A method of determining the position of a downhole tool in a borehole

Abstract

The invention relates to a method and a system of determining the position of a downhole tool in a borehole, comprising introducing a downhole tool into the borehole, the downhole tool comprising an actuating tool and a downhole measurement device, receiving downhole data representing the borehole, where the downhole data include at least a first downhole landmark position representing a location of a landmark in the borehole, receiving a first signal from a downhole measurement device, the first signal representing a downhole landmark of a borehole and a measured position of the downhole landmark, comparing the first signal to the first landmark position of the downhole data and generating a first correction value, generating a first corrected depth value by correcting the first signal with the first correction value, and transmitting a first actuating signal to actuate the actuatable tool in a downhole position based on the first corrected depth value. The invention also relates to a system for performing the method.

Description

[0001] The present invention relates to a method of determining the position of a downhole tool in a borehole, comprising introducing a downhole tool into the borehole, the downhole tool comprising an actuating tool and a downhole measurement device.

[0002] The term "borehole" may be used to collectively refer to any of the various types of holes that may be drilled into a ground surface. Boreholes are created by a drilling process generally performed by a drilling rig, where the borehole may be completed by introducing a casing that is a plurality of well tubulars introduced from the surface, where each well tubular is connected to the next well tubular via a threaded connection, and where the threaded connection is often referred to as a casing collar.

[0003] When the borehole is completed, and during the introduction of the casing into the borehole, a casing tally is compiled, where the casing tally includes data representing the casing and / or the borehole, and where the casing tally may be seen as a list of landmarks, such as casing collars, valves and other parts of the casing, including information on the depth at which each of the landmarks is positioned.

[0004] When a downhole operation is to be performed at a predefined depth in the borehole, it may be seen as important to know the correct depth of the intervention tool before performing the downhole operation in order to ensure that the downhole operation is performed at the correct position. A downhole operation is often performed using a wireline downhole tool, where the downhole tool is introduced into the borehole, and where the position of the downhole tool is estimated before performing the operation. It has been shown that the position estimation of the downhole tool is often flawed, where numerous factors may cause an incorrect estimate of the position of the downhole tool. Thus, there is a need to improve the estimate of the position of the downhole tool to ensure that the downhole operation is performed at the correct position.

[0005] In accordance with the invention, there is provided a method of determining the position of a downhole tool in a borehole, comprising: introducing a downhole tool into the borehole, the downhole tool comprising an actuating tool and a downhole measurement device, receiving downhole data representing the borehole, where the downhole data include at least a first downhole landmark position representing a location of a landmark in the borehole, receiving a first signal from a downhole measurement device, the first signal representing a downhole landmark of a borehole and a measured position of the downhole landmark, comparing the first signal to the first landmark position of the downhole data and generating a first correction value, generating a first corrected depth value by correcting the first signal with the first correction value, and transmitting a first actuating signal to actuate the actuatable tool in a downhole position based on the first corrected depth value.

[0006] The present method allows the downhole tool to be deployed in a correct position, where the known position of the landmark is utilised to generate the correct depth of the downhole tool prior to actuating the actuatable tool. In an example where the actuatable tool is a casing cutter, it is ensured that the downhole tool is in the correct position, and that the casing is cut in the desired position, where the errors related to the positioning of the downhole tool are corrected prior to cutting of the casing.

[0007] The downhole data representing the borehole may be in the form of a list, such as a casing tally, where the casing tally includes details of the tubulars that have been prepared for running. In the casing tally, each tubing joint may be numbered, and the corresponding length of the tubulars have been introduced into the list. The casing tally may further comprise a list of the positions of landmarks in the borehole, such as valves, or other types of landmarks that may be identified using a downhole measurement tool.

[0008] If the actuatable tool is to be used to perform a downhole operation at a specific depth, the downhole tool may be deployed into the borehole, and when the downhole tool passes a predetermined downhole landmark, the first signal representing the downhole landmark may be utilised to compare the measured position of the landmark with the first downhole landmark position which was defined in a casing tally and / or a list. If there is a difference between the measured position of the first landmark and the position defined in the casing tally, the actual position of the downhole tool may be corrected prior to the transmission of an actuating signal to actuate the actuatable tool.

[0009] Thus, the casing tally may be utilised to ensure that the downhole tool is in the correct downhole position when the downhole operation is to be performed. The correct position reduces the risk that the downhole operation is performed in a wrong position. Furthermore, by utilising this method, the position of the downhole tool may be corrected in any position of the downhole tool, as the landmarks in the casing, such as casing collars, are present at intervals in the full length of the casing.

[0010] In one or more exemplary embodiments, the downhole measurement tool may be part of the downhole tool, where the downhole measurement tool generates a first signal which may be measurements that are performed while the downhole tool is being submerged into the borehole. The first signal may be monitored continuously by a computing device, where the first signal may be continuously used to verify the real-time position of the downhole tool while the tool is being submerged.

