King Field AVO Sensitivity to Reservoir Thickness and Amplitude Scaling Gregory A. Partyka and Philip J. Whitaker BP

Goal Illustrate the effect of: –thickness, –layer-stacking, and –amplitude scaling on AVO response.

Outline IntroductionIntroduction AVO Modelling Conclusions

King Field – Location

King Field – Amplitude Map mile

King Field – AVO Map Far - Near Amplitude 1 mile

129-1 Well-Log Signature 8,440 3, ,810 3, ,750 4, TVD (ft) Vs (ft/s) Vp (ft/s) Den (g/cc) 0 1 2,000 4,000 AI Den Vs Vp 40, ,000 12,000 Core Samples Xplot Porosity Water Oil Sand Shale 43ft gross gas pay fining upward sharp basal contact; gradational top Amplitude Map

085-1 Well-Log Signature 9,340 4, ,025 4, ,340 4, ,160 4, ,015 4, TVD (ft) Core Samples Xplot Porosity Water Oil Sand Shale Vs (ft/s) Vp (ft/s) Den (g/cc) 10, ,000 4,000 AI Den Vs Vp 30, ,000 12,000 80ft gross gas pay interbedded sand-shale sharp basal and top contact 85-1 Amplitude Map

Outline Introduction AVO ModellingAVO Modelling –Half-Space –Tuning and Thickness –Amplitude Scaling Conclusions

Half-Space AVO These signatures represent the individual half- space components that comprise the composite tuned reflection. Large amplitudes that increase with offset. Reflection Coefficient Angle of Incidence

AVO Modelling Half-Space Tuning and ThicknessTuning and Thickness energy, phase, and frequency slope and intercept Amplitude Scaling

Energy, Angle, and Thickness Simple reservoirs exhibit simple tuning characteristics. increasing thickness Angle of Incidence Energy Angle of Incidence Energy increasing thickness

The Tuning Curve travel-time (ms) reflection coefficients travel-time (ms) energy travel-time (ms) 200 reflectivity amplitude energy

Phase, Angle, and Thickness increasing thickness Angle of Incidence Phase increasing thickness Angle of Incidence Phase

Phase and Tuning travel-time (ms) reflection coefficients travel-time (ms) 200 phase travel-time (ms) 200 reflectivity amplitude phase

Frequency, Angle, and Thickness increasing thickness Angle of Incidence Frequency Angle of Incidence Frequency

AVO, Thickness, and Tuning AVO-Intercept Gross Reservoir Thickness (ft) EnergyVA Intercept EnergyVA Slope Gross Reservoir Thickness (ft) AVO-Slope

Thickness well-log measured thickness. seismic measured thickness. true-vertical thickness. reservoir thickness. + imaging problems imposed by structural complexity.

Thickness Considerations mt 1 mt 2 tvt 1 st 1 tvt 2 st 2 Case 1: Drilling Updip tvt 1 < mt 1 tvt 1 < st 1 Case 2: Drilling Downdip tvt 2 < mt 2 tvt 2 > st 2 reservoir thickness Where: mt = well-log measured thickness st = seismic-measured thickness tvt = true-vertical thickness

AVO and Amplitude Scaling

Amplitude Scalar EnergyVA Intercept Amplitude Scalar EnergyVA Slope using a constant 50ft thickness AVO-Intercept AVO-Slope

Outline Introduction AVO Modelling ConclusionsConclusions

Conclusions AVO attributes are sensitive to: –thickness, –reservoir layer-stacking, and –amplitude scaling.

Suggestions Reservoir-specific modelling helps interpreters unravel and understand reservoir-specific AVO behaviour. Tuning and thickness can have a large effect on AVO response. Consistent amplitude scaling is important, particularly when: –integrating multiple overlapping or time-lapse seismic volumes. –comparing real and modelled AVO gathers.

King Field – UM70 Net Pay and AVO Far-Near Amplitude Map After 7 penetrations After 2 penetrations

Acknowledgments We wish to thank BP for allowing us to present this material. BP Unix Seismic Processing (USP) Team for providing the technical framework for creative thinking, algorithm development and implementation. –See for related material.