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Quantifying Seismic Reflectivity

A Second Look at the Fluid Factor. Based on UH Dissertation by Dr. Jenny Zhou – Former AGL RA. Quantifying Seismic Reflectivity. Fred Hilterman Distinguished Research Professor – University of Houston Chief Scientist – Geokinetics Data Processing and Interpretation April 28, 2010.

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Quantifying Seismic Reflectivity

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  1. A Second Look at the Fluid Factor Based on UH Dissertation by Dr. Jenny Zhou – Former AGL RA QuantifyingSeismicReflectivity Fred Hilterman Distinguished Research Professor – University of Houston Chief Scientist – Geokinetics Data Processing and Interpretation April 28, 2010

  2. Birth of Fluid Factor George Smith & Maurice Gidlow South Africa - 1986

  3. Smith and Gidlow; Fatti et al. Generate NIP and NIS from AVO inversion RC()  NIP/cos2() – 2 NIS sin2() NIP = P-wave normal incidence NIS = S-wave normal incidence Fluid Factor Review Class 1 AVO 2.9 Stack 3.0

  4. NIS NIP Fluid Factor: F = NIP -  NIS Fluid Factor Review Class 1 AVO 2.9 Stack 3.0 2.9 NIP 3.0 Brine saturated: F = 0 Gas Saturated: F = NIPGAS- NIPWET 2.9 NIS 3.0

  5. Can F discriminate oil from gas ? Fluid Factor Review 2.9 Stack 3.0 2.9 Gas Oil NIP - 0.56 NIS 3.0

  6. Calibrating Fluid Factor to Well-Log Data

  7. Regression Equations NIOIL = -0.052 + 1.09 NIWET R2 = .94 NIGAS = -0.088 + 1.14 NIWET R2 = .83 NIOIL - 1.09 NIWET = - 0.052 NIGAS - 1.14 NIWET = - 0.088 Fluid Factor from Normal Incidence 151 wells from South Marsh Island (NIGAS-NIWET) Wet Oil Gas NIHYDROCARBON-NIWET Fluid Factor NI varies significantly for gas- and brine-saturated sand… but (NIGAS-NIWET) changes little. Reservoir porosity: 10-33 % Encasing shale: 2600-4200 m/s How is Fluid Factor extracted from seismic data?

  8. Based on horizon pore-fluid projection F(t) ≡ NIP(t) – 0.72 NIS(t) + 0.03 therefore … E{FWET} = 0 Gas Oil Wet Linear Equation NIP=0.72NIS-0.03 Wet Oil Gas Fluid Factor = NIP - 0.072NIS + 0.03 Fluid Factor from NIP & NIS F(t) ≡ NIP(t) - NIS(t) (Smith and Gidlow) F  0 In wet zones F  (NIP,GAS-NIP,WET) At top of reservoir 151 wells in South Marsh Island

  9. Unique Properties of Fluid Factor

  10. R R R S S S Shale Shale Gas Sand Gas Sand Wet Sand Wet Sand NIGAS NIWET F  - NIGWC (AIWET SAND–AIGAS SAND) (AIWET SAND+AIGAS SAND) NIGWC = Fluid Factor: Boundary or Layer Property? NIGAS – NIWET = F - -  F relates to gas/water contact -NIGWC … not encasing shale.

  11. Fluid Factor: 9-m Wet Thin Bed VP = 2280 m/s VP = 2280 m/s VP= 2250 m/s VP = 3600 m/s VP = 3490 m/s VP = 2280 m/s NIP NIS F Seismic Section: Fluid Factor = NIP – 0.55 NIS

  12. Fluid Factor: 9-m Gas Thin Bed Two-way time Two-way time 11.1 ms 5.3 ms F Seismic Section: Fluid Factor = NIP – 0.55 NIS 109% increase in two-way time VP = 2280 m/s VP = 2280 m/s VP= 1628 m/s VP = 3370 m/s VP = 3490 m/s VP = 2280 m/s NIP NIS Approximately 109% increase in amplitude

  13. Thin Bed: Fluid Factor vs. NI Fluid Factor Wet ……..… F = 0 * 2 t/T Oil, Fizz…… F = -.058 * 2 t/T Gas ……….. F = -.088 * 2 t/T Normal-Incident Reflectivity NI = f( VP1, VP2, Rho1, Rho2) * 2 t/T t = thin-bed traveltime T = wavelet period • Fluid factor independent: • shale properties • reservoir porosity • upper shale lower shale

  14. Field Data

  15. Oil Gas 1 s 2 s -3000 m 3 s 7.5 km GOM Oil and Gas Reservoir Reservoir exhibits fault shadow velocity anomaly Well Production: Early 1970s Seismic Data: 1996 as OBS Seismic Processing: 2008 Seismic data from Fairfield Industry, Inc.

  16. Producing oil well Abandoned oil well Producing gas well AVO Inversion –NIP & NIS Seismic NIP Seismic NIS 400 1500 WET WET 4.2 miles 0 -200 -1500 -800 Fault Fault 4.6 miles Zhou 2009

  17. Producing oil well Abandoned oil well Producing gas well Fluid-Factor Projection Line Calibrated Fluid Factor NIP(2)=0.3266 NIS(2)+0.0022 R2=0.8408 NIP = 0.33 NIS + .002 R2 = 0.84 0.02 0 Calibrated NIP -0.04 Fault Wet area Whole survey -0.08 Fluid Factor = NIP -.33 NIS - .002 Calibrated NIS Zhou 2009

  18. Fluid Factor Prediction of Pore Fluid Depth Contours Wet sand - 0.02 2 3 Oil sand 4 1 6 5 - 0.066 7 9900 10 9 Fault Gas sand 8 Fluid Factor Producing oil well Abandoned oil well Producing gas well 3 producing wells correctly located Gas zone correctly located Gas and oil zones generally tie depth contours Calibrated fluid factor is an accurate pore-fluid discriminator. Zhou 2009

  19. Summary: Fluid-Factor Properties • … independent of shale properties above or below reservoir. • … independent of reservoir porosity. 3. … independent of wavelet shape. 4. … related to NI of hydrocarbon/water contact. 5. … function of thin-bed traveltime and pore fluid.

  20. Field Study Conclusions • NIP vs. NIS horizon crossplot provides • … E{FWET} = 0. 2. Regional well-log curves provide … Seismic to well-log amplitude calibration. 3. With questionable wavelet and low-frequency control, F was better pore-fluid discriminator than PI or .

  21. Thanks for your attention.

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