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Active valve system for positive displacement pump

Active valve system for positive displacement pump description/claims

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Embodiments described herein relate to positive displacement pumps, and more specifically to devices and methods to improve the efficiency, durability, performance, and operating characteristics of reciprocating positive displacement pumps (of the sort that might be used in pumping wellbore servicing fluids) by actively operating the suction valve(s) of the pump.

Positive displacement pumps, and specifically reciprocating pumps, are used in all phases of oilfield operation to pump water, cement, fracturing fluids, and other stimulation or servicing fluids. Pumps in oil field operations often endure harsh conditions, especially when pumping abrasive fluids (such as fracturing fluids). Thus, there is an ongoing need for improved pumps and methods of operation for pumps, allowing for more effective oil field pumping operations in the face of such harsh operating conditions.

In one aspect, the present disclosure is directed to a device comprising a reciprocating pump having a suction valve through which fluid is drawn into a chamber during a suction stroke in order to be discharged from the pump during a discharge stroke; and an active valve system (typically including an active valve train and often also including a sensor for pump stroke position and a controller) operable to provide force to operate the suction valve. The device may further comprise a timing marker indicative of pump stroke, a sensor operable to detect the timing marker, and a controller operable to activate the active valve train based on the sensed pump stroke. Further, the active valve train may comprise a cylinder with a rod, with the rod connected to or in contact with the suction valve. The active valve train may provide a force directed to open the suction valve prior to or shortly after the suction stroke begins. Alternatively, in embodiments that pre-load the suction valve to open, the active valve train may provide a force directed to open the suction valve during the discharge stroke. Typically, the reciprocating pump further comprises a suction valve spring (closure member) operable to provide force to close the suction valve. The suction valve spring (closure member) may close the suction valve prior to the discharge stroke.

In one embodiment, the suction valve spring (closure member) is sufficiently stiff to minimize valve float as the suction valve closes. The force provided by the active valve train may be greater than the closing force exerted by the suction valve spring (closure member). Additionally, as pressure in the chamber varies during the suction and discharge strokes, the force provided by the active valve train may be less than the closing force exerted by the suction valve spring (closure member) in conjunction with the pressure in the chamber during the discharge stroke. Alternatively, as pressure in the chamber varies during the suction and discharge strokes, the force provided by the active valve train may be less than the force exerted by the suction valve spring (closure member), but sufficient in conjunction with the pressure in the chamber during the suction stroke (such as the pressure differential between the high pressure suction header and the low pressure chamber, for example) to open the suction valve quickly enough to minimize cavitation. The active valve train may release the opening force prior to the discharge stroke. Thus, the active valve train may provide a force directed to open the suction valve during the discharge stroke, and may then release the opening force prior to the discharge stroke.

In an alternative embodiment of the device, the suction valve spring (closure member) may be insufficiently stiff to close the suction valve quickly enough to minimize valve float on its own, and the active valve train may provide a force directed to assist in opening the suction valve and a force directed to assist in closing the suction valve. Then, the force of the suction valve spring (closure member) in conjunction with the closing force provided by the active valve train would typically be sufficient to close the suction valve quickly enough to minimize valve float. Often, the suction valve connects to a fluid header operable to deliver fracturing fluid and the like to the pump for discharge into a well bore. The pump may also be mobile, with the pump being transported via a motorized vehicle, and the pump possibly being powered by the engine of the motor vehicle. In another embodiment in which there is no suction valve spring (closure member), the active valve train may provide a force directed to open the suction valve and a force directed to close the suction valve (actively operating the opening and closing of the suction valve entirely on its own).

In another aspect, the present disclosure is directed to a method for bringing online a reciprocating pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke by a common crankshaft, the method comprising actively opening the suction valves of all cylinders and holding the suction valves open; bringing the crankshaft up to operating speed; and releasing the suction valves to bring the pump online. The suction valves may be released sequentially (such as one at a time, for example). Additionally, the suction valves may each be released at or near the end of the discharge stroke (when the plunger is fully extended and there is maximum mechanical advantage). The suction valves typically would be released when the crankshaft speed is sufficiently high to provide adequate torque from the engine, motor, or other prime mover to start the pump (as the pump can only start operating once the engine's torque is sufficient to overcome the discharge pressure).

In one embodiment, the method may further comprise priming the pump (before normal operation), which may further include actively holding the suction valves open during suction stroke to minimize the pressure drop across the suction valve until each chamber fills completely during the suction stroke. Additionally, the method may further comprise actively opening each suction valve prior to its chamber's suction stroke, and releasing each suction valve prior to its chamber's discharge stroke (once the pump is functioning normally at operating speed). This may require sensing the timing for each suction stroke and discharge stroke. The method may further comprise charging the cylinder during the suction stroke; closing the suction valve prior to the discharge stroke; and discharging the cylinder during the discharge stroke. The suction valve may automatically be closed at or near the end of the suction stroke (prior to the discharge stroke) by a suction valve spring sufficiently stiff to minimize valve float. Alternatively, when the closing of the suction valve operates by a suction valve spring, the method may further comprise actively assisting the closing of the suction valve at or near the end of the suction stroke in order to minimize valve float. In one embodiment, the method further comprises connecting the suction valve to a source of fracturing fluid and/or pumping fracturing fluid into a well bore.

