Patent attributes
A shifting sleeve has differential piston areas so that applied pressure displaces the sleeve against spring bias, which preferably is a series of Belleville washer stacks associated with modular mandrel components, to obtain the desired opposing force to the movement initiated with pressure applied to differential piston areas. An indexing feature is located between the sleeve and the mandrel passage wall and on a predetermined number of cycles disables the Belleville washer stacks from biasing the sleeve in an opposed direction as when pressure is applied. At this time the pressure in the mandrel acting on the differential piston area simply shifts the sleeve to open a lateral port so that fracturing through the cement that was earlier placed with the port closed can take place.
