EP3788234A1

EP3788234A1 - Fluid pumping using electric linear motor

Info

Publication number: EP3788234A1
Application number: EP19796208.7A
Authority: EP
Inventors: Jeffrey Boardman PRUITT; Michael Raymond NETECKE; Jaakko Jalmari HALMARI; Sean M. CLARKE; Ban Q. TRAN
Original assignee: Cameron Technologies Ltd
Current assignee: Cameron Technologies Ltd
Priority date: 2018-05-01
Filing date: 2019-04-30
Publication date: 2021-03-10
Also published as: EP3788234A4; WO2019213041A1; US20210102530A1

Abstract

A drilling fluid pump system includes a plurality of modular pump units that are each driven by a linear electric motor. A control system that can include positional feedback information which is used to control all of the linear motors in the pump system and reduce pressure pulsation. The linear motors can be controlled to reduce fluid pressure pulsation by controlling velocity and relative timing between pistons. To accommodate removal and addition of individual pump units the pump modules can be isolated electrically and hydraulically. This can improve scalability, reliability, and serviceability of the pump system.

Description

FLUID PUMPING USING ELECTRIC LINEAR MOTOR

Reference To Related Application

[0001] This application claims the benefit of and incorporates by reference U.S. Provisional Patent Appl. Ser. No. 62/665039 filed on May 1, 2018.

Technical Field

[0002] The present disclosure relates to systems and methods for drilling fluid pumping. More specifically, the present disclosure relates to a drilling fluid pump designs with a linear actuated motor.

Background

[0003] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0004] In order to meet consumer and industrial demand for natural resources, companies often invest significant amounts of time and money in finding and extracting oil, natural gas, and other subterranean resources from the earth. Particularly, once a desired subterranean resource such as oil or natural gas is discovered, drilling and production systems are often employed to access and extract the resource. These systems may be located onshore or offshore, depending on the location of a desired resource. Further, such systems generally include a wellhead assembly mounted on a well through which the resource is accessed or extracted. These wellhead assemblies may include a wide variety of components, such as various casings, valves, pumps, fluid conduits, and the like, that control drilling or extraction operations.

[0005] As will be appreciated, drilling and production operations employ fluids, referred to as mud or drilling fluids to provide lubrication and cooling of the drill bit, clear away cuttings, and maintain desired hydrostatic pressure during operations. Mud can include all types of water-based, oil-based, or synthetic-based drilling fluids. Mud pumps can be used to move large quantities of mud from surface tanks, down thousands of feet of drill pipe, out nozzles in the bit, back up the annulus, and back to the tanks. Operations come to a halt if the mud pumps fail, and thus, reliability under harsh conditions, using all types of abrasive fluids, is of utmost commercial interest.

Summary

[0006] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining or limiting the scope of the claimed subject matter as set forth in the claims.

[0007] According to some embodiments, a pump system is described that is configured to pump fluid (e.g. drilling mud, circulation fluid, or fracturing fluid) down a wellbore. The system includes: an electrically -powered linear motor including a stationary portion and a moving portion. The moving portion is adapted to move in a reciprocating fashion relative to the stationary portion. The pump system also includes a pump assembly that has a piston and one or more valves configured to pump a fluid into a wellbore. The reciprocating moving portion drives the piston. According to some embodiments, the pump system also includes a sensor configured to detect movement and/or position of at least a portion of the motor and/or pump assembly and to output position information; and a control system. The control system is configured to: control the motion of linear motor; receive the position information; and to make adjustments the control based on the position information thereby reducing error in the motion.

According to some embodiments, the control system can be configured to reduce flow pulsation of fluid pumped by the pump system based at least in part on the position information. According to some embodiments, the pump system further includes a pressure sensor configured to detect discharge fluid pressure of the pump system and output pressure information. The reduction in flow pulsation of fluid pumped by the pump system is can be further based in part on the pressure information.

[0008] According to some embodiments, the motor and pump assembly together form a first pump unit, and the system further includes one or more additional pump units. The control system can be further configured to adjust the relative timing of each motor based on a total number of pump units in the pump system.

