Flexible arm caliper tool for downhole measurements

Abstract

A downhole caliper includes a body having an axis. The downhole caliper includes a flexible arm rigidly attached relative to the body. The flexible arm is elastic and configured to return to a straight orientation when no load is applied thereto. The downhole caliper includes a deflection sensor attached to the flexible arm and configured to determine a deflection of the flexible arm. The flexible arm may be attached relative to the body at an angle relative to the axis. The deflection sensor may include a strain gauge attached at a base of the flexible arm. A well logging apparatus may include a plurality of flexible arms configured to behave as cantilever beams when contacting a wellbore wall, a plurality of deflection sensors configured to measure curvature of the flexible arms, and a buoyancy adjusting mechanism.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 763,383, titled FLEXIBLE CALIPER ARM MEASUREMENT SYSTEM AND METHOD, filed 26 February 2025, which is hereby incorporated by reference in its entirety.BACKGROUND

[0002] Downhole caliper tools are used in wellbore operations to measure the internal dimensions of wellbores and tubulars. Conventional caliper tools often employ mechanical arms or fingers that extend outward to contact the wellbore wall, with the position of these arms being tracked to determine wellbore diameter. However, existing caliper systems may involve complex mechanical assemblies with numerous moving parts, which can increase manufacturing costs and introduce potential failure points in the harsh downhole environment. Additionally, traditional caliper measurement approaches may experience reduced accuracy when subjected to variable downhole conditions, including changes in wellbore geometry, tool eccentricity, or contact forces between the measurement arms and the wellbore wall.SUMMARY

[0003] According to an aspect of the present disclosure, a downhole caliper is provided. The downhole caliper includes a body having an axis. The downhole caliper includes a flexible arm rigidly attached relative to the body. The flexible arm is elastic and configured to return to a straight orientation when no load is applied thereto. The downhole caliper includes a deflection sensor attached to the flexible arm and configured to determine a deflection of the flexible arm.

[0004] According to other aspects of the present disclosure, the downhole caliper may include one or more of the following features. The flexible arm may be attached relative to the body at an angle relative to the axis, the angle being between about 5 degrees and about 85 degrees. The angle may be between about 15 degrees and about 70 degrees. The flexible arm may be attached relative to the body via a pivot mechanism, and the pivot mechanism may be configured to set and firmly hold the angle during a measurement operation. The pivot mechanism may be configured to retract the flexible arm along the body during a free displacement operation. A length of the flexible arm may be less than a length of the body, the length of the body measured along the axis. The length of the flexible arm may be between about 50% and 200% of the diameter of the body. A thickness of the flexible arm may be lower than 5 mm. The deflection sensor may include at least one of a strain gauge or a flex sensor. The strain gauge or flex sensor may be attached at a base of the flexible arm, the base of the flexible arm being closer to an attachment of the arm to the body than a distal end of the arm. The downhole caliper may further include a plurality of flexible arms including the flexible arm and a plurality of deflection sensors including the deflection sensor. Each deflection sensor of the plurality of deflection sensors may be attached to a respective flexible arm of the plurality of flexible arms.

[0005] According to another aspect of the present disclosure, a well-logging apparatus is provided. The well logging apparatus includes a body having a longitudinal axis. The well logging apparatus includes a plurality of flexible arms rigidly attached to the body and configured to extend radially outward beyond an outer surface of the body. Each flexible arm of the plurality of flexible arms is elastic and configured to behave as a cantilever beam when contacting a wellbore wall. The well logging apparatus includes a plurality of deflection sensors. Each deflection sensor of the plurality of deflection sensors is attached to a corresponding flexible arm of the plurality of flexible arms and configured to measure a curvature of the corresponding flexible arm. The well logging apparatus includes a buoyancy adjusting mechanism configured to adjust a buoyancy of the well logging apparatus.

[0006] According to other aspects of the present disclosure, the well logging apparatus may include one or more of the following features. The buoyancy adjusting mechanism may include a ballast tank. The buoyancy adjusting mechanism may include a releasable weight. The releasable weight may be dissolvable. Each deflection sensor of the plurality of deflection sensors may include a strain gauge attached at a base of the corresponding flexible arm of the plurality of flexible arms.

[0007] According to another aspect of the present disclosure, a downhole caliper is provided. The downhole caliper includes a body having an axis. The downhole caliper includes a flexible arm rigidly attached relative to the body. The flexible arm is elastic and configured to return to a straight orientation when no load is applied thereto. The flexible arm has a width and a thickness. The width is at least twice the thickness. The thickness is less than 10 mm. The downhole caliper includes a deflection sensor attached to the flexible arm and configured to determine a deflection of the flexible arm.

[0008] According to other aspects of the present disclosure, the downhole caliper may include one or more of the following features. The thickness may be less than 5 mm. The thickness may be less than 1 mm. The flexible arm may include at least one of a spring alloy, aluminum, titanium, copper alloy, plastic, or elastomer material.BRIEF DESCRIPTION OF FIGURES

[0009] In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0010] FIG. 1A illustrates a caliper positioned within a wellbore, according to aspects of the present disclosure;

[0011] FIG. 1B illustrates a portion of a flexible arm for a downhole caliper, according to aspects of the present disclosure;

[0012] FIG. 2 illustrates a caliper positioned within a wellbore showing contact length and force, according to aspects of the present disclosure;

[0013] FIG. 3 illustrates a caliper positioned within a wellbore showing offset between axes, according to aspects of the present disclosure;

[0014] FIG. 4 illustrates a downhole caliper measurement system showing wellbore profile reconstruction, according to aspects of the present disclosure;

[0015] FIG. 5 illustrates a caliper with a plurality of flexible arms positioned within a wellbore, according to aspects of the present disclosure;

[0016] FIG. 6A illustrates a caliper with pivot mechanisms positioned within a wellbore, according to aspects of the present disclosure;

[0017] FIG. 6B illustrates the caliper of FIG. 6A with the pivot mechanisms, according to aspects of the present disclosure; and

[0018] FIG. 7 illustrates a caliper including floating hubs positioned within a wellbore, according to aspects of the present disclosure.DETAILED DESCRIPTION

[0019] The following description sets forth exemplary aspects of the present disclosure. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.

[0020] Downhole caliper measurement systems may be used to determine the dimensions and profile of a wellbore drilled into a geological formation. Measurements obtained from such systems may inform decisions related to hydrocarbon exploration and production by providing data regarding the characteristics of the wellbore and the surrounding geological region. Caliper measurements may indicate the diameter of the wellbore at various depths, identify irregularities in the wellbore wall, and detect changes in the wellbore profile along the length of the wellbore.

[0021] A well-logging apparatus may be conveyed into a wellbore using various deployment methods. In some embodiments, a well logging apparatus may be an untethered device that relies on buoyancy to travel up and down the wellbore. Such buoyancy-driven devices, sometimes referred to as sensor balls or similar devices, may sink through wellbore fluid when configured with a density greater than the surrounding fluid and may float upward when configured with a density less than the surrounding fluid. The buoyancy of such devices may be adjusted during operation to control the direction of travel within the wellbore.

[0022] Contact caliper measurement may involve physical contact between a measurement element and the inner surface of the wellbore. For buoyancy-driven devices, lightweight and low-friction solutions may be desirable to maintain the ability of the device to travel through the wellbore under buoyancy forces. Lightweight contact elements may reduce the overall mass of the well logging apparatus and may minimize friction between the measurement elements and the wellbore wall during travel.

[0023] Flexible arm solutions may provide a lightweight approach to contact caliper measurement. In some embodiments, flexible arms may be configured to deflect when contacting the wellbore wall, and the deflection of the arms may be measured to determine the dimensions of the wellbore. The flexible arms may be designed to behave as cantilever beams, with the measurement based on the bending or curvature of the arms rather than on rigid arm positioning. Such an approach may distribute contact along a length of the arm rather than concentrating contact at a single point, which may reduce localized wear on the measurement elements.

[0024] Referring to FIG. 1A, a caliper 100 may be positioned within a wellbore 102 extending through a formation 104. The formation 104 defines an inner surface 106 of the wellbore 102. The inner surface 106 establishes a diameter D of the wellbore 102 that may be measured by the caliper 100. In some embodiments, the formation 104 may represent a casing having the diameter D for measurement by the caliper 100.

[0025] The caliper 100 may include a body 108 having an axis 120 extending longitudinally through the body 108. The axis 120 may be a major, longitudinal axis of the body 108. The caliper body 108 may include at least one of aluminum, plastic or elastomer material. The axis 120 may be a central, longitudinal axis of the body 108. The body 108 may have an outer surface from which measurement components extend. In at least one embodiment, a first flexible arm 110a and a second flexible arm 110b are rigidly attached relative to the outer surface of the body 108. The first flexible arm 110a is attached to the body 108 via a first attachment 112a, and the second flexible arm 110b is attached to the body 108 via a second attachment 112b. The first flexible arm 110a and the second flexible arm 110b may extend radially outward and away from the body 108 and toward the inner surface 106 of the wellbore 102 in order to measure the diameter D of the wellbore 102. In at least one embodiment, the first and second flexible arms 110a-b are the same or similar length. In at least one embodiment, the first and second arms 110a-b, or any other flexible arms of the same caliper tool, may be different lengths and / or may extend from the body 108 at different angles.

[0026] In at least one embodiment, the first flexible arm 110a and the second flexible arm 110b are elastic and configured to return to a straight orientation when no load is applied thereto. The first flexible arm 110a and the second flexible arm 110b may be designed to behave as cantilever beams, with measurement based on the deflection of the beam when contacting the inner surface 106. The first flexible arm 110a extends to a first distal end 114a, and the second flexible arm 110b extends to a second distal end 114b. The first distal end 114a and the second distal end 114b represent the portions of the first flexible arm 110a and the second flexible arm 110b positioned away from the body 108 and toward the inner surface 106.

[0027] In at least one embodiment, a first deflection sensor 116a is attached to the first flexible arm 110a near the first attachment 112a, and a second deflection sensor 116b is attached to the second flexible arm 110b near the second attachment 112b. The first deflection sensor 116a and the second deflection sensor 116b are configured to determine a deflection of the first flexible arm 110a and the second flexible arm 110b, respectively. The deflection relative to the axis 120 of the body 108 near the attachment point may cause some specific curvature of the flexible arm 110a-b that can be converted to a caliper measurement. The deflection measurement, along with a known resting angle of the arm and a length of the arm, as well as other known features of the arm, may be used to extrapolate a distance between the first distal end 114a and the second distal end 114b, which corresponds to the diameter D of the wellbore 102.

[0028] In at least one embodiment, the first and second deflection sensors 112a-b are disposed on the respective flexible arms 110a-b and within the body 108. For example, the deflection sensors 112a-b may be disposed within a volumetric footprint of the body 108 such that the body 108 includes outer surfaces extending radially outward beyond the deflection sensors 112a-b. This such examples, the body 108 is configured to protect the deflection sensors 110a-b contact from external features and / or contaminants within the wellbore 102.

[0029] The caliper 100 includes a high-density portion 118 positioned within the body 108. The high-density portion 118 contributes to mass distribution of the caliper 100. The mass distribution may be adjusted such that the mass distribution naturally preserves the system orientation. In some embodiments, a dissolvable load may naturally orient the caliper 100 during descent, and lighter density material may remain at the top for stability while floating up. The high-density portion 118 may include a ballast mechanism configured for buoyancy adjusting of the caliper 100. In some embodiments, the ballast mechanism may include a compressed air tank and a ballast tank. Other features of the caliper 100, such as flow restrictions around the caliper 100, may further help passively adjust the speed of logging. The high-density portion 118 may include a ballast mechanism, a releasable weight, or a dissolvable weight.

[0030] In some embodiments, a buoyancy adjusting mechanism at the high-density portion 118 may include a releasable weight and a release actuator configured to detach the releasable weight from the caliper 100 when a predetermined condition is met. The releasable weight may be dissolvable and include load particles typical of a mud compositions such as barite. The caliper 100 may be configured with a density of about 1.1 g / cc for descent through wellbore fluid and a density of about 0.9 g / cc for ascent through wellbore fluid.

[0031] Referring to FIG. 1B, at least one embodiment of the first flexible arm 110a includes a contact surface 122 configured to make contact with the inner surface 106 of the wellbore 102. The contact surface 122 extends along a portion of the first flexible arm 110a and engages with the wellbore wall during measurement operations. The first flexible arm 110a may include circuitry 124 configured to communicate measurements from the first deflection sensor 116a to a controller, computer, or other device. In some embodiments, the circuitry 124 may include components for signal conditioning, data processing, or wireless transmission of measurement data.

[0032] With continued reference to FIG. 1B, the first flexible arm 110a has an arm width w and an arm thickness t. In at least one embodiment, the arm width w is at least 1.5-times the arm thickness t, for example at least twice the arm thickness t. The arm thickness t defines a surface extending between the contact surface 122 and an opposing surface parallel to the contact surface 122. The first flexible arm 110a is dimensioned and designed to bend within a plane parallel to the surface extending between the contact surface 122 and the opposing surface. In at least one embodiment, the arm thickness t may be less than 1 mm. In some embodiments, the arm thickness t may be less than 10 mm, optionally less than 5 mm, optionally less than 1 mm, or optionally less than 0.5 mm. In some embodiments, the arm thickness t may be less than 0.1 mm. The thin profile of the first flexible arm 110a contributes to the lightweight characteristics of the caliper 100 and enables the first flexible arm 110a to behave as a cantilever beam when contacting the inner surface 106.

[0033] A length of the first flexible arm 110a is defined from a base of the first flexible arm 110a at the first attachment 112a to the first distal end 114a. The length of the first flexible arm 110a may be less than a length of the body 108 as measured longitudinally along the axis 120. In some embodiments, the length of the first flexible arm 110a may be between about 50% and about 200% of the diameter d of the body 108. The second flexible arm 110b may have similar dimensional characteristics to the first flexible arm 110a. The flexure of the first flexible arm 110a and the second flexible arm 110b may be adapted to a specific size depending on maximum expected diameter within the wellbore 102.

[0034] In at least one embodiment, the dimensions of flexible arms 110a, 110b described herein (e.g., thickness, length, width…etc.) and the materials of the arms are such that when the flexible arms 110a-b are deflected inward toward the body 108 of the caliper 100, the flexible arms 110a-b are configured to produce an outward force on the inner surface 106. This outward force also depends on the ratio of diameters of the body 108 and the wellbore 102. In addition, the flexible arms 110a, 110b may be light, flexible, and configured to contact the inner surface 106 with sufficient spring force so that the flexible arms 110a-b are not affected by the relative velocity of the fluid experience in the wellbore 102 during logging and / or tripping up or down the well.

[0035] This outward force may be small enough to reduce friction and drag on the caliper 100 and big enough to maintain contact between the flexible arms 110a-b and the inner surface 106 as the caliper 100 travels through the wellbore 102. Thus, in at least one embodiment, this outward force may be between about 0.5 N and about 10 N.

[0036] The first flexible arm 110a may include a spring alloy, aluminum, titanium, copper alloy, plastic, or elastomer material. In some embodiments, the flexible arm 110a may include any type of isotropic material. In some embodiments, the first flexible arm 110a may include aluminum, plastic, or elastomer material, or other material. The material selection may be based on the desired elastic properties, weight characteristics, and durability requirements for the measurement application. The second flexible arm 110b may include similar materials to the first flexible arm 110a. aluminum, plastic, or elastomer material. The material selection may be based on the desired elastic properties, weight characteristics, and durability requirements for the measurement application. The second flexible arm 110b may include similar materials to the first flexible arm 110a.

[0037] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIGS. 1A and 1B can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIGS. 1A and 1B.

[0038] While the embodiments of caliper tools shown in FIG. 1A and other figures described herein include two opposing flexible arms 110a, 110b, this arrangement is non-limiting and for illustration purposes. Embodiments described herein may include more than two flexible arms, including three flexible arms arranged radially around a circumference of the body 108, for example evenly spaced about the body 108. Other embodiments may include four, five, six, seven, or more than seven flexible arms arranged about the body, each having respective deflection sensors.

[0039] Referring to FIG. 2, a caliper 200 may be positioned within a wellbore 202. The wellbore 202 is defined by an inner surface 206 that surrounds the caliper 200. The caliper 200 includes a body 208 having a longitudinal axis 220 extending longitudinally through the body 208. A first flexible arm 210a and a second flexible arm 210b extend from the body 208 toward the inner surface 206 of the wellbore 202.

[0040] The first flexible arm 210a and the second flexible arm 210b may be attached relative to the body 208 at an angle relative to the longitudinal axis 220. The angle may affect the range of measurement and therefore the sensitivity and adaptability of the caliper 200. Thus, the angle may be between about 5 degrees and about 85 degrees. In some embodiments, the angle may be between about 15 degrees and about 70 degrees. In other embodiments, the angle may be between about 25 degrees and about 55 degrees. The inclined attachment of the first flexible arm 210a and the second flexible arm 210b relative to the longitudinal axis 220 positions the flexible arms to extend outward and away from the body 208 toward the inner surface 206 of the wellbore 202.

[0041] With continued reference to FIG. 2, a first deflection sensor 216a may be attached to the first flexible arm 210a, and a second deflection sensor 216b may be attached to the second flexible arm 210b. The first deflection sensor 216a and the second deflection sensor 216b are configured to measure a curvature of the first flexible arm 210a and the second flexible arm 210b, respectively. In at least one embodiment, the first deflection sensor 216a may include at least one of a strain gauge or a flex sensor. In at least one embodiment, the second deflection sensor 216b may include at least one of a strain gauge or a flex sensor. The strain gauge or flex sensor may be attached at a base of the first flexible arm 210a. The base of the first flexible arm 210a is closer to an attachment 121a of the first flexible arm 210a to the body 208 than a distal end of the first flexible arm 210a. Similarly, the strain gauge of the second deflection sensor 216b may be attached at a base of the second flexible arm 210b. One or more other embodiments may include flexible arms 210a-b having more than one deflection sensor secured thereto, for example two or more deflections sensors. Multiple sensors on any one flexible arm may include a variety of types of sensors, including a strain gauge, flex sensor, or other deflection sensors or any combination thereof. In some embodiments, one or more of the flexible arms 210a-b may include multiple sensors while others have only one.

[0042] A contact length 226 is shown along the second flexible arm 210b. The contact length 226 represents a portion of the second flexible arm 210b that makes contact with the inner surface 206 of the wellbore 202. The contact length 226 demonstrates distributed wear along the second flexible arm 210b rather than localized wear at a tip of the second flexible arm 210b. The first flexible arm 210a may similarly exhibit a contact length along which contact with the inner surface 206 is distributed.

[0043] A force 228 is indicated acting on the first flexible arm 210a and the second flexible arm 210b. The force 228 represents radial reaction forces acting on the first flexible arm 210a and the second flexible arm 210b as the flexible arms contact the inner surface 206 of the wellbore 202. The caliper 200 may provide a centralizing force. When the caliper 200 is left to sink under its own weight or float upward with buoyancy, the centralizing force may position the body 208 toward a center of the wellbore 202 as the first flexible arm 210a and the second flexible arm 210b, which in some embodiments may be the same or similar design and / or stiffness, contact the inner surface 206 on opposite sides of the wellbore 202.

[0044] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIG. 2 can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIG. 2.

[0045] Referring to FIG. 3, a caliper 300 may be positioned within a wellbore 302. The wellbore 302 is defined by an inner surface 306 that surrounds the caliper 300. A central wellbore axis 320 extends vertically through a center of the wellbore 302. The caliper 300 includes a body 308 having a central body axis 330 extending longitudinally through the body 308. The central body axis 330 may be offset from the central wellbore axis 320 when the body 308 is not centered within the wellbore 302.

[0046] A first flexible arm 310a and a second flexible arm 310b are attached to the body 308 on opposite sides. The first flexible arm 310a extends outward from the body 308 and curves toward the inner surface 306 on one side of the wellbore 302. The second flexible arm 310b extends outward from the body 308 and curves toward the inner surface 306 on an opposite side of the wellbore 302. The first flexible arm 310a and the second flexible arm 310b are shown in a deflected state, demonstrating cantilever beam behavior when contacting the inner surface 306.

[0047] With continued reference to FIG. 3, a first deflection sensor 316a is attached to the first flexible arm 310a near a base of the first flexible arm 310a where the first flexible arm 310a connects to the body 308. A second deflection sensor 316b is attached to the second flexible arm 310b near a base of the second flexible arm 310b where the second flexible arm 310b connects to the body 308. The first deflection sensor 316a and the second deflection sensor 316b are configured to measure a curvature or deflection of the first flexible arm 310a and the second flexible arm 310b, respectively.

[0048] Detection of measurement offset may be achieved through asymmetry of bending between the first flexible arm 310a and the second flexible arm 310b. When the central body axis 330 is offset from the central wellbore axis 320, the first flexible arm 310a and the second flexible arm 310b experience different amounts of deflection. The first flexible arm 310a on one side of the body 308 may contact the inner surface 306 at a different radial distance than the second flexible arm 310b on the opposite side of the body 308. The offset from the centerline is given by a delta of curvature between the two sides, where the delta represents a difference between a first radius measured by the first deflection sensor 316a and a second radius measured by the second deflection sensor 316b.

[0049] The configuration of the caliper 300 enables determination of the position of the body 308 relative to the center of the wellbore 302. By comparing the deflection measurements from the first deflection sensor 316a and the second deflection sensor 316b, the caliper 300 may determine whether the body 308 is centered within the wellbore 302 or offset toward one side. When the deflection measurements from the first deflection sensor 316a and the second deflection sensor 316b are equal, and the flexible arms 310a-b are the same or substantially similar in design and / or stiffness, the body 308 may be centered within the wellbore 302 such that the central body axis 330 aligns with the central wellbore axis 320. When the deflection measurements differ, the difference indicates the magnitude and direction of the offset of the body 308 from the center of the wellbore 302.

[0050] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIG. 3 can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIG. 3.

[0051] Referring to FIG. 4, a measurement principle for wellbore profile reconstruction is illustrated. A formation 404 defines an inner surface 406 of a wellbore. A flexible arm 410 is shown at a first position 432a and a second position 432b along a path 434. The path 434 represents a trajectory along which a caliper traverses the wellbore. A direction 436 indicates the direction of movement of the caliper along the path 434 during a logging operation. A deflection sensor 416 is attached to the flexible arm 410 at each position and is configured to measure the curvature or bending of the flexible arm 410 when the flexible arm 410 contacts the inner surface 406.

[0052] The flexible arm 410 is shown in a deflected state at the first position 432a and the second position 432b, demonstrating cantilever beam behavior as the flexible arm 410 contacts the formation 404. At each position along the path 434, the deflection sensor 416 measures the curvature of the flexible arm 410. The curvature measurement corresponds to a radius of a circle defined by the deflected shape of the flexible arm 410 at that position.

[0053] With continued reference to FIG. 4, a measured profile 438 is depicted as a curved line tracing the contour of the wellbore wall. The measured profile 438 represents a mathematical envelope derived from the curvature measurements taken at multiple positions along the path 434. The wellbore profile is derived mathematically as the envelope of circles formed by the flexible arm 410 at every point in time along the probed trajectory. As the caliper moves in the direction 436 along the path 434, the deflection sensor 416 records curvature measurements at successive positions. The envelope of all circle radii corresponding to the curvature measurements reconstructs the wellbore profile along the probed trajectory.

[0054] The minimum curvature of the cantilever controls the depth of rugosity measurement. Rugosity refers to surface irregularities or roughness along the inner surface 406 of the wellbore. The minimum curvature that the flexible arm 410 may achieve determines the smallest surface features that may be detected by the measurement system. Smaller minimum curvature values enable detection of finer surface irregularities, while larger minimum curvature values may smooth over smaller features in the measured profile 438.

[0055] The measurement principle illustrated in FIG. 4 is applicable to open hole measurement and is not restricted to tubular measurement. Open hole measurement refers to measurement within an uncased portion of a wellbore where the inner surface 406 is defined directly by the formation 404. Tubular measurement refers to measurement within an encased portion of a wellbore where the inner surface is defined by a casing or liner. The flexible arm 410 and the deflection sensor 416 may be used to measure the wellbore profile in either configuration, with the measured profile 438 representing the contour of the inner surface 406 regardless of whether the inner surface 406 is formed by the formation 404 or by a tubular element installed within the wellbore.

