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Title: On the applicability of Gassmann model in carbonates
Authors: Sharma R.
Prasad M.
Surve G.
Katiyar G.C.
Published in: Proceedings of Society of Exploration Geophysicists - SEG International Exposition and 76tth Annual Meeting 2006
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 (Vs) when plotted against porosity, clearly shows that there are effects other than density that result in the lowering of Vs. Gassmann's theory slightly overestimates Vp (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 Vp/Vs matches measured Vp/Vs. The pronounced difference in Vp/Vs against VP plots between dry and fluid saturated samples indicates promising result for AVO analyses. The saturated Vp-Vs trend line for all the data sets when plotted with the carbonate mudrock line of Li and Downton (2000) shows a close match. © 1996-2018 Society of Exploration Geophysicists. All rights reserved.
Citation: Proceedings of Society of Exploration Geophysicists - SEG International Exposition and 76tth Annual Meeting 2006, (2018), 1866- 1870
Issue Date: 2018
Publisher: Society of Exploration Geophysicists
Keywords: Carbonates
Elastic moduli
Geophysical prospecting
Sedimentary rocks
Shear flow
Shear strain
Carbonate rock reservoir
Cementation process
Effective pressure
Gassmann's equations
Inverse proportions
Petrophysical properties
Saturated velocity
Seismic velocities
Data reduction
ISBN: 9781604236972
Author Scopus IDs: 55685389800
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, United States
Funding Details: We are extremely grateful to Prof. G Mohan for providing all the computer facilities for the completion of this work. We greatly acknowledge the support by Oil and Natural Gas Corporation Ltd. for conducting this work. We are very thankful to M Batzle and L Adams for their suggestions and comments Figure 1 Trend lines for VS versus VP are plotted for, a) Wang, b) Rogen, c) Lucet’s Sonic, d) Lucet’s Ultrasonic and e) Aseefa’s data set. All these trend lines are compared against the different Mudrock lines. In all the plots, the trend line for saturated velocities better matches the Carbonate Mudrock Line by Li & Downton (2000), except for the Lucet’s sonic.
Corresponding Author: Sharma, R.; Indian Institute of TechnologyIndia
Appears in Collections:Conference Publications [ES]

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