Short stroke piston pump

Abstract

A short stroke piston pump for recovering oil and/or water from marginal stripper wells, tar sands and coal beds includes a motor connected to one end of a drive rod, the motor capable of moving the drive rod in a generally up and down direction. A piston is connected to another end of the drive rod, the piston and drive rod are disposed in a riser pipe, the piston is adapted to transport fluid up the riser pipe as the piston moves up and down in the riser pipe. Additionally, a controller is communicatively connected to the motor, the controller changing speed and direction of the motor in response to a location or status of the drive rod within the riser pipe

Description

BACKGROUND

1. Field of the Disclosure

The disclosure generally relates to short stroke piston pumps and more specifically to short stroke piston pumps used in marginal stripper wells, tar sands, and/or methane dewatering of coal beds.

2. Related Technology

A typical oil well is drilled into the earth and oil is pumped out with heavy duty oil pump jacks. Eventually, the oil in the well is depleted to a point where it is no longer economical to use the high capacity heavy oil pump jack because these heavy oil pumps pump oil out of the well faster than the oil yield. When this happens, the heavy oil pump jack is shut off, or in some cases, it is removed and taken to a new well where it will be more productive, and the first well is idled and eventually capped. These abandoned idled wells are unused “stripper wells.” Sometimes theses stripper wells still have enough yield to be productive with other conventional well pumps. More often, the yield of the stripper wells is too low to make oil production economically feasible with conventional oil well pumps. Generally, the yield in such wells may be less than five barrels per week. These stripper wells are called “marginal” stripper wells in the industry because although they still produce oil, the yield is too low to make oil production in these marginal stripper wells profitable with conventional heavy duty oil pumps.

Typically, oil and gas fields that have stopped flowing use an artificial means of producing the oil. The oil is extracted from these stripper wells typically using four different types of pumps, each being driven by electric power. However, these four types of conventional pumps are not well suited for pumping oil from marginal stripper wells because of each of the four conventional pumps is designed to pump at too high a flow rate for marginal stripper wells.

First, an electrically driven jack pump may be used. The jack pump is constructed of heavy iron and is powered by a direct drive totally enclosed and fan cooled electric motor. The pump jack actuates a sucker rod which, in turn, drives a piston near the bottom of the well in an up and down reciprocating motion. The piston is connected to a large drive motor via a sectioned steel drive rod. A counter weight at the opposite end of the drive rod is used to reduce the power consumption of the jack pump and to help pull the piston up on the return stroke. Because the pump jack is made of heavy iron and set up in a fulcrum configuration with a counter weight to assist the motor in pulling the piston up on the return stroke, typical pump jacks are very heavy and expensive to install.

Second, an electrical submersible pump may be used. The submersible pump is similar to water well submersible pumps and includes a submersible motor that drives a wet impeller end. This electric submersible pump is inserted into the well and connected to the surface by an educator pipe and a power cord. Submersible pumps are used on high yield, high flow wells. Submersible pumps are good for pumping both oil and high water content wells; however, they are not good for shallow low flow wells. Because the impeller of a submersible pump runs at a high RPM, the impeller is susceptible to wear due to the grit and suspended particles in the oil found in stripper wells. Furthermore, submersible pumps can be prone to explosion because the electrical motor wire goes down to the bottom of the well to the electric submersible drive motor. This electric motor wire can fray and, being in proximity to volatile gas in the oil well, can cause an explosion. A short circuit in the motor or the power cord could trigger such an explosion. Moreover, some electric submersible pump motor cannot run in a dry condition. Some electric motors use pumped fluid to cool the electric motor and if fluid is not present the motor can over heat and destroy itself. Electric submersible pumps need to pump at a high rate of speed to keep the electric motor cool and many mature oil fields cannot sustain a high enough pumping rate. Additionally, when pumping at too high a rate, the electric submersible pumps may pump water with the oil. The oil and water are emulsified when pumped and must be separated at the surface; the water is pumped back into deep well injection wells, thereby adding expense to the pumping operation.

