Amit Suman and Tapan Mukerji 25th SCRF Annual Meeting May 9 – 11, 2012 Sensitivity Analysis of Rock Physics Parameters for Modeling Time-Lapse Seismic(4D) response of Norne Field Amit Suman and Tapan Mukerji 25th SCRF Annual Meeting May 9 – 11, 2012

Joint Inversion Loop Predicted flow and seismic response Observed flow and seismic response Model Reservoir SCRF

Δ Pressure Δ Saturation Production data at time t Motivation Dynamic modeling Δ Pressure Δ Saturation Production data at time t Rock physics modeling Velocity at time t Seismic data at time t Optimize mismatch Update parameters 3

Previous Work Last year we investigated parameter sensitivity for modeling time-lapse seismic and flow data of Norne field One of the investigated parameters was rock physics model We didn’t investigate sensitivity of varying rock physics parameters on modeling 4D response SCRF

Questions? “Should we investigate sensitive rock physics parameters in modeling 4D response?” “What are the sensitive rock physics parameters in modeling 4D response?” SCRF

Norne Field Segment E F1H E3H In this study well log data of two wells are used SCRF

Data Available Well logs (Sw, Sonic, Phi) Horizons Well data - Oil , gas and water flow rate - BHP (Bottom hole pressure) SCRF

Rock Physics Modeling Near the Well Rock Physics Reservoir K and G Well Logs K and G (All Brine) Vp and Vs (Initial) K and Phi G and Phi Sonic Sw, Phi Gassmann’s Substitution Calculate Vp and Vs (All Brine) K and G (All Brine) Facies classification K and G (at Reservoir) Populate K ,G based on Phi K : Bulk Modulus G: Shear Modulus SCRF

Facies Classification Shale Brine Sand Vp / Vs Shaly Sand Oil Sand AI Vsh SCRF

Rock Physics Modeling Near the Well Rock Physics Reservoir K and G Well Logs K and G (All Brine) Vp and Vs (Initial) K and Phi G and Phi Sonic Sw, Phi Gassmann’s Substitution Calculate Vp and Vs (All Brine) K and G (All Brine) Facies classification K and G (at Reservoir) Populate K ,G based on Phi K : Bulk Modulus G: Shear Modulus SCRF

Sensitivity Parameters in fluid substitution Clay content Salinity Gas-oil ratio (GOR) Pore pressure The sensitivity of varying above parameters to variations in Response Response: Sum of seismic P-wave velocity after fluid substitution SCRF

Experimental Design Clay content (%) 20 40 Salinity (ppm) 150000 20 40 Salinity (ppm) 150000 155000 160000  GOR 175 200 225 Pressure (Mpa) 25 27 30 SCRF

Results of fluid substitution Response Sensitivity to clay content Sensitivity to GOR Sensitivity to pore pressure Sensitivity to salinity 20 40 25 27 30 175 200 225 15000 15500 16000 Clay content and GOR are the first and second most sensitive parameters in fluid substitution

Rock Physics Modeling Near the Well Rock Physics Reservoir K and G Well Logs K and G (All Brine) Vp and Vs (Initial) K and Phi G and Phi Sonic Sw, Phi Gassmann’s Substitution Calculate Vp and Vs (All Brine) K and G (All Brine) Facies classification K and G (at Reservoir) Populate K ,G based on Phi K : Bulk Modulus G: Shear Modulus SCRF

Varying clay content and GOR (9 cases) Rock physics model Varying clay content and GOR (9 cases) SCRF

Constant cement model Clay content Cement fraction Coordination number

Fluid mixing Seismic velocities depend on fluid saturation as well as saturation scale Reservoirs with gas are very likely to show patchy behavior Sengupta ,2000 SCRF

Effective pressure model Two effective pressure models are selected for sensitivity study SCRF

Sensitivity Parameters in modeling 4D response Clay content Gas-oil ratio (GOR) Coordination number Cement fraction Effective pressure model Fluid mixing (Uniform or Patchy) The sensitivity of varying above parameters to variations in Response Response: L1 Norm of change in seismic P-wave impedance after 4 years

Effective pressure model Experimental Design Clay content (%) 20 40 GOR 175 200 225 Coordination number 5 7 9 Cement fraction (%) 1 3 Effective pressure model Model 1 Model 2 Fluid mixing Uniform Patchy Total number of cases: 324

Methodology Dynamic modeling (1997-2001) Δ Pressure Δ Saturation Rock physics modeling P-wave impedance in 1997 and 2001 Compare Difference in impedance SCRF 21

P-wave impedance change in 4 years (m/s.kg/m3) Results P-wave impedance change in 4 years (m/s.kg/m3) Clay content = 0 % Clay content = 20 % SCRF

Results Response Sensitivity to clay content Sensitivity to coordination number 20 40 5 7 9 175 200 225 1 3 Model 1 Model 2 Uniform Patchy Sensitivity to GOR Sensitivity to cement Response Sensitivity to effective pressure model Sensitivity to fluid mixing

Conclusions and Future Work Clay content is the most sensitive parameter in fluid substitution Salinity and pore pressure have a lesser impact than clay content Coordination number is the most sensitive parameter in modeling 4D response of Norne field The result of this study will be used in joint inversion of time-lapse and production data of Norne field SCRF

Acknowledgement Statoil for data Norwegian University of Science and Technology (NTNU) SCRF

Conclusions and Future Work Clay content is the most sensitive parameter in fluid substitution Salinity and pore pressure have a lesser impact than clay content Coordination number is the most sensitive parameter in modeling the time lapse seismic signature of Norne field The result of this study will be used in joint inversion of time-lapse seismic and production data of Norne field SCRF