Patent Application
20180230992
The technology described herein relates generally to a linear pumping system, and more particularly to systems and methods for pumping fluids from an oil or gas well.
The oil and gas industry relies heavily on pumping systems with seventy percent or more of the world's oil wells requiring some sort of a pump to produce fluids. Linear pump technology is the most commonly used pump technology in the oil industry. More specifically, the most common type of pumps used in wells having a low flow rate or a small well bore size and also with gas wells is the sucker rod driven linear pump. However, sucker rod driven linear pumps are typically not efficient at low flow rates because their slow operation and large pump size requires a very large amount of force to lift fluid, even at a low flow rate. These pumps may also have other disadvantages, such as a moving rod seal on the well head that is prone to leaking, and operating poorly in the presence of gas, as well as a pumping chamber that cannot be stroked until empty because the plunger is on the end of a long rod string, many thousands of feet long. There is therefore a need in the industry for a system for pumping fluids from an oil or gas well that operates efficiently at low flow rates and addresses disadvantages associated with the prior art.
An example linear pumping system and methods of operation are provided. An example linear pumping system may include a pump casing that encloses a linear motor and one or preferably two pumps designated herein for convenience upper and lower pump. In an embodiment, the pump casing includes an upper fluid inlet port, a lower fluid inlet port, and a fluid-outlet port. The linear motor includes a stator and a mover, where the mover may include an upper plunger portion and a lower plunger portion and is configured to move alternately up and down relative to the stator when the motor is powered up. In embodiments, the upper pump may include an upper pump chamber, an upper pump fluid inlet valve, and an upper pump fluid outlet valve, and the lower pump may include a lower pump chamber, a lower pump fluid inlet valve, and a lower pump fluid outlet valve. In operation, hydraulic pressure from the upper and lower pump outlet valves causes fluid within an interior cavity of the pump casing to be expelled through the fluid outlet port of the pump casing.
In embodiments, an upper pump fluid inlet valve may be provided between the upper pump chamber and the upper fluid inlet port and is configured to receive fluid into the upper pump chamber from outside of the pump casing. An upper pump fluid outlet valve may be provided between the upper pump chamber and an interior cavity of the pump casing and is configured to expel fluid from the upper pump chamber into the interior cavity of the pump casing. The upper pump chamber may be configured to receive the upper plunger portion of the linear motor mover, where the upper plunger portion causes fluid to be drawn into the upper pump chamber through the upper pump inlet valve on a downstroke of the linear motor mover and causes fluid to be expelled from the upper pump chamber through the upper pump outlet valve on an upstroke of the linear motor mover.
In embodiments, a lower pump fluid inlet valve may be provided between the lower pump chamber and the lower fluid inlet port and is configured to receive fluid into the lower pump chamber from outside of the pump casing. A lower pump fluid outlet valve may be provided between the lower pump chamber and the interior cavity of the pump casing and configured to expel fluid from the lower pump chamber into the interior cavity of the pump casing. The lower pump chamber may be configured to receive the lower plunger portion of the linear motor mover, where the lower plunger portion causes fluid to be drawn into the lower pump chamber through the lower pump inlet valve on the upstroke of the linear motor mover and causes fluid to be expelled from the lower pump chamber through the lower pump outlet valve on the downstroke of the linear motor mover.
An example method of controlling operation of a linear pumping system for use in an oil or gas well, where the linear pumping system includes a linear motor and one or more pump chambers, may include the steps of: measuring pressure within the one or more pump chambers of the linear pumping system; measuring a position of a plunger rod of the linear motor in relation to the one or more pump chambers; and controlling movement of the plunger rod within the one or more pump chambers based at least in part on the measured pressure and/or position. In embodiments, a stroke length of the linear motor may be controlled based at least in part on the measured position of the plunger rod to cause a maximum penetration of the plunger rod within the one or more pump chambers. In embodiments, movement of the linear motor may be stopped if the measured pressure exceeds a predetermined threshold. Example methods of controlling operation of a linear pumping system for use in an oil or gas well may further include the steps of measuring an operational temperature of the linear motor; and controlling movement of the linear motor based at least in part on the measured operational temperature. In embodiments, movement of the linear motor may be stopped if the measured operational temperature exceeds a predetermined threshold.
The invention is described as advantageously having two pumping chambers, one on either end of the linear motor. This arrangement provides several advantages over other arrangements, principally balanced forces on the motor and near continuous pumping. However it should be noted that this pump arrangement also provides redundancy, and that if one pumping chamber fails the second one may continue to operate, providing some failure tolerance. It is also true that in a vertical well bore one can observe what is known as a pump-off. Pump-off is a phenomenon occurring when pumping action draws the fluid column down below the pump intake. A pump-off situation will significantly increase the gas intake, reducing the pump efficiency. Thus, if the surrounding fluid level gradually drops (pumping off) the upper chamber will draw gas (or gassy fluids) before the lower chamber, and so the pump described herein should not pump off suddenly. This asymmetric behavior of the pump will be an indication to the control system of a pump off condition, and will provide the mechanism to control pumping under such common conditions. This is an additional advantage of the pump design disclosed herein. It is also obvious that when one pump fails or operates in a pump-off condition, the pump in this disclosure will advantageously function as a simplex pump, with either only the upper or lower pump chambers pumping fluid.
The proposed duplex pump design in which two pumps are arranged on either side of the motor is also believed preferable to alternate designs in which the duplex pumps are mounted either completely above or completely below the motor. While such arrangements may potentially provide a simpler mechanical interface between the motor and the pump, this is offset due to a more complicated design of the pumping chambers and the considerable complexity required in the design of flowing fluid paths to achieve full duplex pumping.
The example linear pumping system depicted in
As noted, the linear motor includes a stator 5 and a mover 15. The linear motor mover 15 includes a plunger rod made of mechanically strong material that is surrounded by permanent magnets 9 at a center portion of the rod, defining an upper plunger portion 8 extending above the permanent magnets 9 and a lower plunger portion 19 extending below the permanent magnets 9. In embodiments, the plunger rod of the linear motor may have a small diameter (e.g., less than one inch) to provide a pump system that is suitable for use in deep wells at low flow rates and also pumping fluid from a small diameter oil or gas well. A person of skill in the art will appreciate that the primary advantage of a small pump is that it reduces the force the linear motor has to generate to move the pump plunger, which in turn makes the pump small and cheaper to build. In operation, the linear motor mover 15 is caused to move alternately up and down within the motor assembly when the stator 5 is coupled to a power source. The up and down movement of the linear motor mover 15 within the linear motor assembly is respectively referred to herein as the upstroke and downstroke of the linear motor.
In an embodiment, the linear motor may be an oil-filled motor assembly to improve longevity and provide a highly efficient motor with close tolerances between the mover 15 and stator 5. Oil may be contained in the motor assembly using pressure balancing diaphragms made from a soft material, such as silicone or an elastomer, to allow the oil to expand and contract with temperature. In the example illustrated in
The upper and lower pumps (12 and 6, respectively) each include a fluid inlet valve 7, 10 and a fluid outlet valve 21, 20 respectively, and each define a pump chamber 2 (upper) and 13 (lower) for receiving the upper and lower plunger rod portions 8, 19 of the linear motor mover 15. Specifically, the upper pump chamber 2 is configured to receive the upper plunger portion 8 and the lower pump chamber 13 is configured to receive the lower plunger portion 19, as illustrated by the fully assembled pump shown on the right-hand side 16 of
The fluid inlet (7, 10) and outlet (21, 20) valves to the upper and lower pump chambers 2, 13 are one-way valves (i.e., non-return valves), and are preferably configured to allow the linear pumping system to operate in any orientation without being dependent on gravity. Specifically, the fluid inlet valves 7, 10 are one-way valves that are respectively coupled between the upper and lower pump chambers 2, 13 and the upper and lower fluid inlet ports at 22, 23, and are configured to receive fluid into the pump chambers 2, 13 from outside of the pump casing 11. The fluid inlet valves 7, 10 may preferably be coupled to fluid inlet ports 22, 23 that are oriented such that the fluid inlets are not in line with the length of the pumping chamber, as shown in the illustrated embodiment. The fluid outlet valves 21, 20 are one-way valves that are respectively coupled between the upper and lower pump chambers 2, 13 and an interior cavity 24 of the pump casing 11, and are configured to expel fluid from the pump chambers 2, 13 into the interior cavity 24 of the pump casing. In an embodiment, the one-way inlet (7, 10) and outlet (21, 20) valves may comprise buoyant balls in ball valves that are configured to move with the fluid without being dependent on gravity. The buoyant ball valves may, for example, utilize a retaining spring force provided by a spring return mechanism. In another example, the buoyant ball valves may include buoyant metallic balls (e.g., hollow metal balls) and magnets in the ball seats to attract the balls back into the valve seat. Other one-way valves known in the art may also be used, as appropriate.
