Patent ID: 7866397
Filing Date: 2011-01-11
Classification: E21B

Abstract:
1. An activating mechanism for controlling the operation of a downhole underreamer tool in a drill string and which is intended to be housed in a portion of the drill string upstream of the downhole underreamer tool, in which: (a) the activating mechanism has a first mode in which it allows through-flow of drilling fluid to the downhole underreamer tool in an operative condition and a second mode in which through-flow of fluid is blocked in an inoperative condition; (b) the activating mechanism has a number of through-flow ports permitting through-flow of drilling fluid in said first mode of the mechanism and which are capable of being blocked by launching a number of flow blocking activator balls down the drill string and which each are of such size and shape that they can block access to said through-flow ports in order to activate the mechanism to the second mode and thereby adjust the downhole underreamer tool from one mode of operation to another; and (c) the inoperative condition is obtained when the reamer blades are in a withdrawn position relative to the body of the tool, and in the operative condition the reamer blades are in a radially projected position relative to the axis of the drill string so as to be engageable with the surrounding formation.