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Rock-Physics Modeling of Shallow Marine Sediments

Alok Kumar
Geology & Geophysics, IIT Kharagpur, Kharagpur, India

Predicting the elastic moduli of shallow unconsolidated marine sediments as a function of porosity, mineralogy, effective pressure, & pore-fluid compressibility using different rock-physics theories for unconsolidated sediments and finding the rock-physics model which best fits the observed P- and S-wave velocities for shallow marine sediments along the continental margins of India, estimating the empirical constants associated with such a rock-physics model.

Calculation of the bulk and shear moduli of the marine sediment using different rock-physics theories:
Batzle & Wang equation (for fluid phase).
Wyllie’s time average equation.
Wood’s model.
Nobes, et al equation.
Multi-phase weighted equation.
Effective medium model.
Hamilton (1971, 1976) model.

Predicting the elastic-wave velocities from the elastic moduli and the bulk density. Comparing the elastic-wave velocities calculated using different rock-physics theories with the measured ones in different regions (KG basin, west coast, Mahanadi and Andaman) of the continental margins of India.

In a site specific manner, studying the validity of each rock-physics model and find the one, which is best suited for a given region. Also, calculating its site-specific empirical constants.

Wyllie's & effective medium model overestimates while woods model accurately
Matches the observed data set of Amazon delta. Woods and Effective medium model
Underestimates while three phase and weighted velocity model overestimate the observed
velocity for west coast data set. S-wave velocity from Lee equation matches for
Leg 155_946A & not for Leg155_940A.

This model demarcates the rock physics theories for its applicability to site specific geological condition mostly mineralogy, porosity and differential pressure. Slight change in this T, P & Salinity can greatly affect the velocity for some model.

The science of wave propagation in marine sediments is poorly understood. This proposal will help in understanding the fundamentals of wave propagation in poro-elastic medium.

The required knowledge base for obtaining reliable velocities from above parameters is not available for the continental margins of India (KG basin, west coast, Mahanadi and Andaman). This study will yield this knowledge base and will be useful in interpretation of seismic data.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery