Positive displacement pump monitor

A positive displacement pump monitor. The monitor includes a sensor coupled to a housing of a pump for obtaining acoustic data therefrom. A proximity switch may be simultaneously used to keep real time timing information relative to the cycling of the pump. A data processor of the monitor may then be employed to analyze acoustic data and timing information to distinguish acceptable noise from leak information. An operator thereby may be warned of the presence of a leak in the pump.

BACKGROUND

Embodiments described relate to positive displacement pumps for high pressure applications. In particular, embodiments of monitoring the condition of positive displacement pump valves during operation is described.

BACKGROUND OF THE RELATED ART

Positive displacement pumps are often employed in large high pressure applications. 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 operations such as 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 an abrasive 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 is often the case with large systems and industrial equipment, regular monitoring and maintenance of positive displacement pumps may be sought to help ensure uptime and increase efficiency. In the case of hydraulic fracturing applications, a pump may be employed at a well and operating for an extended period of time, say six to twelve hours per day for more than a week. Over this time, the pump may be susceptible to wearing components such as the development of internal valve leaks. Therefore, during downtime in the operation, the pump may be manually inspected externally or taken apart to examine the internal condition of the valves. However, in many cases external manual inspection fails to reveal defective internal valves. Alternatively, once the time is taken to remove valves for inspection, they are often replaced regardless of operating condition, whether out of habit or for a lack of certainty. Thus, there is the risk that the pump will either fail while in use for undiagnosed leaky valves or that effectively operable valves will be needlessly discarded.

The significance of risks such as those described above may increase depending on the circumstances. In the case of hydraulic fracturing applications, such as those also noted above, conditions may be present that can both increase the likelihood of pump failure and increase the overall negative impact of such a failure. For example, the use of an abrasive containing fluid in hydraulic fracturing not only breaks up underground rock, as described above, it also tends to degrade the physically conformable valve inserts which seal the chamber of the pump, perhaps within about one to six weeks of use depending on the particular parameters of the application. Once the chamber fails to seal during operation, the pump will generally fail in relatively short order.

Furthermore, hydraulic fracturing applications generally employ several positive displacement pumps at any given well. Malfunctioning of even a single one of these pumps places added strain on the remaining pumps, perhaps even leading to failure of additional pumps. Unfortunately, this type of cascading pump failure, from pump to pump to pump, is not an uncommon event where hydraulic fracturing applications are concerned.

Given the ramifications of positive displacement pump failure and the demand for employing techniques that avoid pump disassembly as described above, efforts have been made to evaluate the condition of a positive displacement pump during operation without taking it apart for inspection. For example, a positive displacement pump may be evaluated during operation by employing an acoustic sensor coupled to the pump. The acoustic sensor may be used to detect high-frequency vibrations that are the result of a leak or incomplete seal within the chamber of the positive displacement pump, such a leak being the precursor to pump failure as noted above.

Unfortunately, reliance on the detection of high-frequency vibration requires that the high-frequency level be established for each given application. For example, in the case of a fracturing operation an individual pump may operate under a given set of parameters including use of a particular abrasive containing fluid and operation at a given power level. Furthermore, the pump itself may be coupled to several other pumps or other equipment. These conditions under which the pump operates will result in an expected normal level of noise or vibration unrelated to any possible valve leak. Thus, for any given application of the pump, an expected or normal noise level must be accounted for in employing the acoustic sensor. That is, a baseline level of acceptable noise must be established before the technique may be effectively employed. Performing such calibrations before each new pump operation can be quite time consuming and inefficient, especially given the wide variety of operating conditions a given pump may experience from one operation to the next.

Furthermore, even where a high-frequency level or baseline has been established for a given application of a positive displacement pump, the detection of a leak in the pump is limited to leaks that result in vibrations that actually exceed this baseline frequency. Leaks that fail to present at frequencies above the expected noise level remain undiagnosed, the acoustic data from these leaks remaining buried below the established baseline.

