Analytical Approach of Seismic-Derived Resistivity
Denny M.F. Mendrofa1* and Bambang Widarsono2
1Premier Oil, Indonesia
2Core Laboratory Service, Indonesia
Nowadays, there are several seismic-petrophysical researchers investigating the relationship between seismic waves and water saturation in rocks. Unfortunately, the results always end-up in terms of empirical relationships, even when using geostatistical methods. The application of artificial neural network techniques, as published in recent research papers showed a robust correlation between the two, despite the result being a poorly defined relationship. This suggested that there may be an analytical relationship between seismic characteristics and water saturation in porous rocks. In this research, we have considered the electrical properties of porous rocks as they are related-to and influenced-by water saturation. We succeeded in deriving several conversion equations to prove a valid analytical relationship between acoustic impedance and resistivity. This was followed by satisfactory testing on well data. The theory is based on the analytical definition of acoustic impedance involving a common bulk density and Gassmann’s acoustic velocity formula. We also used the modified Archie equations for a shale-sand model and by arranging those variables within the mathematical operations, we were able to derive true rock resistivity as a function of acoustic impedance. For further application, the constructed amplitude of reflected seismic energy in the range of nearly-normal incidence was used for identifying fluid type in saturated rock, whilst porosity and shale volume can be derived respectively from density, neutron, velocity and gamma ray log from well data.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain