Selecting Seismic Attributes and Proper Display Parameters

1. Selecting Seismic Attributes and Proper Display Parameters  An abridged review of a study conducted on 3-D seismic over Sooner Field, CO By: William C. (Bill) Overman, MS Geophysicist

2. Slide 2: Sooner Field overview • Lower Cretaceous D-sand • Stratagraphic component • valley fill sand body • Structural influence critical to trap • Significant IPP for the D-J Basin W.C. Overman, MS, Geophysicist

3. Slide 3: Amplitude Seismic Attribute • Amplitude from the top of the D sand • Strong energy from the sand body • Strong energy everywhere else! • Does not discriminate prospective vs. back ground W.C. Overman, MS, Geophysicist

4. Slide 4: Peak to Trough Attribute • Anomaly only identifies south half of the sand body • Does not present additional drilling opportunities! W.C. Overman, MS, Geophysicist

5. Slide 5: Instantaneous Frequency • Crossline 82 through heart of the sand body • Flattened on top of D-sand (black line) • Base of D-sand .007 to .009 mils below (heavy red line) • Horizon picks cycle through many colors, results in “noisy” attribute maps • Frequency range 35 to 85 Hertz • Separation of D-sand top and base (isochron) very subtle • Separation of frequency bands un-mistakable W.C. Overman, MS, Geophysicist

6. Slide 6: Instantaneous Frequency • Crossline 82 through heart of the sand body • Base of D-sand .007 to .009 mils below (heavy red line) • Time picks still cycle through white to blue often, “noisy” • Frequency range 62 to 64 Hertz • All data still present but most frequencies display either white or cyan • Separation of D-sand top and base (isochron) very subtle • Downward deflection of the white band still obvious W.C. Overman, MS, Geophysicist

7. Slide 7: D-sand Isochron Map • Isochron variation from 0.007 to 0.009 • Variations mapped at below seismic sample rate • See full text for discussion • Good correlation between isochron and isopach • discriminates prospective vs. back ground • Extends prospective area to NW, along trend • Geometry still does not “look” like a sand body W.C. Overman, MS, Geophysicist

8. Slide 8: Instantaneous Frequencyfrom the Top of the D-Sand pick • Experimentation showed “best” presentation from 35 and 55 CPS • Closest agreement with isopach • Least peripheral “noise” • All frequencies still present, color for most just set to white • Good spatial correlation with isochron map W.C. Overman, MS, Geophysicist

9. Slide 9: Isochron vs. Frequency • Linear relationship of isochron (Slide 7) to frequency (Slide 8). • Lower frequencies with longer time • Higher frequencies with shorter times • Correlation supports validity of sub-sample rate isochron values W.C. Overman, MS, Geophysicist

10. Slide 10: Isochron “Sweet Spots” • Map of narrowly bounded Instantaneous Frequency (62 to 64 Hertz), 4 mils. below the top of the D-sand. • Narrow frequency range eliminates most peripheral events. • Maps within the isochron and below the “noise” of the D-sand interface (Slides 5 and 6). • “Drill the White and avoid the Cyan.” too simple? W.C. Overman, MS, Geophysicist

11. Slide 11: IPP vs. Isochron Time,there is a problem… • Tests assertions vs. real life results! • Color map of Initial Production Potential (IPP) • Green is the color of $ • 900+ BOPD NE Sec.21 • Isochron time contours • Contoured from Slide 10 W.C. Overman, MS, Geophysicist

12. Slide 12: IPP vs. Structureon the D-sand Top • D-sand top depth map, from time structure map. • Thick isochron (Slide 11) crosses 40’ low in W ½, Sec. 21. • Dry holes were drilled on well control. W.C. Overman, MS, Geophysicist

13. Conclusions: • Peak to Trough attribute could properly locate wildcat • High correlation to Instantaneous Frequency in the south • Isochron, though subtle, is a valid and useful attribute • Good visual correlation to isopach • Good numerical correlation to Instantaneous Frequency • Valid mapping at sub-seismic sample rate interval • Instantaneous Frequency “best” seismic attribute • Compact geometry • Looks like expected sand body • Excellent correlation with isopach thick • Suggests field extension along trend W.C. Overman, MS, Geophysicist

14. Conclusions: • Peripheral “noise” is reduced by: • limiting frequency display range • selecting time slice within the isochron interval • Attribute analysis is not the complete story • Geologic fundamentals are critical • Analysis driven to find attributes which reflect the known geology • Attributes would not find the best IPPs, in sands below seismic resolution. • Strong structural influence on IPPs. W.C. Overman, MS, Geophysicist

15. Conclusions: • Selection of display parameters is critical to analysis • Selection of display parameters enhances presentation • Limit display to only data values for best dynamic range • Display limits can be adjusted so as to: • increase visual contrast, • blank out visual “noise” without altering the data and/or • limit presentation to only features of interest. W.C. Overman, MS, Geophysicist

16. Acknowledgments: • Barbara, my wife, for her love and endurance! • William C. Cook, Senior Geophysicist, for helpful suggestions upon reviewing the first draft of the full paper. • Coerte Voorhies, Sr. Geologist and Account Manager, Seismic Micro Technology, Inc. for his patience with “newbee” questions and his supporting comments regarding this work. • Seismic Micro-Technology, Inc., for providing access to The Kingdom Suite of 3D seismic interpretation software, through which this study accomplished. W.C. Overman, MS, Geophysicist