[0011] In one or more exemplary embodiments, the first signal comprises a first landmark signature. The downhole measurement device may perform measurements continuously while the downhole tool is being submerged into the borehole, where the downhole measurement tool may pass all the landmarks that are present above the depth, which the downhole tool is deployed to. The landmarks may be different types of landmarks, e.g. a casing collar, a valve, a casing tubular or any type of landmark that is present in a borehole. When the measurement tool passes a landmark, such as a casing collar, the measurement tool produces a first signal, where the first signal may represent a measurement of the casing collar. The measurement of the landmark, such as a casing collar, may be a landmark signature, where the magnitude and / or the amplitude of the signal may disclose the landmark signature.

[0012] In one or more exemplary embodiments, the downhole measurement device is a magnetic measurement device. The magnetic measurement device may comprise one or more magnets to generate one or more magnetic fields and one or more magnetic sensors to detect changes in the magnitude and / or direction of the magnetic field generated by the magnet. Such a downhole measurement device is disclosed in e.g. WO 2011 / 051429.

[0013] In one or more exemplary embodiments, the downhole measurement device comprises two or more magnetic measurement devices. The magnetic measurement device may comprise two or more magnets to generate one or more magnetic fields and two or more magnetic sensors to detect changes in the magnitude and / or direction of the magnetic field generated by the magnets. Such a downhole measurement device is disclosed in e.g. WO 2011 / 051429. Each magnet may have a dedicated magnetic sensor, where one sensor measures the changes in one magnetic field from one magnet.

[0014] In one or more exemplary embodiments, the first signal comprises two or more measurement channel signals. The first signal may comprise a plurality of signals from a plurality of sensors, where each sensor produces an electric signal. Each of the electric signals may represent one sensor, where the first signal may comprise electric signals from a plurality of sensors. Each of the sensors may be offset in a longitudinal direction along the length of the downhole tool, such that the first signal may comprise a plurality of downhole measurements that measure the signal from different positions along the length of the downhole tool.

[0015] In one or more exemplary embodiments, the downhole landmark in a borehole is a casing collar. A casing collar is a joint that connects one well tubular to another well tubular, where the connected well tubulars may define a casing of a borehole. When a measurement device, such as a magnetic measurement device, comes into the vicinity of a casing collar, the electric signal of the sensor changes, and the measurement signal may have a form that may be recognisable as a casing collar. The computing device may be capable of analysing the electric signal over a predefined amount of time, where the computing device may use a form of pattern recognition to identify a casing collar. The electric signal of a casing collar may be different from the electric signal of a measurement of a downhole valve, where the computing device may be capable of differentiating between a downhole valve and a casing collar based on the magnitude of the signal over a given period of time.

[0016] In one or more exemplary embodiments, the downhole data and / or the first signal are received by a computing device at the surface, and / or the comparing, generating and / or transmitting steps are performed by a computing device at the surface. The downhole tool may be connected to the surface through a data connection via the wireline in the form of electric communication, optical communication, or other forms of suitable data communication protocols, where the electric signal of the downhole measurement device is transmitted from the submerged downhole tool to the surface.

[0017] In one or more exemplary embodiments, the downhole data is in the form of a list comprising details of well tubulars and / or casings that have been introduced into the borehole. The list may be in the form of a casing tally, a completion tally, or any form of list which may be seen as downhole data representing the borehole. The list includes data representing the casing and / or the borehole, where the list may be seen as a list of landmarks, such as casing collars, valves and other parts of the casing, and providing information on the depth at which each of the landmarks is positioned. The list may be compiled during the completion of the borehole or may be in the form of measurements or information introduced after the completion of the borehole.

[0018] In one or more exemplary embodiments, the comparison comprises generating a first data window based on the downhole data for providing an acceptable position of a measured downhole landmark from the first signal. The data window may be provided with information from downhole data representing the borehole, where the data window may be formed from a start depth to a stop depth, and where the data window is positioned at a depth where the downhole data represents a downhole landmark. The data window may start at a predefined downhole location prior to the landmark and end at a downhole location after the landmark. In case the landmark is a casing collar, the start position may e.g. be a predefined position of a well tubular prior to the casing collar, and the stop position may be a predefined position of a well tubular after the casing collar.

[0019] In one or more exemplary embodiments, the comparison comprises analysing the data of the first signal within the first data window. Thus, when the downhole measurement device enters the data window, the computing device may be utilised to analyse the signal within the data window, while discarding the data outside the data window. Thus, the data window allows the downhole tool to reduce the computing power needed to analyse data, as the comparison may only be made inside the data window in order to identify the downhole landmark. Thus, downhole landmarks that are outside the data window will not be considered.

[0020] In one or more embodiments of the present disclosure, the comparison and / or the generation of a first corrected depth value may be formed at a plurality of landmark positions during the deployment of the downhole tool inside the borehole. Thus, it may be possible to provide a first corrected depth value for each landmark which passes the downhole measurement device in order to continuously correct the position of the downhole tool relative to the downhole data representing the borehole.

