Abstract:
A method and system for generating an uncertainty value. At least some of the illustrative embodiments are systems comprising a device in fluid communication with a conduit (wherein the device is configured to collect parametric data regarding fluid flow through a conduit, and wherein the device is configured to generate an accuracy value of the parametric data), and a flow computer electrically coupled to the device (wherein the flow computer is configured to receive the parametric data and the accuracy value from the device). The flow computer is configured to generate a flow value based on the parametric data, and the flow computer is configured to generate an uncertainty value of the flow value based on the parametric data and on the accuracy value received from the device.

Description:
BACKGROUND 
       [0001]    Measurements of mass and volume flow rates of fluid through a conduit are a part of operations in the oil and gas industry. When the ownership of fluid changes hands (custody transfer), a high integrity system that provides reliable flow data with minimal uncertainty is desirable. 
         [0002]    Flow meters such as ultrasonic, turbine, and coriolis provide parametric data such as volume flow rate, flow velocity, and mass flow rate, while temperature, pressure, and differential pressure transmitters measure parametric data such as fluid temperature, differential pressure across an orifice, and static pressure. The parametric data may be used to derive a number of flow variables such as discharge coefficient, expansion factor, and fluid density and viscosity. Also, the parametric data may be used in a flow calculation equation to determine the fluid flow rate (if not determined directly by virtue of the meter used) and the total flow volume. 
         [0003]    While such measurements and flow rate calculations have inherent inaccuracies, the precise measurement of fluid properties is necessitated in order to avoid improperly charging for the transfer of fluid. Currently, static error calculations are performed in an attempt to quantify the uncertainty in measurement. However, static error calculations are based on worse case scenarios, and the delay in such calculations lessens their usefulness. 
       SUMMARY 
       [0004]    The problems noted above are solved in large part by a method and system for generating an uncertainty value. At least some of the illustrative embodiments are systems comprising a device in fluid communication with a conduit (wherein the device is configured to collect parametric data regarding fluid flow through a conduit, and wherein the device is configured to generate an accuracy value of the parametric data), and a flow computer electrically coupled to the device (wherein the flow computer is configured to receive the parametric data and the accuracy value from the device). The flow computer is configured to generate a flow value based on the parametric data, and the flow computer is configured to generate an uncertainty value of the flow value based on the parametric data and on the accuracy value received from the device. 
         [0005]    Other illustrative embodiments are methods comprising collecting parametric data indicative of fluid flow within a conduit generating an accuracy value indicative of the measurement accuracy of the parametric data, computing a flow value based on the parametric data, and computing a value indicative of the uncertainty of the flow value, the computing based on the parametric data and the accuracy value. 
         [0006]    Yet still other illustrative embodiments are flow computers comprising a processor, a memory electrically coupled to the processor, and a communications port electrically coupled to the processor (the communications port configured to receive parametric data indicative of fluid flow and a value indicative of the accuracy of the parametric data). The processor is configured to generate a flow value based on the parametric data, and wherein the processor is configured to generate an uncertainty value of the flow value based on the parametric data and on the value indicative of the accuracy. 
         [0007]    Other illustrative embodiments are systems comprising a device in fluid communication with a conduit (the device configured to collect parametric data regarding fluid flow through the conduit, and the device configured to generate an accuracy value of the parametric data). The device is configured to generate a flow value based on the parametric data, and the device is configured to generate an uncertainty value of the flow value based on the parametric data and on the accuracy value. 
         [0008]    The disclosed devices and methods comprise a combination of features and advantages which enable it to overcome the deficiencies of the prior art devices The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0010]      FIG. 1  illustrates a system in accordance with embodiments of the invention utilizing a transmitter and a flow computer; 
           [0011]      FIG. 2  illustrates a system in accordance with embodiments of the invention utilizing an inline flow meter and a flow computer; 
           [0012]      FIG. 3  illustrates a computer system in accordance with embodiments of the invention; 
           [0013]      FIG. 4  illustrates a system in accordance with embodiments of the invention utilizing a multi-variable transmitter; 
           [0014]      FIG. 5  illustrates a system in accordance with embodiments of the invention utilizing an inline flow meter; and 
           [0015]      FIG. 6  shows an exemplary flow diagram for determining a flow value and an uncertainty value. 
       
    
    
     NOTATION AND NOMENCLATURE 
       [0016]    Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function. 
         [0017]    In the following discussion and in the claims, the term “comprises” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and connections. 
         [0018]    For the purposes of this application, the term “real-time” encompasses the delays associated with the collection of data as well as the delays associated with the subsequent processing and reporting of the data. Thus, “real-time” data may be contemporaneously reported as it is gathered and/or calculated, and its real-time status shall not be negated by collection and/or processing delays. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  illustrates a flow measurement system  100  for measuring a fluid flow value  26  and generating a value indicative of the uncertainty of the flow value  26 , termed herein an uncertainty value  28 . The flow measurement system  100  comprises an orifice plate  20  having an orifice diameter “d” disposed within a conduit  18  having a diameter “D”. The orifice plate  20  may be of varying types (e.g., concentric, eccentric, and segmental). Furthermore, the orifice plate  20  is oriented substantially perpendicular to a fluid flow  24  through the conduit  18 . As the flow  24  passes through the orifice plate  20 , there is a resultant drop in fluid pressure and a corresponding increase in fluid velocity. In the embodiments of  FIG. 1 , the difference in pressure on opposing sides of the orifice plate  20  is measured by a differential pressure transmitter  14  that is in fluid communication with the conduit  18  through taps or inlets  30  and  32 . The differential pressure transmitter  14  is further electrically coupled to a flow computer  16  by way of a conductor  38 . 
         [0020]      FIG. 1  further illustrates a pressure transmitter  12  upstream of the orifice plate  20  that is in fluid communication with the conduit  18  through a tap or inlet  34 . The pressure transmitter  12  measures the pressure upstream of the orifice plate  20 , and the pressure transmitter is electrically coupled to the flow computer  16  by way of the conductor  3   8 . A temperature transmitter  10  has a temperature sensor  22  disposed within the fluid flow  24 , and the temperature transmitter  10  electrically couples to the sensor  22  by way of a conductor  36 . The temperature sensor  22  measures the fluid temperature upstream of the orifice plate  20 . The temperature transmitter  10  is also coupled to the flow computer  16  by way of the conductor  38 . In alternative embodiments, the differential pressure transmitter  14 , pressure transmitter  12 , and temperature transmitter  10  couple to the flow computer  16  by way of individual conductors, or by way of a wireless communications system. 
         [0021]    The transmitters employed in the flow measurement system  100  provide real-time parametric data such as fluid temperature, differential pressure, and static pressure. The parametric data may be used in a flow calculation equation to determine a real-time fluid flow rate. Additionally, the parametric data may also be used to derive a number of flow variables on a real-time basis (e.g., discharge coefficient, expansion factor, and fluid density and viscosity). In alternative embodiments, the transmitters provide real-time statistical data to the flow computer (e.g., arithmetic mean of a process variable, standard deviation, number of samples, and collection period). 
         [0022]    In the embodiments illustrated in  FIG. 1 , the various transmitters are microprocessor-based devices that, in addition to the parametric data collection, also generate accuracy values associated with their parametric data. For the embodiments herein disclosed, accuracy refers to the ability of a device such as a transmitter to measure parametric data that conforms to the real values of the fluid flow variables being measured. Devices may exhibit excellent accuracy that meets or possibly exceeds manufacturer&#39;s specifications in some operational conditions. However, in other operational conditions the device may be subject to fluctuating ambient temperatures or high static line pressure and may even drift out of calibration. Thus, the real-time accuracy value generated, and associated with the parametric data, provides useful information regarding the integrity of the parametric data and of the transmitter. 
         [0023]    The flow computer  16  as illustrated in  FIG. 1  receives the real-time parametric data and accuracy values associated with the parametric data from the temperature transmitter  10 , pressure transmitter  12 , and differential pressure transmitter  14  by way of the conductor  38 . In alternative embodiments, the flow computer  16  provides data or commands to the transmitters, or in response to the data it receives from the transmitters. Moreover, the flow computer  16  generates the real-time flow value  26  and the real-time uncertainty value  28 . The uncertainty calculation in the flow computer  16  provides a real-time uncertainty that can be used to determine the accuracy of the entire custody transfer meter run and as a diagnostic tool to isolate device problems. Significant shifts in the calculated uncertainty value  28  indicate a system change from some initially calibrated condition. The uncertainty value  28  could also be archived or trended over time, and an alarm generated if the uncertainty value  28  goes beyond some user-defined setpoint. Regardless of the type of transmitter or flow meter employed, in some embodiments the real-time uncertainty calculation performed in the flow computer  16  utilizes static equations such as those defined by flow measurement standards such as AGA 3, API NPMS Chapter 14 Section 3 Part 1, ISO 5167 for orifice flow meters, or ISO 5168 for total system uncertainty, except the flow computer  16  uses the equations in real-time with real-time parametric data and accuracy values to calculate the real-time flow value  26  and the real-time uncertainty value  28 . In particular, in some embodiments the total uncertainty may be defined by the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
                     U 
                     2 
                   
                   = 
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         1 
                       
                       n 
                     
                      
                     
                         
                     
                      
                     
                       
                         u 
                         i 
                         2 
                       
                        
                       
                         S 
                         i 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where U is the total uncertainty, u is an uncertainty component herein called the accuracy value for the transmitter i, and S is the sensitivity coefficient for each accuracy value. For example, the effect the accuracy of the differential pressure measurement has on the total uncertainty is greater than the effect of the accuracy of the temperature measurement, and those greater and/or lesser effects are accounted for using the sensitivity coefficient. 
         [0024]      FIG. 2  illustrates a flow measurement system  200  in accordance with alternative embodiments. The orifice plate  20 , temperature transmitter  10 , pressure transmitter  12 , and differential pressure transmitter  14  have been removed in favor of an inline flow meter  41 . The inline flow meter  41  may comprise a coriolis meter, an ultrasonic meter, or a turbine meter, among others. The inline flow meter  41  is positioned such that the fluid flow in the conduit  18  flows through the inline flow meter  41 . The inline flow meter  41  collects parametric data such as volume flow rate, flow velocity, and mass flow rate and also generates accuracy values associated with the parametric data collected. In some embodiments, the inline flow meter  41  also provides real-time statistical data (e.g., arithmetic mean of a process variable, standard deviation, number of samples, and collection period). The inline flow meter  41  is also coupled to the flow computer  16  by way of the conductor  38 . 
         [0025]    The flow computer  16  receives the parametric data and associated accuracy values from the inline flow meter  41  by way of the conductor  38 . In alternative embodiments, the flow computer  16  provides data or commands to the inline flow meter  41 , or in response to the data it receives from the inline flow meter  41 . In accordance with embodiments of the invention, the flow computer  16  uses real-time parametric data and real-time accuracy values to calculate the real-time flow value  26  and the real-time uncertainty value  28 . 
         [0026]      FIG. 3  provides a more detailed illustration of the flow computer  16 . The flow computer  16  comprises a microprocessor  40 , a memory element  42 , a communications port  44 , and a system bus  47 . The system bus  47  electrically couples the microprocessor  40 , the memory element  42 , and the communications port  44 . The memory element  42  comprises any type of removable or non-removable memory device or computer-readable media such as random-access memory (RAM), read-only memory (ROM), or flash memory. The memory element  42  may also comprise mass storage memory devices such as floppy disks, hard disks, optical disks, magnetic storage devices, or universal serial bus (USB) devices. The memory element  42  may further comprise storage devices accessed remotely, such as by way of an Ethernet or wireless network. Moreover, the memory element  42  stores computer-executable instructions that when executed by the microprocessor  40  generates the flow value  26  and the uncertainty value  28 . Additionally, the memory element may store any previously generated flow value  26  and uncertainty value  28  for a variety of purposes such as archiving and trending over time. The communications port  44  comprises analog or digital input/output (I/O) devices or I/O controllers such as modems, wired or wireless network cards, serial and parallel ports, USB ports, and ports in compliance with standards such as EIA-232D, EIA-232, and EIA-422/485. 
         [0027]    The flow computer  16  receives, from a plurality of sources, parametric data  48  and associated accuracy values  46 . Specifically, the parametric data  48  and the accuracy values  46  are directed to the communications port  44  as indicated by arrow  49 . The microprocessor  40 , in electrical communication with the memory element  42  and the communications port  44  by way of the system bus  47 , utilizes the parametric data  48  and the accuracy values  46  in the execution of instructions stored in the memory element  42  to generate the flow value  26  and the uncertainty value  28 . The flow value  26  and the uncertainty value  28  are sent to downstream devices by way of the communications port  44  as indicated by arrow  35  and arrow  37 , respectively. 
         [0028]      FIG. 4  illustrates alternative embodiments of a flow measurement system  400  for determining the flow value  26  and the uncertainty value  28 . The illustrative flow measurement system  400  comprises a multi-variable transmitter  50  and the orifice plate  20  having an orifice diameter “d” disposed within the conduit  18  having a diameter “D”. Additionally, the multi-variable transmitter  50  comprises the microprocessor  40  and the memory element  42  electrically coupled to each other by the system bus  47 . The orifice plate  20  may be of varying types such as concentric, eccentric, and segmental. 
         [0029]    As the flow  24  passes through the orifice plate  20 , there is a resultant drop in fluid pressure and a corresponding increase in fluid velocity. In the embodiments of  FIG. 4 , the difference in pressure on opposing sides of the orifice plate  20  is measured by the multi-variable transmitter  50  that is in fluid communication with the conduit  18  through taps or inlets  56  and  58 .  FIG. 4  further illustrates a tap or inlet  54  that is in fluid communication with the conduit  18  upstream of the orifice plate  20  for measurement of the pressure upstream of the orifice plate  20 . In alternative embodiments, the multi-variable transmitter  50  uses the same tap or inlet for both the differential pressure measurement and the upstream static pressure measurement. The temperature sensor  22  is electrically coupled by way of the conductor  36  to the multi-variable transmitter  50  for measurement of the fluid temperature upstream of the orifice plate  20 . 
         [0030]    In addition to the parametric data collected by the multi-variable transmitter  50 , the multi-variable transmitter  50  also generates accuracy values associated with the parametric data. The microprocessor  40 , in electrical communication with the memory element  42 , utilizes the parametric data and accuracy values in the execution of instructions stored in the memory element  42  to generate the flow value  26  and the uncertainty value  28 . 
         [0031]      FIG. 5  illustrates yet still further alternative embodiments of a flow measurement system  500  for measuring the flow value  26  and the uncertainty value  28 . The flow measurement system  500  comprises the inline flow meter  41 . Additionally, the inline flow meter  41  comprises the microprocessor  40  and the memory element  42  electrically coupled to each other by way of the system bus  47 . The inline flow meter  41  comprises a coriolis meter, an ultrasonic meter, or a turbine meter, among others. The inline flow meter  41  is positioned such that the fluid flow in the conduit  18  flows through the inline flow meter  41 . The inline flow meter  41  collects parametric data such as volume flow rate, flow velocity, and mass flow rate and the inline flow meter  41  also generates accuracy values associated with the parametric data. In accordance with embodiments of the invention, the inline flow meter  41  uses real-time parametric data and real-time accuracy values to calculate the real-time flow value  26  and the real-time uncertainty value  28 . 
         [0032]      FIG. 6  illustrates a flow diagram for an algorithm used for generating the real-time uncertainty value  28  in accordance with embodiments of the invention. The flow diagram of  FIG. 6  is merely illustrative, as the various steps may be combined, separated, or performed in a different order without departing from the scope and spirit of the disclosure. The process starts (block  100 ) and proceeds to the collection of parametric data (block  102 ). The parametric data may be collected, for example, by the temperature transmitter  10 , the pressure transmitter  12 , the differential pressure transmitter  14 , the inline flow meter  41 , or the multi-variable transmitter  50 . The process then proceeds to generating the accuracy value of the collected parametric data (block  104 ), the generating possibly within the transmitter or flow meter. After the generation of the accuracy value, the flow value  26  is computed (block  106 ). In the embodiments as illustrated in  FIG. 1  and  FIG. 2 , the parametric data and accuracy value are sent to the flow computer  16  for computation of the flow value  26 . In the embodiments as illustrated in  FIG. 4  and  FIG. 5 , the parametric data and accuracy value remain wit the multi-variable transmitter  50  or inline flow meter  41  for internal computation of the flow value  26 . The process proceeds to the computation of the uncertainty value  28  of the flow value  26  (block  108 ). In the embodiments illustrated in  FIG. 1  and  FIG. 2 , the parametric data and accuracy value are sent to the flow computer  16  for computation of the uncertainty value  28 . In the embodiments as illustrated in  FIG. 4  and  FIG. 5 , the parametric data and accuracy value remain within the multi-variable transmitter  50  or inline flow meter  41  for internal computation of the uncertainty value  28 . If the computed uncertainty value  28  is greater than some user-defined setpoint (block  112 ), then an alarm may be activated (block  114 ). Otherwise, the process proceeds with the further collection of parametric data (block  102 ). Also, the computed flow and uncertainty values may be archived and trended over time. In accordance with embodiments as illustrated in  FIG. 6 , real-time parametric data is collected and the associated real-time accuracy values are generated in order to calculate real-time flow values and real-time uncertainty values. 
         [0033]    The above discussion is meant to be illustrative of the principles and 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. It is intended that the following claims be interpreted to embrace all such variations and modifications.