SUMMARY

A monitor for a positive displacement pump is provided. The monitor includes a sensor coupled to the pump to obtain acoustic data from the pump during operation thereof and a proximity switch to obtain timing information relative to cycling of the pump during operation. A data processor is coupled to the sensor and the proximity switch to use the acoustic data and the timing information to determine the presence of a leak in a valve of the pump.

DETAILED DESCRIPTION

Embodiments are described with reference to certain positive displacement pumps such as hydraulic fracturing pumps. However, other positive displacement pumps may be employed for operations such as cementing, coil tubing and water jet cutting. Regardless, embodiments described herein employ a monitor to establish a condition of the pump and its internal valves by analyzing acoustic data relative thereto.

Referring toFIG. 1, an embodiment of a positive displacement pump monitor100is shown coupled to a positive displacement pump101. The monitor100includes a sensor110to obtain acoustic data from the pump101during operation. This may be achieved by securely coupling the sensor110to the main housing105of the pump101. Acoustic data up to 100 KHz or more may be effectively detected in this manner. The data may then be analyzed by a data processor120to establish the condition of the pump101as described further herein.

The pump101shown inFIG. 1includes a plunger190for reciprocating within a plunger housing107toward and away from a chamber135. In this manner, the plunger190effects high and low pressures on the chamber135. For example, as the plunger190is thrust toward the chamber135, the pressure within the chamber135is increased. At some point, the pressure increase will be enough to effect an opening of a discharge valve150to allow the release of fluid and pressure within the chamber135. Thus, this movement of the plunger190is often referred to as its discharge stroke. Further, the point at which the plunger190is at its most advanced proximity to the chamber135is referred to herein as the discharge position. The amount of pressure required to open the discharge valve150as described may be determined by a discharge mechanism170such as spring which keeps the discharge valve150in a closed position until the requisite pressure is achieved in the chamber135. In an embodiment where the pump101is to be employed in a fracturing operation pressures may be achieved in the manner described that exceed 2,000 PSI, and more preferably, that exceed 10,000 PSI or more.

As described above, the plunger190also effects a low pressure on the chamber135. That is, as the plunger190retreats away from its advanced discharge position near the chamber135, the pressure therein will decrease. As the pressure within the chamber135decreases, the discharge valve150will close returning the chamber135to a sealed state. As the plunger190continues to move away from the chamber135the pressure therein will continue to drop, and eventually a low or negative pressure will be achieved within the chamber135. Similar to the action of the discharge valve150described above, the pressure decrease will eventually be enough to effect an opening of an intake valve155. Thus, this movement of the plunger190is often referred to as the intake stroke. The opening of the intake valve155allows the uptake of fluid into the chamber135from a fluid channel145adjacent thereto. The point at which the plunger190is at its most retreated position relative to the chamber135is referred to herein as the intake position. The amount of pressure required to open the intake valve155as described may be determined by an intake mechanism175such as spring which keeps the intake valve155in a closed position until the requisite low pressure is achieved in the chamber135.

As described above, a reciprocating or cycling motion of the plunger190toward and away from the chamber135within the pump101controls pressure therein. The valves150,155respond accordingly in order to dispense fluid from the chamber135and through a dispensing channel140at high pressure. That fluid is then replaced with fluid from within a fluid channel145. Movement of the various moving parts of the pump101as described may resonate to a degree throughout the pump101including to its non-moving portions, such as at the main housing105. Thus, as shown inFIG. 1, a sensor110may be secured to the main housing105to obtain acoustic data resonating thereat from the action of the pump101and its valves150,155during operation as described above.

The described sensor110may be a conventional acoustic sensor or accelerometer capable of detecting the above described vibrations resonating through the main housing105. As described further below, the acoustic data or vibrations detected by the sensor110may be attributable to particularly discrete movements within the pump101during operation. For example, the striking closed of the discharge valve150onto the discharge valve seat180following a discharge of fluid from the chamber135may provide a particularly discernable level of acoustic “strike” data to the sensor110as described further herein. For example, in an embodiment where the pump101is employed in a high pressure fracturing operation, a spike of at between 1 KHz to as much as 200 KHz or more may be detected by the sensor110upon the striking closed of the discharge valve150.