[0021] In one or more exemplary embodiments, the standard deviation and / or variance of the first signal is utilised to identify a measured downhole landmark candidate. The standard deviation and / or variance of the first signal may indicate a position at which the downhole measurement device passes a downhole landmark, where the first signal may change significantly when the measurement device is adjacent to the downhole landmark. As an example, where the downhole landmark is a casing collar, the first signal may be stable when passing a central part of a well tubular of the casing, where the signal may change significantly when the measurement device comes closer to a casing collar. The amplitude of the signal may increase or decrease significantly, where the variance or standard deviation of the signal over a predefined time may indicate the presence of a landmark.

[0022] In one or more exemplary embodiments, the comparison defines a detection probability of a measured downhole landmark and / or identifies a measured downhole landmark when the detection probability meets a threshold. Thus, the comparison calculates a detection probability of a downhole landmark, where the detection probability may be seen as a certainty whether the downhole measurement device has detected a landmark. The threshold may be based on the variance of the first signal and / or the variance of the electric signal comprised in the first signal. When the detection probability meets the predefined threshold, the comparison may mark that the measured signal may be identified as a measured downhole landmark.

[0023] In one or more exemplary embodiments, the method further comprises moving the downhole tool in accordance with the corrected depth value. When the corrected depth value has been generated, the downhole tool may be moved in accordance with the corrected depth value to a position where the tool is to be actuated. By actuating the tool in accordance with the corrected depth value, it is possible to improve the precision of the downhole operation, where the movement of the downhole tool ensures that the actuatable tool is in its correct position when used.

[0024] The present disclosure may further comprise a system for performing the method in accordance with the present disclosure.Brief description of the drawings

[0025] The following is an explanation of exemplary embodiments with reference to the drawings in which: Fig. 1 is a process diagram for the method in accordance with the present disclosure, Fig. 2 is a schematic diagram of a downhole tool being deployed, and Fig. 3 is a process diagram for correcting the depth of the downhole tool. Detailed description

[0026] Various exemplary embodiments and details are described below, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practised in any other embodiments even if not so illustrated, or if not so explicitly described.

[0027] Fig. 1 discloses a method of determining 1 the position of a downhole tool in a borehole, comprising introducing 3 a downhole tool into a borehole, the downhole tool comprising an actuating tool and a downhole measurement device receiving 5 downhole data representing a borehole, where the downhole data includes at least a first downhole landmark position representing a location of a landmark in the borehole, receiving a first signal from a downhole measurement device 7, the first signal representing a downhole landmark of a borehole and a measured position of the downhole landmark, comparing 9 the first signal to the first landmark position of the downhole data and generating 11 a first correction value, generating 13 a first corrected depth value by correcting the first signal with the first correction value, and transmitting a first actuating signal to actuate the actuatable tool in a downhole position based on a first corrected depth value 15.

[0028] Fig. 2 shows a schematic diagram of a downhole tool 15 being deployed in a downhole position 17 and a surface controlling device 19 which is positioned on a surface 20 and connected to the downhole tool 15 via a communication pathway 21. The surface controlling device 19 comprises a computing device 23 which receives data from the downhole tool 15 via the communication pathway 21 and receives data from a completion tally 25 (casing tally) which comprises the collar positions of a downhole casing 27 of a borehole 28 in which the downhole tool 15 is deployed. The downhole tool 15 may comprise a downhole computing device 29 that may communicate with the surface controlling device 19 via a communication pathway 33, and where the downhole computing device 29 communicates with a downhole measurement device 31, where measurement data 35 are transmitted to the downhole computing device 29. The downhole computing device 29 may further communicate 37 with an actuatable downhole tool 39, where the downhole computing device 29 may be utilised to actuate the actuatable downhole tool 39.

[0029] The downhole measurement device 31 may be provided with a plurality of magnetic sensors, where the output of the downhole measurement device 31 may be as follows: the raw signal of all sensors, the buffer variance of each sensor, the velocity of the measurement device and the accumulated depth of the measurement device.

[0030] The raw signal of all the sensors may be in 12-bit values, where the sampling rate is 16 kHz, and where the data may be downsampled to 128 samples / second downhole, and the data are sent in packages to the surface. Each sensor may have a buffer size of 512 datapoints, where the buffer size represents approximately four seconds of data, and where the variance of the signal may be calculated downhole. The sampling rate, the downsampling and the buffer sizes of the raw signal may be adjusted for a specific application, where the sampling rate may be between 100 HZ and 64 kHz, the signal may be downsampled to between 64 samples / second and 512 samples / second, and the buffer size may vary depending on the size of the data from 128 datapoints to 2048 datapoints. The variation of the signal at a specific landmark may be used to choose the values of the sampling, downsampling and buffer, where a lower variance may require more data and / or higher resolution of the data.

[0031] The velocity of the downhole tool may be calculated by correlating between each neighbouring sensor data history, where the time lag of each neighbouring sensor can be determined, thereby assessing the velocity of the downhole tool.

[0032] The accumulated depth of the downhole tool is calculated downhole, where the velocity over time is calculated to obtain the accumulated depth or the estimated depth of the downhole tool.

[0033] On the surface, the completion tally 25 may have a list of landmarks, such as casing collars and their positions, where the computing device may be utilised to define acceptance windows for collar candidates in order to compare the signals received from the downhole measurement device 31 that have an estimated depth within the acceptance window. The signals that are outside the acceptance windows may be discarded from being considered as viable candidates for identifying landmark candidates, such as casing collars.

[0034] Fig. 3 shows a process diagram for the method of determining a corrected depth 41, which may be performed using a surface computing device. A first step 43 of the method may be defined as depth processing of the downhole tool. At this step, the depth of the downhole tool is accumulated, and the depth of the downhole device is compared with the acceptance window limits that have been defined in relation to the casing tally. If the accumulated depth is larger than the lower limit of the acceptance window, the number of datapoints are counted, and when the datapoints are outside the acceptance window and / or the collar position, a collar counter may be incremented. When the accumulated depth is outside the limit of the acceptance window, the acceptance window may be evaluated as a candidate window. The candidate window may be defined as the number of data packages received from the downhole tool that are within the acceptance window.

[0035] The evaluation of the candidate window 45 may be performed by evaluating the variance of each sensor of the downhole tool, where the variance of each sensor has proven to be a good indicator of geometric changes in ferromagnetic material in the casing. For each variance window, the last datapoints received by the downhole tool may be evaluated: where the highest value is calculated, the standard deviation is calculated, and where the indices of the values in the variance window, which satisfy that the values are larger than the largest value minus a parameter alpha times the standard deviation. When the indices are found the smallest and largest depth indexes are used to determine a minimum and a maximum depth which define the landmark candidate. Subsequently, a mean value may be taken of all the minimum and maximum depths, and an estimated collar position is determined. By receiving an estimated collar position, it is possible to define the depth of the downhole tool relative to the estimated collar position, so that the depth of the downhole tool may be determined relative to the estimated collar position.

[0036] The step of correcting the depth of a downhole tool 47 may be performed by estimating a depth correction value, where the depth correction value may be seen as a comparison between the collar position defined in the casing tally and the estimated collar position. If the estimated collar position is not identical to the collar position defined in the casing tally, the depth correction value may be a positive or a negative value. The depth correction value may subsequently be utilised to define a corrected depth value for the downhole tool by taking the accumulated depth (measured depth) of the downhole tool and adding or subtracting the depth correction value to / from the accumulated depth of the downhole tool.

[0037] A corrected depth 49 is output from the method 41, where the corrected depth 49 may be utilised in a step 51 to position the downhole tool at a depth using the corrected depth 49 in order to actuate the downhole actuatable tool in the correct downhole position.

[0038] The use of the terms "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., does not imply any particular order, but the terms are included to identify individual elements. Moreover, the use of the terms "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., does not denote any order or importance, but rather the terms "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., are used to distinguish one element from another. Note that the words "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering.

[0039] Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.

[0040] It is to be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed.

[0041] It is also to be noted that the words "a" and "an" preceding an element do not exclude the presence of a plurality of such elements.

[0042] It should further be noted that any reference signs do not limit the scope of the claims.

[0043] Although features have been shown and described, it will be understood that they are not intended to limit the claimed invention, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the claimed invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The claimed invention is intended to cover all alternatives, modifications, and equivalents.

Examples

Embodiment Construction

[0026]Various exemplary embodiments and details are described below, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practised in any other embodiments even if not so illustrated, or if not so explicitly described.

[0027]Fig. 1 discloses a method of determining 1 the position of a downhole tool in a borehole, comprising introducing 3 a downhole tool int...

[0001] The present invention relates to a method of determining the position of a downhole tool in a borehole, comprising introducing a downhole tool into the borehole, the downhole tool comprising an actuating tool and a downhole measurement device.

[0002] The term "borehole" may be used to collectively refer to any of the various types of holes that may be drilled into a ground surface. Boreholes are created by a drilling process generally performed by a drilling rig, where the borehole may be completed by introducing a casing that is a plurality of well tubulars introduced from the surface, where each well tubular is connected to the next well tubular via a threaded connection, and where the threaded connection is often referred to as a casing collar.

[0003] When the borehole is completed, and during the introduction of the casing into the borehole, a casing tally is compiled, where the casing tally includes data representing the casing and / or the borehole, and where the casing tally may be seen as a list of landmarks, such as casing collars, valves and other parts of the casing, including information on the depth at which each of the landmarks is positioned.

