System and method for combining co-located flowmeters

A system and method for ultrasonic flow metering. In one embodiment, an ultrasonic flow metering system includes a passage for fluid flow and a plurality of ultrasonic flowmeters. Each of the ultrasonic flowmeters includes a pair of ultrasonic transducers, and a flow processor. The pair of ultrasonic transducers is configured to form a chordal path across the passage between the transducers. The flow processor is coupled to the ultrasonic transducers. The flow processor is configured to measure the fluid flow through the spool piece based on outputs of the transducers of all of the ultrasonic flowmeters.

BACKGROUND

After hydrocarbons have been removed from the ground, the fluid stream (e.g., crude oil, natural gas) is transported from place-to-place via pipelines. It is desirable to know with accuracy the amount of fluid flowing in the stream, and particular accuracy is demanded when the fluid is changing hands, or “custody transfer.” Even where custody transfer is not taking place, however, measurement accuracy is desirable, and in these situations flowmeters may be used.

Ultrasonic flowmeters are one type of flowmeter that may be used to measure the amount of fluid flowing in a pipeline. In an ultrasonic flowmeter, ultrasonic signals are sent back and forth across the fluid stream to be measured, and based on various characteristics of the ultrasonic signals a measure of fluid flow may be calculated. Ultrasonic flowmeters providing improved flow measurement accuracy are desirable.

SUMMARY

A system and method for ultrasonic flow metering is disclosed herein. In one embodiment, an ultrasonic flow metering system includes a passage for fluid flow and a plurality of ultrasonic flowmeters. Each of the ultrasonic flowmeters includes a pair of ultrasonic transducers, and a flow processor. The pair of ultrasonic transducers is configured to form a chordal path across the passage between the transducers. The flow processor is coupled to the ultrasonic transducers. The flow processor is configured to measure the fluid flow through the spool piece based on outputs of the transducers of all of the ultrasonic flowmeters.

In another embodiment, a method for measuring fluid flow includes determining, by a first ultrasonic flowmeter, a first flow velocity of fluid flowing through the first ultrasonic flowmeter. A second ultrasonic flowmeter determines a second flow velocity of fluid flowing through the second ultrasonic flowmeter. The first ultrasonic flowmeter produces a combined flow rate by combining the first and second flow velocities.

In a further embodiment, a computer-readable medium is encoded with instructions that when executed cause a processor of an ultrasonic flowmeter to determine a first flow velocity of fluid flowing through the first ultrasonic flowmeter. Additional instructions encoded on the medium cause the processor to retrieve from a co-located ultrasonic flowmeter a second flow velocity of fluid flowing through the co-located ultrasonic flowmeter. Yet further instructions encoded on the medium cause the processor to produce a combined flow rate by combining the first and second flow velocities.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” In addition, the term “couple” or “couples” is intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. Further, the term “software” includes any executable code capable of running on a processor, regardless of the media used to store the software. Thus, code stored in memory (e.g., non-volatile memory), and sometimes referred to as “embedded firmware,” is included within the definition of software. The recitation “based on” is intended to mean “based at least in part on.” Therefore, if X is based on Y, X may be based on Y and any number of other factors. The term “flow rate” as used herein refers to the rate of volumetric flow.

DETAILED DESCRIPTION

The following description is directed to various embodiments of the invention. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The disclosed embodiments should not be interpreted, or otherwise used, to limit the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. Further, the various embodiments were developed in the context of measuring hydrocarbon flows (e.g., crude oil, natural gas), and the description follows from the developmental context; however, the systems and methods described are equally applicable to measurement of any fluid flow (e.g., cryogenic substances, water).

FIG. 1shows an ultrasonic flowmeter100in accordance with various embodiments. The ultrasonic flowmeter100includes a meter body or spool piece102that defines a central passage or bore104. The spool piece102is designed and constructed to be coupled to a pipeline or other structure (not shown) carrying fluids (e.g., natural gas) such that the fluids flowing in the pipeline travel through the central bore104. While the fluids travel through the central bore104, the ultrasonic flowmeter100measures the flow rate (hence, the fluid may be referred to as the measured fluid). The spool piece102includes flanges106that facilitate coupling of the spool piece102to another structure. In other embodiments, any suitable system for coupling the spool piece102to a structure may be equivalently used (e.g., weld connections).

In order to measure fluid flow within the spool piece102, the ultrasonic flowmeter100includes a plurality of transducer assemblies. In the view ofFIG. 1five such transducers assembles108,110,112,116and120are in full or partial view. The transducer assemblies are paired (e.g., transducer assemblies108and110), as will be further discussed below. Moreover, each transducer assembly electrically couples to control electronics, illustratively housed in enclosure124. More particular, each transducers assembly electrical couples to the control electronics in the enclosure124by way of a respective cable126or equivalent signal conducting assembly.

