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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/6262
Title: On the applicability of Gassmann model in carbonates
Authors: Sharma R.
Prasad M.
Surve G.
Katiyar G.C.
Published in: SEG Technical Program Expanded Abstracts
Abstract: Petrophysical properties (porosity, permeability), and with them seismic properties, of carbonate rocks can change significantly due to dissolution, precipitation, and cementation processes. There is continuining debate on the use of an appropriate rock model to predict the attributes of the carbonate rock reservoirs. Gassmann's model in particular has been discussed at length, both for and against its applicability for the carbonates. Most laboratory research has shown that the Gassmann's theory can predict the fluid related changes on seismic velocities in sandstones and a few on carbonates also. But as few studies have reported a change of shear modulus upon saturation in a few carbonates, the applicability of this model needs to be tested on more rigorous grounds. In this study, we have used Gassmann's equation to calculate saturated velocities for for predicting fluid effects on a wide range of carbonate rocks with different textures and porosities ranging from at an effective pressure of 50 MPa. A majority of the data shows a reduction of shear modulus by as much as 2.5 GPa for low porosity (5% to 15%) carbonate rocks. This shear modulus reduction becomes negligible for higher porosity (45%) carbonate rocks. The difference in the dry and saturated bulk modulus varies from 15GPa to 5GPa, and is in inverse proportion to porosity. The deviations in saturated shear velocity (V s) when plotted against porosity, clearly shows that there are effects other than density that result in the lowering of V s. Gassmann's theory slightly overestimates V p (300 m/s for lower velocities and reducing with higher values), but it overestimates Vs for most of the data. However, the Gassmann's predicted V p/V s matches measured V p/V ss. The pronounced difference in V p/ V ss against VP plots between dry and fluid saturated samples indicates promising result for AVO analyses. The saturated V p -V ss trend line for all the data sets when plotted with the carbonate mudrock line of Li and Downton (2000) shows a close match. © 2005 Society of Exploration Geophysicists.
Citation: SEG Technical Program Expanded Abstracts (2006), 25(1): 1866-1870
URI: https://doi.org/10.1190/1.2369889
http://repository.iitr.ac.in/handle/123456789/6262
Issue Date: 2006
ISSN: 10523812
Author Scopus IDs: 55685389800
7201465535
15128186200
15136017000
Author Affiliations: Sharma, R., Indian Institute of Technology, Bombay, India
Prasad, M., Indian Institute of Technology, Bombay, India
Surve, G., Indian Institute of Technology, Bombay, India
Katiyar, G.C., Third Eye Centre, Oil and Natural Gas Corporation Ltd., India
Corresponding Author: Sharma, R.; Indian Institute of Technology, Bombay, India
Appears in Collections:Journal Publications [ES]

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