Application of Metering Process in Oil and Gas Production in Niger Delta Fields
Application of Metering Process in Oil and Gas Production in Niger Delta Fields
Application of Metering Process in Oil and Gas Production in Niger Delta Fields
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Baridor Odagme
Federal University Otuoke
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ABSTRACT
The role of oil and gas metering cannot be over emphasized, as it informs the operators of the actual production rates
and allows reservoir engineers to predict well depletion and better control for long term production rates. Despite the
importance of flow meters in the operation of oil and gas in the Niger Delta region. Many flow meters were installed
without proper documentation, maintenance and regular calibration schedules. The recent growth in production cost
and continuous fluctuation in crude oil prices calls for concern to improving fluid flow rate metering by the oil and
gas producing, processing, and production companies. A good metering will enhance flow metering accuracy,
precision and better verification exercise. In this paper, a study on meter proving and calibration was carried out.
Equipments, procedures and precautions that will ensure accurate metering of fluids were considered. The results
from the case study showed that improved metering systems would solve the problem of accuracy and precision. It
was also found that poor metering could lead to losses of products and also resulted in over payment when the meter
reads abnormally high. The result strongly indicates that regular recalibration and check up of meters would improve
metering. Also, improved techniques were developed to avoid undue error readings in crude oil metering.
INTRODUCTION
Flow measurement technology is an economical means to obtain primary information necessary to generate an
invoice for billing purposes and to control or indicate process condition. The business of oil and gas encompasses a
large variety of activities ranging from exploration, production and transportation to terminals, refineries and
distribution of finished products to ultimate consumers. Although, well testing provides the volumetric rate
measurement of produced wellbore fluids, with the metering devices placed downstream of the gas and the liquid
separating vessel in multiphase flow (Angelson et al., 1989). Regular calibration of the custody transfer meter is a
standard practice and the metering accuracy is aided by the nature of the sales product. Metering also provides
instantaneous values thus dose the calculations required indication and also display of flow rate and volume.
Dynamic volumes correction can also be achieved thus temperature measurement are readily simplified and online
product are sampled effectively. Metering systems play important roles in the production and transportation of
produced oil, gas and water. There exist latent errors in production metering operations, these systematic errors
which occur in the operation of these field led to losses that have great economic effect (Steven, 2008).
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Ind. J. Sci. Res. and Tech. 2015 3(6):1-6/Oriji & Odagme ISSN:-2321-9262 (Online)
Online Available at: http://www.indjsrt.com
Research Article
recorded. The sphere was lightly greased and installed into the meter prover as well. Accurate thermometers of
suitable range and resolution were installed into the meter prover inlet and outlet thermo wells.
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Ind. J. Sci. Res. and Tech. 2015 3(6):1-6/Oriji & Odagme ISSN:-2321-9262 (Online)
Online Available at: http://www.indjsrt.com
Research Article
The system was filled with fresh water. The system was pressurized and checked for leakages. The sealing integrity
of the four way outlet valve was tested to ensure no leakages in both directions. The vent and drain valves were
tested to ensure that they are drain free. Vents at high positions were freed of signs of air and the sphere was then
lunched from one end of the meter prover by the use of the four way valve and circulated through the loop at several
times and during this time, venting continued until the system was completely free of air.. As the sphere actuates, the
meter pulse counter was gated and the pulse was counted from the meter pulse generator. During the passage of the
sphere between detectors, the pressure and temperature of the meter prover and master meter are observed and
recorded.
Effective Meter Proving/Linearity Checks
The meter proving/linearity checks of production or custody transfer is carried out in this order:
1. Visually inspect all the inlet and outlet valves of the meter.
2. Ensure that the pressured indicators, transmitters and temperature indicators are well calibrated.
3. Clean the strainer at the inlet of the meter.
4. Proving shall commence after liquid flow through the meter has stabilized.
5. From the proving report the meter k-factor or the meter factor is calculated.
6. The meter performance curve/linearity curve is plotted using the K factor or meter factor obtained.
7. The meter proving shall be witnessed by DPR official and clients representative.
Meter Factor Calculation
Using the temperature and pressure readings compute the correction meters for both meters. The steps taken include:
1. Calculate and use meter factors to correct the master meter and on line meter registrations
2. Arrange the factors in a set sequence, CTS, CPS, CTL, CPL, CSW;
3. Multiply them out, rounding up to four places of decimal to obtain the combined correction factor (CCF) which
should be used in correcting the volume.
