Wells – With below and above ground modification – Eduction pump or plunger in well
Reexamination Certificate
1999-04-02
2001-06-05
Bagnell, David (Department: 3672)
Wells
With below and above ground modification
Eduction pump or plunger in well
C166S104000, C166S105000, C417S441000, C418S206100
Reexamination Certificate
active
06241016
ABSTRACT:
BACKGROUND
The present invention is directed to a drive head assembly for a deep well, submersible, progressing cavity pump; and more particularly, to an assembly for slowing the counter rotation of the polished rod induced by recoil in the sucker rod, and further, to a clamp adapted to coaxially secure the polished rod to a main shaft of the drive head assembly in a manner that allows some relative vertical movement of the sucker rod and associated polished rod without the polished rod becoming disengaged from the main shaft.
Progressing cavity pumps (and other types of rotary pumps) are conventionally used as down-hole pumps in the oil production industry. The helical rotors of such progressing cavity pumps are driven by a rod string or sucker rod coaxially coupled to a polished rod, which is in turn driven by a drive assembly typically located above the surface. The drive assembly, powered by a motor, is adapted to rotatably drive the polished rod and associated sucker rod. Typically, the sucker rod is a metallic rod a few inches in diameter and thousands of feet in length, and is coaxially coupled between the polished rod and the helical rotor of the progressing cavity pump. Because a substantial torsional force is often required to start the helical rotor turning within the progressing cavity pump stator, the drive assembly will turn or twist the sucker rod many times (conventionally in the range of 40 to 50 times) before the rotor begins to turn within the stator. Torsional force used to twist the sucker rod the 40 or 50 times is stored in the elongated sucker rod until the motor is disengaged or shut off. Once the motor is disengaged or shut off, this stored energy (the extra twists in the sucker rod) will immediately begin to be released in the form of a rapid recoil of the sucker rod. Unless this recoil is controlled or slowed, the motor and associated drive belts can become damaged by the rapid counter rotation of the polished rod.
Known ways for controlling such recoil include a disc brake mechanism to slow the counter rotation of the polished rod, or an external hydraulic pump mechanism coupled to the drive assembly. However, these prior art methods have several known disadvantages. With a disc brake mechanism, a great deal of friction is created during recoil releasing a large amount of heat. This causes unnecessary wear on the machinery, often requiring replacement of parts which results in production delays. External hydraulic pump mechanisms, while being more reliable than disc brakes, have their own attendant problems. An external pump contains more parts and is more complex in structure than one that is integral to the drive head assembly. Thus, an external pump is more liable to failure and more expensive to fabricate than a pump that is integral with the drive head assembly.
Also, as a result of this torsional displacement the sucker rod has a tendency to get longer at either end in much the same way a rubber band does when it is twisted longitudinally. Prior art clamps have not been effective in accommodating this longitudinal movement of the sucker rod/polished rod assembly caused by these torsional forces thus causing decreased pump efficiency. Also, the static clamping mechanisms of prior art inventions do not provide an easy method for lifting the rotor from the stator in order to backwash the hole of sand and grit.
Accordingly, there exists a need for a device for controlling polished rod recoil that contains few moving parts, is of fairly simple construction, is integral with the drive head, and is not prone to failure. There is also a need for a clamp for securing a polished rod and associated sucker rod to a main shaft of a pump drive-head assembly in a manner that allows for some longitudinal freedom of movement, so as to account for longitudinal expansion from torsional forces on the sucker rod, and so as to also provide an easy method for backwashing the hole.
SUMMARY
The present invention provides a pump drive assembly that includes an internal hydraulic pump for slowing the counter rotation of the polished rod induced by recoil in the sucker rod. The pump drive assembly includes a housing enclosing a hydraulic fluid reservoir and a separate gear chamber therein. A drive shaft, coupled to a motor by associated motor belts and/or gears, extends into the housing and includes a drive pinion integral with or keyed thereto. This drive pinion is positioned within gear chamber. A main shaft assembly also extends into the housing and includes a main gear integral with or keyed thereto, where the main gear is also positioned in the gear chamber and engaged with the drive pinion therein. The polished rod is coaxially coupled to the main shaft assembly by a polished rod clamp. When the polished rod is coupled to the main shaft assembly, positive rotation of the drive shaft causes an opposite (forward) rotation of the polished rod and associated sucker rod.
The gear chamber includes an inlet and outlet channel providing fluid communication between the chamber and the reservoir so as to form a reversible, hydraulic gear pump within the drive assembly. Operation of the drive assembly in a forward direction causes the gear pump to pump hydraulic fluid in a forward direction, from the reservoir, through the inlet channel, into the gear chamber, and out through the outlet channel, back into the reservoir; and operation of the drive assembly in a reverse direction, causes the gear pump to pump hydraulic fluid in a reverse direction, in through the outlet channel, into the gear chamber, and out through the inlet channel back into the reservoir. Recoil of the sucker rod and associated polished rod will cause counter-rotation of the polished rod, and in turn, reverse operation of the gear pump. Accordingly, to control the speed of counter-rotation of the polished rod, a flow resistor, such as a modified check valve is positioned in the inlet or outlet channel so as to substantially retard or slow the reverse flow of hydraulic fluids therethrough. Preferably, this modified check valve also allows for substantially full throughput of hydraulic fluids passing therethrough when the gear pump operates in the forward direction. Accordingly, the internal hydraulic gear pump of the drive head assembly is used to control and slow the recoil in the sucker rod. Furthermore, because the hydraulic gear pump is integral with the pump drive assembly; no external hydraulic hoses and related components are necessary.
The polished rod clamp, used to coaxially couple the polished rod to the main shaft comprises a pair of semi-cylindrical components which attach to each other to form a collar that encases the polished rod. Each of the semi-cylindrical clamp components includes an axially extending arcuate channel, each of which is adapted to receive a corresponding arcuate arm extending axially from the main shaft assembly. The arcuate arms of the main shaft assembly are substantially longer than the arcuate channels of the polished rod clamp and, therefore, allow the polished rod clamp to slide up and down the main shaft assembly (a few inches in the preferred embodiment) without becoming disengaged from the main shaft assembly. This cures a recognized problem of the polished rod clamp disengaging from the polished rod due to the above mentioned expansion of the sucker rod due to torsional forces. Also, the polished rod clamp of the present invention helps prevent disengagement due to slight disturbances (bouncing) in the polished rod and sucker rod.
Accordingly it is an object of the present invention to provide a pump drive assembly for a deep well progressing cavity pump that includes a reversible, hydraulic gear pump integrated therein, where the hydraulic fluid pumps hydraulic fluid in a forward direction when the polished rod is rotating in a forward direction and pumps hydraulic fluid in a reverse direction when the polished rod is rotating in a reverse direction, and where the hydraulic gear pump includes a flow resistor for substantially retarding flow of hydraulic fluid wh
Bagnell David
R & M Energy Systems
Thompson Hine & Flory LLP
Walker Zakiya
LandOfFree
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