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AAPG Bulletin, Vol. 90 (2006), Program Abstracts (Digital)

7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006

ABSTRACT: Fracture Porosity Inversion from P-Previous HitWaveNext Hit AVOA Data along 2-D Seismic Lines

Abdullatif Abdulrahman Al-Shuhail
Earth Sciences Department, King Fahd University of Petroleum & Minerals, KFUPM Box 5070, Dhahran 31261 Saudi Arabia, phone: 966-3-860-3584, fax: 966-3-860-2595, [email protected]

I present a method for inverting the fracture porosity from 2-D P-Previous HitwaveNext Hit seismic data using amplitude variation with offset and azimuth analysis with examples. The method is based on the assumption that a negative sign of the anisotropic AVO gradient indicates a gas-saturated reservoir, while a positive sign indicates liquid-saturated reservoir. This assumption is accurate as long as the crack aspect ratio is less than 0.1 and the P-Previous HitwaveNext Hit/S-Previous HitwaveNext Hit velocity ratio is greater than 1.8; two conditions that are satisfied in most naturally fractured reservoirs. The inversion then uses the fracture strike, crack aspect ratio, and P-Previous HitwaveNext Hit/S-Previous HitwaveTop velocity ratio to invert fracture porosity from the anisotropic AVO gradient after inferring the fluid - type from the sign of the anisotropic AVO gradient. Applying this method on dip and strike lines from the oil -saturated zone of the fractured Austin Chalk of southeast Texas, I found that the inversion is accurate along the dip line and significantly deteriorates along the strike line, which is expected by the theory.


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