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

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Setting The Stage <ul><li>Canadian Nexen Petroleum Yemen (CNPY) </li></ul><ul><ul><li>2 Million bbls/day total fluid at 95% water cut; </li></ul></ul><ul><ul><li>Asset allocation driven by economic feasibility to produce at high water cut </li></ul></ul><ul><ul><li>Produce from most economically feasible wells </li></ul></ul><ul><ul><li>Step changes in well water cuts triggered action towards reliability of data </li></ul></ul>

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Problem Definition <ul><li>Decline - real or data issues? </li></ul><ul><ul><li>93% - 98% </li></ul></ul><ul><ul><li>1100 to 300 BOPD </li></ul></ul>

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Problem Definition <ul><li>Step changes – real or poor data </li></ul><ul><ul><li>Ruled out well factors </li></ul></ul><ul><ul><ul><li>Reservoir condition or unreliable data? </li></ul></ul></ul><ul><ul><li>Production concerns </li></ul></ul><ul><ul><ul><li>Economically feasible? </li></ul></ul></ul><ul><ul><ul><li>Efforts expended appropriately? </li></ul></ul></ul><ul><ul><ul><li>Reservoir estimates? </li></ul></ul></ul><ul><ul><li>Determined that water cut error must be less than 0.5% </li></ul></ul><ul><ul><ul><li>How to achieve this? </li></ul></ul></ul>

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Background <ul><li>BS&W or water cut </li></ul><ul><li>History (guidance) – </li></ul><ul><ul><li>American Petroleum Institute (API) Manual of Petroleum Measurement Standards (MPMS) </li></ul></ul><ul><ul><li>Alberta Energy Resources Conservation Board (ERCB), Directive 46: Production Audit Handbook </li></ul></ul>

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Background <ul><li>Guidance (ERCB) </li></ul><ul><ul><li>3 volumetric methods </li></ul></ul><ul><ul><ul><li>0 – 10% (centrifuge) </li></ul></ul></ul><ul><ul><ul><li>10% - 80% (volumetric) </li></ul></ul></ul><ul><ul><ul><li>>80% (volumetric) - Nexen Double Water Cut </li></ul></ul></ul><ul><ul><li>Now producing at higher water cut then when methods developed </li></ul></ul>

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Uncertainty <ul><li>Why is uncertainty important </li></ul><ul><ul><li>Every measurement has uncertainty –rule of measurement </li></ul></ul><ul><ul><ul><li>Impacts every person, activity and industry </li></ul></ul></ul><ul><ul><ul><li>Uncertainty/Error is a function of “calibration” </li></ul></ul></ul><ul><ul><li>Error propagates – rule of measurement </li></ul></ul><ul><ul><li>Uncertainty increases exponentially as approach detection limits – rule of measurement </li></ul></ul>

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Volumetric Method <ul><li>Error analysis of volumetric method </li></ul><ul><ul><li>Based on NXN method 214 (>80%) </li></ul></ul><ul><ul><li>Volumetric instruments, no analyst error included </li></ul></ul><ul><ul><li>Theoretical error of method > 2.0% error </li></ul></ul><ul><ul><li>New method required - volumetric method cannot meet goal </li></ul></ul>

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Gravimetric Method <ul><li>Reduce variability by optimizing methodology </li></ul><ul><ul><li>Similar procedure – volumetric interpretation to balance measurement </li></ul></ul><ul><ul><li>Efficiency of system – managing steps – automating, reducing analyst error </li></ul></ul><ul><ul><li><0.1% theoretical error </li></ul></ul><ul><ul><li>Industry reports on volumetric </li></ul></ul><ul><ul><ul><li>Conversion to volumetric via normalizing by density correction </li></ul></ul></ul><ul><ul><ul><li>Automation technologies for density measurements </li></ul></ul></ul>

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Results <ul><li>Step 1 - Method Validation - Accuracy – MCRS </li></ul><ul><ul><li>Accuracy – assessment of methods ability to produce “real” value </li></ul></ul><ul><ul><li>Surrogates created (MCRSs) </li></ul></ul><ul><ul><ul><li>5 created (85% to 99.5% water cut) </li></ul></ul></ul><ul><ul><li>Establishes method detection limit </li></ul></ul>

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Method Accuracy <ul><li>More accurate & reproducible </li></ul><ul><li>Up to >99.7% water cut (detection limit) </li></ul>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 (%)

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Results <ul><li>Step 1 - Method Validation – Accuracy </li></ul><ul><li>Step 2 – Precision/Reproducibility </li></ul><ul><ul><li>Precision – ability of method to measure same value in same sample (duplicates) </li></ul></ul><ul><ul><ul><li>Expressed as RPD(%) </li></ul></ul></ul><ul><ul><li>Method field proofed – multiple wells </li></ul></ul><ul><ul><ul><li>Four wells presented (80% to 98%) </li></ul></ul></ul>

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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

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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

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Results <ul><li>Step 1 - Method Validation – Accuracy </li></ul><ul><li>Step 2 – Precision/Reproducibility </li></ul><ul><ul><li>Method Comparison (volumetric vs. gravimetric) </li></ul></ul>

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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%

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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%

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Results <ul><li>Step 1 - Method Validation – Accuracy </li></ul><ul><li>Step 2 – Precision/Reproducibility </li></ul><ul><li>Costs of error? </li></ul>

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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

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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

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Method Validation Results <ul><li>Accuracy </li></ul><ul><ul><li>Gravimetric, five times more accurate (99.5% water cut) </li></ul></ul><ul><li>Precision – Reproducibility </li></ul><ul><ul><li>Gravimetric, six to ten times more precise (RPD up to 0.41% vs 5.81% for volumetric) </li></ul></ul><ul><ul><li>Achieved goal (<0.5%) </li></ul></ul><ul><li>Cost of error </li></ul><ul><ul><li>Volumetric error - up to $33,000/day over/under estimated production </li></ul></ul>

22.
Overall Results <ul><li>Findings </li></ul><ul><ul><li>Volumetric method reliable to 80% </li></ul></ul><ul><ul><li>>80% water cut, error propagation and uncertainty bias data – unreliable data </li></ul></ul><ul><ul><li>Gravimetric method – </li></ul></ul><ul><ul><ul><li>Accurate and precise beyond 99.7% water cut </li></ul></ul></ul><ul><ul><ul><li>Procedure error <0.5% </li></ul></ul></ul><ul><ul><li>Error represents cost </li></ul></ul><ul><ul><ul><li>Over/under estimated production </li></ul></ul></ul>

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Overall Results <ul><li>Gravimetric method </li></ul><ul><ul><li>The reliable answer at high water cut </li></ul></ul><ul><ul><li>Provides accurate measure for in-line metering/calibration/reservoir engineering </li></ul></ul><ul><ul><li>Identify real step changes in water cut – maximize well economics and field resources </li></ul></ul><ul><ul><li>CNPY implementation has resulted in improvements field wide </li></ul></ul>

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Questions Court D. Sandau, PhD, PChem Senior Chemist Chemistry Matters Email: csandau@chemistry-matters.com Web: http://www.chemistry-matters.com