[0009] According to some embodiments, the moving portion is rod-shaped and the stationary portion is tube-shaped and surrounds the rod-shaped moving portion. In such cases the rod-shaped moving portion can be vertically oriented such that is moves in a vertical direction. According to some other embodiments, the moving portions and the stationary portions are rectangular and planar in shape, and the stationary portion includes two planar portions disposed on either side of and sandwiching the moving portion. The moving portion can be configured to move primarily in horizontal direction. According to some embodiments, the pump unit can be dual-action, whereby the same linear motor drives a second pump assembly that includes a second piston and a set of second valves configured to pump the fluid into the wellbore. [0010] According to some embodiments, a plurality of isolation valves are positioned and configured to hydraulically isolate either of the pump assemblies thereby facilitating servicing and/or replacement of pump system components without loss of pump system operation.

[0011] According to some embodiments, a method of pumping a fluid into a wellbore is described. The method includes: controlling a first electrically-powered linear motor that includes a stationary portion and a moving portion, such that the moving portion moves in a reciprocating fashion relative to the stationary portion and drives a first pump assembly that includes a piston and one or more valves, thereby causing a the fluid to flow into the wellbore; receiving position information from a sensor configured to detect movement and/or position of at least a portion of the motor and/or pump assembly; and adjusting the controlling based at least in part on the position information, thereby reducing error in controlling the position.

[0012] As used herein, the terms "drilling mud" "drilling fluid" and "mud" are synonymous and refer to any of a number of liquid and gaseous fluids and mixtures of fluids and solids (as solid suspensions, mixtures and emulsions of liquids, gases and solids) used in operations to drill boreholes into the earth. Drilling mud includes various categories of fluid including: (1) water-base, (2) non-water-base, (3) gaseous

(pneumatic), and any combinations thereof.

Brief Description of the Drawings

[0013] The subject disclosure is further described in the following detailed description, and the accompanying drawings and schematics of non-limiting

embodiments of the subject disclosure. The features depicted in the figures are not necessarily shown to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form, and some details of elements may not be shown in the interest of clarity and conciseness.

[0014] FIG. 1 is a schematic diagram illustrating a well system that utilizes a mud pump system actuated by one or more linear electric motors, according to some embodiments;

[0015] FIG. 2 is a perspective view of an array of linear motor actuated pump units configured to pump drilling mud, according to some embodiments;

[0016] FIGs. 3A, 3B, 3C and 3D are a perspective view, side view, exploded view and cross section of a linear motor actuated mud pump unit, according to some embodiments;

[0017] FIG. 4 is a diagram illustrating suppling power and control to a linear servo motor configured to actuate a pump unit, according to some embodiments;

[0018] FIGs. 5A and 5B are plots showing examples of piston velocity profiles for a precisely controlled pump piston, according to some embodiments, and conventional crankshaft driven pump piston according to prior art, respectively;

[0019] FIG. 6 is a block diagram illustrating power and control systems associated with a modular pumping system that include a plurality of pump units, according to some embodiments;

[0020] FIGs. 7A, 7B, 7C and 7D are a perspective view, a top view, and two cross sections of a linear motor actuated mud pump unit, according to some embodiments; and [0021] FIGs. 8A, 8B, 8C and 8D are a perspective view, a top view, and two cross sections of a linear motor actuated dual-action pump unit, according to some

embodiments.

Detailed Description [0022] One or more specific embodiments of the present disclosure will be described below. These described embodiments are only exemplary of the present disclosure. Additionally, in an effort to provide a concise description of these exemplary embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation- specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Like reference numerals are used herein to represent identical or similar parts or elements throughout several diagrams and views of the drawings.

[0023] Conventional reciprocating pumps convert rotational motion to linear motion, utilizing conventional mechanical power transmission methods. In some applications, an AC induction motor can be connected to a small sheave that turns a larger sheave mounted to the pinion shaft via a belt. The gear on the pinion shaft meshes with a gear on the crankshaft. The crankshaft is connected to the pistons via connecting rods, which are timed on the crankshaft using equivalently spaced lobes, and a crosshead system. The connecting rods and crossheads are where the rotary motion of the AC motor is converted to purely linear motion. The pistons reciprocate forward and backward, pushing the drilling fluid through the drillstring and downhole.

[0024] There are many costly, complex parts that are required to convert rotary motion to linear motion. Each component has specific maintenance requirements which require time to perform and have potentially major consequences if they are not performed both regularly and correctly, including non-productive time and/or catastrophic failure of the internal components of the pump.