[0004] When a downhole operation is to be performed at a predefined depth in the borehole, it may be seen as important to know the correct depth of the intervention tool before performing the downhole operation in order to ensure that the downhole operation is performed at the correct position. A downhole operation is often performed using a wireline downhole tool, where the downhole tool is introduced into the borehole, and where the position of the downhole tool is estimated before performing the operation. It has been shown that the position estimation of the downhole tool is often flawed, where numerous factors may cause an incorrect estimate of the position of the downhole tool. Thus, there is a need to improve the estimate of the position of the downhole tool to ensure that the downhole operation is performed at the correct position.

[0005] In accordance with the invention, there is provided a method of determining the position of a downhole tool in a borehole, comprising: introducing a downhole tool into the borehole, the downhole tool comprising an actuating tool and a downhole measurement device, receiving downhole data representing the borehole, where the downhole data include at least a first downhole landmark position representing a location of a landmark in the borehole, receiving a first signal from a downhole measurement device, the first signal representing a downhole landmark of a borehole and a measured position of the downhole landmark, comparing the first signal to the first landmark position of the downhole data and generating a first correction value, generating a first corrected depth value by correcting the first signal with the first correction value, and transmitting a first actuating signal to actuate the actuatable tool in a downhole position based on the first corrected depth value.

[0006] The present method allows the downhole tool to be deployed in a correct position, where the known position of the landmark is utilised to generate the correct depth of the downhole tool prior to actuating the actuatable tool. In an example where the actuatable tool is a casing cutter, it is ensured that the downhole tool is in the correct position, and that the casing is cut in the desired position, where the errors related to the positioning of the downhole tool are corrected prior to cutting of the casing.

[0007] The downhole data representing the borehole may be in the form of a list, such as a casing tally, where the casing tally includes details of the tubulars that have been prepared for running. In the casing tally, each tubing joint may be numbered, and the corresponding length of the tubulars have been introduced into the list. The casing tally may further comprise a list of the positions of landmarks in the borehole, such as valves, or other types of landmarks that may be identified using a downhole measurement tool.

[0008] If the actuatable tool is to be used to perform a downhole operation at a specific depth, the downhole tool may be deployed into the borehole, and when the downhole tool passes a predetermined downhole landmark, the first signal representing the downhole landmark may be utilised to compare the measured position of the landmark with the first downhole landmark position which was defined in a casing tally and / or a list. If there is a difference between the measured position of the first landmark and the position defined in the casing tally, the actual position of the downhole tool may be corrected prior to the transmission of an actuating signal to actuate the actuatable tool.

[0009] Thus, the casing tally may be utilised to ensure that the downhole tool is in the correct downhole position when the downhole operation is to be performed. The correct position reduces the risk that the downhole operation is performed in a wrong position. Furthermore, by utilising this method, the position of the downhole tool may be corrected in any position of the downhole tool, as the landmarks in the casing, such as casing collars, are present at intervals in the full length of the casing.

[0010] In one or more exemplary embodiments, the downhole measurement tool may be part of the downhole tool, where the downhole measurement tool generates a first signal which may be measurements that are performed while the downhole tool is being submerged into the borehole. The first signal may be monitored continuously by a computing device, where the first signal may be continuously used to verify the real-time position of the downhole tool while the tool is being submerged.

[0011] In one or more exemplary embodiments, the first signal comprises a first landmark signature. The downhole measurement device may perform measurements continuously while the downhole tool is being submerged into the borehole, where the downhole measurement tool may pass all the landmarks that are present above the depth, which the downhole tool is deployed to. The landmarks may be different types of landmarks, e.g. a casing collar, a valve, a casing tubular or any type of landmark that is present in a borehole. When the measurement tool passes a landmark, such as a casing collar, the measurement tool produces a first signal, where the first signal may represent a measurement of the casing collar. The measurement of the landmark, such as a casing collar, may be a landmark signature, where the magnitude and / or the amplitude of the signal may disclose the landmark signature.

[0012] In one or more exemplary embodiments, the downhole measurement device is a magnetic measurement device. The magnetic measurement device may comprise one or more magnets to generate one or more magnetic fields and one or more magnetic sensors to detect changes in the magnitude and / or direction of the magnetic field generated by the magnet. Such a downhole measurement device is disclosed in e.g. WO 2011 / 051429.

[0013] In one or more exemplary embodiments, the downhole measurement device comprises two or more magnetic measurement devices. The magnetic measurement device may comprise two or more magnets to generate one or more magnetic fields and two or more magnetic sensors to detect changes in the magnitude and / or direction of the magnetic field generated by the magnets. Such a downhole measurement device is disclosed in e.g. WO 2011 / 051429. Each magnet may have a dedicated magnetic sensor, where one sensor measures the changes in one magnetic field from one magnet.

