METHOD OF DETERMINING THE POSITION OF A DOWNHOLE TOOL IN A BOREHOLE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to European patent application EP 24204480.8, filed Oct. 3, 2024, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure 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.

2. Description of Related Art

The term “borehole” can be used to collectively refer to any of the various types of holes that can be drilled into a ground surface. Boreholes are created by a drilling process generally performed by a drilling rig, where the borehole can 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.

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 can 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.

When a downhole operation is to be performed at a predefined depth in the borehole, it can 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 can 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.

SUMMARY OF THE DISCLOSURE

In accordance with the disclosure, 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.

The present method allows the downhole tool to be deployed in a correct position, where the known position of the landmark is utilized 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 the casing.

The downhole data representing the borehole can 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 can be numbered, and the corresponding length of the tubulars has been introduced into the list. The casing tally can further comprise a list of the positions of landmarks in the borehole, such as valves or other types of landmarks that can be identified using a downhole measurement tool.

If the actuatable tool is to be used to perform a downhole operation at a specific depth, the downhole tool can be deployed into the borehole, and when the downhole tool passes a predetermined downhole landmark, the first signal representing the downhole landmark can be utilized 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 can be corrected prior to the transmission of an actuating signal to actuate the actuatable tool. Thus, the casing tally can be utilized 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 utilizing this method, the position of the downhole tool can 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.

This allows for more accurate positioning of the downhole tool prior to operation, mitigating risks associated with incorrect placement during downhole procedures. The downhole tool can include an actuating tool designed to perform a specific function in the borehole, such as cutting or sealing, and a downhole measurement device capable of sensing its location and surrounding environment. Downhole data, which preferably takes the form of a casing tally containing information about tubulars deployed in the borehole, includes at least one landmark position representing the known location of a feature within the wellbore; a “landmark” is defined here as any identifiable point or structure along the borehole's length, such as a casing collar or valve.

Receiving a first signal from the downhole measurement device provides information about a detected landmark and its measured position. Comparing this received signal to the corresponding landmark position stored in the downhole data enables the generation of a correction value representing any discrepancy between expected and actual location. This has the effect of quantifying positional error. Generating a corrected depth value by applying this correction value to the initial measurement refines the tool's estimated depth, resulting in improved accuracy.

The transmission of an actuating signal based on this first corrected depth value then initiates operation of the actuatable tool at the more precise location. Preferably, the downhole data is continuously updated as the tool progresses through the borehole, allowing for dynamic correction and adaptation to changing conditions. Variations can include utilizing multiple landmarks and implementing weighted averaging techniques to further enhance positional accuracy.

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

In one or more exemplary embodiments, the first signal comprises a first landmark signature. The downhole measurement device can perform measurements continuously while the downhole tool is being submerged into the borehole, where the downhole measurement tool can pass all the landmarks that are present above the depth to which the downhole tool is deployed. The landmarks can 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 can represent a measurement of the casing collar. The measurement of the landmark, such as a casing collar, can be a landmark signature, where the magnitude and/or the amplitude of the signal can disclose the landmark signature.

In one or more exemplary embodiments, the downhole measurement device is a magnetic measurement device. The magnetic measurement device can 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.

In one or more exemplary embodiments, the downhole measurement device comprises two or more magnetic measurement devices. The magnetic measurement device can 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 can have a dedicated magnetic sensor, where one sensor measures the changes in one magnetic field from one magnet.

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

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 can 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 can have a form that can be recognizable as a casing collar. The computing device can be capable of analyzing the electric signal over a predefined amount of time, where the computing device can use a form of pattern recognition to identify a casing collar. The electric signal of a casing collar can be different from the electric signal of a measurement of a downhole valve, where the computing device can 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.

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 can 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.

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 can be in the form of a casing tally, a completion tally, or any form of list that can be seen as downhole data representing the borehole. The list includes data representing the casing and/or the borehole, where the list can 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 can be compiled during the completion of the borehole or can be in the form of measurements or information introduced after the completion of the borehole.

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 can be provided with information from downhole data representing the borehole, where the data window can 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 can 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 can, e.g., be a predefined position of a well tubular prior to the casing collar, and the stop position can be a predefined position of a well tubular after the casing collar.

This enables a more robust comparison process by accounting for inherent uncertainties in both the reference data and the real-time measurements, thereby reducing false positive corrections. Generating a first data window establishes a tolerance range around the expected landmark position derived from the downhole data; this can be based on statistical analysis of historical measurement errors or known borehole irregularities.

This has the effect of defining an acceptable band within which the measured landmark position must fall to be considered valid, mitigating the impact of noise or minor deviations in the signal received from the downhole measurement device. The advantage is that small discrepancies due to instrument limitations or localized borehole conditions are less likely to trigger unnecessary corrections. Preferably, the width of this data window can be dynamically adjusted based on factors such as depth, formation type, or the resolution of the downhole measurement device. This solution allows for a more nuanced assessment of positional accuracy and improves the overall reliability of the correction process.

