Austin chalk fracture mapping using frequency data derived from seismic data

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Title: Austin chalk fracture mapping using frequency data derived from seismic data
Author: Najmuddin, Ilyas Juzer
Abstract: Frequency amplitude spectra derived from P -wave seismic data can be used to derive a fracture indicator . This fracture indicator can be used to delineate fracture zones in subsurface layers . Mapping fractures , that have no vertical offset , is difficult on seismic sections . Fracturing changes the rock properties and therefore the attributes of the seismic data reflecting off the fractured interface , and data passing through the fractured layers . Fractures have a scattering effect on seismic energy reflected from the fractured layer . Fractures attenuate amplitudes of higher frequencies in seismic data preferentially than lower frequencies . The amplitude spectrum of the frequencies in the seismic data shifts towards lower frequencies , when a spectrum from a time window above the fractured layer and below the fractured layer is compared with each other . This shift in amplitudes of frequency spectra can be derived from seismic data and used to indicate fracturing . A method is developed to calculate a parameter t* to measure this change in the frequency spectra for small time windows (100ms ) above and below the fractured layer . The Austin Chalk in South Central Texas is a fractured layer and produces hydrocarbons from fracture zones with the layer (Sweet Spots ) . 2D and 3D P -wave seismic data are used from Burleson and Austin Counties in Texas to derive the t* parameter . Case studies are presented for 2D data from Burleson county and 3D data from Austin County . The t* parameter mapped on the 3D data shows a predominant fracture trend parallel to strike . The fracture zones have a good correlation with the faults interpreted on the Top of Austin Chalk reflector . Production data in Burleson County (Giddings Field ) is a proxy for fracturing . Values of t* mapped on the 2D data have a good correlation with the cumulative production map presented in this study .
URI: http : / /hdl .handle .net /1969 .1 /34
Date: 2004-09-30

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Austin chalk fracture mapping using frequency data derived from seismic data. Available electronically from http : / /hdl .handle .net /1969 .1 /34 .

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