Wells – Processes – Placing or shifting well part
Reexamination Certificate
2001-06-25
2004-01-13
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S105000, C417S201000, C417S319000, C418S048000
Reexamination Certificate
active
06675902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed toward artificial lift systems used to produce fluids from boreholes such as oil and gas wells. More particularly, the invention is directed toward an improved downhole progressive cavity pump that is inserted and operated within a borehole, and subsequently removed from the borehole, using a coiled or conventional sucker rod, or other rotatable strings that may be used to transmit torque to the pump.
2. Background of the Related Art
Modern oil and gas wells are typically drilled with a rotary drill bit and a circulating drilling fluid or “mud” system. The mud system (a) serves as a means for removing drill bit cuttings from the well as the borehole is advanced, (b) lubricates and cools the rotating drill bit, and (c) provides pressure within the borehole to balance internal pressures of formations penetrated by the borehole. Rotary motion is imparted to the drill bit by rotation of a drill string to which the bit is attached. Alternately, the bit is rotated by a mud motor which is attached to the drill string just above the drill bit. The mud motor is powered by the circulating mud system. Subsequent to the drilling of a well, or alternately at intermediate periods during the drilling process, the borehole is cased typically with steel casing, and the annulus between the borehole and the outer surface of the casing is filled with cement. The casing preserves the integrity of the borehole by preventing collapse or cave-in. The cement annulus hydraulically isolates formation zones penetrated by the borehole that are at different internal formation pressures.
Numerous operations occur in the well borehole after casing is “set”. All operations require the insertion of some type of instrumentation or hardware within the borehole. Examples of typical borehole operations include:
(a) setting packers and plugs to isolate producing zones;
(b) inserting tubing within the casing and extending the tubing to the prospective producing zone; and
(c) inserting, operating and removing pumping systems from the borehole.
Fluids can be produced from oil and gas wells by utilizing internal pressure within a producing zone to lift the fluid through the well borehole to the surface of the earth. If internal formation pressure is insufficient, artificial fluid lift means and methods must be used to transfer fluids from the producing zone and through the borehole to the surface of the earth.
The most common artificial lift technology utilized in the domestic oil industry is the sucker rod pumping system. A sucker rod pumping system consists of a pumping unit that converts a rotary motion of a drive motor to a reciprocating motion of an artificial lift pump. A pump unit is connected to a polish rod and a sucker rod “string” which, in turn, operationally connects to a rod pump in the borehole. The string can consist of a group of connected, essentially rigid, steel sucker rods sections (commonly referred to as “joints”) in lengths of 25 or 30 feet (ft), and in diameters ranging from ⅝ inches (in.) to 1-¼ in. Joints are sequentially connected or disconnected as the string is inserted or removed from the borehole, respectively. Alternately, a continuous sucker rod (hereafter referred to as COROD) string can be used to operationally connect the pump unit at the surface of the earth to the rod pump positioned within the borehole. A delivery mechanism rig (hereafter CORIG) is used to convey the COROD string into and out of the borehole.
Prior art borehole pump assemblies of sucker rod operated artificial lift systems typically utilize a progressive cavity (hereafter PC) pump positioned within wellbore tubing. A typical prior art insertable PC pump system will be described, and includes a pump subsection consisting of a rotor operating within a stator. A tag bar
o-turn subsection is connected below the stator/rotor assembly. Typically, a flush tube extension is connected above the stator/rotor assembly, with a seating
o-go assembly and a cloverleaf pick-up positioned above the flush tube extension. The prior art insertable PC pump assembly requires a special joint of tubing containing a pin protruding into the interior of the tube. A pump seating nipple is also required above the special joint of tubing. It should be understood that the discussed prior art system is used as an example, and that variations of the discussed system using, as examples, different hold down systems and different torque stopping devices are in the prior art.
The prior art PC pump rotor and stator, flush extension tube, cloverleaf pick-up and seating
o-go components are all assembled prior to insertion into the borehole tubing thereby creating an insertable PC pump assembly.
Before the PC pump is positioned and operated down hole, the previously mentioned special joint of tubing with pin and attached seating nipple must be installed in the tubing string so that the pump will be positioned to lift from a particular producing zone of interest. If the pump assembly is subsequently positioned at a shallower or at a deeper zone of interest within the well, this can be accomplished by removing the tubing string, or by adding or subtracting joints of tubing. This repositions the special joint of tubing as required.
Once the special tubing and seating nipple are installed in the tubing string, the insertable PC pump assembly is run, from surface of the earth, downhole inside of the tubing by a COROD or a conventional sucker rod system. When reaching the special tubing joint, a forked torque slot at the lower end of the insertable PC pump assembly tag bar
o-turn subsection aligns with the pin protruding near the bottom in the special tubing joint. Once the torque fork aligns with and engages the pin, the insertable PC pump assembly is locked radially within the tubing and can not spin within the tubing when the pump is operated. After the torque fork and pin have aligned, the seating
o-go assembly located at the top of the PC pump then slides into and seals in the seating nipple until it is stopped by the no-go. The prior art insertable PC Pump is now completely installed down hole.
The prior art insertable PC pump is removed by lifting the sucker rod string until a coupling on the top of the rotor shoulders out on the clover leaf located on the top of the extension tube just below the seating
o-go assembly. The seating
o-go assembly is then extracted from the seating nipple, and the insertable PC pump assembly can be pulled, using COROD or conventional sucker rod string, to surface for servicing or repositioning. Once pulled, a new insertable PC pump of identical length and identical outside diameter can be installed as outline above.
The operating envelope of an insertable PC pump is dependent upon pump length, pump outside diameter and the rotational operating speed. In the prior art system, the pump length is essentially fixed by the distance between the seating nipple and the no turn pin in the special joint of tubing. Pump diameter is essentially fixed by the seating nipple size. Stated another way, these factors define the operating envelope of the pump. For a given operating speed, production volume can be gained by lengthening stator pitch and decreasing the total number of pitches inside the fixed operating envelope. Volume is gained at the expense of decreasing lift capacity. On the other hand, lift capacity can be gained within the fixed operating envelope by shortening stator pitch and increasing the total number of pitches. Production volume can only be gained, at a given lift capacity, by increasing operating speed. This, in turn, increase pump wear and decreases pump life. For a given operating speed and a given seating nipple sizes, the operating envelope of the prior art system can only be changed by pulling the entire tubing string and adjusting the operating envelope by changing the distance between the seating nipple and the special joint of tubing containing the locking pin. Alternately, the tubing can be pulled and th
Moneta Roland Miles
Rowan Ryan Patrick
Wilson Todd Alan
Bagnell David
Moser, Patterson & Sheridan L.L.P.
Stephenson Daniel P.
Weatherford / Lamb, Inc.
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