[0025] For optimal function and long component life, proper alignment of the internal components of drilling fluid pumps, like know triplex pumps, is important. Unfortunately, it is also difficult and time consuming. A great deal of time is thus spent aligning the pump, and if the pump is not aligned correctly, contamination of the power end (pinion, crankshaft, crosshead, bearings) is likely to occur. This contamination of mud and water can shorten the life of the power end components-bearings, gears, etc. Additionally, if alignment is incorrect, the piston life might also be reduced, causing additional nonproductive time.

[0026] In a known application of a reciprocating pump system to pump drilling fluids, triplex reciprocating pumps are used that typically consist of three cylinders per mud pump with similar parts. If any cylinder has parts that need to be replaced, all cylinders are unable to operate. In order to avoid any production downtime, there are typically 2-3 mud pumps per rig with the second or third pump sitting idle as a backup pump. Triplex mud pumps may also typically have high pulsation (flow variation), and require a pulsation dampener to dampen the pulses.

[0027] According to some embodiments, a mud pump system is described that includes a plurality of pump units. Each pump unit includes a fluid pumping piston assembly that is driven by a linear servo motor servomechanism. According to some embodiments, the servomechanism comprises a motion controller, synchronous linear motor and linear position sensor. The pump system design allows each pump unit/piston to be a separate isolatable module. This contrasts to conventional triplex or similar pumps wherein none of the pistons can be isolated due to: (1) all pistons being tied to a crankshaft; and (2) all pistons being driven by a single motor. According to some embodiments, in the described mud pump system each piston has its own motor, and can be completely isolated and bypassed if an issue arises and it needs to be serviced. The pump system design described here thus allows modularity since it enables the addition and removal of any number of pistons or pump units from the pump system as may be needed for the particular rig. For example, if more flow is needed, the pump system described herein could be retrofitted with additional cylinder assembly(ies) / pump units to adequately provide the needed flow volume. Alternatively, such flow capacity can also be reduced by removing unnecessary pump cylinders assembly and servo motors (pump units).

[0028] According to some embodiments, the pump system described herein might be supplied with high flow, low pressure fluid via a charge pump. Fluids might be drilling fluids such as mud or slurry. During the suction portion of the cycle, the rod on the linear motor which is connected to the piston rod will travel upwards opening the suction valve and pulling the fluid into the liner. Once it reaches the top of the stroke, the motor will push the rod downwards which closes the suction valve, opens the discharge valve and pushes the fluid out of the module, through the drillstring, and downhole. The position, speed, and acceleration of each piston assembly can be coordinated in such a way as to minimize fluid pulsation through the use of a programmable logic based motion controller, linked to an operator’s human machine interface in the drilling control room. Although much of the pump systems are shown and described herein as configured for pumping drilling mud, according to some embodiments, the pump systems can be used in other drilling, circulation, fracturing operations or in any operation where fluids need to be pumped downhole. Any and all of the pump systems shown and described herein can be applied to any of such pumping applications. [0029] FIG. 1 is a schematic diagram illustrating a well system that utilizes a mud pump system actuated by one or more linear electric motors, according to some embodiments. The well system 100 can be configured to extract various minerals and natural resources, including hydrocarbons (e.g., oil and/or natural gas), or configured to inject substances into an earthen surface 103 and a subterranean earthen formation 105 via a well or wellbore 112. In some embodiments, the well system 100 is land-based, such that the surface 103 is a land surface, or subsea, such that the surface 103 is a sea floor. In the embodiment of FIG. 1, well system 100 generally includes a drilling rig or platform 120 disposed at the surfacel03, a well or drill string 122 extending downhole from rig 120 through wellbore 112, a bottomhole assembly (BHA) 124 coupled to the lower end of drill string 122, and a drill bit 126 attached to the lower end of BHA 124 and disposed at a lower end of the wellbore 112. Though the description herein may primarily refer to a drill string, it is understood that other types of well or tool strings can extend into the wellbore 112.

