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Signal Estimation Technology Inc. Porosity or Sidelobes? An Application of Robust Multichannel Inversion Maher S. Maklad et al. Presented at the 1993 CSEG.

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Presentation on theme: "Signal Estimation Technology Inc. Porosity or Sidelobes? An Application of Robust Multichannel Inversion Maher S. Maklad et al. Presented at the 1993 CSEG."— Presentation transcript:

1 Signal Estimation Technology Inc. Porosity or Sidelobes? An Application of Robust Multichannel Inversion Maher S. Maklad et al. Presented at the 1993 CSEG Meeting.

2 Signal Estimation Technology Inc. Overview Introduce the play Introduce the play Problem statement Problem statement Data preparation Data preparation Summary of Robust Multichannel Inversion (Reflect) Summary of Robust Multichannel Inversion (Reflect) Results Results Conclusion Conclusion

3 Signal Estimation Technology Inc. Introduction Inversion can provide a fairly confident and reliable mapping of the reservoir before the drilling program commences, and can be a valuable aid to maximum exploitation of the reservoir. It allow the physical characteristics of a reservoir to be defined with satisfactory precision prior to drilling, enabling engineers and geologists to anticipate results, not only outlining the reservoir limits, in order to avoid dry holes, but also enabling optimum well placement to take advantage of the best porosity and reservoir thickness. This is particularly advantageous for offshore discoveries, where a large and very expensive platform must be located before development drilling can commence. Inversion can provide a fairly confident and reliable mapping of the reservoir before the drilling program commences, and can be a valuable aid to maximum exploitation of the reservoir. It allow the physical characteristics of a reservoir to be defined with satisfactory precision prior to drilling, enabling engineers and geologists to anticipate results, not only outlining the reservoir limits, in order to avoid dry holes, but also enabling optimum well placement to take advantage of the best porosity and reservoir thickness. This is particularly advantageous for offshore discoveries, where a large and very expensive platform must be located before development drilling can commence.

4 Signal Estimation Technology Inc. Play Concept Granite Wash (GW) sandstone play in Northern Alberta Granite Wash (GW) sandstone play in Northern Alberta Clastic Sand Reservoir overlying basement Clastic Sand Reservoir overlying basement Light oil, structurally trapped by Horst blocks Light oil, structurally trapped by Horst blocks Granite Wash is a Devonian clastic oil reservoir in Northern Alberta. The Granite Wash zone is composed of inter-bedded sandstones, saltstones and shales with minor amounts of dolostone and anhydrite. In this area, we have light oil in the Granite Wash structurally trapped on Horst blocks. The paleotopography on the Precambrian erosional surface is extremely irregular throughout Northern Alberta. Exploration for hydrocarbon pools associated with these basement highs is therefore seismically intensive. There is significant risk in this play, particularly in situations where the Granite wash section may be missing due to non deposition or erosion over highs on the precamberian surface and wells are drilled on the flanks of highs in structurally low positions such that they encounter water bearing sandstone.

5 Signal Estimation Technology Inc. Oil water Granite Wash Sandstone Beds Precambrian Basement Granite Wash Sandstone Beds Precambrian Basement water Oil Schematic models of Granite Wash

6 Signal Estimation Technology Inc. Schematic models of Granite Wash Schematic models of Granite Wash zone traps, illustrating the various relationships between the Granite Wash sandstone and the underlying structure on the Precambrian basement. This particular basement high extends about one mile across. The distribution of the Granite Wash was strongly influenced by the paleotopography on the Precambrian surface. In some pools the reservoir sandstone laps out against the flank of a Precambrian high and dips away from it due to differential compaction. In other areas the sandstone is continuous over positive features on the basement and the traps are closures formed by differential compaction. The above two trap types are schematically illustrated in the previous slide. Schematic models of Granite Wash zone traps, illustrating the various relationships between the Granite Wash sandstone and the underlying structure on the Precambrian basement. This particular basement high extends about one mile across. The distribution of the Granite Wash was strongly influenced by the paleotopography on the Precambrian surface. In some pools the reservoir sandstone laps out against the flank of a Precambrian high and dips away from it due to differential compaction. In other areas the sandstone is continuous over positive features on the basement and the traps are closures formed by differential compaction. The above two trap types are schematically illustrated in the previous slide.

