Example 1—Typical of an ultrasonic meter with a modbus uncorrected volumetric flow rate register:
(J.7)
— Sampling/Calculation conditions:
— register read every 1 second;
— modbus register is Uncorrected Volumetric flow rate in (ft3/minute);
— Mf table:
— Equation terms for Hourly QTRs:
Uncorrected Volumetric Flow Rateequals the register value;
i equals the calculation period = 1 second;
n equals 3600/i = 3600;
k-factor equals 1;
mfi is the table lookup of Uncorrected Volumetric Rate for calculation interval i.
Frequency
(Hz) Mf
0 1.0032
3000 1.0032
6000 1.0030
9000 1.0025
12,000 1.0020
IV mfi i=1 i=n
QfiΔti
=
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91
(informative)
Example of Using DPIV , DPY , and a Volumetric Flow Rate Calculator to Recalculate a QCP or QTR
Most volume verification software calculates flow rate and does not directly support QCP calculation of volume which use an IV or QTR recalculation of volume using the reported IV. This problem can be addressed using a three step process to convert the reported flow rate into accumulated volume:
1) Calculate the Flow Rate using the DPIV calculated from the average IV (IV).
This step corrects for the major portion of the volume calculation error introduced by using a linear average of differential pressure and may be all that is required depending on the necessary level of recalculation accuracy.
(See % DPLinear Recalculation Bias in Figure K.1, ”Differences Between DPIV and DPLinear and Recalculated Volumes, Using Hourly QTR Data for a Plunger Lift Production Area.”)
Figure K.1—Differences Between DPIV and DPLinear and Recalculated Volumes, Using Hourly QTR Data for a Plunger Lift Production Area
DPIV vs. DPLinear and DPLinear Volume Recalcuation Bias
DPIV (inches) % DPLinear Recalculation Bias
DPLinear (inches) 0.0
0 250
200
150
100
50
0 % 1 % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % 10 %
50 100 150 200 250
DPIV Volume %
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2) Correct the flow rate for expansion factor errors caused by using DPIV.
(See Figure K.2, “Differences Between DPIV, DPLinear and DPY Calculated from Hourly QTR Data for a Plunger Lift Production Area” and Figure K.3, “Differences Between Expansion Factor (Y) Calculated Using DPIV, DPLinear and DPY for a Plunger Lift Production Area.”)
3) Convert the flow rate into an accumulated volume for the calculation interval:
For example, a flow rate of 100,000 cubic feet per hour and a flow time of 3,240 seconds would equate to:
Figure K.2—Differences Between DPIV, DPlinear, and DPY Calculated from Hourly QTR Data for a Plunger Lift Protection Area
Corrected Flow Rate Reported Flow Rate Y(calculated using DPLinear or DPY) Y(calculated using DPIV) ---
×
=
DPIV and DPY Averages vs. DPLinear Average
DPIV and DPY (inches)
DPLinear (inches) 0.0
0 250
200
150
100
50
50 100 150 200 250
DPIV DPY
Accumulated Volume Flow Rate Flow Time
Flow Rate Interval Converted to Flow Time Units ---
×
=
100,000 3240
1 hour 60 minutes/hour× ×60 seconds/minute ---
× = 90,000 cubic feet
Copyright American Petroleum Institute Provided by IHS under license with API
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Figure K.3—Differences Between Expansion Factor (Y) Calculated Using DPIV, DPlinear, and DPY for a Plunger Lift Production Area
Volume Bias Between DP Averages Used in the Expansion Factor Calculation
Y Calculated Using DPLinear -0.60 %
0.93 0.60 %
0.20 %
0.00 %
-0.20 %
-0.40 % 0.40 %
0.94 0.95 0.96 0.97 0.98 0.99 1
DPIV instead of DPLinear DPLinear instead of DPIV
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94
[1] API Manual of Petroleum Measurement Standards (MPMS), Chapter 1, Vocabulary [2] AGA Report No. 5, Fuel Gas Energy Metering
[3] GPA Std 2261 8, Analysis for Natural Gas and Similar Gaseous Mixtures by Gas Chromatography
[4] GPA Std 2286, Tentative Method of Extended Analysis for Natural Gas and Similar Gaseous Mixtures by Temperature Programmed Gas Chromatography
[5] ISA-5.5 9, Graphic Symbols for Process Displays
8 Gas Processors Association, 6526 E. 60th Street, Tulsa, Oklahoma 74145, www.gasprocessors.com.
9 The Instrumentation, Systems, and Automation Society, 67 Alexander Drive, Research Triangle Park, North Carolina, 22709, www.isa.org.
Copyright American Petroleum Institute Provided by IHS under license with API
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