Similarly, the striking closed of the intake valve155on the intake valve seat185following intake of fluid from the fluid channel145may result in a particularly discernable level of acoustic “strike” data resonating to the sensor110. Again this may be to between 1 KHz to as much as 200 KHz or more for a pump101employed in a high pressure fracturing operation.

Continuing with reference toFIG. 1, the above described collection of acoustic data by the sensor110allows for the continuous real time monitoring of the condition of the pump101. For example, while the striking closed of the valves150,155as described above provides expected normal acoustic data for a pump101operating normally, other acoustic data (i.e. “non-strike” data) may be obtained by the sensor110which is also indicative of normal operations or may be indicative of the pump101operating abnormally as described below. Regardless, all of the data obtained by the sensor110is transmitted to a data processor120for analysis according to techniques described further herein. The data processor120may be a microprocessor affiliated with the individual pump101. Additionally, in one embodiment, the data processor120is coupled to a centralized computer system, wherein the system monitors multiple pumps simultaneously.

Referring now toFIG. 2, an enlarged view of the discharge valve150taken from section lines2-2ofFIG. 1is shown. The discharge valve150is shown biased between the discharge valve seat180and a discharge plane152by way of the spring discharge mechanism170. In the embodiment shown, the discharge valve150includes valve legs250and a valve insert160. The valve legs250guide the discharge valve150into a portion of the pump chamber135in sealing the chamber135off from the dispensing channel140as described above. The chamber135is ultimately sealed off when the discharge valve seat180is struck by the discharge valve150with its conformable valve insert160shown. As described below, employment of a conformable valve insert160for sealing off of the chamber135is conducive to the pumping of abrasive containing fluids through the pump101ofFIG. 1.

As noted above, when the discharge valve150strikes the discharge valve seat180a discernable level of acoustic data, referred to herein as strike data, may be detected by the sensor110. However, this strike data diminishes almost immediately where the valve150makes a complete seal at the discharge valve seat180. That is, following such a strike of the valve150, acoustic data attributable to the precise area of the valve150should be negligible. However, as described below, in circumstances where a completed seal fails to form between the valve150and the valve seat180, acoustic vibration may persist that is attributable to a leak between the chamber135and the dispensing channel140.

As alluded to earlier, a positive displacement pump101is well suited for high pressure applications of abrasive containing fluids. In fact, embodiments described herein may be applied to cementing, coil tubing, water jet cutting, and hydraulic fracturing operations, to name a few. However, where abrasive containing fluids are pumped, for example, from a chamber135and out a valve150as shown inFIG. 2, it may be important to ensure that abrasive within the fluid not prevent the valve150from sealing against the valve seat180. For example, in the case of hydraulic fracturing operations, the fluid pumped through a positive displacement pump101may include an abrasive or proppant such as sand, ceramic material or bauxite mixed therein. By employing a conformable valve insert160, any proppant present at the interface200of the valve150and the valve seat180substantially fails to prevent closure of the valve150. That is, the conformable valve insert160is configured to conform about any proppant present at the interface200thus allowing the valve150to seal off the chamber135irrespective of the presence of the proppant.

While the above technique of employing a conformable valve insert160where an abrasive fluid is to be pumped allows for improved sealability of valves, it also leaves the valve150susceptible to degradation by the abrasive fluid. That is, a conformable valve insert160may be made of urethane or other conventional polymers susceptible to degradation by an abrasive fluid. In fact, in conventional hydraulic fracturing operations, a conformable valve insert160may degrade completely in about one to six weeks of continuous use. As this degradation begins to occur a completed seal fails to form between the valve150and the valve seat180. As noted above, an acoustic vibration may then persist that is attributable to a growing leak between the chamber135and the dispensing channel140. Embodiments described herein reveal techniques for capturing such non-strike acoustic data, establishing the data as attributable to a particular valve150,155, and discerning it as leak information as distinguishable from other expected or normal acoustic noise.

