(1) Field of the Invention
The invention is related in general to pumps such as, but not limited to, fracturing pumps, for example, at the wellsite surface location, and the like.
(2) Description of Related Art Including Information Disclosed under 37 CFR 1.97 and 1.98
Hydraulic fracturing of downhole formations is a critical activity for well stimulation and/or well servicing operations. Typically this is done by pumping fluid downhole at relatively high pressures so as to fracture the rocks. Production fluids and/or gases can then migrate to the wellbore through these fractures and significantly enhance well productivity. Triplex and quintuplex reciprocating pumps are generally used to pump the high pressure fracturing fluid downhole. Typically, the pumps that are used for this purpose have plunger sizes varying from 95 mm (3.75 in.) to 165 mm (6.5 in.) in diameter and operate at pressures up to 140 MPa (20,000 psi (20 ksi)).
A fracturing pump typically consists of four main components: the prime mover or engine, the transmission, the drive line, and the pump. The pump assembly is comprised of two major sub-assemblies—power end and fluid end. The power end includes crank slider mechanism that reciprocates the plungers inside the fluid end, which is a container that holds and discharges pressurized fluid with the pump plungers.
In triplex pumps, the fluid end has three fluid cylinders. For the purpose of this document, the middle of these three cylinders is referred to as the central cylinder, and the remaining two cylinders are referred to as side cylinders. Similarly, a quintuplex pump has five fluid cylinders, including a middle cylinder and four side cylinders.
The pumping cycle of the fluid end is composed of two stages: (a) a suction cycle: During this part of the cycle, a piston moves outward in a packing bore, thereby lowering the fluid pressure in the fluid end. When the fluid pressure is less than the pressure of the fluid in a suction pipe, typically 2-3 times the atmospheric pressure, approximately about 290 kPa (40 psi), the suction valve opens and the fluid end is filled with pumping fluid; and (b) a discharge cycle: During this cycle, the plunger moves forward in the packing bore, thereby progressively increasing the fluid pressure in the pump and closing the suction valve. At a fluid pressure slightly higher than the line pressure, which can range from as low as 14 MPa (2 ksi) to as high as 140 MPa (20 ksi), the discharge valve opens, and the high pressure fluid flows through the discharge pipe.
In fracturing pumping service, large vibrations may be encountered that may lead to damage to pumps, transmissions, and engines. A first order approximation of the pump assembly is to assume the pump may be modeled as a simple flywheel with torque pulsations applied to it, the driveshaft may be modeled as a simple torsional spring, and the transmission supplies a torque with small pulsations overlaid on it. In this model, the pump's rotating mass forms a resonant system with the drive line. When a driving frequency (such as the plunger frequency and its multiples) coincides with the first, second, or third resonant mode of this system, large torque fluctuations are seen in the driveline of the assembly. If the torque fluctuations are less than the prevailing pumping torque, the gears in the transmission and pump stay in contact. When the torque fluctuations exceed the magnitude of the prevailing torque and/or go negative, however, the gear teeth in the transmission and/or the pump will go in and out of contact at the driving frequency with associated impact loads. These impact loads from the alternating contacting gear teeth produce huge stresses and may destroy a transmission very quickly. In the case of standard triplex pumps, this process may occur just above 1600 L/min (10 barrels per minute (BPM)) of pumping rate. Above 1600 L/min (10 BPM), the plunger frequency coincides with a shaft/pump mass resonance, and the transmission will fail. It has been shown that reducing dynamic torque amplitudes under normal operating conditions greatly improves the transmission life on the pumper, due to reduced cyclic loading of the drivetrain and resulting in prolonged life of the stress-bearing members.
Some of the issues associated with such vibration and/or torque fluctuations may be addressed with tougher/heavier duty transmissions, viscous dampeners, and/or harmonic balancers. A typical vibration damper or harmonic balancer is attached to a prime mover and may comprise a ring shaped mass disposed inside a ring shaped housing with oil between them. The housing is attached to the pump input shaft and rotates. When the shaft is turning steadily, there is no motion between the mass and the housing. When the shaft speed varies, the mass moves relative to the housing and energy is dissipated in the oil.
