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Why wellbore trajectory uncertainties are not only a collision management issue!. 26th ISCWSA - SPE WP TS - Anaheim - 15/11/2007. Impact of Wellbore Trajectory uncertainties on Geosciences. Following Regis STUDER & Ludovic MACRESY Wellbore Trajectory uncertainty study. Introduction.

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Impact of Wellbore Trajectory uncertainties on Geosciences


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    1. Why wellbore trajectory uncertainties are not only a collision management issue! 26th ISCWSA - SPE WP TS - Anaheim - 15/11/2007 Impact of Wellbore Trajectory uncertainties on Geosciences Following Regis STUDER & Ludovic MACRESYWellbore Trajectory uncertainty study Philippe SAMSON & Jesse CLARK - GSR/TG/COP

    2. Introduction • Geosciences & Drilling are dealing with Uncertainties • Done independently - No integration • Geosciences consider a wellbore trajectory as a data • Question raised:Impact of wellbore trajectory error models on reserves?Question not addressed so far… (!?) • Study: An Early Quantitative Analysis • Focus on one well • 1/ Error models: display & analysis • 2/ Well Placement consequences • 3/ Geometrical impact on Reservoir Model • 4/ Well Correlation: consider 2 wells • Way Forward - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    3. Error Models Notion of Wellbore Trajectory Error Model Envelope Survey = { MD, AZI, INC } Uncertainties Bias Corrections Global Sag Trajectory from Raw Surveys Residual Sag: No Sag Correction TrajectoriesIFR corrected ISCWSA modelby DD contractor Sag corrected by DD Sag corrected by DSN ISCWSA model DSN by TOTAL & DrillScan) BHA Sag Managementby TOTAL & DrillScan As a first approximation: IFR = Lateral Displacement SAG = Vertical Displacement Rk: Ellipsoids are residual uncertainties after Azimuth correction (IFR) Ellipsoid - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    4. Error Models Along Hole Lateral High Side Along Hole Bias & Uncertainty 3σ @ MD=7594m (survey point near TD) Raw Survey +IFR MD = 7594 m Inc = 86.56° Azim = xxx° TVDSS = xxx m Raw Trajectory Global(no Sag correction) High Side DD(ISCWSA Sag correction) - Directional Drilling Company DSN(ISCWSA Sag correction) -TOTAL & DrillScan BHA Sag Management - TOTAL & DrillScan Lateral Ellipsoid 3σ Drilling direction Drilling direction - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    5. Error Models Bias & Uncertainty 3σ @ MD=1340m Raw Survey +IFR Envelope MD = 1340 m Inc = 27.24° Azim = xxx° TVDSS = xxx m High Side Raw Trajectory Lateral Global (no Sag correction) Distorted DD (ISCWSA Sag correction)Directional Drilling Company DSN(ISCWSA Sag correction)TOTAL & DrillScan Along Hole 3σ BHA Sag ManagementTOTAL & DrillScan Drilling direction Ellipsoid Drilling direction Lateral Distorted Drilling direction High Side 3σ Along Hole - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    6. Error Models Survey Ellipsoids along wellbore Ellipsoid Raw Trajectory Global (no Sag correction) DD ISCWSA Sag Correction DSN ISCWSA Sag Correction(TOTAL & DrillScan) BHA Sag Management(TOTAL & DrillScan) 3σ 3σ Ellipsoid 3σ Ellipsoid - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    7. Well Placement Error Model: Order of Magnitude • Vertical Bias & Uncertainty values along wellbore Same IFR correction ISCWSA • @ TD: Vertical Distance to OWC • Horizontal Drain:Early WaterBreakthroughgeometricalexplanation? 2σ OWC - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    8. Well Placement Well Trajectory Uncertainties vs Well Placement Borehole Envelop • A unique wellbore trajectory certified by Drilling • Consistent processing for all wells • Systematic display of wellbore trajectory uncertainties within Geosciences Modeling Chain 2σ Well Trajectory vs Horizons Ellipsoids along Borehole 2σ Well Trajectory vs Faults 2σ & 3σ - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    9. Reservoir Model Well Trajectory Uncertainties vs Reservoir Model • A first Quick Look evaluation • Shortcuts: • Consider only vertical component of the uncertainties • Mono-well analysis • Only Top Reservoir uncertainty (no uncertainty on thickness) • No uncertainty on OWC (as well does not touch contact) • Method (using Jacta): Impact on Net Rock Volume • Correction of Bias • Multiple realizations within uncertainty range • 3 scenarii: • Global Shift(Constant uncertainty map, full field homogeneous impact) • Fault Block(Ramp & flat uncertainty map, proportional shift or simulation) • Local(Gaussian bias & uncertainty & shift) Global Shift Fault Block Local - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    10. Reservoir Model Net Rock Volume – Global Shift • Bias & Uncertainty Impacts • Note • The impact of bias (mean of histogram shifted) • The impact of uncertainties (histogram spreading) Global DD DSN BHA Q90 Net Rock Volume Distribution – Full Field Q50 Q10 Net Rock Volume – Full Field - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    11. Reservoir Model Net Rock Volume – Fault Block Part of the Fault Block • Bias & Uncertainty Impacts Well Net Rock Volume – Fault Block Part – P-Field 3000m Even if spatially limitedBias & Uncertainties still have asignificant impact on volumetrics uncertainty range Q90 ramp well1 well-refno uncertainty Impact of simulation method Q50 Shift Q10 P-Field NRV– P-Fields vs Shift - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    12. Reservoir Model Net Rock Volume - Local • Bias & Uncertainties Normal draw 3σ 500m (3σ) Volume computedin white region 500m=3σ Gaussian for bias, uncertainty map & draw! • Global or Local ? Still significant - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    13. Correlation Error Model: Well Correlation - TVD Well2 Well1 • Well1 vs Well2 @ a given TVD(vertical bias & uncertainty @ top reservoir) + + Q90 Possible apparent depth difference for the same actual TVD Q10 apparent TVD (m) • Muti-well correlation: OWC, Pressure trends Risk of field over compartmentalization? - Philippe SAMSON & Jesse CLARK – GSR/TG/COP

    14. Conclusion & Way Forward • Conclusion: • Early Analysis, focused on 1 well & vertical component • Show clear impact on Well Placement (Design, Geosteering & Post-Mortem) • Wellbore Trajectory Uncertainty is not only a Collision Management IssueImpacts Geosciences • Generalize Wellbore Trajectory Uncertainty Display in Geosciences software (3D Modeling…) • WellBore Trajectory to provided standard with related uncertainties • Way Forward: • Full field Analysis needed • Include lateral uncertainties (Faults, Sand bodies ex: deep offshore turbidite, channels …) • Need for Transverse actions: • Monte Carlo simulation of possible Trajectory (dependence between wells …) • Well Design combining both Drilling & Geosciences uncertainties to define realistic Targets • Geosciences to include wellbore trajectory in Uncertainty Workflow • At uncertainty quantification stage (ex: uncertainty on time to depth conversion ? …) • In the Monte Carlo Loop • Depth Reconciliation: Multiple MDs • MWD • Logs:  LWD  Wireline  Pipe Conveyed  Mud Logging • Static (WFT, side wall coring, NMR, …) or Log up (conventional logs) - Philippe SAMSON & Jesse CLARK – GSR/TG/COP