Referring now toFIG. 3, with added reference toFIGS. 1 and 2, techniques by which acoustic data may be analyzed over a short time frame are described. As the plunger190reciprocates the valves150,155open and close pumping fluid through the pump101as described above. As noted, acoustic data may be collected by the sensor110during this cycling of the pump101.FIG. 3reveals a schematic representation, in the form of a short time chart, of how this might look in terms of frequency of the collected data plotted over time.

The time based frequency analysis of the data described above is performed by the data processor120in intervals short enough to establish the existence of any leakage occurring within the pump. As described below, this analysis will examine short consecutive periods. Note that the entire x-axis of the chart ofFIG. 3, covering several such periods, is little more than 1.5 seconds long. These periods are no greater than a one half of a full reciprocation of the plunger190. In this manner complete discharge or intake strokes may be evaluated and allow the opportunity for each strike of the valves150,152to be acoustically recorded. One half of a full reciprocation of the plunger190may also be referenced herein as the duration of movement of the plunger190between the intake position and the discharge position as described above.

With continued reference toFIGS. 1-3, the generation of acoustic data during operation of the pump101is described. As the plunger190moves away from its discharge position nearest the chamber135, the pressure therein reduces and the discharge valve150may strike closed at the discharge valve seat180. This discharge valve strike375may be seen visually as strike data atFIG. 3. The discharge valve strike375is discernable, strongly resonating at between about 10 KHz and about 25 KHz or more at a fairly discrete point in time. The intake valve155then opens as the plunger190advances to its intake position away from the chamber135, effecting a low or negative pressure thereon. Then, upon reciprocating back toward the chamber135, the plunger190allows pressure to rise therein such that the intake valve155strikes closed at the intake valve seat185. In the chart ofFIG. 3, this intake valve strike380is also discernable strike data, strongly resonating at between about 10 KHz and about 25 KHz or more at a fairly discrete point in time. As the plunger190continues toward its discharge position, pressure in the chamber135continues to rise and eventually the discharge valve150opens.

Apart from the strikes375,380, the chart ofFIG. 3reveals other non-strike acoustic data300,350as the pump101operates over time. Some of the non-strike acoustic data is merely acceptable noise350, while other data represents a leak information300. However, these types of non-strike acoustic data300,350are discernable from one another when examining their relationship, if any, to the strikes375,380or the duration of a stroke. In fact, in one embodiment, determining a relationship between one of the strikes375,380or stroke periods and one of the types of non-strike acoustic data300,350may establish both the presence of a leak and may also help determine which valve150,155is the source of the leak as described further below (seeFIG. 1). As also described further herein, in another embodiment, such leak information may be deciphered evein in the absence of strike data altogether.

Continuing with reference toFIGS. 1 and 3, a discharge valve strike375at less than 0.5 seconds is shown at the far left of the chart. The data processor120is able to establish this signal as a discharge valve strike375through a technique that employs stored information relative to what constitutes a strike and the use of a proximity switch125. That is, the data processor120may have stored information relative to what constitutes a strike over a broad range of possible operation parameters for a given pump101. For example, in one embodiment, the data processor120may be programmed to interpret any substantially uninterrupted signal over a 1 KHz range and less than about 5 milliseconds in duration to be indicative of a strike.

In one embodiment, once the presence of a strike is established, the determination as to whether the strike is a discharge valve strike375or an intake valve strike380may be established with the aid of the proximity switch125. The proximity switch125is mounted to the plunger housing107. In the embodiment shown, the proximity switch125detects the position of the plunger190via conventional means such as by detection of a passing plunger clamp or other detectable device secured to the plunger190. This position and timing information is conveyed to the data processor120. The data processor120has stored information relative to the timing and order of the moving parts of the pump101. Thus, with the timing feedback from the proximity switch125, the data processor120is able to establish that the strike at less than 0.5 seconds is, for example, a discharge valve strike375as opposed to an intake valve strike380. Similarly, the strike just after 0.5 seconds may be established as an intake valve strike380.

