Plunger for lifiting fluids within a tubing string

Abstract

There is disclosed a rotary-pad gas lift plunger. In an embodiment, the pads rotate around the mandrel. This rotation movement results from two features. The first one is the assembly of the mandrel and the pad retaining rings. The second one is the shape of the wearing pad. The rotation movement results from the plunger travel up and down within the tubing. Rotation with uniform wearing helps to maintain the sealing effect between the wearing pads and the inside of the tubing. This uniform wearing on the surface of pads improves efficiency to displace oil and water from oil and gas wells. The uniform wearing also causes a significant increase in the service life of the plunger. Because of the rotation movement, this gas lift plunger can operate in deviated wells where a typical gas lift plunger is restricted.

What is claimed is: 
     
         1 . A plunger for lifting fluids within a tubing string of a hydrocarbon well, comprising:
 an elongated mandrel having a mandrel axis and a circumferential surface;   
       at least 2 arcuate pads having each a pad upper end and a pad lower end and disposed circumferentially around the mandrel to form a pad set, each arcuate pad having a wear surface cooperating to form a substantially contiguous cylindrical seal against an inner surface of the tubing string;
 at least one spring disposed between the mandrel and the arcuate pad for biasing the arcuate pad outwardly radially such that the wear surfaces are moveably in contact with the inner surface of the tubing string; 
 at least one circular guide disposed on the mandrel and each engaging a complementary receptacle of the arcuate pad for substantially restricting the motion of the arcuate pad to be circumferential around the mandrel axis; 
 
       an annular retainer disposed around the mandrel and positioned to enclose one of the pad upper end, the pad lower end, the pad upper end of one pad set and the pad lower end of another pad set, the annular retainer limiting outward radial movement of the arcuate pad; and
 wherein the at least one circular guide, the complementary receptacles, the springs, and the annular retainers cooperate to allow rotation of the arcuate pads about the mandrel axis while radially biasing the arcuate pads against the inner surface of the tubing string, thereby lifting fluids within the tubing string. 
 
     
     
         2 . The plunger of  claim 1 , further comprising a bypass for conducting fluid axially through a central portion of the mandrel and comprising an elongated mandrel hollow, a bypass inlet, and a bypass actuator, where the bypass actuator opens the bypass inlet and allows fluid into the mandrel hollow. 
     
     
         3 . The plunger of  claim 1 , further comprising at least two pad sets stacked axially along the mandrel, wherein 4 arcuate pads comprise the pad set, each pad set independently forming a cylindrical seal with the inner surface of the tubing string. 
     
     
         4 . The plunger of  claim 3 , further comprising maintaining an angular offset between a first pad set and a second pad set, where a pad gap between a pad side edge of each of two adjacent arcuate pads forms a channel allowing fluid slippage, the pad gap of the first pad set being circumferentially offset from the pad gap of the second pad set, thereby creating the angular offset limiting fluid slippage. 
     
     
         5 . The plunger of  claim 1 , wherein the annular retainer is a cylindrical sleeve having a collar lip for retaining one of the pad upper end and the pad lower end. 
     
     
         6 . The plunger of  claim 1 , further comprising a plurality of spiral grooves in at least one of a top end and a bottom end of the mandrel for encouraging rotation of the plunger traveling in a fluid. 
     
     
         7 . The plunger of  claim 1 , wherein 4 arcuate pads comprise the pad set and each arcuate pad is shaped as a rhombus for establishing a pad gap oblique to the mandrel axis by a pad slant angle of less than approximately 35 degrees, the pad gap separating a pad side edge of each of two adjacent arcuate pads and providing a channel for fluids to flow between the pad upper end and the pad lower end, thereby encouraging rotation of the arcuate pads traveling in a fluid. 
     
     
         8 . The plunger of  claim 1 , wherein the circular guide comprises a mandrel end capping an end of the mandrel and a finger ring bearing rotatably on the circumferential surface and restrained axially outwardly by the mandrel end, each finger ring projecting a finger axially inwardly into the complementary receptacle at one of the pad upper end and the pad lower end of each arcuate pad, where the complementary receptacle is a pad cutout opening axially outwardly, where the fingers and the pad cutouts retain the arcuate pads while allowing radial movement, and where the annular retainer is an end collar disposed around each finger ring. 
     
     
         9 . The plunger of  claim 8 , further comprising a bypass for conducting fluid axially through a central portion of the mandrel and comprising an elongated mandrel hollow, a bypass inlet, and a bypass actuator, where the bypass actuator opens the bypass inlet and allows fluid into the mandrel hollow. 
     
     
         10 . The plunger of  claim 8 , wherein 4 arcuate pads comprise the pad set and each arcuate pad is shaped as a rhombus for establishing a pad gap oblique to the mandrel axis by a pad slant angle of less than approximately 35 degrees, the pad gap separating a pad side edge of each of two adjacent arcuate pads and providing a channel for fluids to flow between the pad upper end and the pad lower end, thereby encouraging rotation of the arcuate pads traveling in a fluid. 
     
     
         11 . The plunger of  claim 8 , further comprising multiple pad sets and a central finger ring bearing rotatably on the circumferential surface lying between two adjacent pad sets, the central finger ring projecting fingers into the pad cutouts of one pad set, and further comprising a clocking ring mating with the central finger ring such that they rotate together, the clocking ring projecting fingers into the pad cutouts of the adjacent pad set such that both pad sets are clocked at an angular offset for restricting fluid slippage axially though a pad gap between adjacent arcuate pads. 
     
     
         12 . The plunger of  claim 11 , where the annular retainer is a central collar disposed around both the finger ring and the clocking ring and having a collar lip at each end for limiting outward radial movement of the pad upper ends and the pad lower ends. 
     
     
         13 . The plunger of  claim 11 , wherein 4 arcuate pads comprise the pad set. 
     
     
         14 . A plunger for lifting fluids within a tubing string of a hydrocarbon well, comprising:
 an elongated mandrel having a mandrel axis and a circumferential surface;   
       at least 2 arcuate pads having each a pad upper end and a pad lower end and disposed circumferentially around the mandrel to form a pad set, each arcuate pad having a wear surface arcing between two pad side edges and cooperating to form a substantially contiguous cylindrical seal against an inner surface of the tubing string; 
       at least one spring disposed between the mandrel and the arcuate pad for biasing the arcuate pad outwardly radially such that the wear surfaces are moveably in contact with the inner surface of the tubing string;
 an annular retainer disposed around the mandrel and positioned to enclose one of the pad upper end, the pad lower end, the pad upper end of a first pad set and the pad lower end of a second pad set, the annular retainer limiting outward radial movement of the arcuate pad; 
 a pad gap separating the pad side edges of two adjacent arcuate pads and providing a channel for fluids to flow between the pad upper end and the pad lower end; and 
 wherein each arcuate pad is shaped as a rhombus for slanting the pad gap oblique to the mandrel axis by a pad slant angle of less than approximately 35 degrees, thereby encouraging rotation of the arcuate pads. 
 
     
     
         15 . The plunger of  claim 14 , wherein a bypass for conducting fluid axially through a central portion of the mandrel and comprising an elongated mandrel hollow, a bypass inlet, and a bypass actuator, where the bypass actuator opens the bypass inlet and allows fluid into the mandrel hollow. 
     
     
         16 . The plunger of  claim 14 , further comprising at least two pad sets stacked axially along the mandrel, wherein 4 arcuate pads comprise the pad set, each pad set independently forming a cylindrical seal with the inner surface of the tubing string. 
     
     
         17 . The plunger of  claim 16 , further comprising maintaining an angular offset between the first pad set and the second pad set. 
     
     
         18 . The plunger of  claim 14 , wherein the annular retainer is one of a cylindrical sleeve having a collar lip for retaining the arcuate pad, an annular lip disposed on the circumferential surface of the mandrel for retaining the arcuate pad. 
     
     
         19 . The plunger of  claim 14 , further comprising at least one circular guide disposed on the mandrel and each engaging a complementary receptacle of the arcuate pad for substantially restricting the motion of the arcuate pad to be circumferential around the mandrel axis, wherein the at least one circular guide, the complementary receptacles, the springs, and the annular retainers cooperate to allow rotation of the arcuate pads about the mandrel axis while radially biasing the arcuate pads against the inner surface of the tubing string, thereby lifting fluids within the tubing string. 
     
     
         20 . The plunger of  claim 14 , further comprising a plurality of spiral grooves in at least one of a top end and a bottom end of the mandrel for encouraging rotation of the plunger traveling in a fluid.