4. Obtain the meter factor (MF).
MF = (corrected master meter volume / corrected online meter volume) at meter case pressure
The principal correction factors involved in the meter factor calculation are all dimensionless and they include; CTS,
CPS, CTL and CPL and are calculated using Equation 1, 2 and 3
CTS = 1 + (T - 60) * Y (1).
CPS = 1 + (PD/Et) (2)
CPL = 1/{ 1- (P - Pe) F }. (3)
It is important to note that the internal pressure of the prover is obtained from the gauges of the prover inlet and
outlet. Comparing the new established and the previous volume, there was an increase in volume of 0.0094%.Table
3A shows a report revealing the performance characteristics of the PD meters used for crude oil metering at a
company flow station. The meter proving exercise was carried out at various flow rates.
Shortcomings in Oil and Gas Metering
Shortcoming in Oil and Gas metering can be classified into three such as Error, Equipment/ installation problem and
Metering Problem.
Error
The Primary sources of error in crude oil measurement include
a. Volume measurement
b. Basic Sediment and water (BS&W)
c. Temperature rise
Errors in metering are usually due to ignorance on the part of the calibration personnel or lack of awareness on the
proper procedures and precautions required for proper execution of these precision operations.
Equipment Problems
I. Faulty equipment or none installation of vital subroutine equipment is a major issue. Poor installation procedure
and over used meter leads to error reading
2. Equipment calibration status.
3. Wrong installation of equipment:
4. Location of meter on the Test separator relative to liquid head.
5. Connection of pressure tubing from orifice meter to pressure chart recorder.
Metering Problems
a. None consideration of meter linearity and application erroneous meter factor.
b. Applying meter factors not established using the actual operating liquid.
c. Use of false meter K factors.
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Ind. J. Sci. Res. and Tech. 2015 3(6):1-6/Oriji & Odagme ISSN:-2321-9262 (Online)
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Research Article
Tables 1: The raw data and calculations made at the meter factors using the master meter method
METER TYPE/MODIE G6-57
METER S/N BB01022400
METER TAG METER 1
LIQUID TYPE CRUDE OIL
GRAVITY @ TEMP 0.9070@116 OF
O
GRAVITY @ 60 F 0.9273
APL @ 60 21
TEST NO A
STATION 1
No. of METER UNDER TEST
Run Metered Volume Temp Pressure CTL CPl CCF Government Volume
(bbl) (0F) (psi) (m) (m) (m) (bbl)
1 20.00 117.0 275 0.9772 1.00132 0.97849 19.37
2 20.00 117.0 280 0.9772 1.00134 0.997850 19.57
3 20.00 117.0 280 0.9772 1.00134 0.985669 19.71
1 20.00 117.0 300 0.9772 1.00144 0 1957
2 20.00 117.0 290 0.9772 1.00139 0.978558 19.57
3 20.00 117.0 290 0.9772 1.00139 0.978558 19.57
1 20.00 117.0 275 0.9772 .00132 0.97849 19.37
2 20.00 117.0 280 0.9772 1.00134 0.997850 19.57
3 20.00 117.0 280 0.9772 1.00134 0.985669 19.71
1 20.00 117.0 300 0.9772 1.00144 0 1957
2 20.00 117.0 290 0.9772 1.00139 0.978558 19.57
3 20.00 117.0 290 0.9772 1.00139 0.978558 19.57
1 20.00 117.0 300 0.9772 1.00144 0.978607 1957
2 20.00 117.0 335 0.9772 1.00160 0.978764 19.58
3 20.00 116.5 340 0.9774 1.00162 0.978983 19.58
1 20.00 117.0 300 0.9772 1.00144 0.978607 19.57
2 20.00 116.0 295 0.9776 1.00141 0.978978 19.51
3 20.00 116.0 290 0.9776 1.00139 0.984001 19.57
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Ind. J. Sci. Res. and Tech. 2015 3(6):1-6/Oriji & Odagme ISSN:-2321-9262 (Online)
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Research Article
This is in line with recommended standards (DPR, API). Repeatability is the probability of a meter registering the
same value given the same operating conditions. Repeatability is used to measure the reliability of meters during a
proving operation; a higher value indicates that meter repeatability is questionable. Particularly if repeatability is
below 0.02%, since a master meter is usually used as a reference to calibrate all other meters and it follows that if
the master meter is not reliable then the accuracy of the meter to be calibrated would be questionable.However,
when the operating temperature is higher than the initial temperature (E.g. when the loop is fabricated and calibrated
in cold region) reduction in the volume of the active prover loop is expected or noticed. There was a significant
increase in base prover volume from 5.343 to 5.3435, representing a gain in volume of 0.0094% (see Table 3-4 and
Fig. 1 and Fig. 3).This implies a corresponding increase in meter factor by 0.0094% for all meters proved using the
prover loop. This reflects the earlier submission that if the prover loop is not calibrated over a period of say 7 years
or more years, the volume difference will increase. However, in handling the shortcoming arising from Meter
Factors, the following recommendations were found to be profitable in mitigating problems of meter factors.
Ensure that CTL, CPL, CTS, and CPS are validated
Compare series of meter factors (i.e. series 1/series 2).
Proving operation should not exceed ±0.005. Above this limits proving is unsuccessful.
An initial meter factor should be established for the meter before it is put back into use.
The difference between the meter factors obtained for any two successive proving for a meter should not exceed
±0.0025.
CONCLUSION
The shortcomings in oil and gas metering have been identified and solutions recommended. It was found that meter
Linearity curves and tables which are key factors in obtaining accurate oil and gas metering were not established for
each meter in Nigeria. Where a linearity proving is done, it was found that operators do not apply it in daily
production accounting. Furthermore, most meters do not have quality control charts to monitor meter performance
and determine when the meter is due for maintenance. Moreover, Meters are hardly proved. Operating control and
royalty meters are never proved and in calculating meter factors, optimum or mean k-factors are used. The Fiscal
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Ind. J. Sci. Res. and Tech. 2015 3(6):1-6/Oriji & Odagme ISSN:-2321-9262 (Online)
Online Available at: http://www.indjsrt.com
Research Article
instruments are not installed and used in metering except at custody transfer points. Using the meter factors to
correct production from the station, there will be an increase in daily prediction by about 15.59% for meter 1, 3.27%
to 18.99% for meter 2 and 8.35% of 16.83% for meter 3. However, the percentage linearity of the meters 1, 2 and 3
were 6.51%, 7.07% and 3.77% respectively showing the possible error that can be incurred when applying the mean
meter factors in production as practiced by most companies. Also, it was observed that the meter factor band was too
wide: as meter 1 gave 0.1419, meter 2 was 10.1572 and 0.0848 for meter 3, compared to those of master meter
calibration (Table 4). Therefore, the proving conditions for a meter should correspond or be equal to the operating
conditions. This will reduce error and enhance the life of the meters. Secondly regular calibration and maintenance
can improve the efficiency and accuracy of meters. Most importantly, proper installation and fit for purpose
principle is key to overcoming the challenges of metering.
Nomenclature
CTL = Correction factor of the effect of temperature on liquid
(CPL) = The correction factor of the effect of pressure on the liquid
P = Internal pressure in psig
D = Internal diameter in inches of water.
E = Modulus of elasticity for container material.
t = Wall thickness of container in inches
Pe = equilibrium vapor pressure at temperature (in psig), for high density liquids.
Pe < atmospheric pressure, Pe = 0, psig.
F = Compressibility factor API. Standard 1101.
T = Temperature in degrees Fahrenheit of the steel walls.
CTS = Correction factor for the effect of temperature on steel of the Prover
Y = Coefficient of cubical expansion per degrees Fahrenheit of the steel (mild steel or stainless steel)
CPS = Correction factor for the effect of Pressure on the steel of the Prover.
REFERENCES
Angelson S, Kvernvold O, Linglem M & Oslen S (1989). Long Distance Transport of Unprocessed Hydrocarbon:
Sand Settling in Multiphase Flow lines. Proceedings of 4th International Conference on Multi-Phase Flow, BHRA,
Nice, France.
APl (1991). Recommended practices for the Design and Installation of Offshore production platform Piping
Systems. APl RP 14E, American Petroleum Institute, Fifth Edition, Washington DC.
Bratli RK, Dusseault MB, Santarelli FJ & Tronvoll J (2000). sand management protocol increases production
rate, reduces completion costs. Proceedings Trinidad and Tobago Biennial SPE Conference, Port-of-Spain.
Steven R (2008). Diagnostic Methodologies for Generic Differential Pressure Flow Meters. North Sea Flow
Measurement Workshop St Andrews, Scotland, UK.