Third, a progressive cavity pump may be used. The progressive cavity pump may include a single external helical section and a stator with an internal shape of a two start helix. The stator is an elastomer bonded inside an alloy steel tube. When a steel rotor is placed inside the stator a series of sealed cavities are formed. As the rotor turns, these cavities progress from the suction end of the pump to the discharge end, thereby transporting fluid through the pump. The fluid flow rate for progressive cavity pumps is directly proportional to the speed of rotation. This type pump unit also cannot run in a dry condition. The long rotating shaft that imparts the circular motion to drive the down hole progressive cavity pump is driven from the surface by a rotatary top head drive motor.

Forth, linear sucker rod pumps may be used. Linear sucker rods use a reversible motor and servo positioners to directly control a sucker rod using a rack and pinion mechanism. The linear sucker rod pump mounts directly to a well head. A rigid drive rod runs through a channel inside the rack and is suspended from the top by a conventional rod clamp. An induction motor, coupled to the rack and pinion mechanism through a gear box, cycles the rack up and down to reciprocate the rod and thus pump up the oil.

Unlike the marginal stripper wells, bitumen yield rate from oil sands is pumped as fast as possible to take advantage if the flowing heated bitumen before it cools off and flow slows. Oil sands are a mixture of sand, bitumen and water. Bitumen does not flow well in its naturally occurring state. Generally, bitumen is extracted from the oil sands through open pit mining and the deep oil sands by injected steam recovery. A middle layer of tar sand can be extracted by electro—thermal stripping system process. Deep in situ thermal recovery involves drilling a well and injecting steam to heat the bitumen thereby allowing the bitumen to flow out of the sand and into the well bore. Conventional pumps cannot recover bitumen from the middle tar sands between surface mining and deep steam injection and recovery.

Similarly, sustained methane gas well dewatering operations are generally low yield rate operations. Methane gas dewatering is the dewatering of coal beds that contain methane. Water suppresses the release of the methane gas because of methane's affinity for the water molecule. In other words, in the presence of water, methane rapidly dissolves in the water and becomes unusable. Coal beds often have isolated (perched) pockets of water that when breached yield a transitory high flow rate of water into a typical dewatering well. Eventually the flow rate decreases into a relatively stable low flow rate. The typical submersible pump is well adapted to handle the initial high flow rate, but as the flow rate decreases, the submersible pump begins to pump high levels of grit and suspended particles which quickly wear out the internal components of the submersible pump. In order to keep the water from flooding the well, a low pump rate must be maintained (generally under 5 gallons per minute). These low flow rates are also insufficient to cool the typical submersible pump which uses the pumping fluid to cool its electric motor. The conventional pumps described above are not well suited for methane gas dewatering operations.

SUMMARY OF THE DISCLOSURE

A short stroke piston pump for recovering oil and/or water from marginal stripper wells, tar sands and coal beds is described herein. The short stroke piston pump includes a motor connected to one end of a flexible drive rod, the motor is capable of moving the flexible drive rod in a generally up and down direction. A piston is connected to another end of the flexible drive rod. The piston and flexible drive rod are then disposed in a riser pipe and the piston transports fluid up the riser pipe as the piston moves up and down in the riser pipe. Additionally, a controller is communicatively connected to the motor. The controller may change the speed and direction of the motor, and may even pause the motor, in response to a location and/or status of the drive rod within the riser pipe.

Also disclosed herein is a method of extracting oil from marginal stripper wells, and includes providing a short stroke piston pump and installing the short stroke piston pump on the marginal stripper well. The controller is programmed to vary the speed and/or frequency of the motor based on the depth of the marginal stripper well, the discharge pressure, the yield of the marginal stripper well, and the viscosity of the oil in the marginal stripper well.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of the present disclosure will become apparent upon reading the following description in conjunction with the drawing figures, in which:

FIG. 1 is a side sectional view of a short stroke piston pump constructed in accordance with the teachings of the disclosure;

FIG. 2 is a close up side sectional view of the short stroke piston pump of FIG. 1; and

FIGS. 3A-3C are side exploded views of the internal components of the short stroke piston pump of FIG. 1.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 illustrates a short stroke piston pump 201 constructed in accordance with the teachings of the disclosure. The short stroke piston pump 201 includes a riser pipe 200 and a valve assembly 220 attached to one end of the riser pipe 200. The valve assembly 220 includes a piston 230 connected to a flexible drive rod 232. The flexible drive rod may be made of fiberglass, or any similar flexible material. The flexible drive rod 232 extends through a flow chamber 233 to a motor 234 which moves the piston 230 in a reciprocating normally up and down motion through the flow chamber 233 thereby pumping liquid in a direction from the valve assembly 220 towards the motor 234. The motor 234 is attached to the drive rod 232 by an actuator 242. Limit switches 244 measure travel of the actuator 242 as the motor 234 moves the actuator 242. The limit switches 244 send signals to a controller 240 as a portion of the actuator 242 contacts each respective limit switch 244. The controller 240 sends signals to the motor 234 based on input from the limit switches 244 and a programmed operational routine, thereby controlling the frequency and direction that the motor 234 moves the actuator 242, and thus the drive rod 232 and piston 230. The motor 234 may be a variable speed motor to move the actuator at different speeds and/or frequencies. The motor 234 may be electrically or pneumatically actuated. Generally, the drive motor 234 produces a stroke length of between 10 and 30 inches. However, shorter or longer stroke lengths may be used if required. Further, the motor 234 preferably is one that produces less than about five horsepower, although larger motors may be used if required for greater depths or greater discharge pressures.

Generally, piston pumps with flexible dive rods have been used for shallow well pumping viscous and non-viscous fluids (e.g., wastewater pumping at landfills, coal tar recovery of bunker C oil, and recovery of #6 fuel oil). Such pumps were previously limited to shallow wells because they lacked the hp and mechanical strength to lift at the greater depths. At depths greater than about 1000 ft., rod stretch (or “float”) becomes a significant problem, such that the motor can become overloaded because the piston may be moving in an upward direction for a significant amount of time (due to the stretch) even after the motor has reversed direction and is moving the drive rod in a downward direction. More viscous fluids present a similar problem, especially at deeper depths. Viscous fluids, such as oil, produce more resistance in the piston during operation. This additional resistance magnifies the issue of drive rod stretch. As a result, piston pumps used to pump viscous fluids, or to pump from deep wells, tend to employ non-flexible drive rods (e.g., steel drive rods). However, non-flexible drive rods add significant amounts of weight and cost to the piston pump, and to maintenance costs, as well as additional momentum-related forces for the motor to overcome.

To overcome the drive rod float problem, the disclosed pump 201 has an electronic controller 240 that varies and controls the speed and time of the motor 234 and thus the number of strokes per minute of the flexible drive rod 232. For example, when pumping viscous fluids, such as oil, the controller 240 may pause the motor 234 at a bottom of a down stroke to allow energy stored in the flexible drive rod 232 (due to stretch) to fully unload, thereby driving the piston 230 fully into the viscous fluid. A similar pause of the motor at a top of an upstroke may also allow energy stored in the drive rod 232 (from stretch) to unload. Likewise, for very deep wells, the controller 240 may pause the motor 234 at the bottom of the down stroke to unload any energy stored in the flexible drive rod 232 due to the stretch. Also for deeper wells, the controller may vary motor speed to change the speed of the piston during the upstroke of the pump as compared to a speed of the piston during the downstroke of the pump. During the upstroke, additional force is exerted on the flexible drive rod 232 due to the extra weight of the fluid being moved upwards through the flow chamber 233. Thus, the flexible drive rod 232 may experience more stretch during the upstroke. To counter this additional stretch, the controller 240 may slow the motor 234 during the upstroke, thereby allowing the flexible drive rod 232 to stretch more gradually and reducing the stress on the flexible drive rod 232 and the motor 234 due to drive rod stretch. In this manner, the disclosed piston pump 201 advantageously has a lightweight, inexpensive flexible drive rod 232, requiring less overall energy to operate and producing less momentum issues as seen by the pump motor 234, while still having the ability to pump viscous fluid from deep wells (e.g., wells up to about 2000 ft. in depth). Generally, the speed of the motor 234 may be varied, during the upstroke and downstroke, between about 50 Hz and about 10 Hz, which produces between approximately 27 piston strokes per minute and approximately 5 piston strokes per minute. However, virtually any motor speed or frequency can be programmed into the controller 240. The motors are commanded via the controller 240, to slow down when being turned off and to have a slow initial ramp up speed when being turned on. This is done to eliminate any sudden stop or start that can damage a motor gear coupling, a slip gear or break a coupling key.

