GB1460873A - Hydraulic drilling jar - Google Patents

Abstract

1460873 Boring earth &c J L DOWNEN 5 Feb 1975 [21 June 1974] 4813/75 Heading E1F An hydraulic drilling jar comprises an upper sub 21 Fig. 1 having an integral mandrel 35, a lower sub 25 terminating upwardly in an external sleeve 28, a spline sub 68 connected at its lower end to the lower sub, a sleeve 67 provided on the upper end of the spline sub, and a dashpot jar tensioning and tripping mechanism located in the annular space between the mandrel and sleeve 67. An annular anvil face is provided on the lower end of the spline sub 68 and a hammer 61 is connected to the lower end of the mandrel. In operation the mandrel is first lowered through the sleeve 67 and splined sub 68 with operating oil passing up the outside of an orifice ring 56, Fig. 7, between ground faces 59, 54 of the ring and a sleeve valve 53, then upwardly between the sleeve valve and mandrel and between the sleeve valve and a stop 39 via notches 55. Tensioning of the string and thus raising of the mandrel brings the faces 54, 59 into sealing contact and passage of the oil downwardly is only possible through a metering gap 57 between the ring and mandrel. The high buildup of pressure in the oil is suddenly released to cause jarring when the sleeve valve moves out of the closely fitting bore 75 into the enlarged bore 83.