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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
Data
along 2-D Seismic Lines
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-wave 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-wave/S-wave
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-wave/S-wave
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.