[0056] Beyond a given curvature, which may be derived for flexible arm design, the curvature produced by contact with the inner surface 406 may exceed a length of the flexible arm 410 itself. Thus, in at least one embodiment, the wellbore profile defined by the inner surface 406 may be determined using a position of a distal tip 414 of the flexible arm 410 extrapolated using the measured curvature of the deflection sensor 416. In addition, one or more embodiments of the flexible arm 410 shown in FIG. 4, as well as other flexible arms described herein, may include one or more features or components disposed at the distal tip 414 configured to reduce friction, and thus a drag force on the caliper tool, as well as reducing wear of the flexible arm 410 over time, especially frictional wear at the distal tip 414. These friction reducing features may include, but are not limited to, rollers, bearings, low friction material coatings, material portions at the tip including hard materials (e.g., ceramics such as glass, diamond…etc.), and so forth.

[0057] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIG. 4 can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIG. 4.

[0058] Referring to FIG. 5, a caliper 500 may be positioned within a wellbore 502. The caliper 500 includes a body 508 having a longitudinal axis extending through the body 508. The body 508 serves as the structural support for measurement components of the caliper 500. A plurality of flexible arms is rigidly attached to the body 508 and configured to extend radially outward beyond an outer surface of the body 508.

[0059] The plurality of flexible arms includes a flexible arm 510a and a flexible arm 510b positioned on opposite sides of the body 508. The flexible arm 510a and the flexible arm 510b are oriented for caliper measurements as the body 508 travels downward through the wellbore 502. The flexible arm 510a extends from one side of the body 508 toward a wall of the wellbore 502, and the flexible arm 510b extends from an opposite side of the body 508 toward the wall of the wellbore 502. Each flexible arm of the plurality of flexible arms is elastic and configured to behave as a cantilever beam when contacting a wellbore wall.

[0060] With continued reference to FIG. 5, a flexible arm 510c and a flexible arm 510d are shown in dotted lines to illustrate an alternative or optional configuration. The flexible arm 510c and the flexible arm 510d are configured for caliper measurements as the body 508 travels upward through the wellbore 502. The flexible arm 510c and the flexible arm 510d extend from the body 508 in an orientation opposite to the flexible arm 510a and the flexible arm 510b, enabling measurement during ascent through the wellbore 502. In at least one embodiment, all four arms 534a-d may be included in a single tool.

[0061] The caliper 500 includes a plurality of deflection sensors. Each deflection sensor of the plurality of deflection sensors is attached to a corresponding flexible arm of the plurality of flexible arms and configured to measure a curvature of the corresponding flexible arm. The plurality of flexible arms is provided along a perimeter of the outer surface of the body 508, and each flexible arm is equipped with a deflection sensor. In some embodiments, each deflection sensor of the plurality of deflection sensors includes a strain gauge attached at a base of the corresponding flexible arm of the plurality of flexible arms.

[0062] A wireline 540 is shown in dotted lines connected to the body 508. The wireline 540 represents an optional feature or alternative configuration for deployment of the caliper 500. The wireline 540 or other tethering mechanism may actively move the caliper 500 through the wellbore 502 instead of relying on buoyancy and ballast mechanisms as described previously with respect to other configurations. The wireline 540 may provide power and communication capabilities to the caliper 500 in addition to mechanical conveyance through the wellbore 502.

[0063] In at least one embodiment, an acquisition logger is provided within the body 508 of the caliper 500. The acquisition logger may record measurement data from the plurality of deflection sensors during logging operations. The acquisition logger may store curvature measurements from each deflection sensor as the caliper 500 traverses the wellbore 502, enabling reconstruction of the wellbore profile based on the recorded data.

[0064] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIG. 5 can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIG. 5.

[0065] Referring to FIG. 6A, a caliper 600 may be positioned within a wellbore 602. The caliper 600 includes a body 608 from which a first flexible arm 610a and a second flexible arm 610b extend toward walls of the wellbore 602. The first flexible arm 610a is attached to the body 608 via a first pivot mechanism 642a, and the second flexible arm 610b is attached to the body 608 via a second pivot mechanism 642b. The first pivot mechanism 642a and the second pivot mechanism 642b are positioned at the connection points between the respective flexible arms and the body 608.

[0066] The first flexible arm 610a is attached relative to the body 608 via the first pivot mechanism 642a, and the second flexible arm 610b is attached relative to the body 608 via the second pivot mechanism 642b. The first pivot mechanism 642a is configured to set and firmly hold an attachment angle of the first flexible arm 610a during a measurement operation. Similarly, the second pivot mechanism 642b is configured to set and firmly hold an attachment angle of the second flexible arm 610b during a measurement operation. The attachment angle may be between about 5 degrees and about 85 degrees relative to a longitudinal axis of the body 608, as described previously with respect to other configurations.

