Embodiments described relate to valve assemblies for positive displacement pumps used in high pressure applications. In particular, embodiments of positive displacement pumps employing mechanisms and supports for extending the life of pump valves, minimizing pump damage during operation, and improving volumetric efficiency are described.
Positive displacement pumps are often employed at oilfields for large high pressure applications involved in hydrocarbon recovery efforts. A positive displacement pump may include a plunger driven by a crankshaft toward and away from a chamber in order to dramatically effect a high or low pressure on the chamber. This makes it a good choice for high pressure applications. Indeed, where fluid pressure exceeding a few thousand pounds per square inch (PSI) is to be generated, a positive displacement pump is generally employed.
Positive displacement pumps may be configured of fairly large sizes and employed in a variety of large scale oilfield operations such as drilling, cementing, coil tubing, water jet cutting, or hydraulic fracturing of underground rock. Hydraulic fracturing of underground rock, for example, often takes place at pressures of 10,000 to 15,000 PSI or more to direct a solids containing fluid through a well to release oil and gas from rock pores for extraction. Such pressures and large scale applications are readily satisfied by positive displacement pumps.
As noted, a positive displacement pump includes a plunger driven toward and away from a pressurizable chamber in order to achieve pumping of a solids containing fluid. More particularly, as the plunger is driven away from the chamber, pressure therein reduces allowing a discharge valve of the chamber to close. The chamber is thus sealed off from the external environment while the plunger remains in communication with the chamber. As such, the plunger continues its retreat away from the chamber generating a lowered pressure with respect to suction therein. Eventually, this lowered pressure will reach a level sufficient to open a suction valve of the pump in order to allow an influx of fluid into the chamber. Subsequently, the plunger may be driven toward the chamber to once again effect a high pressure therein. Thus, the suction valve may be closed, the discharge valve re-opened, and fluid expelled from the chamber as indicated above.
The actuation of the suction and discharge valves is achieved primarily through reliance on pressure conditions generated within the chamber. That is, the amount of pressure required to open or close each valve is a function of the physical characteristics of the valve along with a spring employed to hold the valve in a naturally closed position relative to the chamber. Unfortunately, this results in a lack of direct control over valve actuation and leaves an inherent inefficiency in operation of the valves. For example, opening of a valve requires generation of enough of a pressure change so as to overcome the weight of the valve and nature of its spring. This is of particular note regarding the suction valve where, rather than opening immediately upon closure of the discharge valve, a lowered pressure sufficient to overcome the weight and nature of the suction valve and its spring must first be generated within the chamber (i.e. net positive suction head (NPSH)). This time delay in opening of the suction valve is an inherent inefficiency in operation of the pump. Indeed, for a standard positive displacement pump employed at an oilfield, a pressure of between about 10 PSI and about 30 PSI may be required within the chamber before the suction valve is opened.
Reliance solely upon internal chamber pressure to actuate valves results in an inherent inefficiency and a lack of direct control as indicated above. Of potentially greater concern however, is the fact that this manner of valve actuation often leaves the pump itself susceptible to significant damage as a result of cavitation and ‘water hammering’. That is, as the plunger moves away from the chamber decreasing pressure therein, the inherent delay in opening of the suction valve may lead to the cavitation and subsequent water hammering as described below.
During the delay in opening of the suction valve, and in conjunction with the generation of lowered pressure in the chamber, the fluid may undergo a degree of cavitation. That is, pockets of vapor may form within the fluid and it may begin to vaporize in the face of the lowered pressure. Formation of vapor in this manner may be followed by rapid compression of the vapor back into liquid as the plunger once again advances toward the chamber. This rapid compression of the liquid is accompanied by a significant amount of heat and may also result in transmitting a degree of shock through the pump, referred to as water hammering. All in all, a significant amount of pump damage may naturally occur based on the pressure actuated design of a conventional positive displacement pump.
In order to address pump damage resulting from cavitation and water hammering, techniques are often employed in which acoustic data generated by the pump is analyzed during its operation. However, reliance on the detection of acoustic data in order to address pump damage fails to substantially avoid the development of pump damage from cavitation and water hammering in the first place. Furthermore, it is not uncommon for the damaged pump to be employed in conjunction with an array of additional pumps at an oilfield. Thus, the damage may see its effects at neighboring pumps, for example, by placing added strain on these pumps or by translation of the damaging water hammering effects to these pumps. Indeed, cascading pump failure, from pump to pump to pump, is not an uncommon event where a significant amount of cavitation and/or water hammering is found.
A positive displacement pump is provided with a housing for a pressurizable chamber. The chamber may be defined in part by a valve thereof which may be employed for controlling fluid access to the chamber. The positive displacement pump may also include a valve actuation guide that is positioned at least partially external to the chamber and coupled to the valve so as to assist the controlling of the fluid access to the chamber.