It remains desirable to provide improvements in wellsite surface equipment in efficiency, flexibility, reliability, and maintainability.
In one embodiment, a pump assembly comprises a prime mover, a multiplex fluid pump connected to a drive line, a transmission connected to transfer torque from the prime mover to rotate the drive line, a source of harmonic excitation originating from one or a combination of any of the prime mover, the multiplex fluid pump, driveline and transmission, preferably from at least one of the multiplex fluid pump, driveline and transmission and a counteracting resonant system coupled to the harmonic excitation source.
The system components giving rise to the harmonic excitation may be referred to herein as a primary resonant system, and the counteracting resonant system may also be referred to herein as an auxiliary resonant system. A counteracting resonant system is one that is synchronized with the primary resonant system but has a displacement component opposite a displacement component of the primary resonant system such that vibration is inhibited, the resonant frequency is altered, or the like. In one embodiment, where synchronization is achieved by coupling the primary and counteracting resonant systems via a rotating shaft, the resonant systems are balanced to inhibit vibration and/or to increase the speed of rotation at which excessive vibration occurs.
In an embodiment, the counteracting resonant system has an oscillatory frequency matching an oscillatory frequency of the harmonic excitation source.
In an embodiment, the harmonic excitation source and the counteracting resonant system have matching resonant frequencies. In an embodiment, the counteracting resonant system absorbs fluctuations in torque transferred between the prime mover and the multiplex fluid pump, preferably inhibiting the torque fluctuations up to or above a predetermined magnitude.
In an embodiment, the counteracting resonant system comprises a mirrored pump and drive shaft having a resonant frequency harmonically matched with respect to the multiplex fluid pump. A mirrored pump is one that has similar components to the main or primary pump, but their position with respect to an axis of the drive line is generally opposite that of the mirrored pump as if reflected with respect to a plane containing the axis. In an embodiment, the mirrored pump and drive shaft are substantially identical with respect to the multiplex fluid pump and drive line of the primary resonant system. In one embodiment, the counteracting resonant system comprises a mirrored pump and drive shaft connecting the mirrored pump to the multiplex fluid pump, and in another connecting the mirrored pump to the transmission.
In an embodiment, the counteracting resonant system comprises a tuned mass-spring system. In various embodiments, the tuned mass-spring system comprises a variable inertia flywheel, a rotating pendulum, a bifilar pendulum, a roller-type pendulum, a ring-type pendulum, a harmonic balancer, or a combination thereof.
In an embodiment, the tuned mass-spring system comprises another multiplex fluid pump connected to a drive shaft to mirror the primary resonant system. In embodiments, the multiplex fluid pump of the tuned mass-spring system is loaded (pumping fluid) or unloaded (“pumping” air).
In one embodiment, a pumping method comprises connecting the transmission to transfer torque from the prime mover to rotate the drive line, connecting the drive line to the multiplex fluid pump to reciprocate a plurality of plungers in a like plurality of cylinders to discharge a pressurized fluid from the pump, wherein one or a combination of the torque transfer, the drive line rotation and the plunger reciprocation induces harmonic excitation at one or more variable oscillating frequencies, coupling a counteracting resonant system to the prime mover, the transmission, the driveline, the multiplex fluid pump, or a combination thereof, and tuning the counteracting resonant system to the induced harmonic excitation. For example, the multiplex fluid pump and the drive line can define a primary resonant system having an oscillating frequency depending on a rotational speed of the drive line. In an embodiment, the method can include inhibiting a torsional component of the induced harmonic excitation.
In one embodiment, a method is provided to inhibit vibration of a pump assembly comprising a prime mover, a multiplex fluid pump connected to a drive line, and a transmission connected to transfer torque from the prime mover to rotate the drive line and reciprocate a plurality of plungers in a like plurality of cylinders in the fluid pump to discharge a pressurized fluid from the pump. The method comprises coupling a counteracting resonant system to the pump assembly, wherein the counteracting resonant system has an oscillatory frequency matching an oscillatory frequency matching an oscillatory frequency of the harmonic excitation source.
