Deriving Pore
Structure and Permeability from Sonic Velocity in Carbonates
Weger, Ralf J.1, Gregor Eberli2,
Gregor Baechle1, Jose Luis Massaferro3, Yueng Fen Sun4,
Guido Bracco Gartner5 (1) University of Miami, Miami, FL (2)
University of Miami, RSMAS, CSL, Miami, FL (3) Repsol YPF, Madrid, Spain (4)
The Petroleum Institute, Abu Dhabi, United Arab Emirates (5) Shell, Rijswijk,
Netherlands
Two significant questions in carbonate
petrophysics are: (1) which objective, quantifiable aspects of pore geometry best
explain commonly observed scatter in carbonate velocity-porosity cross-plots;
and (2) what is the importance of geometrical characteristics of pore space on
acoustic velocity relative to other physical properties? Quantitative
descriptions of pore geometry in carbonates and laboratory measurements of
acoustic properties are used in this study to develop an empirical link between
quantitative digital pore space parameters, acoustic velocity, and
permeability. Comparison of petrophysical attributes of carbonate core plugs,
geologic description, and quantitative digital parameters describing pore space
geometry demonstrate that: (1) geometric information captured by geological
descriptions of pore type in carbonates explains some scatter in
velocity-porosity cross-plots; (2) four quantitative geometrical parameters
that capture pore size, pore surface roughness, aspect-ratio, and pore network
complexity statistically capture characteristics that quantitatively
differentiate thin sections from each other; (3) two of these parameters
(perimeter-over-area and dominant-pore-size) clearly quantify the deviation of
acoustic velocity from Wyllie's time average equation; (4) internal rock
geometry influences acoustic velocity and permeability most strongly in high porosity
carbonate rocks. The findings from this study imply that: (1) estimating
porosity from acoustic data can be substantially improved by incorporating
information on quantitative pore space geometry; and (2) in cases where good
estimates of porosity are available (e.g. from well or seismic data )
quantitative pore geometric characteristics can be estimated directly from
acoustic data. These quantitative geometric characteristics of the pore space
can be used to estimate permeability from acoustic data.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California