[0030] In this embodiment, well system 100 further includes a mast 128, a traveling block 130, a standpipe 132, a fluid line or mud return line 134, a mud tank 136, and a mud pump system 138. The drill string 122 is suspended from travelling block 130, which is in turn supported by mast 128. Drilling fluid is pumped using mud pump system 138 into an upper end of drill string 122 via pump discharge pipe 152 and standpipel32, where the drilling fluid is pumped through a passage of drill string 122 down to the drill bit 126. The drilling fluid is pumped through ports in the drill bit 126 and recirculated to the surface 103 through an annulus of wellbore 112, formed between an inner surface 114 of the wellbore 112 and an outer surface of drill string 122. At the surface 103, the recirculated drilling fluid is flowed through the mud return line 134 into the mud tank 136. Mud pump system 138 is configured to pump drilling fluid disposed in mud tank 136 using pump inlet pipe 150 back to the standpipe 132 using pump discharge pipe 152, such that the drilling fluid may be flowed back into the passage of the drill string 122. Well system 100 may further include other components, such as shale shakers, for removing entrained cuttings and other debris in the recirculated drilling fluid passing through mud return line 134 prior to being flowed back into the standpipe 132 by mud pump system 138. As will be discussed further herein, in various embodiments, mud pump system 138 is driven by a linear electric motor.

[0031] FIG. 2 is a perspective view of an array of linear motor actuated pump units configured to pump drilling mud, according to some embodiments. The mud pump array 210 shown in this example includes five mud pump units 220, 222, 224, 226 and 228, and can form part of mud pump system for use in a well drilling system, such as mud pump system 138 shown in FIG. 1. The plurality of mud pump units in mud pump array 210 are configured to collectively draw drilling mud from the suction manifold 250, which is in fluid communication with inlet pipe 150 shown in FIG. 1, and push drilling mud into discharge manifold 252, which is in fluid communication with discharge pipe 152, shown in FIG. 1. According to some embodiments, each of the pump units in the pump array is a piston-type positive displacement pump and has its own linear electric motor for reciprocation of the pump piston. In this example, pump units 220, 222, 224, 226 and 228 are actuated with a linear electric motors 230, 232, 234, 236 and 238, respectively. Also shown in FIG. 2 are pump subassemblies 240, 242, 244, 246 and 248 which include suction and discharge valves for pump units 220, 222, 224, 226 and 228, respectively. According to some embodiments, the pump system 138 can be configured such that each of the pump units 220, 222, 224, 226 and 228 in the array 210 can be individually brought "on-line" or taken "off line." In some examples, relative timing of the pump strokes of each of the pump units can be altered to accommodate different numbers of pump units when operating pump units are added or removed from the array. In this way, a modular design can be achieved, such that if one pump unit fails or otherwise needs to be taken off-line it can be hydraulically isolated (e.g. using gate valves 350 and 352) and worked on while the remaining pump units continue to operate in the array. This modular design can significantly increase equipment availability, and reduce the potential for excessive non-productive time in the event of an unplanned failure. Although the example of FIG. 2 shows that the pump array consists of five pump units, in general such arrays can include other numbers of pump units such as two, three, four, five, six, seven, or more pump units.

[0032] FIGs. 3A, 3B, 3C and 3D are a perspective view, side view, exploded view and cross section of a linear motor actuated mud pump unit, according to some embodiments. Shown is further detail of a single pump unit 220, which can form part of a pump array in mud pump system for use in a well drilling system, such as mud pump array 210 shown in FIG. 2 and mud pump system 138 shown in FIG. 1. A linear electric motor 230 is used to animate the pump unit. Known motors include linear motors that create linear motion in response to a control input. According to some embodiments, motor 230 is a tubular-type linear servo motor. Many of the components of the pump unit are visible in the exploded view of FIG. 3C. The linear motor 230 includes a stationary stator 306 and reciprocating mover rod 308. The stator 306 is energized by a series of coils. Mover rod 308 can include a series of permanent magnets configured to interact with magnetic forces induced by current in and the arrangement of coils in stator 306. The mover rod 308 is attached to piston 324 via coupling adapter 312. Piston 324 slides within a central cylindrical opening of liner 330. A seal 314 is fixed to the end of piston 324 that is sized and configured to form a seal with the inner surface of liner 330. Stator 306 of motor 230 is mounted on frame 332 which is, in turn, mounted to valve module 340. Within the frame 332, also shown is liner lock 328 and linear lock nut 326. The valve module 340 includes suction valve 370 and discharge valve 372 disposed on the upstream and downstream ends, respectively, of central conduit 342. When the piston 324 is actuated by the mover rod 308 as shown by dashed arrows in FIG. 3D, alternating low fluid pressure (suction) and high fluid pressure (discharge) is generated within the central conduit 342. The suction and discharge valves 370 and 372 act to open and close, thereby pumping fluid from suction conduit 380, through central conduit 342, and outwards through discharge conduit 382 as shown by the dotted arrows in FIG. 3D. Also visible in FIGs. 3A-D are suction and discharge gate valves 350 and 352, as well as valve covers 360 and 362.