[0067] With continued reference to FIG. 6A, the first flexible arm 610a and the second flexible arm 610b are shown in an extended configuration for measurement operations. In the extended configuration, the first flexible arm 610a and the second flexible arm 610b extend outward from the body 608 and curve toward the walls of the wellbore 602. The first pivot mechanism 642a and the second pivot mechanism 642b maintain the preset attachment angles of the first flexible arm 610a and the second flexible arm 610b, respectively, enabling the flexible arms to contact the wellbore 602 walls and deflect as cantilever beams during measurement.

[0068] A collapse mechanism may act on the preset pivot angle articulation of the first pivot mechanism 642a and the second pivot mechanism 642b. The collapse mechanism may include a release of spring load that allows the first flexible arm 610a and the second flexible arm 610b to retract from the extended configuration. A preload system such as an O-ring may be provided to hold the weight of the first flexible arm 610a and the second flexible arm 610b in the extended configuration. The preload system may be strong enough to hold the position of the arms during measurement operations while allowing release when triggered.

[0069] An optional locking and unlocking system, such as a magnetic system, may be used to disconnect a weight and, or, to release the preload system in a simultaneous or sequential operation. As an example, when the caliper 600 reaches a predetermined location within the wellbore 602, the system retaining the weight may concurrently disengage the preload system, thereby allowing the collapse mechanism to retract the first flexible arm 610a and the second flexible arm 610b. In some embodiments, the caliper 600 stops descent upon contact with a central pillar positioned within the wellbore 602. Upon contact with the central pillar, the system may releases the weight and preload system and initiate retraction of the flexible arms around the pivot under the effect of the spring load.

[0070] Referring to FIG. 6B, the first pivot mechanism 642a is configured to retract the first flexible arm 610a along the body 608 during a free displacement operation. Similarly, the second pivot mechanism 642b is configured to retract the second flexible arm 610b along the body 608 during a free displacement operation. In the retracted configuration shown in FIG. 6B, the first flexible arm 610a and the second flexible arm 610b are positioned closer to the body 608 than in the extended configuration shown in FIG. 6A.

[0071] The configurations shown in FIGS. 6A and 6B may be used to deploy the caliper 600 in one direction while the first flexible arm 610a and the second flexible arm 610b are extended to measure the diameter of the wellbore 602. As shown in FIG. 6A, the caliper 600 may travel in a downward direction with the first flexible arm 610a and the second flexible arm 610b extended and contacting the walls of the wellbore 602 for measurement. As shown in FIG. 6B, the first flexible arm 610a and the second flexible arm 610b may be retracted to return or move the caliper 600 upward without the arms catching or snagging on the way back up. The retracted configuration reduces the radial extent of the first flexible arm 610a and the second flexible arm 610b, enabling the caliper 600 to travel through the wellbore 602 with reduced friction and without interference from wellbore wall irregularities.

[0072] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIGS. 6A and 6B can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIGS. 6A and 6B.

[0073] FIG. 7 illustrates another embodiment of a caliper 700 having an upper floating hub 707 slidably coupled, or otherwise movably engaged, with a lower floating hub 709. A first flexible arm 710a may be connected to the upper floating hub 707 at a first point of attachment 712a and connected to the lower floating hub 709 at a second point of attachment 712b. Similarly, a second flexible arm 710b may be connected to the upper floating hub 707 at a third point of attachment 712c and connected to the lower floating hub 709 at a fourth point of attachment 712d. Angles α and β describe the angle at which the flexible arms 710a, 710b are secured to the upper and lower floating hubs 707, 709 relative to a longitudinal axis 720 of the caliper 700.

[0074] In at least one embodiment, the caliper 700 also includes first and second deflection sensors 716a, 716b attached to the first flexible arm 710a and third and fourth deflection sensors 716c, 716d attached to the second flexible arm 710b. As the caliper travels through the wellbore 702, the flexible arms 710a, 710b may contact the inner surface 706 defining a variable diameter of the wellbore 702. The contact between the flexible arms 710a, 710b and the inner surface 706 may also define a length / magnitude 746 of a flat arm contact portion of the flexible arms 710a, 710b in contact with the inner surface 706. The upper floating hub 707 and the lower floating hub 709 may move relative to one another to define a gap 744 between the upper and lower floating hubs 707, 709, allowing the flexible arms 710a, 710b to deflect, thus changing curvatures, which can be measured by the deflection sensors 716a-d. The measured curvatures may be used to extrapolate and determine the diameter of the wellbore 702, including the profile of the wellbore 702 as the diameter is measured over time.

[0075] In at least one embodiment, in such a configuration shown in FIG. 7, as the first and second flexible arms 710a-b contact the inner surface 706 defining the wellbore 702, the upper floating hub 707 may move toward or away from the lower floating hub 709 to define the gap 744 therebetween. A magnitude of the gap 744 may change over time as the caliper 700 moves through the wellbore 702 and a diameter of the wellbore 702 varies. The gap 744 may be measured, for example via one or more sensors, and the diameter of the wellbore 702 may be determined based on the magnitude of the gap 744 and the known dimensions and properties of the flexible arms 710a, 710b.