In operation, on an upstroke of the linear motor mover 15, fluid is drawn into the lower pump chamber 13 and expelled from the upper pump chamber 2, and on a downstroke of the linear motor mover 15, fluid is drawn into the upper pump chamber 2 and expelled from the lower pump chamber 13. Fluid from both pump chambers 2, 13 is expelled into the interior cavity 24 of the pump casing 11, and the resulting hydraulic pressure causes the fluid to be expelled through the fluid outlet port 1 of the casing, for example into a fluid pipeline. The linear pump system may preferably be configured to operate in an oil or gas well at a minimum of 20 strokes per minute and a maximum of 1200 strokes per minute, such that the pump system may achieve reasonable flow rates with small diameter pumping chambers. An example of the fluid pumping action of the linear pumping system is shown in the diagrams of
The example illustrated in
In the third stage of operation (
In embodiments of the disclosure, the linear pumping system includes one or more sensors (not shown here) that are configured to measure the location of the motor mover 15 within the motor assembly. In embodiments, the linear pumping system may further include a motor controller (not illustrated) that is configured to regulate the movement and stroke of the pumping system based at least in part on the measured location of the motor mover 15. In this way, the upper and lower plunger rod portions 8, 19 may be cycled to the end of their respective pump chambers 2, 13, providing a maximum compression ratio for the pump.
In specific embodiments of the disclosure, the linear pumping system may include one or more sensors (not shown) that are configured to measure the pressure and/or temperature within the pump chambers 2, 13. In embodiments, the linear pumping system may further include a motor controller (not shown) that is configured to regulate the movement and stroke of the pumping system based at least in part on the measured pressure within the pump chambers 2, 13 in order to regulate pressure, e.g., to prevent the pump from becoming hydraulically locked. In this way, the linear pumping system may provide full compression on gassy fluids and reduced compression on fluids.
In another example, a feedback system similar to that shown in
In yet additional embodiments, the linear pumping system may be further configured to measure or compute the amount of gas in the pump based on the motor current and chamber pressures. In this way, the stroke length of the linear motor may be altered to better suit the fluid being pumped, allowing the linear pumping system to operate effectively with fluids of different viscosities and with varying amounts of intermixed gas.
Linear motors can be implemented with a simple coils and metal structure where the induction of large currents in the mover creates movement, a linear induction motor. A linear motor can also be implemented with a reluctance linear motor with several windings and an alternating magnetic mover so that moving the field along the length of the motor provides movement of the mover. This implementation is a synchronous linear reluctance motor. The third possibility is to incorporate permanent magnets into the mover and/or stator increasing the flux density and energy density of the motor, which is a synchronous permanent magnet linear motor.
In
In
The issue of the manner in which motion can be controlled in a linear oscillating motor as shown above has several important aspects. The main areas of concern in controlling the motor motion is starting and controlling the stops and starts at the ends of the motion range.
This principle of operation requires the stator fields to be reversed at a frequency dependent on the distance between the magnetic components and the linear speed of the motor. Accordingly, for this motor to operate, the stator field coils must be switched at the correct point to create a moving field which is always creating motion in one direction. When the mover approaches the end of its stroke, the rate of field switching should preferably be slowed to slow down the motion of the mover, and also finally be applied out of phase to stop the motion. Preferably, the system will ramp down the linear mover velocity toward the end of the stroke, bringing the mover to a halt a very small distance away from the end of the mechanical travel, without making contact with the end of the pump chamber. Such operation requires sensing of the position of the mover and in particular determining how close the mover is to the end of the stroke.