Referring now to
A typical system comprises a prime mover 102, a transmission 104, and a single pump 106 or 108. During testing, it has been found that at the speed where a single triplex/single drive shaft system approach 100% torque fluctuations (between 1.6-2.2 cubic meters (10-14 42-gal barrels) per minute pumping rate at a pump speed of 220-300 revolutions per minute), the system 100 comprising two triplexes 106 and 108 (with triplex 108 running unloaded only as a flywheel) and two drive shafts only had less than 50% torque fluctuations. After further investigation, it was determined that the second pump 106 or 108 and the second shaft acted as a tuned vibration absorber for the pump assembly 100, and the reduced torque fluctuations were not due to a shift in the resonance due to the additional mass or due to the smaller torque pulsations from using two pumps 106 and 108 with the correct phasing.
Referring now to
In an embodiment, the vibration absorber 208 comprises a dedicated mass and spring dampener tuned to the right frequency. The mass and spring dampener preferably comprises a predetermined amount of mass such that absorbing and returning energy at the resonant frequency does not over-stress the spring element. This may be accomplished at a lower total mass than a pump with careful design. Additionally, the mass element may comprise a torsional vibration damper or harmonic balancer as described herein to further improve the performance. In an embodiment, the vibration absorber 208 comprises a harmonic balancer, as described herein.
In an embodiment, the vibration absorber 208 comprises a rotating pendulum vibration absorber, as described in Nestorides, E. J., A handbook on torsional vibration, British Internal Combustion Engine Research Association, p. 582 (1958), which is hereby incorporated herein by reference. In embodiments seen in
The rotating pendulum vibration absorbers 308A, 308B, 308C, and 308D each provide a tuned vibration absorber whose frequency is related to shaft speed and may be chosen to damp a specific multiple of shaft speed or the pump speed. In an embodiment, a multiple is three times the ratio of the gear reduction in the pump power end corresponding to the frequency of the plunger pulses, so that the plunger pulses are damped. In an embodiment, the vibration absorber 208 is operable to attenuate and/or absorb multiple vibration modes, such as three, six, nine, twelve, and fifteen for a triplex pump and five, ten, fifteen, and twenty for a quintuplex pump. This may be accomplished by stacking multiple rotating pendulum vibration absorbers 308A, 308B, 308C, and 308D or by providing such a capability into a single vibration absorber 208. In an embodiment, a disk-type crankshaft incorporates damping elements in a manner similar to engine applications. This may increase the weight, which is a concern in some applications, but effectively reduces the shaking caused by the reciprocating masses.
In an embodiment, referring now to
The rotating pendulum vibration absorbers 308A, 308B, 308C, 308D, and/or 408 may be advantageously added to a pump assembly 200 as a retrofit solution to reduce overall torque fluctuations from the pump 206 to the remainder of the elements in the pump assembly 200.
In an embodiment, best seen in
In an embodiment, best seen in
The system 700 shown in
Accordingly, the present invention provides the following embodiments:
A. A pump assembly, comprising:
coupling a counteracting resonant system to the pump assembly;
wherein the counteracting resonant system has an oscillatory frequency matching an oscillatory frequency of the harmonic excitation source.
EEE. The method of embodiment DDD, wherein the counteracting resonant system and the pump assembly have matching resonant frequencies.
FFF. The method of embodiment DDD or embodiment EEE, wherein the counteracting resonant system absorbs fluctuations of the transferred torque.
GGG. The method of any one of embodiments DDD to FFF, wherein the counteracting resonant system inhibits the torque fluctuations above a predetermined magnitude.
HHH. The method of any one of embodiments DDD to GGG, wherein the counteracting resonant system inhibits the torque fluctuations up to a predetermined magnitude.
III. The method of any one of embodiments DDD to HHH, wherein the counteracting resonant system comprises a mirrored pump harmonically matched with respect to the multiplex fluid pump.
JJJ. The method of any one of embodiments DDD to III, wherein the counteracting resonant system comprises a mirrored pump and drive shaft harmonically matched with respect to the multiplex fluid pump and drive line.
KKK. The method of any one of embodiments DDD to JJJ, wherein the counteracting resonant system comprises a mirrored pump and drive shaft connecting the mirrored pump to the multiplex fluid pump.
