Patent Abstract:
An automatic choke has two piston-cylinder assemblies mounted within a housing having an inlet and an outlet. The piston-cylinder assemblies are connected in a closed hydraulic loop configuration. One piston-cylinder assembly is responsive to pressures at the inlet and the other piston-cylinder assembly controls valve at the outlet.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns an automatic choke and in particular to an automatic choke which will compensate for irregular pressures developed in producing petroleum wells and to assist in their unloading and production flow. 
     2. The Prior Art 
     wells producing oil and gas rely upon pressure within the well to drive the fluids to the surface. Sometimes wells have, for one reason or another, temporary or periodic irregular pressures caused by fluid loading. These variants in pressure adversely affect the production by lowering the flow rate from the well. As a well produces fluid, the pressure driving the fluid will normally drop. Production also goes down with the pressure as it is pressure dependent. 
     SUMMARY OF THE INVENTION 
     The present invention is an automatic choke unit having a pair of piston-cylinder assemblies one of which is spring loaded and the other of which controls valve means. The piston-cylinder assemblies are of different diameters and connected to form a hydraulic system which is responsive to fluid pressure in associated system thereby controlling production in that system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a longitudinal diagrammatic section through the automatic choke of the present invention in a first condition; and 
     FIG. 2 is a view similar to FIG. 1 showing the subject automatic choke in a second condition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention 10 is shown in FIGS. 1 and 2 as it would be mounted in a production pipe 12. The subject automatic choke 10 has a cylindrical housing 14 having a first end plate 16 defining an inlet port 18 and a second end plate 20 defining an outlet port 22 and a central chamber 24. The inlet and outlet ports 18, 22 are oppositely axially offset. A pair of piston-cylindrical assemblies 26, 28 are mounted within chamber 24. 
     The first assembly 26 is generally aligned and coaxial with the inlet port 18 and the second assembly 28 is generally aligned with and coaxial with the outlet port 22. The first assembly 26 has a cylinder 30 closed at end 32 by end plate 20, a piston 34 mounted therein and biased by spring 36 mounted between the piston 34 and the end plate 20. The cylinder 30, end plate 20 and piston 34 define a variable volume chamber 38. 
     The second assembly 28 has an open ended outer cylinder 40 and an inner cylinder 42 coaxially mounted within the outer cylinder 40. The inner cylinder 42 is closed at one end by plate 44 and contains therein a piston 46. The cylinder 42, end plate 44 and piston 46 define a variable volume chamber 48. The chamber 48 is in fluid connection with the chamber 38 in cylinder 30 via conduit 50. A valve seat 54 is mounted in cylinder 40 directed towards the inlet end of the housing 14 and a valve member 54 is mounted on the piston 46 so as to operatively engage the valve seat 52. 
     The present invention will compensate for irregular pressure and flow rate of fluids in some oil and gas producing wells. As the well produces fluid, the pressure in the production pipe 12 will drop and as this happens the larger piston 34 will be pushed by spring 36 to the position shown in FIG. 1. This will reduce the fluid pressure in chambers 38 and 48 and allow the smaller piston 46 to travel away from the valve seat 52 under the pressure of the fluid flow thereby opening the valve 54 and allow flow at a faster flow rate. As the fluid is unloaded, the gas flow will return, as will the pressure, forcing the larger piston 34 to override the force of spring 36. This will cause a rise in the fluid pressure in chambers 38 and 48 causing the smaller piston 46 to begin to control the rate of gas production by closing valve member 54 towards seat 52. 
     This device should prove to be of particular use in inland waters and offshore areas where changing bottom-hole chokes is expensive and time consuming. The main purpose of the present invention is to control the bottom-hole pressure and blow fluid to return to the surface at a faster rate thereby keeping the well unloaded. The bottom-hole is set in the well by means of a wire line and the top section is a set of slips to hold the choke in place and bottom section consists of a seal to seal off between the tubing and choke apparatus. 
     While this invention has been shown and described in a downhole embodiment, it is clear that a surface automatic choke would work equally as well and would find a variety of uses in wells, pipelines etc. 
     The present invention may be subject to many modifications and changes without departing from the spirit or essential characteristics thereof. The present embodiment should therefore be considered is all respects as illustrative and not restrictive of the scope of the invention as defined the appending claims.

Technology Classification (CPC): 4