--> ABSTRACT: Measurement of Attenuation and Frequency-Dependent Impedance from 2-D Seismic Data: An Example from NE China, by Alshangiti, Abdullah M.; Chapman, Mark; Wilson, Adam; Clark, Roger; #90141 (2012)
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Measurement of Attenuation and Previous HitFrequencyNext Hit-Dependent Impedance from 2-D Seismic Data: An Example from NE China

Alshangiti, Abdullah M.*1; Chapman, Mark 2; Wilson, Adam 2; Clark, Roger 3
(1) Geophysical Data Processing Division, Saudi ARAMCO, Dhahran, Saudi Arabia. (2) Edinburgh Anisotropy Project, British Geological Survey, Edinburgh, United Kingdom. (3) School of Earth and Environment, University of Leeds, Leeds, United Kingdom.

Analysis of seismic data suggests that hydrocarbon saturated and/or fractured zones are often associated with high values of attenuation; this attenuation causes strong velocity dispersion. Due to dispersion, the impedance will be Previous HitfrequencyNext Hit-dependent. The measurement of attenuation and Previous HitfrequencyNext Hit-dependent impedance from seismic data may help in distinguishing between reservoir and non-reservoir zones. They measurements can also be used as a tool to detect fractures.

A recently developed method was applied to measure the Previous HitfrequencyNext Hit-dependent impedance from synthetic and field data. For a three-layer model of elastic and dispersive interfaces, Previous HitfrequencyNext Hit-dependent impedances were measured, and the results show that the impedance varies strongly with Previous HitfrequencyNext Hit in the dispersive interface (i.e., fractured and gas-saturated sandstone) but not in the elastic one (i.e., homogenous and isotropic shale). The Previous HitfrequencyNext Hit-dependent inversion produced results with error between 7.5-10%. The Previous HitfrequencyNext Hit-dependent impedances were then measured from field CMPs that fall in the same Fresnel zone. The results are very consistent along these CMPs, where two events with strong variations of impedance with Previous HitfrequencyNext Hit may be related to the shallow multiple gas-reservoirs. The inversion of these CMPs produced results with an error of 30% for the full-bandwidth inversion and 40% for the Previous HitfrequencyNext Hit-dependent inversion.

As an independent supportive measurement, attenuation 1/Q was measured using the prestack Q inversion method. This method produced accurate 1/Q values from a synthetic CMP gather with error of only 4%. The measured 1/Q values from the field CMPs are very consistent with very small uncertainties.

The results from both methods agree with each other in the following manner: where the interfaces with large variations of impedance with Previous HitfrequencyNext Hit have small Q, and those with small variations have large Q. These results are in agreement with the relationship between the Previous HitfrequencyTop-dependent impedance and Q.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain