Patent ID: 6045335
Filing Date: 2000-04-04
Classification: E21B,F04B

Abstract:
A differential pressure operated free piston for lifting well fluids from a subterranean reservoir to the surface through a well conduit which extends upwardly from said reservoir to said surface and which is provided near the lower end thereof with stop means, said free piston comprising:a piston body adapted for up and down sliding disposition within said conduit having an upper portion, a lower portion and an intermediate portion of reduced diameter, downwardly facing surfaces of said upper portion, upper facing surfaces of said lower portion and the exterior of said intermediate portion substantially defining an elongated cylindrical space having a central axis which coincides with the axis of said piston body; andsealing means carried in said cylindrical space comprising upper and lower juxtaposed sets of longitudinally separated cylindrical segments, each of said segments providing relatively smooth cylindrical surfaces on the exterior thereof for sliding and sealing contact with inner walls of said conduit, the lower ends of each segment of said upper set and the upper ends of each segment of said lower set providing relatively smooth mutually engaging surfaces for sliding and sealing contact therebetween, said upper and lower set of segments being radially oriented so that separations between the segments of said upper set and separations between the segments of said lower set are not aligned, said separations of each set of segments being blocked by mutually engaging surfaces on the opposing set of segments, said sealing means including a rigid ring member surrounding said intermediate portion of said piston body having upper and lower surfaces mutually and respectively, sealingly engageable by corresponding surfaces on said lower ends of said upper set of cylindrical segments and said upper ends of said lower set of cylindrical segments, said sealing means providing a seal which allows said free piston to gravitate through said conduit toward said stop means and providing sufficient sealing, when pressure in said well conduit near said surface is subsequently reduced, to elevate said piston and well fluids thereabove to said surface.