Plunger list assembly with an improved free piston assembly

Abstract

An improved free piston assembly for use in combination with a plunger lift assembly is provided. The piston assembly includes a sleeve member, a retention sleeve, and a flow restriction member. The sleeve member has an inner surface defining an opening for the flow of formation fluids. The opening includes a first section and a second section. The retention sleeve is configured to be affixed to the first section of the opening. The flow restriction member is not latched to the sleeve member and is configured to have an interference fit with the retention sleeve. The interference fit provides a force that is sufficient to overcome the force of gravity on the flow restriction member when formation fluid forces acting on the flow restriction member are decreased or removed. The second section of the opening is configured to prevent the passage of the flow restriction member.

What is claimed is: 
     
         1 . A piston assembly comprising:
 (a) a sleeve member having an inner surface, the inner surface providing a seat to accommodate a flow restriction member;   (b) the flow restriction member without being latched to the sleeve member configured to move between a seated position and an unseated position, wherein in the seated position the flow restriction member is in physical contact with the seat and prevents the flow of fluids through the sleeve member, and wherein in the unseated position the flow restriction member permits the flow of fluids through the sleeve member;
 wherein the sleeve member includes a raised lip for retaining the flow restriction member in the sleeve member, wherein the raised lip provides sufficient retention force to overcome the force of gravity on the flow restriction member when fluid forces acting on the flow restriction member are decreased or removed, the raised lip is physically spaced apart from the flow restriction member when the flow restriction member is in the seated position, and the raised lip is in physical contact with the flow restriction member when the flow restriction member is in the unseated position; and 
 wherein the entire flow restriction member is within the sleeve member. 
   
     
     
         2 . The piston assembly of  claim 1 , wherein the sleeve member further includes a first section and a second section, wherein the raised lip is located in the first section and the second section includes an opening that is configured to prevent the passage of the flow restriction member through the opening. 
     
     
         3 . The piston assembly of  claim 2 , wherein the flow restriction member is configured to move between the seated position and the unseated position in the first section. 
     
     
         4 . The piston assembly of  claim 2 , wherein the raised lip retains the flow restriction member in the first section. 
     
     
         5 . The piston assembly of  claim 2 , wherein the opening is configured to receive a separator rod. 
     
     
         6 . The piston assembly of  claim 2 , wherein the flow restriction member is configured to seal the opening in the seated position. 
     
     
         7 . The piston assembly of  claim 1 , wherein the raised lip is located on the inner surface of the sleeve member. 
     
     
         8 . The piston assembly of  claim 1 , wherein the sleeve member further includes an outer contoured surface configured to create a turbulent fluid flow when the piston assembly is transported in a production tubing. 
     
     
         9 . The piston assembly of  claim 1 , wherein the sleeve member is cylindrical. 
     
     
         10 . The piston assembly of  claim 1 , wherein the raised lip is a discontinuous raised lip. 
     
     
         11 . The piston assembly of  claim 1 , wherein the flow restriction member is a ball. 
     
     
         12 . The piston assembly of  claim 1 , wherein the sleeve member is made from a material selected from the group consisting of stainless steel, chrome steel, cobalt, zirconium ceramic, tungsten carbide, silicon nitride and titanium alloys. 
     
     
         13 . The piston assembly of  claim 1 , wherein the flow restriction member is made from a material selected from the group consisting of stainless steel, chrome steel, cobalt, zirconium ceramic, tungsten carbide, silicon nitride and titanium alloys.