourced by the detection device 10 at the casing exit provides essential torque and drag information especially when used in extended reach drilling (ERD) wells, deepwater developments or offshore drilling.

Informed by the data from the detection device 10, the operator must take remedial action. Prompt intervention in such a scenario is desirable to avoid any of the following: adverse bending moments in the milling BHA 17 causing parts of the assembly to twist-off requiring extensive fishing operations to recover drill pipe and BHA; key-seat of the drill pipe resulting in mechanical sticking of the BHA; increased torque on the drill assembly caused by a tortuous path resulting from the dog-leg; and limited ability to pass and set new casing in the angled rat-hole 219.

Since departure from the intended rat-hole 219 path has been identified, an additional 24 hours are required to address and obtain rat-hole departure, the operational steps for which are outlined in the table of Figure 11. The timely intervention of the well operator resulting from the data available as a result of the detection device 10 means that approximately 24 additional hours of rig, tool and man costs are saved.

According to alternative embodiments, the detection device 10 including the sensors 4, 7, the power unit 2 and the central processing unit 6, is embedded within or provided as part of the milling assembly 17, such as within the body of the starter mill or watermelon mill.

According to another embodiment, a more basic version of the detection device 10 contains a magnetometer, a power source and printed circuit board (PCB).

According to some embodiments, unprocessed or 'raw' data may be transmitted to surface and analysis and interpretation of the signal by appropriate algorithms will occur at surface. Alternatively, the data may be processed or partially processed for appropriate transmission and/or download by the central processing unit 6 of the detection device 10.

Although particular embodiments of the invention have been disclosed herein in detail, this is by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the statements of invention and/or the appended claims. Relative terms such as "above", "below", "outer" or "inner" are illustrative and are not universally representative of the components which they describe.

It is contemplated by the inventor that various substitutions, alterations, and modifications may be made to the invention without departing from the scope of the invention as defined by the statements of invention and/or the claims. Examples of these include the following: The order of the method steps may be changed so that the method steps may occur in any appropriate order.

Different operations at a variety of well sites, including but not limited to subsea drilling extended reach drilling, deepwater drilling, vertical wells, multilateral wells and the like may require additional steps or equipment in order to achieve new rat-hole 119 formation, but in each case the method of the invention including provision of a detection device 10 associated with the milling/drilling assembly 17 is provided to confirm accuracy of casing exit departure and/or rat-hole 119 path.

The casing diameter in which the whipstock 14 may be set can range from 30 foot (9.15m) in diameter for surface casing to approximately 2.6 foot (0.76m) in diameter for production tubing. The whipstock 14 can be set in different locations from the vertical (at 0 degrees from vertical) to horizontal (at 90 degrees from the vertical) or at inclinations between 90 and 180 degrees from the vertical. Setting depth may be from just below ground or the sea bed (for offshore wellb ores 16) to many thousands of metres below the surface.

Rat-holes 119 may be drilled for a variety of purposes including accessing new formations, different parts of existing formations, downhole tool storage or any other reason.

Examples in the specification relate to oil and gas wells, but the method and apparatus of the invention is equally applicable to all types of subterranean well or conduits.

