Modeling Sonic Velocity in Carbonates Using Thin Sections
Gregor Baechle1, Arnout Colpaert2, Gregor P. Eberli1, and Ralf J. Weger1
1Comparative Sedimentology Laboratory, University of Miami, Miami, FL
2Statoil Research Center, Trondheim, Norway
The differential effective medium theory (DEM) is used to model high frequency (1MHz) laboratory velocity measurements of carbonates under dry and water saturated conditions. Velocity-porosity data from laboratory experiments show that micropores have a strong softening effect on the sonic velocity of carbonates. Quantitative image analysis of 250 thin sections enables us to quantify the concentration of micropores and macropores, which forms the base of our rock physics modeling study. We model the effect of the varying stiffness of those two pore populations on velocity: (a) compliant micropores and (b) stiff macropores.
To verify the model results, we compare the elastic
moduli derived from ultrasonic velocities and density information with
elastic
moduli obtained by DEM modeling of the same samples. This DEM model that uses measured input parameters from quantitative digital image analysis of the pore structure results in an excellent prediction of acoustic properties of carbonates. The velocity predictions also show significant improvement compared to velocity prediction using other empirical equations, e.g. the Wyllie times average equation. In addition, we show how a low rock stiffness identifies carbonates of low permeability, indicating the potential of improved reservoir characterization from acoustic data.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas