Patent Application
20100223976
Not applicable.
The disclosed subject matter relates generally to hydrocarbon production and transportation and, more particularly, to a high flow rate prover and meter for custody transfer measurement.
In the hydrocarbon industry, meters are employed to measure large quantities of fluid, such as oil, that are transferred from one entity to another (e.g., a custody transfer). Generally, the accuracy of a meter may be affected by the characteristics of the metered fluid, such as viscosity, specific gravity, temperature, and pressure. Meters are proven under normal operating conditions to provide traceability of the meter registration to an internationally recognized volumetric or gravimetric standard. Typically, a prover is used in conjunction with a meter prior to or during a custody transfer to calculate a meter factor that is applied to correct the meter's measurements. The meter factor relates the meter output at operating conditions to the certified standard. The measured quantity times the meter factor represents the actual quantity delivered.
A conventional prover employs an elastomer sphere that passes through a section of pipe in series with the meter. High integrity block and bleed valves are employed to switch the prover into and out of the fluid stream to facilitate proving. A high integrity four-way valve is used to reverse the flow in a bi-directional prover. A somewhat complex interchange valve and launching device is used to pass the sphere in a uni-directional prover. The sphere passes between two detectors or sensors. The distance the sphere traverses between the sensors defines a known volume. Hence, by counting high resolution (typically 10,000 or more) meter pulses during traversal of the sphere, the precise number of meter pulses per calibrated volume and thus a meter factor may be determined. Proving may involve a uni-directional or bi-directional movement of the sphere.
To prove a large diameter ultrasonic meter (e.g., 10-24 inches or larger), a conventional uni- or bi-directional prover would be very large, have a prohibitively high cost, and would be difficult and expensive to maintain. Presently, multiple smaller meter runs and a smaller prover are used. This arrangement is necessitated by velocity limits imposed on provers due to hydraulic considerations in starting, stopping, diverting, and reversing the large mass of the sphere and fluid.
As the price of crude oil and refined products increases, the need for accurate proving is increased. Mis-measurement of even 0.05% on a stream flowing at 2,000 BPH or 48,000 BPD of $90 crude oil can result in an error of $790,000 per year. Under-registration deprives the company of entitled revenue, and over registration raises the issue of customer complaints or retroactive rebates.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.
One aspect of the disclosed subject matter is seen in a method that includes introducing a tag into a fluid stream, the tag being suspended in the fluid stream. The tag is detected at a first end of a calibrated volume and a first detection signal is generated responsive thereto. The tag is detected at a second end of the calibrated volume and a second detection signal is generated responsive thereto. A flow parameter for the fluid stream is determined based on the first and second detection signals and the calibrated volume.
Another aspect of the disclosed subject matter is seen is a proving system including piping for carrying a fluid stream, a meter, a tag insertion unit, first and second tag sensors, and a control unit. The meter is operable to generate pulses, each pulse representing a volume of fluid flowing through the meter. The tag insertion unit is operable to introduce a tag into the fluid stream, the tag being suspended in the fluid stream. The first tag sensor is operable to detect the tag at a first end of a calibrated volume defined in the piping and generate a first detection signal. The second tag sensor is operable to detect the tag at a second end of the calibrated volume and generate a second detection signal. The control unit is operable to count the pulses from the meter between the first and second detection signals to determine a measured pulse count and generate a meter correction factor for the meter based on the measured pulse count and the calibrated volume.
The disclosed subject matter will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
While the disclosed subject matter is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosed subject matter as defined by the appended claims.
One or more specific embodiments of the disclosed subject matter will be described below. It is specifically intended that the disclosed subject matter not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the disclosed subject matter unless explicitly indicated as being “critical” or “essential.”
The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the disclosed subject matter with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to
In general, the tag insertion unit 22 introduces a tag 26 into the production fluid (e.g., liquid, gas, or mixed) passing through the piping 14 at the request of the control unit 24. The control unit 24 measures high resolution pulses from the meter as the tag 26 traverses between the tag sensors 18, 20 to determine a number of meter pulses representative of the prover calibrated volume. The determined pulses are compared to the nominal pulses of the meter 12 to generate a meter factor to be applied to the meter 12. The control unit 24 may be implemented using various devices, such as a flow computer coupled to the tag sensors 18, 20, the meter 12, and the tag insertion unit 22. The control unit 24 may be a programmable device executing software to perform the function described herein.
The prover 16 may be employed with relatively large diameter (e.g., 10 inch or greater), high flow rate metering applications. Such applications would otherwise require very large, expensive conventional provers. The prover 16 may be used with a variety of meter types, such as an inferential ultrasonic meter, a positive displacement meter, or a turbine meter.
The position of the tag sensors 18, 20 in the piping 14 relative to the meter 12 may vary. Although the tag sensors 18, 20 are illustrated upstream of the meter 12, they may be installed downstream of the meter 12, or they may straddle the meter 12, as illustrated in
The section of piping 14 between the between the tag sensors 18, 20 represents a calibrated volume. The bore of the piping 14 in the prover 16 may be ground and coated with a corrosion resistant coating to protect the validity of the known volume. The volume may be calibrated offline using conventional water draw displacement techniques using a sphere or cylindrical pig including one or more tags 26 for triggering the sensors 18, 20. The prover 16 may be temporarily isolated from the production stream using valves to allow calibration, or alternatively, the piping run including the prover 16 may be disconnected and rolled out of the line for calibration.
The control unit 24 uses the calibrated volume in conjunction with signals from the tag sensors 18, 20 to determine the pulses per volume and flow rate of fluid passing through the prover 16 and the meter 12 being proved. The flow rate is determined by dividing the calibrated volume by the tag traversal time. The meter factor is determined by dividing the prover calibrated volume by the pulses measured by the meter 12. The calculation may also be corrected for the effects of temperature, pressure, and specific gravity on the fluids and the materials of construction of the meter 12 and prover 16 per American Petroleum Institute (API) standards. Techniques for performing these corrections are known to those of ordinary skill in the art, so they are not described in greater detail herein. Because the tags 26 are suspended in the fluid stream, they do not introduce variations in the flow rate, as is common in conventional provers that employ displacers that must be pushed through the piping.
To implement a proving cycle, the control unit 24 signals the tag insertion unit 22 to inject a tag 26 into the process fluid. The first tag sensor 18 detects the presence of the tag 26 and sends a detection signal to the control unit 24. The control unit 24 initiates a pulse counter and timer upon receipt of the first detection signal. When the tag 26 passes the second tag sensor 18, the control unit 24 receives a second detection signal and terminates the pulse counter and timer. Based on the pulses collected and tag traversal time tracked by the control unit 24, the meter registered volume and/or flow rate of the fluid may be determined. The proving cycle may include the injection and pulse counting and timing of multiple tags 26 to demonstrate repeatability.
There are various techniques that may be employed to implement the tags 26 and associated tag sensors 18, 20. In one embodiment, the tags 26 may be radio frequency identification (RFID) tags. Generally, RFID tags include an integrated circuit and an antenna. An RFID tag may be passive (i.e., uses power from the detection signal to answer the detector) or active (i.e., uses on-board battery power to answer the detector). In the illustrated embodiment, passive RFID tags may be used as they might introduce more benign materials into the process fluid as compared to an active tag.
In some embodiments, a string 36 of RFID tags 28 may be used, as shown in
In another embodiment, the tags 26 may be implemented by injecting a volume of a tag material (e.g., liquid or solid) into the process stream. The sensors 18, 20 may be configured to detect the presence of the tag material particles at the boundaries of the calibrated volume. The particular type of sensor employed depends on the nature of the tag material. For example, an optical sensor may be used to detect a fluorescent, colored, or reflective material, or a radiation detector may be used to detect a radioactive material.
One example of an optical detection technique is illustrated in
It is also contemplated that other types of waveforms may be used in lieu of or in addition to light based waveforms. For example, sonic, ultrasonic, or radio waves may be used to detect the presence of the tags 26 based on a similar broadcast/reflection technique.
In yet another embodiment illustrated in
Because, the prover 16 provides a measure of flow rate, the detection techniques may also be applied to provide metering functionality without the use of an actual meter. As shown in
The proving techniques described herein have various advantages over conventional provers. The prover 16 may be implemented for larger piping diameters than may be serviced by a conventional prover due to hydraulic limits on conventional provers. The prover 16 also allows the elimination of the multiple meter runs, associated high integrity valves and instruments, and the large quantity of pipe, and fittings associated with a typical prover. Instead, the prover 16 may be installed in the upstream and downstream piping that is already reserved for the meter 12.
The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below.