As shown in FIG. 2 limit switches 244a, 244b, 244c reverse the motor 234 direction thereby imparting linear up-down motion to the actuator 242. The motor 234 is mounted on top of the actuator 242 over the well head 260 and discharge tee 262. This configuration ensures a stable, balanced, and aligned motor assembly above the well. The actuator 242 includes a ball screw 242a that is connected to a lower actuator tube 242b. A lower limit switch 244c and a middle limit switch 244b normally reverse the motor 234 to keep a ball screw nut 264 (see FIG. 3B) that is threadedly attached to the ball screw 242a between the lower limit switch 244c and the middle limit switch 244b. A top limit switch 244a is a safety mechanism to reverse the motor should the middle limit switch 244b fail or in the event that the ball screw nut 264 coasts past the middle limit switch 244b when the motor 234 is turned off. The motor 234 always begins in the retract direction because gravity may pull the ball screw nut 264 down to the bottom of the stroke when the motor 234 is turned off.

FIGS. 3A-3C show a side exploded view of the short stroke piston pump of FIGS. 1 and 2. The ball screw nut 264 is also attached to the lower actuator tube 242b that moves up and down with the ball screw nut 264 as the ball screw 242a turns. A bearing mount 274 houses bearings and attaches the ball screw 242a to the motor 234. The lower actuator tube 242b extends and retracts outside the bottom of a landing plate 276 and connects to a drive rod 232 (FIG. 1). The landing plate 276 is sealed by a rod seal 278 to ensure that no dirt, dust or liquid is drawn upward into the ball screw 264. Below the landing plate 276 is a stuffing box 280 that includes more seals and/or wipers to clean the lower actuator tube 242b of any residue. By altering the thread on the ball screw 242a, the pump 201 may be configured for faster or slower pump rates. For example, a thread configuration that produces 1 inch of travel per turn of the ball screw 242a will pump faster than a thread configuration that produces 1 inch of thread for every two turns of the ball screw 242a. However, the thread configuration that produces 1 inch of travel per turn will create a greater load on the motor 234 than the thread configuration that produces 1 inch of travel per two turns. Examples of loads and pump rates of different motor and stroke length combinations are summarized in the table below.

TABLE 1
Limit	10	10	10	10	10	10	20	10	10	10
Switch
Separation
(in)
Stroke	14	14	14	14	14	14	24	14	14	14
Length (in)
Load (lbs)	206	406	502	545	550	598	740	808	993	1187
Motor HP	0.5	1	1.5	1.5	1.5	1.5	2	2	3	3
TDH	385	800	1000	1000	1100	1100	1500	1500	1500	1800
Rod	0.95	4.12	6.44	3.62	7.80	4.38	14.50	8.15	3.62	5.22
Stretch
(in)
Gallons	0.06	0.04	0.03	0.04	0.03	0.04	0.04	0.02	0.04	0.04
per stroke
Strokes	18.00	23.85	31.28	22.73	38.23	24.57	25.19	40.97	22.87	27.24
per gallon
Barrel per	38.05	28.73	21.90	30.13	17.92	27.88	17.48	16.72	29.95	25.15
day

As discussed earlier, marginal stripper wells have a relatively low yield of oil. In some cases, the yield of a stripper well may be as little as five barrels of oil per week, or less. Large heavy iron jack pumps, as geared to high yield wells, do not have the ability to reduce their pumping capacity to capture such low yields of oil, without the potential of over-pumping the formation and pumping water instead of oil. This pumped water then needs to either be treated and discharged at surface, or sent back down an injection well, where then yet more cost is incurred to pump and transfer this water.