Sensing of the mover position is therefore important in the control of a linear synchronous motor. There are several methods of control that can be used in different embodiments. One simple control mechanism in applications where the motor will operate a long way from the power supply in a deep well, is to sense the current drawn by the stator coils. This current is proportional to the relative position of the mover magnetic circuit (whether passive, as in a reluctance motor or active with a permanent magnet motor). Thus, by sensing the current drawn by the stator it is possible to establish where the mover is relative to the stator. It is, however, problematic to determine how close the mover is to the end of travel. One possible method of establishing this end of travel position is to switch fields slowly at start up until the mover comes in contact with the end of the pump chamber, at which point the stator coil current will increase rapidly, and the mover will not move. Once the end position is known, the controller can simply count the stator current changes as the mover moves through the stator windings. Since the size of the motor is known and the number of coils is known, counting the current changes can be used as a position sensor.
In alternative embodiments, electronic position sensors may be fitted to the motor so that its absolute position and velocity can be sensed real time. This approach provides more accurate and direct feedback for controlling the motion of the mover. A person of skill in the art will appreciate details of the implementation of such control mechanisms, which are thus not discussed in further detail.
Controlling the motion of the mover in the manner described above is another aspect of this invention. In particular, in this aspect the general control mechanism which in its simplest form is used to create linear oscillating motion of the mover relative to the stator, is also further controlled to adapt the pump behavior to respond more appropriately to changing fluid conditions in the pump. The main additional aspects of control include prevention of over pressure, adapting the motor speed to react to motor winding over temperature, and dealing with gassy fluids and gases.
Over pressure can happen because of stuck valves, or heavy fluids, deep wells, etc. To address such conditions, in a specific embodiment a pressure sensor can be fitted to one or both of the pumping chambers. Data from this pressure sensor(s) can be used to regulate the motor velocity and stop the motor short of the end position to prevent over pressure. Mechanisms to take into account pressure sensor data to control the mover are described in more detail below.
In alternative embodiments, if the motor winding temperature is measured or computed, this temperature can be regulated by simply shutting the motor off if it gets too hot, or slowed down to reduce the power consumption to a level where the temperature rise becomes stable.
Additionally, it will be appreciated that gassy fluids will cause reduced pressure build up as the gas compresses with the stroking of the pump. This means that the pump and motor can move a lot faster during the compression stroke and only slow down again as the gas reaches the opening pressure of the non-return valve. With this understanding, in accordance with another embodiment the velocity profile of the pump can be changed to make it pump gassy fluids more effectively. Such a change can be implemented in practice by measuring the pressure in the pumping chamber or, where no pressure sensor is available, the current drawn by the motor. At any given depth this current will be proportional to the force developed, and so the force required to stroke the pump can be calculated from the motor current. It will also be appreciated that the motor current is also proportional to the depth of the pump and the friction in the seals, which can also be taken into account for more accurate control.
Implementation details of these and other control mechanisms will be appreciated by those of skill in the art, and employed in practical implementations without departing from the principles of this invention. The following description is intended to provide additional detail and illustration.
It is an intention of this invention that either using pressure sensors and/or current measurement one can measure the pressure behavior in the pump chambers and determine the fluid and gas mix the pump is working with. Importantly, in accordance with an aspect of the invention, information about the fluid mix in the chamber can be used to adjust the pump control, so the piston movement suits the property of the mix.
Note that in the event the pump is immersed in gas only, this will alter the pressure and current behavior as indicated above, but also reduce the cooling available to the motor, and accordingly would also result in increased motor winding temperatures. The measurement of motor temperature is therefore a useful measurement, as well as the pressure to determine what fluid or gas mixture the pump is working in.
This application uses examples to illustrate the invention, the scope of which is determined by the attached claims. Other examples falling within the scope of the invention may be apparent to those of skill in the art. It is noted that the figures described herein are not necessarily to scale. Certain features of the instant disclosure may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. It is to be recognized that the different teachings of the embodiments discussed herein may be employed separately or in any suitable combination to produce the desired results.