[0076] Any of the features, components, and / or parts, including the arrangements and configurations thereof shown in FIG. 7 can be included, either alone or in any combination, in any of the other examples of devices, features, components, and parts shown in the other figures described herein. Likewise, any of the features, components, and / or parts, including the arrangements and configurations thereof shown and described with reference to the other figures can be included, either alone or in any combination, in the example of the devices, features, components, and parts shown in FIG. 7.

[0077] The embodiments of downhole tools have been primarily described with reference to wellbore monitoring, evaluation, and surveillance operations; the downhole tools described herein may be used in other environments or applications, such as drilling and open hole inspection. In other embodiments, downhole tools according to the present disclosure may be used outside a wellbore or other downhole environment used for the exploration or production of natural resources. For instance, downhole tools of the present disclosure may be used in a borehole used for placement of utility lines. Accordingly, the terms “wellbore,”“borehole” and the like should not be interpreted to limit tools, systems, assemblies, or methods of the present disclosure to any particular industry, field, or environment.

[0078] One or more specific embodiments of the present disclosure are described herein. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual embodiment may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one embodiment to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0079] Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

[0080] A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

[0081] The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A downhole caliper, comprising:a body having an axis;a flexible arm rigidly attached relative to the body, the flexible arm being elastic and configured to return to a straight orientation when no load is applied thereto; anda deflection sensor attached to the flexible arm and configured to determine a deflection of the flexible arm.

2. The downhole caliper of claim 1, wherein the flexible arm is attached relative to the body at an angle relative to the axis, the angle being between about 5 degrees and about 85 degrees.

3. The downhole caliper of claim 2, wherein the angle is between about 15 degrees and about 70 degrees.

4. The downhole caliper of claim 2, wherein the flexible arm is attached relative to the body via a pivot mechanism, and wherein the pivot mechanism is configured to set and firmly hold the angle during a measurement operation.

5. The downhole caliper of claim 4, wherein the pivot mechanism is configured to retract the flexible arm along the body during a free displacement operation.

6. The downhole caliper of claim 1, wherein a length of the flexible arm is less than a length of the body, the length of the body measured along the axis.

7. The downhole caliper of claim 6, wherein the length of the flexible arm is between about 50% and 200% of the diameter of the body.

8. The downhole caliper of claim 1, wherein a thickness of the flexible arm is less than 5 mm.

9. The downhole caliper of claim 1, wherein the deflection sensor comprises at least one of a strain gauge or a flex sensor.

10. The downhole caliper of claim 9, wherein the at least one of the strain gauge of the flex sensor is attached at a base of the flexible arm, the base of the flexible arm being closer to an attachment of the flexible arm to the body than a distal end of the flexible arm.

11. The downhole caliper of claim 1, further comprising:a plurality of flexible arms including the flexible arm; anda plurality of deflection sensors including the deflection sensor, each deflection sensor of the plurality of deflection sensors attached to a respective flexible arm of the plurality of flexible arms.

12. A well logging apparatus, comprising:a body having a longitudinal axis;a plurality of flexible arms rigidly attached to the body and configured to extend radially outward beyond an outer surface of the body, each flexible arm of the plurality of flexible arms being elastic and configured to behave as a cantilever beam when contacting a wellbore wall;a plurality of deflection sensors, each deflection sensor of the plurality of deflection sensors being attached to a corresponding flexible arm of the plurality of flexible arms and configured to measure a curvature of the corresponding flexible arm; anda buoyancy adjusting mechanism configured to adjust a buoyancy of the well logging apparatus.

13. The well logging apparatus of claim 12, wherein the buoyancy adjusting mechanism comprises a ballast tank.

14. The well logging apparatus of claim 12, wherein the buoyancy adjusting mechanism comprises a releasable weight.

15. The well logging apparatus of claim 14, wherein the releasable weight is dissolvable.

16. The well logging apparatus of claim 12, wherein each deflection sensor of the plurality of deflection sensors comprises a strain gauge attached at a base of the corresponding flexible arm of the plurality of flexible arms.

17. A downhole caliper, comprising:a body having an axis;a flexible arm rigidly attached relative to the body, the flexible arm being elastic and configured to return to a straight orientation when no load is applied thereto, the flexible arm having a width and a thickness, wherein the width is at least 1.5-times the thickness, and wherein the thickness is less than 10 mm; anda deflection sensor attached to the flexible arm and configured to determine a deflection of the flexible arm.

18. The downhole caliper of claim 17, wherein the thickness is less than 5 mm.

19. The downhole caliper of claim 18, wherein the thickness is less than 1 mm.

20. The downhole caliper of claim 17, wherein the flexible arm comprises at least one of a spring alloy, aluminum, titanium, copper alloy, plastic, or elastomer material.

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