One advantage of the disclosed pump is that the controller 240 can adapt pumping capacity to the yield of the particular well. In other words, the controller 240 may operate the motor 234 at a speed that pumps oil out, makes less water of the marginal stripper well at a rate that substantially matches the inflow yield of the marginal stripper well. In doing so, the pump 201 withdraws less water and foreign material (i.e., sand) because the pump rate is matched to the rate at which oil is filling in the well. Thus, the disclosed pump 201 requires less maintenance and produces less wear due to foreign objects being pumped through the flow chamber 233. Essentially, the pump 201 is customizable to each and every individual marginal stripper well, e.g. with respect to yield, depth, and discharge pressure. Furthermore, the flexible nature of the drive rod 232 and riser pipe 200 allow the pump 201 to be used in well bores that are not entirely vertical (e.g., a well bore that changes direction to avoid subterranean features), or one having a casing shift.

Yet another advantage of the pump 201 is that the relatively light weight of the drive rod 232 gives the pump 201 low inertia. This means that the pump 201 is easily stopped and started. Moreover, this low inertia enables the motor 234 to vary its speed and even pause pumping at any time, thus enabling the pump 201 to overcome problems due to drive rod 232 stretch, yield over-pumping, and pumping on command.

Still another advantage of the pump 201 is that the pump 201 can generally be installed with a work team of as few as three. This is due again to the lightweight nature of the pump 201. This reduction in manpower results in a lower initial capital expense and thus causes more marginal stripper wells to become economically feasible to pump. This thus eliminates the need for an expensive so-called “makeover rig” to install the down hole pump, and to set up the pump jack over the well.

Typically, a marginal stripper well is identified and analyzed for its potential yield. Once the potential yield is determined a cost estimate is performed based on the cost of the pump 201 and the energy required to run the pump 201 for a given oil yield. The cost estimate is then compared to an expected profit based on the estimated yield of the marginal stripper well. Once an economically feasible marginal stripper well is identified, an installation team installs the pump 201 on the marginal stripper well. A technician adjusts the controller 240 to maintain a motor setting conforming to the estimated yield of the marginal stripper well. Additionally, the technician calculates the amount of drive rod stretch based on the marginal stripper well depth and programs the controller 240 to compensate for the drive rod stretch. Once the initial set up is complete, the technician may monitor the pump 201 (even remotely if desired) to analyze the true yield of the marginal stripper well. Adjustments may be made (again remotely if desired, by telemetrics) on a periodic basis as the yield fluctuates.

Although certain pumps have been described herein in accordance with the teachings of the present disclosure, the scope of the appended claims is not limited thereto. On the contrary, the claims cover all embodiments of the teachings of this disclosure that fairly fall within the scope of permissible equivalents.

Claims

1. A method of extracting oil from marginal stripper wells comprising:

providing a short stroke piston pump comprising: a motor connected to one end of a flexible drive rod, the motor capable of moving the flexible drive rod in a generally up and down direction; a piston connected to another end of the flexible drive rod, the piston and the flexible drive rod being disposed in a riser pipe, the piston adapted to transport fluid up the riser pipe as the piston moves up and down in the riser pipe; a controller communicatively connected to the motor, the controller changing speed and direction of the motor in response to a location or status of the flexible drive rod within the riser pipe;

installing the short stroke piston pump in a marginal stripper well;

adjusting the controller to set a speed of the motor based on an oil yield of the marginal stripper well.