[0014] In one or more exemplary embodiments, the first signal comprises two or more measurement channel signals. The first signal may comprise a plurality of signals from a plurality of sensors, where each sensor produces an electric signal. Each of the electric signals may represent one sensor, where the first signal may comprise electric signals from a plurality of sensors. Each of the sensors may be offset in a longitudinal direction along the length of the downhole tool, such that the first signal may comprise a plurality of downhole measurements that measure the signal from different positions along the length of the downhole tool.

[0015] In one or more exemplary embodiments, the downhole landmark in a borehole is a casing collar. A casing collar is a joint that connects one well tubular to another well tubular, where the connected well tubulars may define a casing of a borehole. When a measurement device, such as a magnetic measurement device, comes into the vicinity of a casing collar, the electric signal of the sensor changes, and the measurement signal may have a form that may be recognisable as a casing collar. The computing device may be capable of analysing the electric signal over a predefined amount of time, where the computing device may use a form of pattern recognition to identify a casing collar. The electric signal of a casing collar may be different from the electric signal of a measurement of a downhole valve, where the computing device may be capable of differentiating between a downhole valve and a casing collar based on the magnitude of the signal over a given period of time.

[0016] In one or more exemplary embodiments, the downhole data and / or the first signal are received by a computing device at the surface, and / or the comparing, generating and / or transmitting steps are performed by a computing device at the surface. The downhole tool may be connected to the surface through a data connection via the wireline in the form of electric communication, optical communication, or other forms of suitable data communication protocols, where the electric signal of the downhole measurement device is transmitted from the submerged downhole tool to the surface.

[0017] In one or more exemplary embodiments, the downhole data is in the form of a list comprising details of well tubulars and / or casings that have been introduced into the borehole. The list may be in the form of a casing tally, a completion tally, or any form of list which may be seen as downhole data representing the borehole. The list includes data representing the casing and / or the borehole, where the list may be seen as a list of landmarks, such as casing collars, valves and other parts of the casing, and providing information on the depth at which each of the landmarks is positioned. The list may be compiled during the completion of the borehole or may be in the form of measurements or information introduced after the completion of the borehole.

[0018] In one or more exemplary embodiments, the comparison comprises generating a first data window based on the downhole data for providing an acceptable position of a measured downhole landmark from the first signal. The data window may be provided with information from downhole data representing the borehole, where the data window may be formed from a start depth to a stop depth, and where the data window is positioned at a depth where the downhole data represents a downhole landmark. The data window may start at a predefined downhole location prior to the landmark and end at a downhole location after the landmark. In case the landmark is a casing collar, the start position may e.g. be a predefined position of a well tubular prior to the casing collar, and the stop position may be a predefined position of a well tubular after the casing collar.

[0019] In one or more exemplary embodiments, the comparison comprises analysing the data of the first signal within the first data window. Thus, when the downhole measurement device enters the data window, the computing device may be utilised to analyse the signal within the data window, while discarding the data outside the data window. Thus, the data window allows the downhole tool to reduce the computing power needed to analyse data, as the comparison may only be made inside the data window in order to identify the downhole landmark. Thus, downhole landmarks that are outside the data window will not be considered.

[0020] In one or more embodiments of the present disclosure, the comparison and / or the generation of a first corrected depth value may be formed at a plurality of landmark positions during the deployment of the downhole tool inside the borehole. Thus, it may be possible to provide a first corrected depth value for each landmark which passes the downhole measurement device in order to continuously correct the position of the downhole tool relative to the downhole data representing the borehole.

[0021] In one or more exemplary embodiments, the standard deviation and / or variance of the first signal is utilised to identify a measured downhole landmark candidate. The standard deviation and / or variance of the first signal may indicate a position at which the downhole measurement device passes a downhole landmark, where the first signal may change significantly when the measurement device is adjacent to the downhole landmark. As an example, where the downhole landmark is a casing collar, the first signal may be stable when passing a central part of a well tubular of the casing, where the signal may change significantly when the measurement device comes closer to a casing collar. The amplitude of the signal may increase or decrease significantly, where the variance or standard deviation of the signal over a predefined time may indicate the presence of a landmark.

[0022] In one or more exemplary embodiments, the comparison defines a detection probability of a measured downhole landmark and / or identifies a measured downhole landmark when the detection probability meets a threshold. Thus, the comparison calculates a detection probability of a downhole landmark, where the detection probability may be seen as a certainty whether the downhole measurement device has detected a landmark. The threshold may be based on the variance of the first signal and / or the variance of the electric signal comprised in the first signal. When the detection probability meets the predefined threshold, the comparison may mark that the measured signal may be identified as a measured downhole landmark.

[0023] In one or more exemplary embodiments, the method further comprises moving the downhole tool in accordance with the corrected depth value. When the corrected depth value has been generated, the downhole tool may be moved in accordance with the corrected depth value to a position where the tool is to be actuated. By actuating the tool in accordance with the corrected depth value, it is possible to improve the precision of the downhole operation, where the movement of the downhole tool ensures that the actuatable tool is in its correct position when used.