In yet another aspect, the present disclosure is directed to a method for actively assisting the opening of a suction valve in a reciprocating pump having a suction stroke and a discharge stroke, the method comprising providing a spring operable to close the suction valve prior to each discharge stroke; actively applying an opening force to the suction valve during each discharge stroke (and actively holding the suction valve open during the suction stroke by maintaining the opening force on the suction valve); and releasing the opening force prior to each discharge stroke. In one embodiment, the method further comprises sensing the timing of the pump stroke. The spring may provide a closing force sufficient to close the suction valve fast enough to minimize valve float. The pump may further comprise a chamber in which the pressure varies during suction and discharge strokes; and the opening force actively applied may be greater then the spring closing force, but less than the spring closing force in conjunction with the pressure in the chamber during the discharge stroke.

In still another aspect, the present disclosure is directed to a method of servicing a wellbore with a servicing fluid (e.g., a fracture fluid) using a reciprocating pump having multiple chambers each with a suction valve and a discharge valve and operable to provide a suction stroke and a discharge stroke, the method comprising connecting each suction valve to a source of wellbore servicing fluid; connecting each discharge valve to the wellbore; providing a force to actively open each suction valve prior to the suction stroke of its chamber; charging each chamber with wellbore servicing fluid during its suction stroke; releasing the opening force on each suction valve prior to the discharge stroke of its chamber; and discharging wellbore servicing fluid from each chamber during its discharge stroke and into the wellbore. When the suction stroke and discharge stroke of each chamber is driven by a common crankshaft, the method may further comprise sensing the timing of the suction stroke and the discharge stroke based on rotation of the crankshaft. Each suction valve may also be opened sufficiently fast to minimize cavitation.

In an embodiment, the method may further comprise providing a force for closing the suction valve of each chamber prior to its discharge stroke. Each suction valve may then be closed sufficiently fast to minimize valve float. The method may further comprise providing one or more springs operable to close the suction valve of each chamber prior to its discharge stroke (with the springs providing the closing force). In one embodiment, the opening force provided to actively open each suction valve prior to the suction stroke of its chamber is greater than the closing force provided to close the suction valve of each chamber prior to its discharge stroke. In another embodiment, the pressure in the chamber varies during the suction and discharge strokes; and the opening force provided to actively open each suction valve prior to the suction stroke of its chamber is less than the closing force provided to close the suction valve of each chamber prior to its discharge stroke, but is sufficient in conjunction with the pressure in the chamber during the suction stroke to open the suction valve quickly enough to minimize cavitation.

In still another embodiment, the method may further comprise actively holding all suction valves open to prime the pump. Alternatively, the method may further comprise actively holding all suction valves open during start-up; bringing the pump up to operating speed; and releasing one or more suction valves to bring the pump online. The suction valves may be released sequentially. Further, the engine may have sufficient torque at operating speed for start-up (so that the engine may be brought up to operating speed to have sufficient torque to bring the pump online during start-up). The suction valves also may be released at or near the end of the discharge stroke to take advantage of maximum mechanical advantage.

In another embodiment, a method of pumping wellbore servicing fluid comprises sensing the position of a reciprocating pump stroke and actively assisting the opening, closing or both of a suction valve in response to the sensed position of the pump stroke. In an embodiment, the active assistance applies a force to overcome a static or passive force applied to the suction valve, for example a static or passive force applied by a biasing spring or other closure device.

In still another aspect, the present disclosure is directed to a method for draining a pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke, the method comprising actively opening the suction valves of all cylinders (all suction valves); holding all suction valves open as the pump runs/is driven (or as the plunger cycle through suction and discharge strokes); and running/driving the pump so that each plunger goes through multiple suction and discharge strokes. In one embodiment, the method may further comprise flushing fluid out of the pump (specifically the chambers and the suction valves). In another embodiment, the method may further comprise sucking air in and out of each chamber through the open suction valves in order to dry the pump. Typically this draining, cleaning, and drying technique would be used at the end of a pumping process/job, after fluid pumping is completed. In yet another embodiment, the method further comprises closing all suction valves and stopping running/driving the pump.

In yet another aspect, the present disclosure is directed to a method for varying the available displacement of a pump having multiple chambers each with a suction valve and a plunger driven through a suction stroke and a discharge stroke, the method comprising running/driving the pump so that each plunger cycles through suction and discharge strokes; actively opening one or more suction valves and holding the one or more opened suction valves open (throughout both suction and discharge strokes); and continuing to run/drive the pump (with the plungers cycling through suction and discharge strokes). When running the pump while one or more suction valves are held open, only the cylinders whose suction valves are not being held open will actually pump fluid (be on line). Actively opening and holding one or more suction valves open serves to drop the cylinders associated with the one or more opened suction valves out of active pumping/pumping operation (so that the pump acts as a pump having fewer cylinders/less fluid displacement). This allows the pump to pump fluid at a rate less than possible if all cylinders are pumping (with suction valves opening and closing in time with the suction and discharge strokes). In fact, dropping cylinders out of use allows the pump to pump fluid at a rate less than it would be able to even if the engine driving the pump were operating at its lowest speed (in first gear) with all cylinders operating/pumping. It may also provide more precise control of the pump/flow rate (by offering smaller intervals of available displacement).

• Provisional Patent
• Utility Patent

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