With the strikes375,380established, other non-strike acoustic data may be analyzed with reference thereto. For example, immediately after the initial discharge valve strike375at the far left of the chart ofFIG. 3, other acoustic data is revealed in the form of leak information300and in the form of acceptable noise350. When examined visually and as analyzed by the data processor120, it can be determined that leak information300presents in the form of a pattern that dissipates at some point after the initial discharge valve strike375, such that just prior to the next discharge valve strike375at between 0.5 and 1.0 seconds, leak information300is no longer present. However, upon this next discharge valve strike375, leak information300immediately reappears. As described further below, this leak information300is persisting for about a duration of a stroke, discharge or intake, of the pump101(seeFIG. 1).

When considering the timing and order of the moving parts within the pump101, it is apparent that the leak information300shown inFIG. 3is revealing a leak at the discharge valve150. That is, with added reference toFIG. 2, as the discharge valve150strikes closed against the discharge valve seat180(i.e. as shown at375), a complete seal of the chamber135fails to occur. Thus, leakage of fluid back into the chamber135occurs at the interface200, most likely the result of a degrading valve insert160. This results in a vibration or acoustic data which can be seen as leak information300inFIG. 3. However, as the motion of the pump101continues the discharge valve150opens just after the closure of the intake valve155(visible as the intake valve strike380). This opening of the leaky discharge valve150allows vibrations from the leak at the interface200to dissipate and thus, the leak information300disappears. In one embodiment, a properly programmed data processor120coupled to a graphical user interface (GUI), beyond the chart ofFIG. 3, may then inform an operator of the presence of the leak at the discharge valve150.

The chart ofFIG. 3plots acoustical data for a single pump101with a single plunger190and assembly of valves150,155. However, in certain embodiments (such as inFIG. 6. discussed in more detail below) the pump101includes more than one plunger and valve assembly. Nevertheless, as described below, a single monitor100having a sensor110at the common main housing105and a proximity switch125at one of the plunger housings107may still provide all of the above-referenced acoustic data in a discernable fashion.

In one embodiment, the pump101is a pump400shown schematically inFIG. 6and includes three plunger and valve assemblies having individual chambers135A,135B, and135C sharing a common housing (i.e. a “triplex” pump), as will be appreciated by those skilled ion the art, shown schematically at400inFIG. 6and including plungers190A,190B, and190C and valves,150A,150B,150C, and155A,155B, and155C. Therefore, over a given period of time it might seem likely that three times the number of strike data would be recorded by the monitor100. Thus, establishing or associating a particular leak pattern with a given valve or valve assembly may seem problematic. However, in such an embodiment, the timing and positioning of the plungers may be offset from one another, for example, by 120° from one plunger to the next. Thus, a proximity switch125at just one of the plunger housings allows for extrapolation by the data processor120in order to associate each piece of acoustic data with the proper striking valve or stroke of the pump101. As a result, any detected leak information300may be associated with the proper leaky valve, even in such a multi-valve assembly pump101or400. In fact, even in the case of multiple leaks that give rise to the overlap of leakage data, the increased amplitude of the leak infonnation300for the period of the overlap allows for proper identification of the leaks with analysis by the data processor120.

With added reference toFIG. 1, the strikes375,380ofFIG. 3are fairly distinct allowing the data processor120and even manual visual analysis to distinguish leak information300. However, as mentioned above, even in circumstances where strikes375,380fail to present in a distinct fashion, a determination of the presence of leak information300may be made. For example, based on the operating speed of the pump101, the length of the discharge or intake stroke is known. Thus, acoustic information of a particular range of frequency that persists for about the duration of a stroke is leak information300regardless of the presence of decipherable strike data375,380. That is, recalling the cycling of the pump101as described above, a given valve150,155remains closed for about a period equal to a stroke of the plunger190. Thus, acoustic data that persists in intervals of such a duration is leak information300.

Continuing with reference toFIGS. 1-3, other acoustic data in the form of acceptable noise350is detected as shown inFIG. 3. However, this acceptable noise350fails to present for substantially the duration of a stroke or to form a pattern relative to the strikes375,380. That is, this acceptable noise350may be from other nearby operating equipment or even the pump101itself. However, with no particular connection to the strikes375,380, or stroke duration the acceptable noise350is not indicative of a leak at the interface200of a valve150,155and a valve seat180,185. Therefore, this information need not be selected by the data processor120for highlighting to an operator.

