Anti-gas lock valve for a reciprocating downhole pump

A method of overcoming gas-lock in a pump positioned in a subterranean wellbore, the pump having a barrel forming a pump chamber and a reciprocating plunger positioned therein, the plunger reciprocating uphole on an upstroke and downhole on a downstroke, and the pump having at least one standing valve in fluid communication with a downhole inlet end of the barrel, for receiving a charge of fluid from the subterranean wellbore into the pump chamber, and at least one traveling valve in fluid communication with a downhole inlet end of the plunger, the method comprising:

• providing a pre-valve having a downhole inlet end forming a chamber valve in fluid communication with the pump chamber, for receiving the charge of fluid from the pump chamber into a staging chamber formed therein, and having an uphole outlet end in fluid communication with the at least one traveling valve for discharging fluid from the pre-valve staging chamber through the at least one traveling valve, the pre-valve comprising:
• a mandrel operatively reciprocated with the plunger, the mandrel having a first uphole annular stop and a second downhole annular stop, and forming a space between the first and second annular stops, and
• a sleeve, having a length, located concentrically about the mandrel and movable therealong between the first and second annular stops, wherein the chamber valve is formed by the clearance between the length of the sleeve and the space between the first and second annular stops;
• reciprocating the plunger uphole, shifting the sleeve downhole along the mandrel, closing the chamber valve and opening the at least one standing valve to receive the charge of fluid from the subterranean wellbore into the pump chamber;
• reciprocating the plunger downhole, compressing the charge of fluid in the pump chamber, shifting the sleeve uphole along the mandrel, opening the chamber valve and receiving at least a portion of the charge of fluid from the pump chamber into the staging chamber;
• reciprocating the plunger uphole, shifting the sleeve downhole along the mandrel, closing the chamber valve and sealably retaining the at least a portion of the charge of fluid within the staging chamber while re-opening the at least one standing valve and drawing a further charge of fluid from the subterranean wellbore into the pump chamber;
• reciprocating the plunger downhole, compressing the further charge of fluid in the pump chamber, shifting the sleeve uphole along the mandrel, opening the chamber valve and receiving at least a portion of the further charge of fluid from the pump chamber into the staging chamber;
• and
• repeatedly reciprocating the plunger uphole and downhole wherein on each downstroke, a pressure of the charge of fluid received in the pump chamber increases until it exceeds the hydrostatic head uphole of the at least one travelling valve, opening the at least one traveling valve for normal fluid pumping.