FIG. 2shows a cross-sectional overhead view of the ultrasonic flowmeter100taken substantially along line2-2ofFIG. 1. Spool piece102has a predetermined size and defines the central bore104through which the measured fluid flows. An illustrative pair of transducers assemblies112and114is located along the length of spool piece102. Transducers112and114are acoustic transceivers, and more particularly ultrasonic transceivers. The ultrasonic transducers112,114both generate and receive acoustic signals having frequencies above about20kilohertz. The acoustic signals may be generated and received by a piezoelectric element in each transducer. To generate an ultrasonic signal, the piezoelectric element is stimulated electrically by way of a signal (e.g., a sinusoidal signal), and the element responds by vibrating. The vibration of the piezoelectric element generates the acoustic signal that travels through the measured fluid to the corresponding transducer assembly of the pair. Similarly, upon being struck by an acoustic signal, the receiving piezoelectric element vibrates and generates an electrical signal (e.g., a sinusoidal signal) that is detected, digitized, and analyzed by the electronics associated with the flowmeter100.

A path200, also referred to as a “chord,” exists between illustrative transducer assemblies112and114at an angle θ to a centerline202. The length of chord200is the distance between the face of transducer assembly112and the face of transducer assembly114. Points204and206define the locations where acoustic signals generated by transducer assemblies112and114enter and leave fluid flowing through the spool piece102(i.e., the entrance to the spool piece bore). The position of transducer assemblies112and114may be defined by the angle θ, by a first length L measured between the faces of the transducer assemblies112and114, a second length X corresponding to the axial distance between points204and206, and a third length “d” corresponding to the pipe inside diameter. In most cases distances d, X and L are precisely determined during flowmeter fabrication. A measured fluid, such as natural gas, flows in a direction208with a velocity profile210. Velocity vectors212,214,216and218illustrate that the gas velocity through spool piece102increases toward the centerline202of the spool piece102.

Initially, downstream transducer assembly112generates an ultrasonic signal that is incident upon, and thus detected by, upstream transducer assembly114. Some time later, the upstream transducer assembly114generates a return ultrasonic signal that is subsequently incident upon, and detected by, the downstream transducer assembly112. Thus, the transducer assemblies exchange or play “pitch and catch” with ultrasonic signals220along chordal path200. During operation, this sequence may occur thousands of times per minute.

The transit time of an ultrasonic signal220between illustrative transducer assemblies112and114depends in part upon whether the ultrasonic signal220is traveling upstream or downstream with respect to the fluid flow. The transit time for an ultrasonic signal traveling downstream (i.e., in the same direction as the fluid flow) is less than its transit time when traveling upstream (i.e., against the fluid flow). The upstream and downstream transit times can be used to calculate the average velocity along the signal path, and the speed of sound in the measured fluid. Given the cross-sectional measurements of the flowmeter100carrying the fluid, the average velocity over the area of the central bore104may be used to find the volume of fluid flowing through the spool piece102.

Ultrasonic flowmeters can have one or more chords.FIG. 3illustrates an end elevation view of ultrasonic flowmeter100. In particular, illustrative ultrasonic flowmeter100comprises four chordal paths A, B, C and D at varying levels within the spool piece102. Each chordal path A-D corresponds to a transducer pair behaving alternately as a transmitter and receiver. Transducer assemblies108and110(only partially visible) make up chordal path A. Transducer assemblies112and114(only partially visible) make up chordal path B. Transducer assemblies116and118(only partially visible) make up chordal path C. Finally, transducer assemblies120and122(only partially visible) make up chordal path D.

A further aspect of the arrangement of the four pairs of transducers is shown with respect toFIG. 4, which shows an overhead view. Each transducer pair corresponds to a single chordal path ofFIG. 3; however, the transducer assemblies are mounted at a non-perpendicular angle to the center line202. For example, a first pair of transducer assemblies108and110is mounted at a non-perpendicular angle θ to centerline202of spool piece102. Another pair of transducer assemblies112and114is mounted so that the chordal path loosely forms the shape of an “X” with respect to the chordal path of transducer assemblies108and110. Similarly, transducer assemblies116and118are placed parallel to transducer assemblies108and110, but at a different “level” or elevation. Not explicitly shown inFIG. 4is the fourth pair of transducer assemblies (i.e., transducer assemblies120and122). ConsideringFIGS. 2, 3 and 4, the transducers pairs may be arranged such that the upper two pairs of transducers corresponding to chords A and B form an the shape of an “X”, and the lower two pairs of transducers corresponding to chords C and D also form the shape of an “X”. The flow velocity of the fluid may be determined at each chord A-D to obtain chordal flow velocities, and the chordal flow velocities are combined to determine an average flow velocity over the entire pipe. From the average flow velocity, the amount of fluid flowing in the spool piece, and thus the pipeline, may be determined.

Embodiments of the present disclosure couple a plurality of ultrasonic flowmeters (e.g., instances100A/B of the flowmeter100) to provide enhanced flow measurement accuracy.FIG. 5shows a flow metering system500including a pair of co-located ultrasonic flowmeters100coupled in series. Other embodiments may include a different number of coupled co-located flowmeters and/or a different number of total or per flowmeter chordal paths. The electronics of the pair of flowmeters are communicatively coupled using a communication link502, which may be a local area network (LAN). The electronics of each flowmeter100exchanges flow measurement values with the other flowmeter, and computes a combined flow rate value based on flow measurements provided by both meters100. By combining the pair of four path meters100, the system500forms an eight path flowmeter that provides improved measurement accuracy over each individual four path flowmeter100while allowing each flowmeter100to operate as a four path flowmeter100should the other flowmeter100fail. In some embodiments, the ultrasonic transducers of the two or more flowmeters100may be disposed in a single spool piece and/or the electronics of the two or meters may be disposed in a single enclosure. In further embodiments, the two or more flowmeters100may include different chordal configurations, for example, different chord elevations, angles, etc. relative to the flow path that provide for improved measurement accuracy when the measurements of the flowmeters100are combined.

FIG. 6shows a block a diagram of the flow metering system500that includes co-located ultrasonic flowmeters100A/B in accordance with various embodiments. Each of the flowmeters100includes a set of transducer a pairs602(e.g.,108and110,112and114,116and118,120and122) and electronics comprising a transducer controller604, a flow processor606, and a communications transceiver608. Some embodiments may also include one or more sensors614for measuring fluid attributes. The transducer controller604is coupled to the transducer pairs602, and controls generation of ultrasonic signals by the transducer pairs602by, for example, generating drive signals that induce oscillation in the transducers. In some embodiments of the system500, a transducer controller604of one of the flowmeters100generates a synchronization signal610that is provided to each of the transducer controllers604of the other flowmeters100. The synchronization signal may be propagated by electrical conductors, optical channels, wireless channels, etc.

The synchronization signal610establishes the timing of ultrasonic signal generation by the meters100, thereby preventing ultrasonic signals generated by flowmeter100A from interfering with measurements made by flowmeter100B and vice versa. In some embodiments, the signal610specifies the start time and duration for each transducer. In other embodiments, the signal610, via phase, voltage level, etc. may indicate a time period in which each flowmeter100performs ultrasonic measurements free of interference from other meters100. In some embodiments, the synchronization signal610is provided as a message transferred over a communication link, e.g., link502, between the meters100. Other embodiments of the system500may lack or selectively perform transducer synchronization, for example, in embodiments where interference is unlikely. In some embodiments, the ultrasonic flowmeter100that controls transducer timing by generation of the synchronization signal is termed “primary” and flowmeters100receiving the signal610are termed “secondary.” The status of each flowmeter100as primary or secondary may be established when the flowmeter is manufactured or put into service.

The flow processor606is coupled to the transducer controller604, and is configured to process outputs of the transducer pairs602to generate measurements of fluid flow within the spool piece102. For a given chord, the chordal flow velocity v may be given by

v=L22⁢X·Tup-TdnTup⁢Tdn
where:L is the path length (i.e., face-to-face separation between upstream and downstream transducers),X is the component of L within the flowmeter bore in the direction of the flow, andTupand Tdnare the upstream and downstream transit times of sound energy through the fluid.

The flow processor606combines the chordal flow velocities to determine an average flow velocity for the fluid flowing through flowmeter100, and computes the volumetric flow rate through the flowmeter100as a product of the average flow velocity for the flowmeter100and the cross-sectional area of the flowmeter100.

The flow processor606may also compute an uncorrected flow rate and a corrected flow rate. The uncorrected flow rate adjusts the raw flow rate to account for the flow profile and fluid expansion due to pressure and temperature. The corrected flow rate adjusts the uncorrected flow rate to account for differences in base and flow condition pressure, temperature, and fluid compressibility.

Embodiments of the flow processor606are also configured to compute flow through the spool piece102by combining flow measurements provided by one flowmeter100with those provided by a different flowmeter100. Thus, the flow processor606of each flowmeter100may be configured to produce combined flow measurement values based on flow measurements generated by all communicatively coupled flowmeters100. The combined flow measurements may be more accurate than the flow measurements generated by any one of the meters100individually.

To generate a combined flow value, the flow processor606is configured to periodically (e.g., a periodic flow computation time interval—every 250 milliseconds (ms), every second, etc.) generate ultrasonic signals, and compute one or more initial flow values based on the outputs of the transducer pairs602controlled by the flowmeter (e.g., the flowmeter100A). The initial flow values may include speed of sound along a chord, average speed of sound, flow velocity along a chord, average flow velocity, flow measurement quality, etc. The flow processor makes the initial flow values available for retrieval by other meters100in real-time (i.e., the time period (e.g., 250 ms) set for generating flow values by the meter100is unaffected by the retrieval and associated operations). In some embodiments, the flow processor606provides the initial flow values to a server disposed in the flowmeter100A. The server is configured to process requests from another flowmeter100for the initial flow values computed by the flowmeter100A, and provide the initial flow values to the other flowmeter100responsive to the request. The flow processor may also provide, for retrieval by other meters100, an expiration time value that defines the time interval during which initial flow values are considered valid.

The flow processor606generates a message requesting initial flow values from a different flowmeter100, and transmits the message via the communication transceiver608. The transceiver608is communicatively linked to instances of the transceiver608in other meters100. The transceiver608may be, for example, configure to provide communication in accordance with a networking standard, such as IEEE 802.3, IEEE 802.11, etc. The instance of the flowmeter100receiving the message (e.g., the flowmeter to which the message is addressed by internet protocol address) provides the requested initial flow values to the requesting flowmeter100via a message transferred over the communication link formed by the transceivers608.

The flow processor606verifies the initial flow values received from the other flowmeter100. For example, the flow processor606may verify that the expiration time value associated with the flow values has not expired, that a provided flow measurement quality value indicates valid measurements, that message check characters indicate valid data, etc. If the verification indicates that the initial flow values are valid, then the flow processor606combines the initial flow values provided by the other flowmeter100with the initial flow values computed by the flow processor606to generate a combined flow value. Some embodiments may combine the initial flow values by computing an average of the initial flow values generated by each flowmeter100. The flow processor606may compute fluid flow rate (raw, corrected, uncorrected), flow volume, flow mass, etc. based on the combined flow value.

The flow processor606may store the combined flow value and/or the flow rate derived from the combined flow value in memory, provide the value to a database, and/or generate signals representative of flow rate, flow volume, etc. based on the combined flow value. For example, some embodiments of the flow processor606may generate an output signal having a frequency representative of a flow rate derived from the combined flow value.

If the flow processor606of the flowmeter100A (or any flowmeter100) is unable to verify the initial flow values received from another flowmeter100, then the flow processor606may compute a final flow value based on only the initial flow values produced by the flowmeter100A. Thus, the system500provides redundancy in that each flowmeter100can provide flow measurements based on the outputs of only the transducer pairs602of the flowmeter100when other instances of the flowmeter100fail, and provide enhanced flow measurement accuracy based on the outputs of all transducer pairs602when all of the meters100are operating properly.

Some embodiments of the flowmeter100also include sensors614that measure attributes of the fluid flowing in the spool piece102. The sensors614may include, for example, one or more of a temperature sensor, a pressure sensor, and a gas composition sensor that measure fluid temperature, fluid pressure, and fluid composition respectively. The sensor measurement values may be shared between meters100as described above with regard to initial flow values. The meters100may apply the sensor measurement values to improve the accuracy of the computed flow values, flow rates, etc.

Various components of the flowmeter100including at least some portions of the flow processor606and the transducer controller604can be implemented using a processor, included in the flowmeter100. The processor executes software programming that causes the processor to perform the operations described herein. In some embodiments, the flow processor606includes a processor executing software programming that causes the processor to generate flow values, such as the initial flow values, combined flow values, flow rates, etc., and perform other operations described herein.

Suitable processors include, for example, general-purpose microprocessors, digital signal processors, and microcontrollers. Processor architectures generally include execution units (e.g., fixed point, floating point, integer, etc.), storage (e.g., registers, memory, etc.), instruction decoding, peripherals (e.g., interrupt controllers, timers, direct memory access controllers, etc.), input/output systems (e.g., serial ports, parallel ports, etc.) and various other components and sub-systems. Software programming that causes a processor to perform the operations disclosed herein can be stored in a computer readable storage medium internal or external to the flowmeter100. A computer readable storage medium comprises volatile storage such as random access memory, non-volatile storage (e.g., a hard drive, an optical storage device (e.g., CD or DVD), FLASH storage, read-only-memory, or combinations thereof.

Some embodiments can implement portions of the ultrasonic flowmeter100, including portions of the flow processor606and transducer controller604, using dedicated circuitry (e.g., dedicated circuitry implemented in an integrated circuit). Some embodiments may use a combination of dedicated circuitry and a processor executing suitable software. For example, some portions of the transducer controller604may be implemented using a processor or hardware circuitry. Selection of a hardware or processor/software implementation of embodiments is a design choice based on a variety of factors, such as cost, time to implement, and the ability to incorporate changed or additional functionality in the future.

FIG. 7shows a flow diagram for a method700for operating a flow metering system500that includes co-located ultrasonic flowmeters100in accordance with various embodiments. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some embodiments may perform only some of the actions shown. In some embodiments, the operations ofFIG. 7, as well as other operations described herein, can be implemented as instructions stored in a computer readable medium and executed by processors included in the meters100.

In the method700, a plurality of ultrasonic flowmeters100are co-located (e.g., serially connected or disposed in a single spool piece) and each flowmeter100is generating flow values based on the ultrasonic transducer pairs602of all of the flowmeters. In block702, the generation of ultrasonic signals by the transducers of the plurality of flowmeters100is synchronized to reduce interference between the flowmeters100. One of the flowmeters100may be designated the primary flowmeter and generate the synchronization signal610that is provided to each of the other co-located flowmeters to effect the synchronization.

Each flowmeter100generates ultrasonic signals in block704. The signals traverse the interior of the spool piece102, and are detected by an ultrasonic transducer. Electrical signals representative of the detected ultrasonic signals are provided to the flow processor606.

In block706, sensors614measure attributes of the fluid flowing in the spool piece102, such as fluid temperature, fluid pressure, fluid composition, etc. The attribute measurements are provided to the flow processor606for use in computing fluid flow.

In block708, each flowmeter100, computes a set of initial flow values. The initial flow values are based on the ultrasonic signals generated and detected only by the transducer pairs602of the flowmeter100. In some embodiments, the initial flow values may also be based on the fluid attributes measured by the sensors. The initial flow values may include an average speed of sound, average flow velocity, flow rate value, etc. for the flowmeter100.

In block710, the initial flow values, and optionally the sensor measurements, are made accessible to co-located meters100. For example, the initial flow values may be provided to a server in the flowmeter100, and each of the co-located meters100operates as a client of the server to access the initial flow values via the communication link502.

In block712, each flowmeter100retrieves initial flow values from each other co-located flowmeter100. Retrieval may include generating a request message that is communicated to each other flowmeter100(e.g., to a server included in each flowmeter100). On receipt of the request message, each flowmeter100may generate a response message that includes the initial flow values, and transfer the response message to the requesting flowmeter100.

In block714, each flowmeter100verifies the initial flow values received from the other co-located meters100. The verification may include computation of check values (such as cyclic redundancy check values) applied to the initial flow values, verification that a flow value lifetime value has not expired, and verification that the quality of the flow measurements exceeds a predetermined threshold.

In block716, if a flowmeter100finds the retrieved initial flow values to be invalid, then, in block718, the some embodiments of the flowmeter100compute a final flow rate value based only on the flow information generated by the flowmeter100(i.e., an individual final flow value). The individual final flow value is not based on initial flow values generated by other co-located meters100. The flowmeter100also generates a fluid flow rate based on the individual final flow value.

If, in block716, a flowmeter100finds the retrieved initial flow values to be valid, then, in block720, the flowmeter100computes a final flow value based on the initial flow values generated by the plurality of co-located meters100(i.e., a combined final flow value). The flowmeter100applies the combined final flow value to generate a fluid flow rate based on the total number of chordal paths provided all of the co-located meters100. The fluid flow rate may also be based on the sensor measurements retrieved from one or more of the co-located meters100.

In block722, the final flow value, which may be the individual or combined final flow rate explained above, and a flow rate based on the final flow value is stored for access by other components of the flow measurement system (e.g., access by a user interface/display/input sub-system or a flow control system). A signal representative of the flow rate may also be generated for communication of the flow rate to other equipment.

The above discussion is meant to be illustrative of various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, while embodiments of the invention have been discussed with relation to a pair of co-located ultrasonic flowmeters, those skilled in the art will understand that embodiments are applicable to any number of co-located flowmeters. Furthermore, while embodiments have been discussed with regard to flowmeters having four chordal paths, those skilled in the art will understand that embodiments encompass flowmeters having any number of chordal paths, including co-located flowmeters each having a different number of chordal paths. It is intended that the following claims be interpreted to embrace all such variations and modifications.