In one or more exemplary embodiments, the comparison comprises analyzing the data of the first signal within the first data window. Thus, when the downhole measurement device enters the data window, the computing device can be utilized to analyze 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 analyze data, as the comparison can 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.

A “data window” in this context refers to a defined range of data points surrounding the initial detection of the landmark signal, used for more robust analysis.

The use of a first data window can have the effect of mitigating the influence of noise or transient signals associated with the downhole measurement process. This results in a more stable and reliable determination of the actual position of the landmark, even in challenging borehole environments. Preferably, the width of this data window is determined based on the signal-to-noise ratio of the measurements obtained from the downhole tool; higher noise levels can necessitate wider windows to encompass sufficient valid data points.

The advantage is that the solution provides a means for filtering out spurious signals and improving confidence in the positional correction. Furthermore, this approach can preferably be implemented using various signal processing techniques, such as averaging or weighted filtering, within the defined first data window to further enhance accuracy. The first data window can also be dynamically adjusted based on factors like borehole inclination or formation properties, allowing for optimized performance across diverse wellbore conditions.

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

This allows for continuous refinement of the positional accuracy of the downhole tool as it traverses the wellbore, rather than relying on a single correction point. This enables more precise execution of downhole operations and reduces uncertainty associated with depth determination. Performing the comparison and/or generation of a corrected depth value at multiple landmark positions provides redundancy in the positioning process, enhancing reliability and mitigating the impact of individual measurement errors.

The plurality of landmark positions can comprise any number of identifiable features within the borehole, such as casing collars, valves, or other pre-defined markers. The use of multiple landmarks has the effect of averaging out positional discrepancies and providing a more robust depth model for the downhole tool. This results in improved accuracy even in complex wellbore geometries or when encountering variations in tubular dimensions. Preferably, these landmark positions are spaced at regular intervals along the borehole; however, it is also possible to utilize irregularly spaced landmarks depending on the specific well construction and operational requirements. The advantage is that this approach can adapt to varying well conditions and optimize correction frequency based on local accuracy needs. Furthermore, the comparison process can be performed sequentially or concurrently at these multiple positions, allowing for real-time depth updates as the tool progresses.

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

This allows for a robust determination of potential landmark positions by leveraging statistical properties of the received signal data. A “first signal” in this context represents a measurement indicative of a borehole feature, such as an acoustic or electromagnetic response generated when passing a landmark. Utilizing the standard deviation and/or variance provides a quantitative metric to assess the consistency and reliability of the signal, thereby distinguishing genuine landmark detections from noise or spurious reflections.

Employing the standard deviation has the effect of quantifying the spread of data points around the mean value of the first signal; a low standard deviation suggests a strong, consistent signal indicative of a valid landmark detection. Conversely, a high standard deviation can indicate a noisy or ambiguous signal that is less likely to represent an actual downhole feature. The variance, representing the square of the standard deviation, provides a similar measure of data dispersion and can preferably be used in conjunction with the standard deviation for enhanced discrimination. This has the advantage of reducing false positive landmark identifications, which could lead to inaccurate depth corrections. Preferably, a threshold value is applied to the calculated standard deviation or variance; signals exceeding this threshold are considered candidate landmarks. The specific threshold value can be dynamically adjusted based on borehole conditions and signal characteristics. Furthermore, alternative statistical measures, such as the median absolute deviation, can also preferably be incorporated to further refine landmark identification.

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 can be seen as a certainty of whether the downhole measurement device has detected a landmark. The threshold can 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 can mark that the measured signal can be identified as a measured downhole landmark.

This allows for enhancing the reliability of landmark identification within the borehole environment, particularly in situations where signal quality can be compromised or ambiguous.

The concept of “detection probability” can represent a statistical confidence level indicating the likelihood that a received signal genuinely corresponds to a downhole landmark as opposed to noise or other interference. This has the effect of providing a quantitative measure for assessing the validity of each potential landmark identification, thereby reducing false positive detections. Preferably, this detection probability is calculated using statistical methods such as correlation analysis, spectral decomposition, or machine learning algorithms trained on representative signal data. The advantage is that it provides a robust means to differentiate between true landmarks and spurious signals, even in challenging downhole conditions.

Furthermore, the threshold value against which the detection probability is compared can be dynamically adjusted based on factors such as borehole geometry, formation lithology, sensor sensitivity, or noise levels. This has the advantage of optimizing landmark identification performance across a wide range of operational scenarios. Alternatively, multiple thresholds could be implemented to categorize landmarks into different confidence levels, enabling prioritized processing or selective actuation of downhole tools. A measured downhole landmark is preferably identified only when its detection probability surpasses this threshold, ensuring that subsequent operations are based on highly reliable positional data.

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 can 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.

This allows to precisely position the downhole tool following the determination of positional error and subsequent depth correction. The overall purpose of this element of the solution is to ensure accurate placement of the downhole tool for performing a desired downhole operation, thereby maximizing operational efficiency and minimizing risks associated with incorrect positioning.

