# US 2021/0239448 A1 · Apparatus and method for determining borehole size with a borehole imaging tool > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0239448 A1 - Document ID: US20210239448A1 - Status: Published application - Kind: A1 - Application number: 17/217,734 - Filed: 2021-03-30 - Published: 2021-08-05 - Earliest claimed: 2015-02-17 - Assignees: Schlumberger Technology Corporation - Applicants: Schlumberger Technology Corporation - Inventors: Julien Toniolo; Alan J. Sallwasser; Peter Wells; Mark A. Fredette - Web page: https://patentgrep.com/patent/US20210239448A1 ## CPC - E21B 47/08: Measuring diameters or related dimensions at the borehole - G01B 7/13: Internal diameters - E21B 47/0025: {generating an image of the borehole wall using down-hole measurements, e.g. acoustic or electric} - G01B 5/0014: {due to temperature (on machine tools B23Q11/0003)} - G01B 5/12: internal diameters - G01V 3/26: operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device (with electromagnetic waves G01V3/30) - G01V 3/38: Processing data, e.g. for analysis, for interpretation, for correction - G01B 3/26: Plug gauges - E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) ## Abstract A downhole borehole imaging tool and methods for determining a borehole size includes a magnetoresistive system and a hub moveably coupled to a fixed tool string. The hub includes a magnet. The magnetoresistive system includes magnetoresistive sensors disposed within the fixed tool string and segregated from the magnet. During operation, a routine scan of all sensors measures, for example, the output voltage V, angle θ of magnetic field, and temperature. Measurements from each sensor may then be characterized to account for temperature and input voltages variation of the sensors. The most accurate measurement can be used to derive the position of the hub 44 using the previous baseline parameters stored in the tool. ## Claims ### Claim 1 A borehole imaging logging tool, comprising: at least two borehole microresistivity measuring pads, wherein each pad is disposed on a spring and the springs are disposed opposite one another and about a longitudinal axis of the logging tool; a hub disposed about and moveably coupled to a fixed tool string and to an end of each spring, wherein the hub comprises a magnet having a magnetic field; and an array of magnetoresistive sensors sensitive to an angle of the magnetic field of the magnet, the magnetoresistive sensors disposed in the tool string and configured to move along the longitudinal axis and through the hub. ### Claim 2 (depends on 1) The borehole imaging logging tool of claim 1, wherein the springs are bow springs and are oriented about the logging tool such that a distance across the longitudinal axis between the bow springs is greater than a diameter of the borehole. ### Claim 3 (depends on 1) The borehole imaging logging tool of claim 1, wherein the hub moves axially along the fixed tool string. ### Claim 4 (depends on 1) The borehole imaging logging tool of claim 1, wherein the magnetoresistive sensors are configured to measure the angle of the magnetic field relative to an axis of the array in response to an axial position of the hub, and wherein the magnetoresistive sensors are further configured to interact with the magnet spaced radially apart from the magnetoresistive sensors. ### Claim 5 (depends on 1) The borehole imaging logging tool of claim 1, further comprising a logging tool stored within a drill string extending into the borehole, wherein the array of magnetoresistive sensors is coupled to the logging tool and the logging tool is configured to extend through a drill bit disposed on an end of the drill string. ### Claim 6 (depends on 5) The borehole imaging logging tool of claim 5, wherein the logging tool is configured to make borehole measurements while the drill string is being removed from the borehole. ### Claim 7 (depends on 1) The borehole imaging logging tool of claim 1, further comprising a controller configured to determine an axial position of the hub based on angle measurements of the magnetic field relative to an axis of the array. ### Claim 8 (depends on 1) The borehole imaging logging tool of claim 1, further comprising: an additional at least two borehole microresistivity measuring pads, wherein each pad is disposed on an additional spring and the additional springs are disposed opposite one another and about the longitudinal axis of the logging tool; and an additional hub disposed about and moveably coupled to the fixed tool string and to an end of each additional spring, wherein the additional hub comprises an additional magnet having a magnetic field; wherein the array of magnetoresistive sensors is sensitive to an angle of the magnetic field of the additional magnet. ### Claim 9 A method for determining a borehole diameter from a borehole imaging tool, comprising: measuring an angle of a magnetic field relative to an axis of an array of magnetoresistive sensors where each magnetoresistive sensor will have a measured angle in response to an axial position of a hub; calibrating each sensor for temperature and input voltage; identifying sensors with more accurate calibrations; converting the angle measurements of magnetoresistive sensors into borehole diameter size using a relationship between a radial distance between sensing pads and an axial displacement of the hub. ### Claim 10 (depends on 9) The method of claim 9, comprising receiving a signal indicative of the hub position via a controller. ### Claim 11 (depends on 1) The method of claim 1, comprising sending the signal indicative of the hub position to the controller via a communication system communicatively coupled to the magnetoresistive sensors and to the controller. ### Claim 12 (depends on 9) The method of claim 9, comprising extending the borehole imaging tool through a drill bit in a borehole.