SUBPRO SUBSEA PRODUCTION AND PROCESSING Analysis of Influence of Sensor Degradation on Flowrate Estimates by Virtual Flow Metering Systems PhD candidate: Timur Bikmukhametov Supervisor: Associate Professor Johannes Jäschke

Virtual Flow Metering system Mass conservation Momentum equation Energy equation

Influence of sensor degradation Heat transfer modelling It does! Topics Influence of sensor degradation Heat transfer modelling It does! Simple doesn’t mean bad

Pressure/temperature sensor degradation ± 0.1 % uncertainty ± 0.5 % uncertainty ± 1 % uncertainty

VFM software

Monte Carlo Simulations 98% confidence 40 - 130 simulations per case Simulation setup Twh, Pwh Twf, Pwf Pwh_meas = 0.99·Pwh ... 1.01·Pwh Twh_meas = 0.99·Twh ... 1.01·Twh 1 % uncertainty Monte Carlo Simulations 98% confidence 40 - 130 simulations per case Optimizer min ∑ ( 𝑋 𝑚𝑒𝑎𝑠 – 𝑋 𝑂𝐿𝐺𝐴 ) 2 𝑚 1 % uncertainty Pwf_meas = 0.99·Pwf ... 1.01·Pwf Twf_meas = 0.99·Twf ... 1.01·Twf

System Parameter Value Pwh 40 bar Pwf 160 bar Twh 57 ⁰C Twf 70 ⁰C

Standard deviation, bbl/day Pressure/temperature sensor degradation Case Mean, bbl/day Standard deviation, bbl/day 0.1% 16073 23.03 0.5% 16069 110.03 1% 16079 212.7

Standard deviation, SCM/day Pressure/temperature sensor degradation Case Mean, SCM/day Standard deviation, SCM/day 0.1% 393991 565.67 0.5% 393906 2697.26 1% 394149 5214.47

Temperature sensor failure

Temperature sensor failure Study 2 Temperature sensor failure True Twf does not change True Twf changes +5% drop - 5% drop

Standard deviation, bbl/day Temperature sensor failure, Twf does not change Case Mean, bbl/day Standard deviation, bbl/day No failure 16079.3 212.68 Sensor failure 16054.2 242.66

Temperature sensor failure, Twf changes 160 105

Heat transfer modeling 𝑄=𝑈( 𝑇 𝑓 − 𝑇 𝑎𝑚𝑏 )

Total (unique) U-value Multiple U-value method Heat transfer modeling Total (unique) U-value method Twh U1 U2 U total U3 U4 U5 Twf

+ 2𝛑𝑅𝐿 𝐾 𝑓𝑜𝑟𝑚 𝑇 𝑐𝑒𝑚 − 𝑇 𝑤𝑎𝑙𝑙 𝑇 𝐷 + 𝑄=𝑈 𝑇 𝑓 − 𝑇 𝑎𝑚𝑏 = 2𝛑𝑅𝐿 ℎ 𝑖𝑛𝑛𝑒𝑟 𝑇 𝑓 − 𝑇 𝑤𝑎𝑙𝑙 + + 2𝛑𝑅𝐿 𝐾 𝑓𝑜𝑟𝑚 𝑇 𝑐𝑒𝑚 − 𝑇 𝑤𝑎𝑙𝑙 𝑇 𝐷 + 2𝛑𝑅𝐿 𝐾 𝑖 𝑇 𝑖+1 − 𝑇 𝑖 𝑙𝑛 𝑅 𝑖 𝑅 𝑖+1

Well structure 57 ⁰C 70 ⁰C

Temperature profile

Sensitivity study m = 35 + 2; 4; 6 … kg/s T = 57; …; …; … ⁰C 𝚫𝑇 𝚫𝑚 = ?

Conclusions Sensor degradation has an impact on flowrate estimates Failure of temperature sensors makes estimates less accurate Segmented approach does not give an advantage if Twh is known Segmented approach might be better if Twh is unknown or T is measured along the wellbore

Further work Perform the analysis for different GOR values and a gas well Identify the most critical points in the system

Order of magnitude analysis

𝑈2 𝑈1 =1.5 Matching the wellhead temperature = 20 𝑊 𝑚 2 𝐾 21 𝑊 𝑚 2 𝐾 = 20 𝑊 𝑚 2 𝐾 21 𝑊 𝑚 2 𝐾 22 𝑊 𝑚 2 𝐾 𝑈2 𝑈1 =1.5 = 30 𝑊 𝑚 2 𝐾 31.5 𝑊 𝑚 2 𝐾 33 𝑊 𝑚 2 𝐾 Uunique= 24 𝑊 𝑚 2 𝐾