2. The method of claim 1 further comprising adjusting the controller to pause the motor at a bottom of a downstroke of the flexible drive rod to compensate for drive rod float or stretch.

3. The method of claim 1 further comprising adjusting the controller to pause the motor at a top of an upstroke of the flexible drive rod to compensate for drive rod float or stretch.

4. The method of claim 1, wherein the flexible drive rod is made of a fiberglass material.

5. The method of claim 1, wherein the flexible drive rod is greater than approximately 1000 ft in length.

6. The method of claim 1, further comprising adjusting the motor to produce an upstroke speed that is different from a downstroke speed.

7. The method of claim 1, further comprising adjusting the motor speed between approximately 50 Hz and about approximately 10 Hz.

8. The method of claim 7, wherein the motor speed is approximately 30 Hz.

9. The method of claim 1, wherein the motor moves the drive rod between about 27 strokes per minute and about 5 strokes per minute.

10. The method of claim 1 further comprising determining the oil yield of the marginal stripper well.

11. A short stroke piston pump comprising:

a motor connected to one end of a flexible drive rod, the motor capable of moving the flexible drive rod in a generally up and down direction;

a piston connected to another end of the flexible drive rod, the piston and the flexible drive rod being disposed in a riser pipe, the piston adapted to transport fluid up the riser pipe as the piston moves up and down in the riser pipe;

a controller communicatively connected to the motor, the controller changing speed and direction of the motor in response to a location of the drive rod within the riser pipe.

12. The short stroke piston pump of claim 11, wherein the controller pauses the motor at a bottom of a downstroke of the flexible drive rod to allow energy stored in the flexible drive rod to push the piston into a fluid in a well.

13. The short stroke piston pump of claim 11, wherein the controller pauses the motor at a top of an upstroke of the flexible drive rod to allow energy stored in the flexible drive rod to release.

14. The short stroke piston pump of claim 11, wherein the flexible drive rod is made of a fiberglass material.

15. The short stroke piston pump of claim 11, wherein the flexible drive rod is greater than about 1000 feet in length.

16. The short stroke piston pump of claim 11, wherein a flexible drive rod stroke length is between approximately 10 inches and approximately 30 inches.

17. The short stroke piston pump of claim 11, wherein less than 10 barrels per week of oil are removed from a well.

18. The short stroke piston pump of claim 11, wherein the controller adjusts the speed of the motor between approximately 50 Hz and approximately 10 Hz.

19. The short stroke piston pump of claim 18, wherein the controller adjusts the speed of the motor to approximately 30 Hz.

20. The short stroke piston pump of claim 11, wherein the controller adjusts the motor to produce a flexible drive rod stroke frequency in the range of about 27 strokes per minute to about 5 strokes per minute.

21. The short stroke piston pump of claim 11, wherein the controller adjusts a speed at which the flexible drive rod is actuated.

22. The short stroke piston pump of claim 21, wherein the controller sets an upstroke speed of the flexible drive rod different from a downstroke speed of the flexible drive rod.

23. The short stroke piston pump of claim 11, wherein the controller adjusts motor speed based on a liquid yield of a well.

24. The short stroke piston pump of claim 11, wherein the motor is electric.

25. The short stroke piston pump of claim 11, wherein the motor is pneumatic.

26. The short stroke piston pump of claim 11, wherein the controller can be remotely adjusted.

27. The short stroke piston pump of claim 11, wherein the short stroke piston pump pumps oil from a marginal stripper well.

28. The short stroke piston pump of claim 11, wherein the short stroke piston pump pumps heated bitumen from a tar sands well.

29. The short stroke piston pump of claim 11, further including a ball screw connected to the motor and the flexible riser pipe, wherein one revolution of the ball screw raises the piston one inch.

30. The short stroke piston pump of claim 11, further including a ball screw connected to the motor and the flexible riser pipe, wherein two revolutions of the ball screw raises the piston one inch.

31. The short stroke piston pump of claim 11, wherein the short stroke piston pump pumps water from coal beds during methane dewatering operations.