LLL. The method of any one of embodiments DDD to KKK, wherein the counteracting resonant system comprises a mirrored pump and a drive shaft connecting the mirrored pump to the transmission.
MMM. The method of any one of embodiments DDD to LLL, wherein the counteracting resonant system comprises a tuned mass-spring system.
NNN. The method of embodiment MMM, wherein the tuned mass-spring system comprises a variable inertia flywheel.
OOO. The method of embodiment MMM or embodiment NNN, wherein the tuned mass-spring system comprises a rotating pendulum.
PPP. The method of any one of embodiments MMM to OOO, wherein the tuned mass-spring system comprises a bifilar pendulum.
QQQ. The method of any one of embodiments MMM to PPP, wherein the tuned mass-spring system comprises a roller-type pendulum.
RRR. The method of any one of embodiments MMM to QQQ, wherein the tuned mass-spring system comprises a ring-type pendulum.
SSS. The method of any one of embodiments MMM to RRR, wherein the tuned mass-spring system comprises a harmonic balancer.
TTT. The method of any one of embodiments MMM to SSS, wherein the tuned mass-spring system comprises a mirroring pump connected to a drive shaft to mirror the multiplex fluid pump.
UUU. The method of embodiment TTT, wherein the mirroring pump of the tuned mass-spring system is unloaded.
VVV. The method of embodiment TTT, wherein the mirroring pump of the tuned mass-spring system is loaded.
WWW. The method of any one of embodiments DDD to VVV, wherein the pump assembly comprises a plurality of harmonic excitation sources, wherein the counteracting resonant system comprises a plurality of stacked vibration absorbers having different oscillatory frequencies, and further comprising selecting and deselecting ones of the vibration absorbers to match an active oscillatory frequency of the harmonic excitation sources.
XXX. The method of embodiment WWW, wherein the stacked vibration absorbers are selectively coupled and decoupled by clutches.
YYY. The method of any one of embodiments DDD to XXX, further comprising selecting one of a plurality of gears in the transmission, wherein the counteracting resonant system comprises a plurality of stacked vibration absorbers coupled to the transmission, and clutching one or more of the stacked vibration absorbers based on the gear selected in the transmission.
ZZZ. The method of any one of embodiments DDD to YYY, wherein the counteracting resonant system absorbs fluctuations of the transferred torque, wherein the counteracting resonant system comprises a plurality of stacked vibration absorbers, and further comprising selecting and deselecting ones of the plurality of stacked vibration absorbers to adjust a magnitude of the torque fluctuation absorption.
AAAA. The pumping method of any one of embodiments DDD to ZZZ, wherein the counteracting resonant system comprises a plurality of stacked vibration absorbers, and further comprising selecting and deselecting ones of the stacked vibration absorbers to selectively adjust a magnitude of the counteracting oscillatory frequency.
BBBB. A pump assembly, comprising:
a prime mover;
a first multiplex fluid pump connected to a drive line;
a transmission connected to transfer torque from the prime mover to rotate the drive line;
a second multiplex fluid pump connected to harmonically mirror the first multiplex pump.
CCCC. The pump assembly of embodiment BBBB, wherein the second multiplex fluid pump is unloaded.
DDDD. A pump assembly, comprising:
a prime mover;
a multiplex fluid pump connected to a drive line;
a transmission connected to transfer torque from the prime mover to rotate the drive line wherein the transmission comprises a plurality of selectable gears;
a source of harmonic excitation originating from one or a combination of any of the prime mover, the multiplex fluid pump, driveline and transmission; and
a plurality of stacked vibration absorbers coupled to the transmission, and
a clutch to selectively engage or disengage each of the stacked vibration absorbers based on the gear selected in the transmission.
The preceding description has been presented with reference to present embodiments. Persons skilled in the art and technology to which this disclosure pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this invention. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.
This application claims the benefit of and priority to provisional application US 61/250,280, filed Oct. 9, 2009. Not applicable Not applicable INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC Not applicable
Number | Date | Country | |
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61250280 | Oct 2009 | US |