7 Signal Estimation Technology Inc. Interpretation Method Slave Point-basement isochron for structural mapping Slave Point-basement isochron for structural mapping Character mapping to delineate reservoir interval (though above basement peak) Character mapping to delineate reservoir interval (though above basement peak) The time interval Slave Point to Precambrian is significant in delineating the structural and stratigraphic configuration of the reservoir type oil traps. It decreases as the Granite wash section thins. An important criterion for the prediction of Granite Wash is to look for a combination of two events, high amplitude trough (anhydrite-sand) over high amplitude Precambrian peak.

8 Signal Estimation Technology Inc. Problems Pick basement event accurately Pick basement event accurately Identify Granite Wash interval and resolve tuning with basement Identify Granite Wash interval and resolve tuning with basement Data is poor to fair quality and noise filtering removes subtle character changes Data is poor to fair quality and noise filtering removes subtle character changes These events (high amplitude trough over high amplitude peak) are often obscured by multiple energy. A loss in amplitude is observed when the Granite Wash section is missing and the high velocity muskeg formation evaporates directly overlie the high velocity Precambrian basement. As the Granite Wash section thins, both the trough and underlying peak weaken in amplitude. Sometimes a zone of low velocity, weathered Precambrian section located between the Muskeg and the unweathered Precambrian basement can cause similar character (high amplitude trough over high amplitude peak).

9 Signal Estimation Technology Inc. Approach Use Resolve to improve seismic resolution and SNR Use Resolve to improve seismic resolution and SNR Use Robust Multichannel Inversion (ROBIN) to resolve the events of interest from the noisy data Use Robust Multichannel Inversion (ROBIN) to resolve the events of interest from the noisy data Reflect uses an input wavelet to reduce a stacked seismic section into a reflectivity section with the locations and amplitudes of the spikes optimally selected to minimize the number of bits required to describe the error and the resulting synthetic model. In order to ensure the robustness of the spike location detection under noisy and band limited wavelet conditions, Reflect uses a multichannel detection scheme. This ensures the continuity of the detected events and guards against detecting false events.

10 Signal Estimation Technology Inc. Processing Sequence Stacked Seismic Data Dephasing Robust Multichannel Inversion SNR Estimation & Decon of Noisy Data Wavelet Estimation Reflectivity & Pseudo-impedanceSection

11 Signal Estimation Technology Inc. Original Data Basement Slave Point

12 Signal Estimation Technology Inc. Phase Correction: Synthetics, Seismic, and Error Seismic LEFTSyntheticSeismic RIGHTReflectivity Current Impedance Original Impedance

13 Signal Estimation Technology Inc. Phase Correction: Wavelet Estimation Using Well Control

14 Signal Estimation Technology Inc. Event Detection By Addition and Deletion Input Trace & True R.C.’s Add Best Single Spike Add Best 2nd Spike & Check Significance Add Best 3rd Spike & Check Significance Delete Insignificant Spike Add Best New 3rd Spike

15 Signal Estimation Technology Inc. Multichannel Weighing For Continuity Weighting Function Central Trace Candidate Event Position

16 Signal Estimation Technology Inc. Rotated Data Slave Point Basement

17 Signal Estimation Technology Inc. Bandwidth Analysis Power Spectrum After DECON SNR Spectrum After Decon

18 Signal Estimation Technology Inc. Rotated Data After Resolve Slave Point Basement

19 Signal Estimation Technology Inc. Estimated Wavelet At Location Of Interest (Using Seismic Only) Truncated Wavelet Power Spectrum Cepstrum Computed Wavelet

20 Signal Estimation Technology Inc. Estimated Reflectivity Slave Point Basement

21 Signal Estimation Technology Inc. Estimated reflectivity and pseudo-impedance wavelet phase -zero Slave Point Basement

22 Signal Estimation Technology Inc. Results The salt bearing zone (Muskeg), Granite Wash interval and basement are all detected in inversion with excellent lateral continuity. The slave point, Watt Mountain and Muskeg events have improved in continuity. This result can be used to calculate accurate Slave Point - Basement isochrones and to detect the Granite Wash interval.

23 Signal Estimation Technology Inc. Conclusions Reflect is effective on noisy data Reflect is effective on noisy data Reflect proved useful for exploratory drilling: Reflect proved useful for exploratory drilling: –Accurate basement pickup –Identification of Granite Wash interval.


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