GB716761A - Improvements in or relating to drill assemblies - Google Patents

Abstract

716,761. Earth-boring apparatus. STANDARD OIL DEVELOPMENT CO. Nov. 6, 1952 [Jan. 29, 1952], No. 28019/52. Class 85. Secured to the lower end of a rotatable string of drill pipe or casing is a collar 1 adapted to receive a drill which is passed through the drill string, the bore of the collar being formed with grooves 4, 5 and an outward taper 3. The drill consists of a mandrel 8 having spring-biased latches 30 at the upper end, a tapered lower end and two or more, preferably three, longitudinal grooves. In each groove slide a member 13, 14 having a spring-biased latch 6 at the upper end and, at the lower end a flexible suspension arm 15 on which is pivotally mounted a cutter support. To remove the drill from the operating position, as shown in Fig. 1, a spearhead is lowered down the drill string to contact latches 30 and disengage and maintain them clear of the groove 4 and the interior of the drill string. The spearhead is then raised, so drawing up the mandrel 8 to thus remove the tapered lower end of it from out of contact with the cutter supports. The members 13, 14 remain stationary with respect to the collar owing to the frictional engagement of the latches therewith until abutments 24, 26 on the mandrel engage abutments 23, 25 on said members 13, 14. Subsequent upward movement of the mandrel results in withdrawal of the drill through the drill string. The abutments 23, 25 are disposed at different distances from the upper ends of members 13, 14 respectively so that the members 13, 14 start to move upwards in a controlled sequence. To set the drill, it is lowered through the string. Latches 6 move out into the groove 5 to prevent further downward movement of the members 13, 14 whilst the mandrel 8 continues to move downwards until its tapered nose has wedged the cutter supports against the taper 3 of the bore of the collar. At this point latches 30 move out into grooves 4 to prevent upward movement of the drill when the weight of the drill string is transferred to the cutters to rotate them. In a modified form the latches 30 have an adjustable mounting on the mandrel, the mounting being used to set a packer sleeve when the drill is in position. A single groove of suitable dimensions may replace the grooves 4. 5.