25 – 26 February 2015 Houston, TX

Uncertainty of Coriolis-Based LACT Units

A.Amin

Content

• LACT unit – Requirements

• Regulations

• Why Coriolis Meters?

• Coriolis uncertainties specifications

• Proposed calculation workflow – formulation

• Shale Gas LACT case study

• Conclusion

2

Lease Automatic Custody Transfer

Requirements of a LACT unit – Control operation of the system

– Accurately measure the quantity transferred

– Monitor the crude oil quality and prevent transfer of non-merchantable oil

– Obtain a representative sample

– Provide facilities for periodic proving 3

Regulations

• BLM Order # 4 Oil Measurement: – Only tank gauging and PD meters are endorsed – Variance application is needed to use Coriolis – New updates to Orders# 3,4,5 (2013):

• Add Coriolis to meters list (subject to API) • Set liquid measurement uncertainty limits:

– > 10,000 bbls/month: ± 0.35% overall uncertainty – < 10,000 bbls/month: ± 1.00% overall uncertainty

• N. Dakota Industrial Commission (NDIC) – Order# 9381 (Feb 2003) approved Coriolis – Issued subsequent to API Standard: MPMS 5.6 (2002) – Order specifies equipment to use with Coriolis – Coriolis should register volumes in bbls

4

Coriolis Meters • Why Coriolis Meters?

– Multi-variable Measurement • Mass, Volume, Density, Temperature

– Accuracy • <0.15% accuracy on volume flow • High turndown ratio

– Non-intrusive measurement • No moving parts • Measures slurries • Not damaged by slugs of air • No straight pipe runs required

– Maintenance • No mechanical parts to wear • Reduced calibration

5

Coriolis Uncertainty Specifications

Mass Flowrate Uncertainty

• Base Uncertainty • Includes linearity, repeatability,

hysteresis • Specified in % mass rate (relative)

• Zero Stability • Specified in mass rate (absolute) • Important at low flow rate

• Pressure Effect • % mass rate per pressure unit • Compensation uses external pressure

transmitter

• Temperature Effect • Compensation uses internal RTD • Residual uncertainty included in Base

Liquid Density Uncertainty

• Base Uncertainty • Includes linearity, repeatability,

hysteresis • Specified in density unit (absolute)

• Pressure Effect • Specified in density per pressure unit • Compensation uses external pressure

transmitter

• Temperature Effect • Compensation uses internal RTD • Residual uncertainty included in Base

• Flow rate effect

6

Issues with Uncertainty Evaluation

• Performance specifications vary by vendor

• Additional calculation steps required to evaluate volumetric flow uncertainty:

– Pressure effect on mass rate and density

– Conversions from mass to volume at STD

• Existing flow measurement uncertainty tools:

– Require parameters not in meter specifications

– Do not include Coriolis

7

Pressure Effect on Mass and Density

• Similar treatment for the density

8

𝐹 = 𝑞𝑚

𝑞𝑚𝑡=

1

1+𝑃𝑒𝑓𝑓

100(𝑃𝑓−𝑃𝑐𝑎𝑙)

𝜌 = 𝜌𝑡 − 𝜌𝑒𝑓𝑓 𝑃𝑓−𝑃𝑐𝑎𝑙

Uncertainty Workflow Coriolis Meter

Fluid Density

ρtransmit.

Mass Flowrate

qmtransmit.

Pressure Effect

Compensation

qm

Uqm

Pressure Effect

Compensationρ

Uρ

Pressure

Transmitter

Temperature

Transmitter

TemperatureCoriolis RTD

Up

Ctpl=CtlxCpl=ρ/ ρsc

UCtplUProver

Transmitters

Uwc

Temperature Effect

Built-in coriolis

tol. specs.

Uqv @LC

Uqvsc @SC

Ut

9

Uncertainty Formulation

𝑞𝑣 = 𝑞𝑚

𝜌

𝑞𝑣𝑠𝑐 = 𝑞𝑚

𝜌 𝐶𝑡𝑙 𝐶𝑝𝑙

𝑈𝑞𝑣𝑠𝑐 ∗2 = 𝑈𝑞𝑚

∗2 + 𝑈𝜌∗2 + 𝑈𝐶𝑡𝑙

∗2 + 𝑈𝐶𝑝𝑙

∗2

𝑈𝜌∗ =

𝑈𝜌𝑡2 + 𝜌𝑒𝑓𝑓

2 𝑈𝑃𝑓

2

𝜌𝑡 − 𝜌𝑒𝑓𝑓(𝑃𝑓−𝑃𝑐𝑎𝑙)

𝑈𝑞𝑚 ∗2 = 𝑈𝑞𝒎𝒕

∗2 + 𝑈𝐹∗2

𝑈𝐹∗

= − 𝑃𝑒𝑓𝑓

100 𝐹 𝑈𝑃𝑓 𝑈𝑞𝑚𝑡

∗ = 𝑈𝐵𝑎𝑠𝑒∗ +

𝑍𝑒𝑟𝑜 𝑆𝑡𝑎𝑏𝑖𝑙𝑖𝑡𝑦

𝑀𝑎𝑠𝑠 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒

10

𝐹 = 𝑞𝑚

𝑞𝑚𝑡

Case Study - Shale Gas / Condensate

11

Base Mass Rate Accuracy

% of mass rate 0.100%

Zero Stability 40.9 kg/hr % rate 0.045%

Total intrinsic % of mass rate (per specs) 0.1450%

U*(F) Pressure Effect - mass 0.0051%

U*(qm) Mass rate uncertainty 0.1683%

Base Density Accuracy

Kg/m3 0.5

U*(ρ) Density uncertainty 0.0669%

U*(qv) Volumetric rate uncert. at LC 0.1811%

U*(Ctpl) Conversion factor to SC 0.0645%

U*(qvsc) Volumetric rate uncert. at SC 0.1922%

Conclusions

• Regulations increasing acceptance of Coriolis meter for custody transfer – updates

• Coriolis uncertainty specifications can be higher when factoring other effects/components

• Current uncertainty evaluation tools do not cover Coriolis

• A workflow is proposed to fill this gap

12

13

UNCERTAINTY EVALUATION

System LACT UnitSummary Input data and Results Summary

Operating Conditions

Case Study

Temperature ˚F 95.00 Maximum process temperature (95 ˚F)

Pressure psig 500.00 Process pressure

Flowrate bbl/d 18,000 Average flowrate (750 bbl/hr)

Density (SC) kg/m3 754.67 56 ˚API

Density (LC) kg/m3 741.04 Computed (API 11.1)

VCF % 98.194% Volume Correction Factor = CplxCtl

BS&W % 0.1%

Coriolis Calibration Conditions

Coriolis S/N

Model CMF400M

Temperature ˚F 73.00

Pressure psig 22.40

ΔT ˚F 22.00

ΔP psi 477.60

Outputs

Mass Flowrate

qm Kg/d 2.160E+06

U(qm) Kg/d 3.634E+03

U*(qm) % 0.1683

Volume Flowrate (LC)

qv bbl/d 18,000

U(qv) bbl/d 32.59

U*(qv) % 0.1811

Volume Flowrate (SC)

qvsc stb/d 17,675

U(qvsc) stb/d 33.97

U*(qvsc) % 0.19221