Hydraulic lock apparatus

A downhole hydraulic lock apparatus, comprising:

• a lock operator piston arranged to be axially moveable in a piston chamber, the lock operator piston sealing the piston chamber to define a first seal area;
• a fluid release valve comprising a valve port, a valve chamber a valve member, and a seal assembly axially moveable within the valve chamber, wherein the fluid release valve is reconfigurable from a sealing arrangement, in which the seal assembly seals between the valve chamber and the valve member, to an open arrangement, in which the seal assembly does not seal between the valve chamber and the valve member, and wherein the seal assembly defines a second seal area when in the sealing arrangement;
• and
• a hydraulic chamber extending between the piston chamber and the valve chamber such that the first seal area of the lock operator piston and the second seal area of the seal assembly are operatively associated with each other by said hydraulic chambers,
• wherein the first seal area defined by the lock operator piston in the piston chamber is larger than the second seal area defined by the valve member between the valve chamber and the valve members, and
• wherein the fluid seal assembly is moveable in the valve chamber by a first distance, from the sealing arrangement, in which the hydraulic chamber is isolated from the valve port by the seal assembly, to the open arrangement, in which the hydraulic chamber is in fluid communication with the valve port via the valve chamber, in response to a differential pressure cycle being applied to the seal assembly over the second seal area by movement of the lock operator piston in the piston chamber, the movement of the lock operator piston in the piston chamber being in a direction towards the hydraulic chamber and over a second distance, wherein the second distance is less than the first distance.