Claims

CLAIMS1. A method for detecting the departure path of an angled borehole, relative to an existing wellbore lined with at least one tubular, the method comprising the steps of: providing a proximity detection device, wherein the proximity detection device is arranged to detect the proximity of the at least one tubular lining the existing wellbore; locating the proximity detection device on a cutting tool assembly, said cutting tool assembly adapted and arranged to cut out an angled borehole; cutting a borehole angled relative to the existing wellbore using said cutting tool assembly; and detecting the proximity of the at least one tubular using the proximity detection device located on the cutting tool assembly.
2. A method according to claim 1, including the steps of: providing the proximity detection device with at least one sensor; and sensing the proximity of the at least one tubular using the proximity detection device
3. A method according to claim 1 or claim 2, including the step of detecting the strength of the magnetic field of the at least one tubular using the proximity detection device to determine proximity of the tubular relative to the proximity detection device and cutting tool assembly.
4. A method according to any preceding claim, including the step of measuring at least one of: direction, strength and/or relative change of the magnetic field, using the proximity detection device as the cuffing tool assembly cuts out the angled borehole
5. A method according to any preceding claim, including the step of providing the proximity detection device with at least one proximity sensor comprising a 30 magnetometer.
6. A method according to any preceding claim, including the step of detecting the path of the angled borehole created by the cutting tool using the proximity detection device.
7. A method according to any preceding claim, including the steps of: providing the proximity detection device with at least one inclination sensor adapted to detect inclination of the cutting tool assembly relative to the existing wellbore; and detecting inclination of the angled borehole using the proximity detection device.
8. A method according to any preceding claim, including the steps of: cutting through the at least one tubular prior to cutting the angled borehole; and detecting the path of travel of the cutting tool assembly using the proximity detection device.
9. A method according to any preceding claim, including the steps of: setting a whipstock in the at least one tubular to guide the cutting tool assembly in a predetermined location and orientation; and detecting the proximity of the whipstock using the proximity detection device.
10. A method according to any preceding claim, including the step of incorporating the proximity detection device as part of the cutting tool assembly.
11. A method according to any preceding claim, including the step of embedding the proximity detection device within part of the cutting tool assembly by providing one or more chambers within the cutting tool assembly arranged to accommodate the proximity detection device.
12. A method according to any one of claims 1 to 10, including the steps of: locating the proximity detection device within a subcomponent of a cutting tool assembly; and interconnecting the subcomponent and the cutting tool assembly.
13. A method according to claim 12, including the step of incorporating the subcomponent containing the proximity detection device into the cutting tool assembly prior to cutting the angled borehole using said cutting tool assembly.
14. A method according to any preceding claim, including the step of transmitting data from the proximity detection device to surface in real time.
15. A method according to any preceding claim, including the steps of: electrically connecting the proximity detection device to at least one communication cable; and transmitting data from the proximity detection device via the at least one communication cable to a different location.
16. A method according to any preceding claim, including providing an electronic storage means forming part of the proximity detection device and storing data within, and retrieving stored data from, the electronic storage means.
17. A method according to any one of claims 1 to 13 or claim 16, including the steps of: retrieving the proximity detection device from downhole; and downloading data from the electronic storage means at a location remote from the wellbore.
18. A method according to any preceding claim, including the step of interpreting data from the proximity detection device and thereby determining the path of the angled borehole.
19. A method according to any preceding claim, including the steps of: powering electronic components of the proximity detection device using a 30 downhole power source; and providing the proximity detection device with an electronics pack comprising a processing means.
20. A method according to any preceding claim, including the step of calculating the path of the angled borehole using at least some of the following data obtained by the proximity detection device: proximity measurements; inclination measurements; and 5 time.
21. A method according to any preceding claim, including the step of continuing normal operations where data is interpreted to show the cutting tool assembly is following the predetermined path for the angled borehole.
22. A method according to any preceding claim, including the step of taking remedial action where data is interpreted showing deviation from the predetermined path for the angled borehole.
23. A detection device for detecting a departure path of an angled borehole relative to an existing wellbore lined with at least one tubular, wherein the detection device is adapted to form part of a cutting tool assembly, and wherein the detection device comprises at least one proximity sensor for detecting proximity of the at least one tubular within an existing wellbore, and at least one inclination sensor adapted to detect inclination of the angled borehole relative to the existing wellbore.
24. A detection device according to claim 23, wherein the proximity sensor comprises a sensor for detecting magnetic field and is arranged to detect an adjacent tubular within the existing wellbore.
25. A detection device according to claim 23 or claim 24, wherein the proximity sensor comprises a magnetometer.
26. A detection device according to any one of claims 23 to 25, wherein the detection device comprises a data storage means electrically coupled to the sensors, wherein the data storage means is arranged to record and store data acquired by the sensors.
27. A detection device according to any one of claims 23 to 26, wherein the detection device comprises a processing means electrically connected to the sensors, wherein the processing means is adapted to process data acquired by the sensors.
28. A detection device according to any one of claims 23 to 27, wherein the detection device comprises a power source for providing power for the electronic components.
29. A detection device according to any one of claims 23 to 28, wherein the detection device comprises a communication means electrically connected the sensors and arranged for transmitting data acquired by the sensors to a different location.
30. A detection device according to any one of claims 23 to 29, wherein the detection device comprises a sub-component of a cutting tool assembly and wherein the subcomponent has end connectors arranged to interconnect with end connectors of a cutting tool assembly.
31. A detection device according to any one of claims 23 to 30, wherein the detection device has a body for housing the electronic components and the body comprises a nonmagnetic mandrel.
32. A detection device according to any one of claims 23 to 29, wherein the detection device is embedded within a cutting tool assembly.
33. A cutting tool assembly comprising the detection device according to any one of claims 23 to 32.