GB846332A - Improvements in or relating to well drilling - Google Patents

Abstract

846,332. Boring earth. HILL, J. E. Jan. 1, 1958, No. 77/58. Class 85. [Also in Group XXVI]. A tool, interposed in a drill string, comprises a tubular body 14, 15, connected to an upper part of the string, a tubular mandrel 16 slidable in the body and connected to a lower part of the string, means limiting the longitudinal and rotational movement of the mandrel within the body, a seal 27 within the body adjacent the top of the mandrel and having a bore providing communication between the bores of the body and mandrel, and means urging the seal into engagement with the end of the - mandrel and the wall of the body. The tool shown is designed to give optimum pressure on a rotary drill bit, and to act as a spudding mechanism or a jar should the lower part of the string become stuck. The seal is pressed on to the mandrel by a cup 29 urged by a spring 30. The mandrel has formed on each side a key comprising bosses 40 joined by a rib 41, and the body has formed on each side of the interior a row of bosses 39, the arrangement being that when the string is rotated for drilling the ribs 41 each engage a side of a row of bosses 39. The pressure on the bit may be adjusted by adding or subtracting collars to the string below the tool, the bit pressure being obtained by subtracting the reading of a weight indicator when the bit just touches the hole bottom with the tool extended from the reading when the bit is just clear of the hole bottom. At the start of a drilling operation the tool is contracted, and as drilling proceeds, the ribs slide down the ends of the bosses 39 until the tool is fully extended when the operation stops. The upper part of the string is then lowered to contract the tool and the operations are repeated as required. Should the string below the tool become stuck, the upper part of the string may be worked up and down as in a spudding operation to free the lower part of the string, so the tool may be used as a jar. To use the tool to jar in the downward direction, the upper part of the string is raised to extend the tool, a torque in the drilling direction is applied to twist the upper part of the string, the torque is slowly released to urge the bosses 39 to engage in the keys, and pressure is exerted on the upper part of the string which is then rotated in the drilling direction to free the keys and cause the part A of the body to strike the connector 17. To use the tool to jar in the upward direction, the upper part of the string is lowered to contract the tool, a torque in the drilling direction is applied to the upper part of the string, the torque is slowly released to urge the bosses 39 to engage with the keys, and a tension is applied to the upper part of the string which is then rotated in the drilling direction to free the keys and cause the part C of the body to strike the part D of the mandrel. In a modified tool, which is primarily used as a jar, the ribs are at the other ends of the bosses 40. Specification 846,333 is referred to.