Novel Approach To High Water Cut Measurement In A Mature Oil Field Abu Dhabi SPE 2008

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Presentation on the optimization of water cut measurements for crude oil reserves in mature fields that have very high water cut values. Traditional volumetric methodologies cannot accurately measure …

Presentation on the optimization of water cut measurements for crude oil reserves in mature fields that have very high water cut values. Traditional volumetric methodologies cannot accurately measure water cut measurements when the water cut is greater than 90%. This methodology demonstrates that gravimetric techniques can be used to measure water cuts as they approach 100% to provide valid data for assessing production.

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  • 1. SPE 117354 - Novel Approach To High Water Cut Measurement In A Mature Oil Field Presented in Abu Dhabi, SPE Conference Nov 3-6, 2008 Court Sandau, PhD, P.Chem Jevins Waddell, C.E.T. Tony Berthelet P.Eng, PMP http://www.onepetro.org/mslib/servlet/onepetropreview?id=SPE-117354-MS
  • 2. Setting The Stage
    • Canadian Nexen Petroleum Yemen (CNPY)
      • 2 Million bbls/day total fluid at 95% water cut;
      • Asset allocation driven by economic feasibility to produce at high water cut
      • Produce from most economically feasible wells
      • Step changes in well water cuts triggered action towards reliability of data
  • 3. Problem Definition
    • Decline - real or data issues?
      • 93% - 98%
      • 1100 to 300 BOPD
  • 4. Problem Definition
    • Step changes – real or poor data
      • Ruled out well factors
        • Reservoir condition or unreliable data?
      • Production concerns
        • Economically feasible?
        • Efforts expended appropriately?
        • Reservoir estimates?
      • Determined that water cut error must be less than 0.5%
        • How to achieve this?
  • 5. Background
    • BS&W or water cut
    • History (guidance) –
      • American Petroleum Institute (API) Manual of Petroleum Measurement Standards (MPMS)
      • Alberta Energy Resources Conservation Board (ERCB), Directive 46: Production Audit Handbook
  • 6. Background
    • Guidance (ERCB)
      • 3 volumetric methods
        • 0 – 10% (centrifuge)
        • 10% - 80% (volumetric)
        • >80% (volumetric) - Nexen Double Water Cut
      • Now producing at higher water cut then when methods developed
  • 7. Uncertainty
    • Why is uncertainty important
      • Every measurement has uncertainty –rule of measurement
        • Impacts every person, activity and industry
        • Uncertainty/Error is a function of “calibration”
      • Error propagates – rule of measurement
      • Uncertainty increases exponentially as approach detection limits – rule of measurement
  • 8. Volumetric Method
    • Error analysis of volumetric method
      • Based on NXN method 214 (>80%)
      • Volumetric instruments, no analyst error included
      • Theoretical error of method > 2.0% error
      • New method required - volumetric method cannot meet goal
  • 9. Gravimetric Method
    • Reduce variability by optimizing methodology
      • Similar procedure – volumetric interpretation to balance measurement
      • Efficiency of system – managing steps – automating, reducing analyst error
      • <0.1% theoretical error
      • Industry reports on volumetric
        • Conversion to volumetric via normalizing by density correction
        • Automation technologies for density measurements
  • 10. Results
    • Step 1 - Method Validation - Accuracy – MCRS
      • Accuracy – assessment of methods ability to produce “real” value
      • Surrogates created (MCRSs)
        • 5 created (85% to 99.5% water cut)
      • Establishes method detection limit
  • 11. Method Accuracy
    • More accurate & reproducible
    • Up to >99.7% water cut (detection limit)
    y = 0.987 + 1.66 r 2 = 0.9996 85.0 90.0 95.0 100.0 85.0 90.0 95.0 100.0 MCRS Water Cut (%) Measured Water Cut (%)