[0033] Pump units such as shown can have one or more advantages over conventional pumps, including: scalability in size, optimal compactness of size, and increased control precision. Using a linear motor in a reciprocating fluid pump as described enables a reduction in the amount of parts on the mud pump itself when compared to conventional mud pumps. Furthermore, mechanical alignment of a linear motor can be achieved more easily than with conventional mud pumps. According to some embodiments using such a linear motor, a modular design can be achieved, such that if one unit or“cylinder” fails it can be isolated and worked on while the other units or cylinders continue to work. This leads to increased equipment availability, and reduced the potential for excessive non-productive time in the event of an unplanned failure. The modular design as described herein, according to some embodiments, enables a drilling rig to have as many units or cylinders as needed. The pump units / cylinders can added or removed as rig requirements change.

[0034] According to some embodiments, the units or cylinders can be mounted in any number of orientations, vertical, horizontal or angular. The linear motor, with an individual servo motor actuating each piston, enables control over the speed, acceleration and stroke length to higher degree of precision and repeatability than with known conventional mud pumps. This enhanced precision enables manipulation of the velocity profile of the pistons that conventional (e.g. crankshaft type) mud pump designs do not allow because in such designs all the pistons are mechanically linked and forced to operate in a sinusoidal way. FIGs. 5A and 5B are plots showing examples of piston velocity profiles for a precisely controlled pump piston, according to some embodiments (profile 510 in FIG. 5 A), and conventional crankshaft driven pump piston (profile 512 in FIG. 5B.) The linear motor and servo motor-based designed, according to some embodiments, can therefore allow for timing and control of the pistons individually such that one can significantly reduce or eliminate the use of pulsation dampeners, which are a costly maintenance item. The reduction in fluid pulsation can have significant benefits for downhole technology, which often relies on mud pulse telemetry to transmit valuable data about downhole conditions. Reduced pump-induced pulsation can therefore lead to transmission and reception of higher quality/resolution data. This can in turn allow for greater visibility of downhole conditions, and can result in significant cost savings for the field operator.

[0035] FIG. 4 is a diagram illustrating suppling power and control to a linear servo motor configured to actuate a pump unit, according to some embodiments. A programmable controller 410 sends speed and force control signals to module controller 412. Module controller 412 is configured to control the piston position, piston speed and/or piston force according to the control signals received from controller 410.

According to some embodiments, module controller 412 is configured to send speed voltage reference signals to the drive unit 420. Drive unit 420 is configured to receive electrical power from power supply 422 and drive the linear servo motor 230 of a pump unit such as pump unit 220 shown in FIG. 2. Voltage and frequency output from drive 420 control the motor 230. The module controller 412 can use current feedback to control piston force.

[0036] The power supply 422 in many cases will be an AC power supply. In such cases the drive unit 420 receives power from AC power supply 422 and through a converter and inverter, the amplitude and frequency can be adjusted to properly control the servo motor 230. According to some embodiments, the servo motor 230 includes a piston position encoder 430. The encoder 430 can be configure to detect linear motion and/or position of motor shaft 308. The encoder output can by feed back to module controller 412. Module controller 412 can include speed adjustment, position adjustment and/or current adjustment functionality and controller 412 can use feedback from an encoder 430 as shown to more accurately control the current from inverter 424.

According to some embodiments, a pressure sensor can be mounted on the discharge manifold 250 and/or discharge pipe 150 (e.g. sensor 662 in FIG. 6). In such cases the pressure data can also be used by module controller 412 to more accurately control the pump. Using the feedback signal(s), the motor linear extension/retraction can be controlled so as to minimize or eliminate the error. With the close loop control, the motor 230 can carry out highly accurate positioning operations.

