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of the borehole changes, creating a varying electrical signal that represents the changing shape of the borehole. This variation in output is translated into changes of diameter after a simple calibration and the caliper log is printed as a continuous series of values of hole diameter with depth.
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In most cases, the borehole's circumference will not be a perfect circle and therefore a caliper tool with several arms is required to obtain a true understanding of the size and shape of the borehole. The current state of the art is six independent mechanical arms that simultaneous record the
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logging. Electrical borehole imaging logs are typical created with 4, 6, or 8 armed tools, which can also be used to create a caliper log. Acoustic borehole imaging tools can create the most accurate and detailed caliper logs, using the pulse echo transit times with an independent acoustic
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radial distance from the center of the tool. Abrupt changes in borehole diameter, such as a washout at the bottom of casing, or thin fractures may not be accurately measured due to the geometry or range of the measurement arms.
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The caliper tool measures the variation in borehole diameter as it is withdrawn from the bottom of the hole, using two or more articulated arms that push against the borehole wall. Each arm is typically connected to a
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The borehole can also change to an oval shape while drilling, which typically occurs in doglegs where the axis of borehole is bending to
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velocity, but the range of this type of measurement is often limited by the high acoustic attenuation of the drilling fluid.
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tool may also be used to create a crude caliper log, which is limited along a single, high-side axis.
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as it drills, leading to spiraling shapes in the wellbore wall, as if the hole had been drilled by a
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This article related to natural gas, petroleum or the petroleum industry is a
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swelling in the borehole, which can affect the results of other well logs.
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tool that provides a continuous measurement of the size and shape of a
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http://www.glossary.oilfield.slb.com/Display.cfm?Term=caliper%20log
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Caliper logs may also be created from both acoustic and electrical
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