  • 12. Results
    • Step 1 - Method Validation – Accuracy
    • Step 2 – Precision/Reproducibility
      • Precision – ability of method to measure same value in same sample (duplicates)
        • Expressed as RPD(%)
      • Method field proofed – multiple wells
        • Four wells presented (80% to 98%)
  • 13. Method Precision Measured Water - Cut (%) b) Haru 16 (5,534 bbls/day) 87.2 87.2 82.0 84.0 86.0 88.0 90.0 0.08% a) Camaal 75 (975 bbls/day) 78.5 78.2 77.0 78.0 79.0 80.0 81.0 0.41% Measured Water - Cut (%) 0.15% Gravimetric Water Cut (%) – Density Corrected Relative Percent Difference (RPD) LEGEND
  • 14. Method Precision Measured Water - Cut (%) Measured Water - Cut (%) c) Haru 18 (1,518 bbls/day) 89.5 89.7 87.0 89.0 91.0 93.0 95.0 0.14% d) Heijah 39 (14,406 bbls/day) 98.4 98.4 95.0 97.5 100.0 0.002% 0.15% Gravimetric Water Cut (%) – Density Corrected Relative Percent Difference (RPD) LEGEND
  • 15. Results
    • Step 1 - Method Validation – Accuracy
    • Step 2 – Precision/Reproducibility
      • Method Comparison (volumetric vs. gravimetric)
  • 16. Precision Comparison Measured Water - Cut (%) Measured Water - Cut (%) 0.15% Gravimetric Water Cut (%) – Density Corrected Volume Water Cut (%) Relative Percent Difference (RPD) LEGEND b) Haru 16 (5,534 bbls/day) 87.2 83.9 86.9 87.2 82.0 84.0 86.0 88.0 90.0 0.08% 3.51% a) Camaal 75 (975 bbls/day) 78.5 78.2 80.0 77.6 77.0 78.0 79.0 80.0 81.0 0.41% 3.05%
  • 17. Precision Comparison Measured Water - Cut (%) Measured Water - Cut (%) d) Heijah 39 (14,406 bbls/day) 96.2 98.5 98.4 98.4 95.0 97.5 100.0 0.002% 2.36% 0.15% Gravimetric Water Cut (%) – Density Corrected Volume Water Cut (%) Relative Percent Difference (RPD) LEGEND c) Haru 18 (1,518 bbls/day) 88.6 93.9 89.5 89.7 87.0 89.0 91.0 93.0 95.0 0.14% 5.81%
  • 18. Results
    • Step 1 - Method Validation – Accuracy
    • Step 2 – Precision/Reproducibility
    • Costs of error?
  • 19. Cost of Error Measured Water - Cut (%) Measured Water - Cut (%) b) Haru 16 (5,534 bbls/day) 87.2 83.9 86.9 87.2 82.0 84.0 86.0 88.0 90.0 0.08% $384 3.51% $16,602 a) Camaal 75 (975 bbls/day) 78.5 78.2 80.0 77.6 77.0 78.0 79.0 80.0 81.0 0.41% $312 3.05% $2,340 0.15% Gravimetric Water Cut (%) – Density Corrected Volume Water Cut (%) Relative Percent Difference (RPD) RPD Water Cut as Cost ($) – $100/bbl LEGEND $312
  • 20. Cost of Error Measured Water - Cut (%) Measured Water - Cut (%) d) Heijah 39 (14,406 bbls/day) 96.2 98.5 98.4 98.4 95.0 97.5 100.0 0.002% $31 2.36% $33,134 c) Haru 18 (1,518 bbls/day) 88.6 93.9 89.5 89.7 87.0 89.0 91.0 93.0 95.0 0.14% $188 5.81% $8,045 0.15% Gravimetric Water Cut (%) – Density Corrected Volume Water Cut (%) Relative Percent Difference (RPD) RPD Water Cut as Cost ($) – $100/bbl LEGEND $312
  • 21. Method Validation Results
    • Accuracy
      • Gravimetric, five times more accurate (99.5% water cut)
    • Precision – Reproducibility
      • Gravimetric, six to ten times more precise (RPD up to 0.41% vs 5.81% for volumetric)
      • Achieved goal (<0.5%)
    • Cost of error
      • Volumetric error - up to $33,000/day over/under estimated production
  • 22. Overall Results
    • Findings
      • Volumetric method reliable to 80%
      • >80% water cut, error propagation and uncertainty bias data – unreliable data
      • Gravimetric method –
        • Accurate and precise beyond 99.7% water cut
        • Procedure error <0.5%
      • Error represents cost
        • Over/under estimated production
  • 23. Overall Results
    • Gravimetric method
      • The reliable answer at high water cut
      • Provides accurate measure for in-line metering/calibration/reservoir engineering
      • Identify real step changes in water cut – maximize well economics and field resources
      • CNPY implementation has resulted in improvements field wide
  • 24. Questions Court D. Sandau, PhD, PChem Senior Chemist Chemistry Matters Email:  csandau@chemistry-matters.com Web:   http://www.chemistry-matters.com