MARK HAY Operations Manager, KELTON

Graduated in Electronic and Electrical Engineering Various roles have included: • Research into differential pressure generating devices at

the UK National Physical Laboratory • Measurement Consultant KELTON Engineering • Head of Allocation and Measurement for Maersk Oil

North Sea

Now responsible for the KELTON range of software products.

Comparison between using historical look-up tables vs. algorithms for crude oil volume correction factor (VCF) determination.

Study conducted by James Speight and Mark Hay of KELTON Engineering.

Recurring questions Should we use tables?

Should we interpolate between values?

How should we interpolate?

Can the value be calculated?

What are the requirements?

Volume correction Oil is sold by volume at standard conditions

Measured at different pressure and temperature

Method of correcting to standard conditions is required

It’s good to fill cars on a cold day

Tables vs. calculation

ASTM-IP Petroleum Measurement Tables Table 54

Table 6

Calculated VCF ASTM D1250, IP 200 - Report on the Development, Construction, Calculation, and Preparation of the ASTM-IP Petroleum Measurement Tables (1960)

Implemented in FLOCALC®.net

Calculation F073 - Table 54:1952

Calculation F084 - Table 6:1952

Table 54 vs. calculation

75°C 15°C -20°C 100°C

600 kg/m°

840 kg/m°

1000 kg/m°

Table 6 vs. calculation

150°F 60°F 0°F 250°F

0 °API

40 °API

1000 kg/m°

Comparison between tables and calculation Table 54

17121 Data points

Max error 0.0001 (approximately 0.01%)

1299 positive errors (approx. 1 in 13)

759 negative errors (approx. 1 in 22)

Table 6

19480 Data points

Max error 0.0001 (approximately 0.01%)

142 positive errors (approx. 1 in 140)

245 negative errors (approx. 1 in 80)

Comparison between tables and calculation

1952 Tables

250,000 punch cards

Weighing over 2 tons used in calculation and proofing

Significance of discrepancy

0.9770

0.9775

0.9780

0.9785

0.9790

0.9795

41.5 42.0 42.5 43.0 43.5 44.0

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Temperature/°C

Table 54: 1952

850 kg/m³ 855 kg/m³ 860 kg/m³ 865 kg/m³ 870 kg/m³

Significance of discrepancy

0.9765

0.9770

0.9775

0.9780

0.9785

0.9790

0.9795

41.0 41.5 42.0 42.5 43.0 43.5 44.0 44.5

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Temperature/°C

Table 54: 1952 vs. 2004

1952: 865 kg/m³ 1952: 870 kg/m³ 2004: 865 kg/m³ 2004: 870 kg/m³

Flow computer implementation Look-up tables

Tables implemented to include error

Interpolation between API or Density

Temperature rounded to nearest interval

Calculation

Interpolation not required

Which is correct?

Does it make any difference to the integrity of the measurement system?

Conclusions 1952 Tables are not 100% consistent with the calculations they are based

on.

The discrepancy is generally less than the least significant digit (0.0001).

The error is insignificant compared with uncertainty in the measurement and differences between table editions.

The method of interpolation is insignificant and will not result in a detectable bias

Recommend using the calculation as this is easier to reproduce and validate.

Thank you