History Of The Caliper

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Joseph A. Houston’s caliper was suspended in the well with threaded joints of pipe. In 1920, a patent was issued to Jean Amedée Hardel for a device to line oil wells with cement. Part of the 1920 patent was a caliper to be used to determine the amount of cement required for the lining operation, perhaps the first caliper to be run on flexible cable. This early caliper contained an internal chart recorder, and spring loaded arms with wheels rolling against the borehole wall. The arms were not retractable (unnecessary with wheeled arms), and used an interesting cable arrangement to transmit the arm movement to the recording mechanism. In 1929, a patent was issued to James J. Cabot entitled "Cave Finder", perhaps the first caliper to be run on electric wireline. Mr. Cabot wished to provide a device whereby drillers or operators could determine the actual depths of caves in a borehole (washouts in rotary holes or simple caving areas in cable tool holes). This device used a spring loaded articulated arm comprised of three separate elements. The arms were not retractable, and the articulated design allowed logging up or down. The arms were connected to a switch that opened when the arms extended past a set point. An incandescent indicator lamp would extinguish at the surface when the Cabot device found a cave. Caliper development continued through the 1940's, driven in part by the new dipmeter log concept. Halliburton also acquired the 1944 Finley T. Robidoux caliper patent. The Robidoux device more closely resembled a modern caliper tool with conventional spring loaded arms that could be held closed while entering the well, then released at will. The original design used an explosive squib to break a band that retained the arms. Later an electromechanical latch was used (solenoid), a design that survived into the 1980's in the Dowell / Worth Well / Bell caliper

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