ES344977A1 - Well tool - Google Patents

Abstract

A retrievable bridge plug for a well bore has expanding grips for the bore wall which are urged against the wall by a pressure differential across the seal in either direction. The plug has a body 10 with a central bore 11 communicating with ports 12 (at the bottom) and 17 (near the top) in the body which facilitates sinking the plug in a liquid filled well. The plug is lowered by a tube string which engages a socket 14 and sleeve valve 20 for the port 17 at the top of the plug. Expandable grips 70 are resiliently mounted on a cage 50 mounted by buttressthreaded split nuts 57, 58 on the body 10. Further wall grips 53 hold the cage against rotation so that the body can be rotated to release the nut 57, the nut 58 then engaging threads 63 (Fig. 5B, not shown so that on continued rotation, the body is screwed down inside the cage and the grips 70 are pressed against the wall by a conical skirt 73 of a piston 36, and at the same time the plug seal ring 31 is compressed between the piston 36 and an abutment 27 on the body, and squeezed against the wall. When the tube string is disconnected from the socket 14 it also lifts the sleeve valve 20 to close the port 17, which would otherwise by-pass the seal 31. The top of the piston 36 is in communication with the bore below the seal 31, and the bottom of the piston is in communication, via bores 80, 81, 82 with the bore above the seal. Thus, if the pressure below the seal is greater than that above it, the piston will be urged downwardly and through the conical skirt 73, will increase the force on the grips 70. If the pressure above the seal is greater, then the pressure on the seal is transmitted by abutment with the flange 30 to the piston 36, and the resultant force is downwards. That is, the top of piston 36 is effectively always subjected to the greater of the two pressures, and partial areas beneath the piston are subject to each of the pressures, so that the resultant force is always downwards. In a modification, (Fig. 6, not shown), the flange 46 below the piston 36 is replaced by a free piston.