Multi-stage pressure maintenance device for subterranean well tool

摘要

A thermal compensating apparatus and method for maintaining a substantially constant fluid pressure within a subterranean well tool of the type that includes a bladder that is selectively expandable upon the introduction of pressurized actuation fluid for actuating said tool at a location in a well. A multi-stage piston is movable in a housing. The piston includes a first surface in contact with the actuating fluid and a plurality of second surfaces in contact with well fluid surrounding the apparatus. The combined surface areas of the second surfaces are greater than the surface area of the first surface, so that expansion or contraction changes in the volume of the actuating fluid caused by temperature changes in the vicinity of the tool will result in movement of the piston for maintaining the actuating fluid at a relatively constant pressure.