The movement of the downhole tool can be achieved through various techniques known in the art, such as utilizing a wireline system, coiled tubing, or hydraulic actuators integrated within the downhole assembly. Preferably, this movement is controlled by a surface-based control system that receives data regarding the corrected depth and initiates appropriate adjustments to the downhole tool's position. This has the effect of actively compensating for discrepancies between expected and actual positions, leading to improved accuracy in subsequent operations. The advantage is that it eliminates reliance on passive positioning methods, which can be susceptible to accumulated errors over extended deployment depths.

Furthermore, the rate and manner of movement can be adjusted based on factors such as borehole conditions, tool design, and the sensitivity of the downhole operation being performed. For example, a slower, more controlled movement might be preferred when deploying a casing cutter to ensure precise engagement with the casing, while faster movements could be suitable for less critical positioning tasks. Preferably, feedback mechanisms are incorporated to monitor the downhole tool's position during movement and provide real-time adjustments to maintain the desired depth. A “downhole operation” in this context refers to any activity performed by an actuatable tool within the borehole, including but not limited to cutting, perforating, cementing, or logging.

The present disclosure can further comprise a system for performing the method in accordance with the present disclosure.

The system can comprise at least one downhole tool configured for deployment into a borehole, and an actuatable component integrated within or connected to the downhole tool. The inclusion of an actuatable component has the effect of enabling performance of operations such as cutting, cementing, perforating, or logging directly within the wellbore environment. This results in increased efficiency by consolidating functionality within a single deployable unit. Preferably, the system further includes a data acquisition module capable of generating signals representative of downhole landmarks encountered during deployment. The advantage is that this provides real-time positional information for comparison against pre-existing borehole data.

Furthermore, the system can incorporate a processing unit configured to compare measured landmark positions with corresponding positions defined in a list, such as a casing tally, and generate correction signals if discrepancies are detected. This has the effect of mitigating errors associated with downhole tool positioning prior to actuating the component. The advantage is that it ensures accurate operation even in complex wellbore geometries or dynamic conditions. Variations can include wired or wireless communication between the data acquisition module and processing unit, as well as integration of multiple sensors for redundancy and improved accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is an explanation of exemplary embodiments with reference to the drawings.

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.

FIG. 3 is a process diagram for correcting the depth of the downhole tool.

DETAILED DESCRIPTION OF THE DISCLOSURE

Various exemplary embodiments and details are described below, with reference to the figures when relevant. It should be noted that the figures are not necessarily 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 need 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 practiced in any other embodiments, even if not so illustrated, or if not so explicitly described.

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.

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 can comprise a downhole computing device 29 that can 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 can further communicate 37 with an actuatable downhole tool 39, where the downhole computing device 29 can be utilized to actuate the actuatable downhole tool 39.

The downhole measurement device 31 can be provided with a plurality of magnetic sensors, where the output of the downhole measurement device 31 can 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.

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

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

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.

On the surface, the completion tally 25 can have a list of landmarks, such as casing collars and their positions, where the computing device can be utilized 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 can be discarded from being considered as viable candidates for identifying landmark candidates, such as casing collars.

FIG. 3 shows a process diagram for the method of determining a corrected depth 41, which can be performed using a surface computing device. A first step 43 of the method can 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 is counted, and when the datapoints are outside the acceptance window and/or the collar position, a collar counter can be incremented. When the accumulated depth is outside the limit of the acceptance window, the acceptance window can be evaluated as a candidate window. The candidate window can be defined as the number of data packages received from the downhole tool that are within the acceptance window.

The evaluation of the candidate window 45 can 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 can 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 indices are used to determine a minimum and a maximum depth, which define the landmark candidate. Subsequently, a mean value can 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 can be determined relative to the estimated collar position.

The step of correcting the depth of a downhole tool 47 can be performed by estimating a depth correction value, where the depth correction value can 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 can be a positive or a negative value. The depth correction value can subsequently be utilized 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.

A corrected depth 49 is output from the method 41, where the corrected depth 49 can be utilized 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.

The use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary”, and the like, 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”, and the like, does not denote any order or importance, but rather the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary”, and the like, are used to distinguish one element from another. Note that the words “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary”, and the like, are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering.

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

It is to be noted that the word “comprising” does not necessarily exclude the presence of other elements or steps than those listed.

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.

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

By “fluid” or “well fluid” is meant any kind of fluid that can be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, and the like. By “gas” is meant any kind of gas composition present in a well, completion, or open hole, and by “oil” is meant any kind of oil composition, such as crude oil, an oil-containing fluid, and the like. Gas, oil, and water fluids can thus all comprise other elements or substances than gas, oil, and/or water, respectively.

By “casing”, “well tubular” or “well tubular metal structure” is meant any kind of pipe, tubing, tubular, liner, string, and the like, used downhole in relation to oil or natural gas production.

In the event that the tool is not submergible all the way into the casing, a driving unit such as a downhole tractor can be used to push the tool all the way into position in the well. The downhole tractor can have projectable arms having wheels, wherein the wheels contact the inner surface of the casing for propelling the tractor and the tool forward in the casing. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor®.

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