Downhole pump with a pressure sequencing valve

Abstract

A downhole pump has a master piston having a first side and a second side in a first piston chamber. The first piston chamber has a first inlet and a second inlet for alternatingly applying fluid pressure to the first side of the master piston to move the piston toward the top of a piston stroke, and to the second side of the master piston to move the piston toward the bottom of the piston stroke. A valve is carried by the master piston that relieves fluid pressure from the respective side of the master piston once the top or bottom of the stroke is reached. There is a sequencing valve with a first state that applies fluid pressure to the first inlet and a second state that applies fluid pressure to the second inlet. The sequencing valve switches between the first state and the second state once a drop in pressure occurs. A slave piston is driven by the master piston in a second piston chamber. The second piston chamber has at least one fluid inlet and at least one fluid outlet.

What is claimed is: 
     
         1 . A downhole pump, comprising:
 a master piston having a first side and a second side in a first piston chamber, the first piston chamber comprising a first inlet and a second inlet for alternatingly applying fluid pressure to the first side of the master piston to move the piston toward the top of a piston stroke, and to the second side of the master piston to move the piston toward the bottom of the piston stroke;   a valve carried by the master piston that relieves fluid pressure from the respective side of the master piston once the top or bottom of the stroke is reached;   a sequencing valve having a first state that applies fluid pressure to the first inlet and a second state that applies fluid pressure to the second inlet, the sequencing valve switching between the first state and the second state once a drop in pressure occurs; and   a slave piston driven by the master piston in a second piston chamber, the second piston chamber having at least one fluid inlet and at least one fluid outlet.   
     
     
         2 . The downhole pump of  claim 1 , wherein the valve is a poppet valve that opens a flow passage through the master piston. 
     
     
         3 . The downhole pump of  claim 1 , wherein the slave piston is a double-acting piston and the second piston chamber has a fluid inlet and a fluid outlet on each side of the slave piston. 
     
     
         4 . The downhole pump of  claim 1 , wherein the master cylinder is driven by a gas. 
     
     
         5 . The downhole pump of  claim 1 , wherein the gas expelled from the master cylinder is expelled into at least one fluid outlet of the second piston chamber. 
     
     
         6 . The downhole pump of  claim 1 , further comprising a travelling liquid seal carried by the slave piston that engages an inner surface of the second piston chamber, the travelling liquid creating a seal against fluid while permitting gas to pass. 
     
     
         7 . The downhole pump of  claim 6 , wherein the second piston chamber comprises a first outlet on a first side of the slave piston and a second outlet on a second side of the slave piston, wherein the gas that passes the travelling liquid seal exits through the second outlet. 
     
     
         8 . A downhole pump, comprising:
 a piston in a piston chamber;   a motive force for driving the piston;   a travelling liquid seal carried by the piston that engages an inner surface of the second piston chamber, the travelling liquid creating a seal against fluid while permitting gas to pass; and   the second piston chamber comprising a fluid inlet and a first outlet on a first side of the slave piston and a second outlet on a second side of the slave piston, wherein the gas that passes the travelling liquid seal exits through the second outlet.