The above described monitor100and technique may be applied to vast array of positive displacement pump operations by properly securing the monitor100and proximity switch110to the pump101and having preprogrammed a broad range of possible strike data into the data processor120. The monitor100and technique do not require a unique baseline of acoustic data be established for each and every given pump operation. As frequency levels, overall noise and other acoustic indications change from one operation of the pump to the next, the parameters of the above described technique need not be reset.

Continuing with reference toFIG. 4, multiple positive displacement pumps101are shown in simultaneous operation at the same hydraulic fracturing site401. These pumps101may be no more than 10-12 feet from one another. Each pump101may operate at between about 700 and about 2,000 hydraulic horsepower to propel an abrasive fluid410into a well425. The abrasive fluid410contains a proppant such as sand, ceramic material or bauxite for disbursing beyond the well425and into fracturable rock415or other earth material.

In the embodiment shown inFIG. 4each pump101may generate between about 2,000 and about 15,000 PSI or more. Further, in addition to the six pumps101shown, other equipment may be directly or indirectly coupled to the well head450for the operation. This may include a manifold475for fluid communication between the pumps101. A blender490, and other equipment capable of generating considerable acoustic noise during an operation may also be present. Nevertheless, with added reference toFIGS. 1-3and as described above, this extraneous noise fails to significantly impact the performance of a monitor100properly coupled to each pump101as shown. That is, this extraneous acceptable noise350fails to reveal a relationship to any strike375,380, or stroke duration and is thus discarded by the data processor120when analyzing acoustic data for leak information300. Alternatively, as described above, any pattern of leak information300generated from within a pump101to which the monitor100is coupled, will be detectable by the monitor100according to the techniques described above.

Continuing with reference toFIGS. 1-4, in a multi-pump operation each data processor120for each monitor100of each pump101may be independently coupled to a centralized computer system, for example, employing the GUI noted above, where an operator may review the operating condition of each pump101simultaneously. In a multi-pump operation, the operator may be able to monitor the severity of any given leak information300and, where necessary, interact with the GUI to effect modifications in the parameters of the operation, including at individual pumps101. In this manner, the efficiency and effectiveness of the overall pump operation may be maximized.

Referring now toFIG. 5, an embodiment of monitoring the condition of a positive displacement pump in operation is summarized in the form of a flow chart. Namely, the positive displacement pump is operated while an acoustic sensor detects acoustic data therefrom as indicated at520and530. The acoustic data is relayed to a data processor for short time analysis thereof as indicated at550. At this same time, timing information is accounted for, for example, by monitoring with a proximity switch tracking the position of a plunger reciprocating within the pump (see540). As indicated at570, the acoustic data and the timing information may be used by the data processor to distinguish acceptable noise from leak information.

The embodiments described herein provide for effective monitoring of a positive displacement pump without the requirement of additional equipment or procedures often found in other conventional monitoring techniques and assemblies. For example, in the above described embodiments a single monitor and sensor may be employed even where multiple plunger and valve assemblies sharing a common pump housing are involved (such as in the above described triplex pump).

Embodiments described herein include monitoring techniques that may be achieved without requiring that a baseline frequency level be predetermined for each new application of a given pump. As such, any leak information detected is not merely discarded due to the particular frequency at which it presents. No calibrations need to be performed for each new set of pump operating conditions encountered nor does a pump need to operate under the same conditions from application to application. Further, embodiments described herein allow for the recognition of leak information without requiring training of the monitor and data processor for recognition of patterns of acoustic data at the outset of a given operation.

In a multi-pump operation, there is no requirement that a history of pumps or other equipment be taken into account in employing embodiments described herein. In fact, such pumps do not need to operate under the same speed, pressure or other conditions as one another in a given operation.

Although exemplary embodiments describe monitoring of particular positive displacement pumps such as hydraulic fracturing pumps, additional embodiments are possible. Furthermore, many changes, modifications, and substitutions may be made without departing from the spirit and scope of the described embodiments.