Embodiments are described with reference to certain high pressure positive displacement pump assemblies for fracturing operations. However, other positive displacement pumps may be employed for a variety of other operations including cementing. Regardless, embodiments described herein employ positive displacement pumps with valves that are equipped with external actuation assistance. As such, valve actuation is not left solely to the buildup of cavitation-inducing conditions within a chamber of the pump which would have the potential to create significant pump damage through water hammering.
Referring now to
Continuing with reference to
With particular reference to
Continuing with reference to
In spite of the potential development of lowered pressure within the chamber 235 as indicated above, significant cavitation may be avoided. That is, valve actuation assistance may be provided to the suction valve 255 to effect its opening as depicted in
Avoidance of significant vaporization of operation fluid in this manner may substantially minimize the amount of pump damage that may otherwise result as the plunger 290 re-pressurizes and condenses the operation fluid. That is, water-hammering damage due to the rapid condensing of vaporized operation fluid may be largely avoided. As such, in the embodiment shown, the plunger 290 may be thrust toward the chamber 235, increasing the pressure therein. The pressure increase will ultimately be enough to effect opening of the discharge valve 250 overcoming the force supplied by the discharge spring 270.
In an embodiment where the pump 101 is to be employed in a fracturing operation, pressures may be achieved in the manner described above that exceed 2,000 PSI, and more preferably, that exceed 10,000 PSI or more. Furthermore, such a positive displacement pump 101 is particularly well suited for high pressure applications of abrasive containing operation fluids. In fact, embodiments described herein may be applied to cementing, coil tubing, water jet cutting, and hydraulic fracturing operations as indicated, to name a few.
As indicated, the valve actuation guide 200 is configured to assist in actuation of the suction valve 255 as detailed above. However, the valve actuation guide 200 may take a variety of configurations in order to provide such assistance. For example, in the particular embodiment of
As indicated above, the proper timing for actuation of the suction valve 255 is dependent upon the position of the plunger 290, relative to the chamber 235. Thus, as described below, a mechanism for synchronizing the timing of the valve actuation guide 200 and its crankshaft 207 with the plunger 290 may be provided. Additionally, in the embodiment shown, the arm 205 is reciprocated in a rectilinear manner so as to maintain isolation between the guide assembly 100 and the operation fluid supply 245. This may be achieved through the employment of a crankshaft 207 of a conventional rectilinear effectuating crank design. Alternatively, other methods of sealing between the guide assembly 100 and the operation fluid supply 245 may be employed or a tolerable degree of communication there-between may be allowed.
As indicated above, and with added reference to
Continuing with reference to
The valve actuation guide 200 described above includes a crankshaft 207 for actuating the suction valve 255 in both an open direction, as depicted in
Similarly, the embodiments depicted reveal the guide assembly 100 and actuation guide 200 adjacent only to the suction valve 255. That is, actuation of the discharge valve 250 is left to pressure conditions within the chamber 235. This may allow for ease of design similar to cam actuation noted above and may be a practical option in light of the fact that significant cavitation is unlikely correlated to any discharge valve 250 position. However, in one embodiment external assistance is provided to the discharge valve 250 in addition to the suction valve 255. That is, an additional actuation guide similar to the embodiments described above may be positioned adjacent the discharge valve 250 and coupled thereto in order to further enhance pump efficiency. This may take place by reducing the amount of time that might otherwise be required to open or close the discharge valve 250 based solely on the pressure within the chamber 235.
Referring now to
Continuing with reference to
Returning to the embodiment depicted in
Similar to the crank-driven configuration of
As in the case of the crank-driven configuration of
Continuing now with reference to
In the embodiment of
As with prior embodiments detailed above, the electromagnetic driven configuration of
With particular reference to
Continuing with reference to the embodiments of
Referring now to
In the particular depiction of
Embodiments described hereinabove address cavitation, pump damage and even pump efficiency in a manner that does not rely solely upon internal pump pressure for valve actuation. As a result, delay in opening of the suction valve in particular may be avoided so as to substantially eliminate cavitation and subsequent water hammering. Indeed, as opposed to mere monitoring of pump conditions, embodiments described herein may be employed to actively avoid pump damage from water hammering.
The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. For example, valve actuation assistance may be achieved through the use of servo and/or stepped motors. The assistance as detailed herein may also be employed to extend the life of valves by increasing the rate of valve closure so as to ensure more effective crushing of abrasives carried by operation fluid. Additionally, volumetric efficiencies enhanced by valve actuation assistance as described herein may be even further enhanced by ensuring that valve opening is maximized during pumping. Furthermore, 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 Patent Document claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/917,366, entitled Valve for a Positive Displacement Pump filed on May 11, 2007, and Provisional Application Ser. No. 60/985,874, entitled Valve for a Positive Displacement Pump filed on Nov. 6, 2007, both of which are incorporated herein by reference in their entirety.
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