[0037] FIG. 6 is a block diagram illustrating power and control systems associated with a modular pumping system that include a plurality of pump units, according to some embodiments. The control system shown is used to control several pump units, such as pump units 220, 222, 224, 226 and 228 shown in FIG. 2. Human-machine interface 610 is shown which can include a display screens, knobs, and/or sliders, etc. to allow the operator to control and adjust the speed and force for the pumping system as well as to monitor condition of the pump units and drive units. Programmable controller 410 is used for overall control of the pump system, and a system controller 620 is used to control each pump unit by determining which pump units are active, the positions each pump as well as to monitor pressure and adjust the system to optimize (or minimize) pressure pulsation. Note that a pressure transducer 662 is positioned on discharge manifold 252 and/or discharge pipe 152 and sends pressure signals to system controller 620.

[0038] System controller 620 is in communication with each of the module controllers 412, 612, 616 and 618. As described with respect to FIG. 4, the module controllers (in this case, 412, 612, 616 and 618) are configured to control the drive units (in this case 420, 622, 624, 626 and 628). As shown, the module controllers each receive feedback signals from the linear motors and from the pump sub-assemblies. Position encoder 430 can be used (as described, supra) to detect linear motion and/or position of motor shaft 308 (shown in FIGs. 3C and 3D). The feedback from encoder 430 is sent to module controller 412. Similarly, other driver and/or motor status signals 630, 632, 634, 636 and 638 include: winding temperature, resistance, bearing temperature, and vibration sensor output. Also shown for the other pump units are encoders 633, 635, 637 and 639. Power supply 422 is also shown which supplies AC power to drive units 420, 622, 624, 626 and 628. Also shown in FIG. 6 are the gate valves 350, 352, 653, 656, 654, 655,

656, 657, 658 and 659 that are used to allow hydraulic isolation of any of the pump units.

[0039] FIGs. 7A, 7B, 7C and 7D are a perspective view, a top view, and two cross sections of a linear motor actuated mud pump unit, according to some embodiments. In this example, the linear motor 730 has a moving element configured as a flat plate rather than a tubular shaped rod as shown in FIGs. 2 and 3A-D. The flat linear motor pump unit 720 is similar in many respects to the pump units 220, 222, 224, 226 and 228 shown in FIGs. 2, and much of the description of those pump units and unit 220 in further detail, applies equally to the pump unit 720. According to some embodiments, pump system 138 shown in FIGs. 1 and 2, and pump array 210 shown in FIG. 2, can include a plurality (e.g. 2, 3, 4, 5, 6 or more) of pump units 720 instead of pump units 220, 222, 224, 226 and 228. According to some embodiments, pump system 138 shown in FIGs. 1 and 2, and pump array 210 shown in FIG. 2, can include a combination of pump units with tubular-type linear motors (such as unit 220), and pump units with flat-type linear motors (such as unit 720). The resulting arrays and pump systems will benefit from the same advantages (e.g. pulse control, modularity, scalability, cost savings) that are described elsewhere herein. Pumping systems based on a flat-configured motor, as in the case of pump unit 720, especially when oriented in a horizontal configuration as shown, provide benefits in flexibility of pumping system layout, increased force density, and possible savings in space and cost for the overall drilling operation.

[0040] Pump unit 720 includes a flat linear motor 730 and a pump subassembly 740. The linear motor 730 includes a moving plate 708 sandwiched between two stationary stator plates 702 and 704. The stator plates 702 and 704 are energized by coils 706 and 707 respectively. Note that the coils 706 and 707 continue within stator plates 702 and 704, respectively. Moving plate 708 can include a series of permanent magnets configured to interact with magnetic forces induced by current in and the arrangement of coils 706 and 707. Moving plate 708 and the attached piston 724 can translate side to side as indicated by the dashed arrows. Motion of plate 708 is guided by linear guide bars 716 and 718 and linear bearings 726. Note that there is a small air gap formed at the interfaces between stator plate 702 and moving plate 708, and between stator plate 704 and moving plate 708. A linear sealing element 728 provides isolation between the motor 730 and the opening within yoke 732. A seal 714 is fixed to the end of piston 724 that is sized and configured to form a seal with the inner surface of liner 712. The pump subassembly 740 includes suction valve 770 and discharge valve 772 disposed on the upstream and downstream ends, respectively, of a central conduit. The inlet of the pump unit 720 is at a suction port 780, visible in FIG. 7C, and the outlet is through either or both of two discharge ports 782 (one of which is visible in FIG. 7A). When the piston 724 is actuated by the motor 730 as shown by dashed arrows, alternating low fluid pressure (suction) and high fluid pressure (discharge) is generated within the central conduit and within the liner 712. The suction and discharge valves 770 and 772 act to open and close thereby pumping fluid from suction port 780 to discharge ports 782, as shown by the dotted arrows.