[0024] The present disclosure may further comprise a system for performing the method in accordance with the present disclosure.Brief description of the drawings

[0025] The following is an explanation of exemplary embodiments with reference to the drawings in which: Fig. 1 is a process diagram for the method in accordance with the present disclosure, Fig. 2 is a schematic diagram of a downhole tool being deployed, and Fig. 3 is a process diagram for correcting the depth of the downhole tool. Detailed description

[0026] Various exemplary embodiments and details are described below, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practised in any other embodiments even if not so illustrated, or if not so explicitly described.

[0027] Fig. 1 discloses a method of determining 1 the position of a downhole tool in a borehole, comprising introducing 3 a downhole tool into a borehole, the downhole tool comprising an actuating tool and a downhole measurement device receiving 5 downhole data representing a borehole, where the downhole data includes at least a first downhole landmark position representing a location of a landmark in the borehole, receiving a first signal from a downhole measurement device 7, the first signal representing a downhole landmark of a borehole and a measured position of the downhole landmark, comparing 9 the first signal to the first landmark position of the downhole data and generating 11 a first correction value, generating 13 a first corrected depth value by correcting the first signal with the first correction value, and transmitting a first actuating signal to actuate the actuatable tool in a downhole position based on a first corrected depth value 15.

[0028] Fig. 2 shows a schematic diagram of a downhole tool 15 being deployed in a downhole position 17 and a surface controlling device 19 which is positioned on a surface 20 and connected to the downhole tool 15 via a communication pathway 21. The surface controlling device 19 comprises a computing device 23 which receives data from the downhole tool 15 via the communication pathway 21 and receives data from a completion tally 25 (casing tally) which comprises the collar positions of a downhole casing 27 of a borehole 28 in which the downhole tool 15 is deployed. The downhole tool 15 may comprise a downhole computing device 29 that may communicate with the surface controlling device 19 via a communication pathway 33, and where the downhole computing device 29 communicates with a downhole measurement device 31, where measurement data 35 are transmitted to the downhole computing device 29. The downhole computing device 29 may further communicate 37 with an actuatable downhole tool 39, where the downhole computing device 29 may be utilised to actuate the actuatable downhole tool 39.

[0029] The downhole measurement device 31 may be provided with a plurality of magnetic sensors, where the output of the downhole measurement device 31 may be as follows: the raw signal of all sensors, the buffer variance of each sensor, the velocity of the measurement device and the accumulated depth of the measurement device.

[0030] The raw signal of all the sensors may be in 12-bit values, where the sampling rate is 16 kHz, and where the data may be downsampled to 128 samples / second downhole, and the data are sent in packages to the surface. Each sensor may have a buffer size of 512 datapoints, where the buffer size represents approximately four seconds of data, and where the variance of the signal may be calculated downhole. The sampling rate, the downsampling and the buffer sizes of the raw signal may be adjusted for a specific application, where the sampling rate may be between 100 HZ and 64 kHz, the signal may be downsampled to between 64 samples / second and 512 samples / second, and the buffer size may vary depending on the size of the data from 128 datapoints to 2048 datapoints. The variation of the signal at a specific landmark may be used to choose the values of the sampling, downsampling and buffer, where a lower variance may require more data and / or higher resolution of the data.

[0031] The velocity of the downhole tool may be calculated by correlating between each neighbouring sensor data history, where the time lag of each neighbouring sensor can be determined, thereby assessing the velocity of the downhole tool.

[0032] The accumulated depth of the downhole tool is calculated downhole, where the velocity over time is calculated to obtain the accumulated depth or the estimated depth of the downhole tool.

[0033] On the surface, the completion tally 25 may have a list of landmarks, such as casing collars and their positions, where the computing device may be utilised to define acceptance windows for collar candidates in order to compare the signals received from the downhole measurement device 31 that have an estimated depth within the acceptance window. The signals that are outside the acceptance windows may be discarded from being considered as viable candidates for identifying landmark candidates, such as casing collars.

[0034] Fig. 3 shows a process diagram for the method of determining a corrected depth 41, which may be performed using a surface computing device. A first step 43 of the method may be defined as depth processing of the downhole tool. At this step, the depth of the downhole tool is accumulated, and the depth of the downhole device is compared with the acceptance window limits that have been defined in relation to the casing tally. If the accumulated depth is larger than the lower limit of the acceptance window, the number of datapoints are counted, and when the datapoints are outside the acceptance window and / or the collar position, a collar counter may be incremented. When the accumulated depth is outside the limit of the acceptance window, the acceptance window may be evaluated as a candidate window. The candidate window may be defined as the number of data packages received from the downhole tool that are within the acceptance window.

