Uncertainty of Coriolis-Based LACT Units

Transcription

1 Uncertainty of Coriolis-Based LACT Units A.Amin February 2015 Houston, TX

2 Content LACT unit Requirements Regulations Why Coriolis Meters? Coriolis uncertainties specifications Proposed calculation workflow formulation Shale Gas LACT case study Conclusion 2

3 Lease Automatic Custody Transfer 3 Requirements of a LACT unit Control operation of the system Accurately measure the quantity transferred Monitor the crude oil quality and prevent transfer of nonmerchantable oil Obtain a representative sample Provide facilities for periodic proving

4 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

5 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

6 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

7 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

8 Pressure Effect on Mass and Density F = q m q mt = 1 1+ P eff 100 (P f P cal ) Similar treatment for the density ρ = ρ t ρ eff P f P cal 8

9 Uncertainty Workflow Coriolis Meter Transmitters Mass Flowrate qm transmit. Fluid Density ρ transmit. Temperature Coriolis RTD Pressure Transmitter Temperature Transmitter Pressure Effect Compensation qm Pressure Effect Compensation ρ Temperature Effect Built-in coriolis tol. specs. U p U t U qm Uρ C tpl =C tl xc pl =ρ / ρ sc U wc U Prover U U Ctpl U 9

10 Uncertainty Formulation U qmt = U Base + Zero Stability Mass Flowrate F = q m q mt U F = P eff 100 F U P f U 2 qm = U 2 qmt + U F 2 q v = q m ρ U ρ = U ρt + ρ eff U Pf ρ t ρ eff (P f P cal ) q vsc = q m ρ C tl C pl U 2 qvsc = U 2 qm + U 2 ρ + U 2 Ctl 2 + U Cpl 10

11 Case Study - Shale Gas / Condensate 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) % U*(F) Pressure Effect - mass % U*(qm) Mass rate uncertainty % Base Density Accuracy Kg/m3 0.5 U*(ρ) Density uncertainty % U*(qv) Volumetric rate uncert. at LC % U*(Ctpl) Conversion factor to SC % U*(qvsc) Volumetric rate uncert. at SC % 11

12 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 Unit Summary Operating Conditions Input data and Results Summary Case Study Temperature F Maximum process temperature (95 F) Pressure psig Process pressure Flowrate bbl/d 18,000 Average flowrate (750 bbl/hr) Density (SC) kg/m API Density (LC) kg/m Computed (API 11.1) VCF % % Volume Correction Factor = CplxCtl BS&W % 0.1% Coriolis Calibration Conditions Coriolis S/N Model CMF400M Temperature F Pressure psig ΔT F ΔP psi Outputs Mass Flowrate qm Kg/d 2.160E+06 U(qm) Kg/d 3.634E+03 U*(qm) % Volume Flowrate (LC) qv bbl/d 18,000 U(qv) bbl/d U*(qv) % Volume Flowrate (SC) qvsc stb/d 17,675 U(qvsc) stb/d U*(qvsc) %