[0041] FIGs. 8A, 8B, 8C and 8D are a perspective view, a top view, and two cross sections of a linear motor actuated dual-action pump unit, according to some embodiments. In this example, the linear motor 830 of pump unit 820 is similar or identical to motor 730 shown in FIGs. 7A, 7B, 7C or 7D, but is configured to drive two pumping subassemblies 842 and 843. The dual-action configuration of pump unit 820 can provide significant benefits in terms of pumping efficiency. In particular dual-action configurations such as shown can provide higher flow volume for the amount of pump space. The pump unit 820 is similar in many respects to the pump unit 720 shown in 7A, 7B, 7C or 7D and pump units 220, 222, 224, 226 and 228 shown in FIGs. 2. Much of the description of those pump units applies equally to the pump unit 820. According to some embodiments, pump system 138 shown in FIGs. 1 and 2, and pump array 210 shown in FIG. 2, can include a plurality (e.g. 2, 3, 4, 5, 6 or more) of pump units 820 instead of, or in combination with pump units 720, 220, 222, 224, 226 and 228. The resulting arrays and pump systems will benefit from the same advantages (e.g. pulse control, modularity, scalability, cost savings) that are described elsewhere herein.

[0042] Pump unit 820 includes a flat linear motor 830 and two pumping subassemblies 842 and 843. The linear motor 830 includes a moving plate 808 sandwiched between two stationary stator plates 802 and 804. The stator plates 802 and 804 are energized by coils 806 and 807 respectively. Note that the coils 806 and 807 continue within stator plates 802 and 804, respectively, although not visible in FIGs. 8A, 8B, 8C or 8D. Moving plate 808 can include a series of permanent magnets configured to interact with magnetic forces induced by current in and the arrangement of coils 806 and 807. Moving plate 808 and the attached pistons 824 and 825 can translate side to side as indicated by the dashed arrows. Motion of plate 808 is guided by linear guide bars 816 and 818 and linear bearings 826. Note that there is a small air gap formed at the interfaces between stator plate 802 and moving plate 808, and between stator plate 804 and moving plate 808. A linear sealing elements 828 and 829 provides isolation between the motor 830 and the opening within yokes 832 and 833, respectively. Seals 814 and 815 are fixed to the ends of pistons 824 and 825 respectively, and are sized and configured to form a seal with the inner surface of liner 812 and 813, respectively. The pumping subassembly 842 includes suction valve 870 and discharge valve 872 disposed on the upstream and downstream ends, respectively, of a central conduit connected to the cylinder within liner 812. Similarly, the pumping subassembly 843 includes suction valve 871 and discharge valve 873 disposed on the upstream and downstream ends, respectively, of a central conduit connected to the cylinder within liner 813. The inlet of pumping subassembly 842 is at a suction port 880, and the outlet is through either or both of two discharge ports 882. The inlet of pumping subassembly 843 is at a suction port 881, and the outlet is through either or both of two discharge ports 883. When the pistons 824 and 825 are actuated by the motor 830 as shown by dashed arrows, alternating low fluid pressure (suction) and high fluid pressure (discharge) is generated within the central conduits of pumping subassemblies 842 and 843. The suction and discharge valves 870, 871, 872 and 873 act to open and close thereby pumping fluid from suction ports 880 and 881 to discharge ports 882 and 883 as shown by the dotted arrows. Also shown in FIGs. 7D and 8D are alternate bearing positions 790 and 890, respectively.

[0043] Although the tubular-type linear motors are described herein and are shown in FIGs. 2, 3A, 3B, 3C and 3D as vertically oriented, according to some embodiments, such linear motors can be oriented horizontally, such that the moving rod and piston translate in a primarily horizontal rather than vertical direction. Although the tubular- type linear motors are described herein and are shown in FIGs. 2, 3A, 3B, 3C and 3D as being single-action, according to some embodiments, such tubular-type linear motors can be adapted to dual action (i.e. alternatively suctioning and pressurizing two opposing cylinders) similar to that shown in FIGs. 8A, 8B, 8C and 8D. Furthermore, although the linear motors have been described thus far as either tubular-type or flat-type, according to some embodiments other types and shapes of linear motors can be used.

[0044] While the disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims.

[0045] The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as“means for” or“step for” performing a function, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f). While the subject disclosure is described through the above embodiments, it will be understood by those of ordinary skill in the art, that modification to and variation of the illustrated embodiments may be made without departing from the concepts herein disclosed.

Claims

CLAIMS What is claimed is:

1. A pump system configured to pump fluid down a wellbore, the system

comprising:

an electrically-powered linear motor including a stationary portion and a moving portion, the moving portion adapted to move in a reciprocating fashion relative to the stationary portion; and

a pump assembly including a piston and one or more valves configured to pump a fluid into a wellbore, the piston being driven by the reciprocating moving portion.

2. A pump system according to claim 1 further comprising:

a sensor configured to detect movement and/or position of at least a portion of the motor and/or pump assembly and output position information; and a control system configured to control the motion of linear motor, to receive the position information and to make adjustments the control based at least in part on the position information thereby reducing error in said motion.

3. A pump system according to claim 2 wherein said control system is further

configured to reducing flow pulsation of fluid pumped by the pump system based at least in part on said position information.

4. A pump system according to claim 3 further comprising a pressure sensor configured to detect discharge fluid pressure of the pump system and output pressure information, and said reducing flow pulsation of fluid pumped by the pump system is further based at least in part on said pressure information.

5. A pump system according to claim 2 said motor and said pump assembly together form a pump unit, and said system further comprising one or more additional pump units, each of which includes at least one linear motor and at least one pump assembly, and wherein said control system is further configured to adjust relative timing of each motor based on a total number of pump units in the pump system.

6. A pump system according to claim 1 wherein the moving portion is rod-shaped and the stationary portion is tube-shaped and surrounds the rod-shaped moving portion.

7. A pump system according to claim 6 wherein the rod-shaped moving portion is vertically oriented and is configured to move in a vertical direction.

8. A pump system according to claim 1 wherein the moving portions and the

stationary portions are rectangular and planar in shape, and the stationary portion includes two planar portions disposed on either side of and sandwiching the moving portion.

9. A pump system according to claim 8 wherein the moving portion is configured to move primarily in horizontal direction.

10. A pump system according to claim 1 further comprising a second pump assembly including a second piston and a set of second valves configured to pump the fluid into the wellbore, the second piston being driven by said reciprocating moving portion.

11. A pump system according to claim 10 further comprising a plurality of isolation valves positioned and configured to hydraulically isolate either of said pump assembly or said second pump assembly thereby facilitating servicing and/or replacement of pump system components without loss of pump system operation.

12. A pump system according to claim 1 wherein said fluid is selected from a group consisting of: drilling mud, circulation fluid, and fracturing fluid.

13. A method of pumping a fluid into a wellbore comprising:

controlling a first electrically-powered linear motor that includes a stationary portion and a moving portion, such that the moving portion moves in a reciprocating fashion relative to the stationary portion and drives a first pump assembly that includes a piston and one or more valves, thereby causing a fluid to flow into the wellbore;

receiving position information from a sensor configured to detect movement and/or position of at least a portion of the motor and/or pump assembly; and

adjusting said controlling based at least in part on the position information

thereby reducing error in said controlling.

14. A method according claim 13 wherein said first motor and said first pump assembly together form a first pump unit, and said controlling includes controlling a plurality of additional pump units, said first pump unit and said additional pump units forming a pump system.

15. A method according to claim 14 further comprising:

altering the number of pump units being controlled; and

adjusting relative timing of each motor based on a new total number of pump units in the pump system.

16. A method according to claim 14 further comprising receiving pressure

information from a sensor configured to detect pressure of the fluid being discharged from said pump system, and said controlling further includes controlling said first pump unit and said plurality of additional pump units to reduce pressure pulsations bases at least in part on information from said pressure sensor.

17. A method according to claim 16 wherein said reducing pressure pulsations is achieved at least in part by controlling piston velocity profiles of each pump unit and phase angles between the pump units.

18. A method according to claim 13 wherein the pump said moving portion of the first electrically -powered linear motor further drives a second pump assembly including a second piston and a set of second valves configured to pump the fluid into the wellbore.

A method according to claim 13 wherein said fluid is selected from a group consisting of: drilling mud, circulation fluid, and fracturing fluid.