WELL BACKSURGING APPARATUS AND METHOD

摘要

A well backsurge tool for lowering down an oil or gas well at the end of a tubing or drill string comprises a body (10) having an upper end securable to the string and ports (22) in the wall thereof, a detachable cap (12) normally closing the ports (22) and the lower end of the body (10) and retained in place by releasable balls (13), themselves retained by a displaceable sleeve (30) sealed to the body by O-ring (32) and larger diameter O-ring (33) and located thereto by shear pin (31). Reduction of pressure in the string causes downward displacement of the sleeve (30), release of the balls (13), and consequent downward movement of the cap (12), assisted by spring (24). In alternative embodiments the sleeve (30) is mechanically displaced by dropping a bar or by breaking plugs to release a fluid from a hydraulic reservoir previously resisting displacement of the sleeve by differential well bore hydrostatic pressure. Sudden release of a higher well bore hydrostatic pressure in the region of the perforations to a lower hydrostatic pressure within the string, causes fluid flow from the reservoir to the wellbore and thus backsurges the perforations.