[0035] The evaluation of the candidate window 45 may be performed by evaluating the variance of each sensor of the downhole tool, where the variance of each sensor has proven to be a good indicator of geometric changes in ferromagnetic material in the casing. For each variance window, the last datapoints received by the downhole tool may be evaluated: where the highest value is calculated, the standard deviation is calculated, and where the indices of the values in the variance window, which satisfy that the values are larger than the largest value minus a parameter alpha times the standard deviation. When the indices are found the smallest and largest depth indexes are used to determine a minimum and a maximum depth which define the landmark candidate. Subsequently, a mean value may be taken of all the minimum and maximum depths, and an estimated collar position is determined. By receiving an estimated collar position, it is possible to define the depth of the downhole tool relative to the estimated collar position, so that the depth of the downhole tool may be determined relative to the estimated collar position.

[0036] The step of correcting the depth of a downhole tool 47 may be performed by estimating a depth correction value, where the depth correction value may be seen as a comparison between the collar position defined in the casing tally and the estimated collar position. If the estimated collar position is not identical to the collar position defined in the casing tally, the depth correction value may be a positive or a negative value. The depth correction value may subsequently be utilised to define a corrected depth value for the downhole tool by taking the accumulated depth (measured depth) of the downhole tool and adding or subtracting the depth correction value to / from the accumulated depth of the downhole tool.

[0037] A corrected depth 49 is output from the method 41, where the corrected depth 49 may be utilised in a step 51 to position the downhole tool at a depth using the corrected depth 49 in order to actuate the downhole actuatable tool in the correct downhole position.

[0038] The use of the terms "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., does not imply any particular order, but the terms are included to identify individual elements. Moreover, the use of the terms "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., does not denote any order or importance, but rather the terms "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., are used to distinguish one element from another. Note that the words "first", "second", "third" and "fourth", "primary", "secondary", "tertiary", etc., are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering.

[0039] Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.

[0040] It is to be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed.

[0041] It is also to be noted that the words "a" and "an" preceding an element do not exclude the presence of a plurality of such elements.

[0042] It should further be noted that any reference signs do not limit the scope of the claims.

[0043] Although features have been shown and described, it will be understood that they are not intended to limit the claimed invention, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the claimed invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The claimed invention is intended to cover all alternatives, modifications, and equivalents.

Examples

Embodiment Construction

[0026]Various exemplary embodiments and details are described below, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practised in any other embodiments even if not so illustrated, or if not so explicitly described.

[0027]Fig. 1 discloses a method of determining 1 the position of a downhole tool in a borehole, comprising introducing 3 a downhole tool int...

Claims

1. A method of determining the position of a downhole tool in a borehole, comprising: - introducing a downhole tool into the borehole, the downhole tool comprising an actuating tool and a downhole measurement device, - receiving downhole data representing the borehole, where the downhole data include at least a first downhole landmark position representing a location of a landmark in the borehole, - receiving a first signal from a downhole measurement device, the first signal representing a downhole landmark of a borehole and a measured position of the downhole landmark, - comparing the first signal to the first landmark position of the downhole data and generating a first correction value, - generating a first corrected depth value by correcting the first signal with the first correction value, and - transmitting a first actuating signal to actuate the actuatable tool in a downhole position based on the first corrected depth value.

2. A method in accordance with claim 1, wherein the first signal comprises a first landmark signature.

3. A method in accordance with claim 1 or 2, wherein the downhole measurement device is a magnetic measurement device.

4. A method in accordance with any of the preceding claims, wherein the downhole measurement device comprises two or more magnetic measurement devices.

5. A method in accordance with any of the preceding claims, wherein the first signal comprises two or more measurement channel signals.

6. A method in accordance with any of the preceding claims, wherein the downhole landmark in a borehole is a casing collar.

7. A method in accordance with any of the preceding claims, wherein the downhole data and / or the first signal are received by a computing device at the surface, and / or where the comparing, generating and / or transmitting step is performed by a computing device at the surface.

8. A method in accordance with any of the preceding claims, wherein the downhole data is in the form of a list comprising details of well tubulars and / or casings that have been introduced into the borehole.

9. A method in accordance with any of the preceding claims, wherein the downhole measurement tool may be part of the downhole tool.

10. A method in accordance with any of the preceding claims, wherein the comparison comprises generating a first data window based on the downhole data for providing an acceptable position of a measured downhole landmark from the first signal.

11. A method in accordance with any of the preceding claims, wherein the comparison comprises analysing the data of the first signal within the first data window.

12. A method in accordance with any of the preceding claims, wherein the standard deviation and / or variance of the first signal is utilised to identify a measured downhole landmark candidate.

13. A method in accordance with any of the preceding claims, wherein the comparison defines a detection probability of a measured downhole landmark and / or identifies a measured downhole landmark when the detection probability meets a threshold.

14. A method in accordance with any of the preceding claims, wherein the method further comprises moving the downhole tool in accordance with the corrected depth.

15. A system for performing the method in accordance with claims 1-14.

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