CA1208538A - Self-reversing hydraulic control mechanism - Google Patents

Abstract

TITLE
SELF-REVERSING HYDRAULIC CONTROL MECHANISM

ABSTRACT OF THE DISCLOSURE
A self-reversing hydraulic control mechanism directs the flow of inlet and exhaust fluids into and out of a reciprocating pumping unit. The mechanism has cooperating poppet valves with fluid passages thereto disposed so that a difference in pressure between inlet and exhaust fluids exerts a holding force. This force maintains the valves in their set position until overcome by an altering force, which is developed by travel of a piston of the pumping unit.

Description

~2V8538 BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates generally to a control mechanism for directing the flow of inlet and exhaust fluids into and out of a reciprocating pumping unit. It relates particularly to a self-reversing hydraulic control mechanism for directing the flow of inlet and exhaust fluids into and out of a reciprocating oil pump, especially one in a downhole assembly.

Prior Art There has been a long standing need in the art for a self-reversing hydraulic control mechanism for directing the flow of inlet and exhaust fluids into and out of a reciprocating oil pump, especially such a pump in a downhole as embly. Over the years a number of attempts have been made to supply thls need, and certain embodiments have been devised and some patented. Of pertinence are the following U.S. patents: 2,870,749; 2,966,893; 2,966,894;

2,966,895; and 2,984,224. Notwithstandin~ the efficacy of th0se and similar expedients, they are all found wanting in that they do not provide the combination of benefits of simplicity and economy of construction, durability, economy of repair, and efficiency in operation--whlch combination is required by producers, especially small producers, in today's operations. Particularly, the devices of the prior art all employ spool valves which require very close tolerances, resulting in increased costs for manufacture and repair, and the necessity to employ purlfled fluid as power fluid. Moreover, the deslgn lnherent in such devices does not provide for passageways which are large enough to prevent the necessity of an excessive amount of surface power to force fluid through small openings before it is utilizable as p~r fluid. Moreover, no device of the prior art is capable of operating in the field using readlly avallable API standard parts excluslvely. ;

~` 120l 3538 SU~ARY OF THE PRESENT INVENTION

It is accordingly the primary object of the present invention to obviate the difficulties inherent in prior art expedients and to provide that combination of benefits which the prior art has been unable to supply. This ob~ect has been achieved by the provision of a self-reversing hydraulic control mechanism for directing the flow of inlet and exhaust fluids into and out of a reciprocatin~ pumping unit such as an oil well pump, particularly a downhole pump.
The mechanism comprises cooperating poppet valves having fluid passages thereto disposed so that a difference in pressure between inlet and exhaust fluids exerts a holding force which maintains the valves in their set position until overcome by an altering force (e.g., as exerted by resilient means such as a spring) which is developed by travel of a piston of the pumplng unit.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, including its primary object and combination of benefits, xeference should be made to the Detailed Description of the Preferred Embodiments, which is set forth below. This de-scription should be read together with the accompanying drawings, wherein:
Fig. 1 is a schematlc view showing the relationship of the component parts of a pumping system wherein an embo~iment of the present invention is an integral part;
Fig. 2 is a schematic view showing detallq of an embodiment of the present lnvention in the upward stroke configuration;
Flg. 3 is a schematic view showing details of an embodiment of the present invention at the start of the reversing operation;
Fig. 4 is a schematic viéw showing details of an embodiment of the present invention at the instant of reversal; and lZ(J85315 Fig. 5 is a schematic view showing details of an embodiment of the present invention in the downward stroke configuration, DETAILED DESCRIPTION OF T~IE PREFERRED EMBODIMENTS

Referring now to Fig. 1, power fluid is supplied by an above ground pump 1 downward through well tubing 2 to a pumping unit 3, consisting of a downhole hydraulically operated pump set in a special receiving assembly referred to as the down hole assembly. A packing unit 4 forms a seal between -the well tubing 2 and the well casing 5. The power fluid supplied by the above ground pump 1 operates the downhole pumplng unit 3, causing well fluid from the production zone 6 to be pumped through the packer 4 and into a space between the well tubing 2 and the well casing 5, hereafter referred to as the annulus 7. Well fluid 50 produced along with expended power fluid is returned upward through the annulus 7 to a receivlng tank 8. A portion of this combined fluid returns to the above ground pump 1 as power fluid. The remainder of the fluid leaves the receiving tank at the overflow 9 as production fluid.

Referring now to Fig. 2, power fluid from the above ground pump 1 pumped through the well tubing 2 travels around the ~op header 10 through bypass 11 in the downhole assembly and into the cavity 12 between the down hole assembly and the downhole pump barrel 13, entering center section (re-versing valve body) 20, continulng past the inlet valve 1~, and into the upper motor chamber 15. The continuing flow of power fluid into the upper motor chamber 15 forces the upper piston 16 to travel upward, forcina well fluid from the upper pumping chamber 17 out through the check valves in the upper header 10 into the annulus 7, and to the above ground receiv~ng tank 8 shown in Fig. 1. As the upper plston 16 is forced upward, it pulls the lower piston 18 -" ~Z5~853~

upward by means of connecting rods 19, which pass through the reversing valve body 20. The upward travel of the lower piston 18 forces expended power fluid from the lower motor chamber 21 out past the lower discharge valve 22, and subsequently into the annulus and upward to the receiv-ing tank 8 shown in Fig. 1. The upward travel of the lower piston 18 also causes well fluid from the production zone 6 to be drawn through the check valves in the lower header 23 and into the lower pump chamber 24. During this upward stroke the power fluid in the upper motor chamber 15 must exert a force on both the upper piston 16 and the lower piston 18 sufficient to force well fluid from the upper pump chamber 17 and the expended power fluid from the lower motor chamber 21 into the annulus 7. The force moving the lower piston 18 is received through pull from the,two rods connecting the pistons. Since the area below the upper piston 16 is e~ual to the area above each o~ the upper and lower pistons 16 ~ 18, disregarding pressure drop due to fluid flow and/or bottom hole pressure exerted by the incomlng well fluid, it can be seen that the unit pressure of the power fluid in the upper motor chamber 15 must be more than the unit pressure in the upper pump chamber 17 and the lower motor chamber 21, which will also be the pressure in the annulus 7. Bottom hole pressure is the force exerted from a formation or zone below the surface of the earth. It can be seen further that the total force exerted downward by the pres~ure fluld on the inlet valve 14 and the upper discharge valve 25 wlll be more than the upward force exerted on ~hese valves by the annulus pressure below them. This difference in forces will be referred to hereafter as the "pressure holding force", and it can be seen that thls ~'orce wlll tend to hold the valves ln position until changed by a reversing procedure.
Referring now to Fig. 3, as the pistons continue to travel upward, a lower valve operating spring 26 makes contact with the valve rods 27 and begins exerting a force in -` ~Z~8538 opposition to the pressure holding force. When the pressure exerted by the lower valve operating spring 26 becomes greater than the pressure holding force, the valves are forced to open, whereupon the pressure on the inlet valve 14 and the upper discharge valve 25 forces fluid past these valves and eliminates the pressure holding force, allowing the valve operating spring 26 to expand and force the valves to their reverse position as shown in Fig. 4.
Fig. 5 shows the fluid flow on the downward stroke where well fluid is drawn through a port 28 in the downhole assembly and into the upper pump chamber 17, while expended power fluid is forced from the upper motor chamber 15 past the upper discharge valve 25 and into the well annulus 7 -along with discharged well fluid from the lower pump chamber 24. As the piston~s reach the lower end of their travel, the upper valve operating spring 29 contacts the valve rods 27, overcomes the pressure holding force, and shifts the valves back to their original position as shown in Fig. 2, thereby completing the cycle.
For repairs the entire downhole pump can be pulled from the downhole assembly by means of an overshot puller, which can be lowered through the well tubing by means of a cable.
The overshot puller will automatically grasp the "fishing"
neck 30 which is shown in Fig. 4, whereupon the pump can be pulled to the surface.
The present invention has been described in detail with respect to certain preferred embodiments thereof. As is understood by those of skill in the art, variations and modifications in this detail may be made without departlng from the spirit and scope of the present invention, as defined in the hereto-appended claims.

Claims (6)

WE CLAIM:

1. A self-reversing hydraulic control mechanism for directing the flow of inlet and exhaust fluids into and out of a reciprocating pumping unit, the mechanism comprising cooperating poppet valves having fluid passages thereto disposed so that a difference in pressure between inlet and exhaust fluids exerts a holding force which maintains the valves in their set position until overcome by an altering force developed by travel of a piston of the pumping unit.

2. A self-reversing hydraulic control mechanism for directing the flow of inlet and exhaust fluids into and out of a reciprocating pumping unit, the mechanism comprising cooperating poppet valves having fluid passages thereto disposed so that a difference in pressure between inlet and exhaust fluids exerts a holding force which maintains the valves in a first of two defined positions, until overcome by an altering force developed by travel of a piston of the pumping unit in a first direction, whereupon the valves are moved to their second defined position and maintained in such position by the difference in pressure between the inlet and exhuast fluids, until overcome by an altering force developed by travel of a piston of the pumping unit in a direction opposite to the first direction of travel thereof, thereby returning the valves to their first defined position to complete the cycle.

3. The device of claim 2, wherein the altering force is exerted by resilient means.

4. The device of claim 3, wherein the resilient means is a spring.

5. The device of claim 4, wherein the reciprocating pumping unit is an oil pump.

6. The device of claim 5, wherein the oil pump is a downhole oil pump.