M. A. Gutierrez, J. Dvorkin, and A. Nur

Rock Physics Laboratory, Geophysics Department, Stanford University, Stanford, CA

ABSTRACT: Bypassed Oil Identification and Reservoir Monitoring Using Open- and Cased-hole Sonic Logging, La Cira-Infantas Oil Field (Colombia)

We use a theoretical rock physics model that links porosity, lithology, pressure, and pore fluid to the elastic rock properties in fluvial reservoirs in La Cira-Infantas oil field (Colombia) to interpret compressional- and shear-wave log data in a cased hole. As a result, we identify bypassed hydrocarbon-saturated sands. Our theoretical results are consistent with Vp/Vs empirical relations. Theoretical modeling has an advantage over empirical relations because it is based on sound physical principles and as such can be generalized and fine-tuned to a site-specific geological situation. It is straightforward to forward model porosity, lithology, pressure, and pore-fluid effect on Vp/Vs using a theoretical model as opposed to empirical models. Our model predictions are also consistent with time-lapse sonic log data where the P-wave velocity shows a drop in the intervals open for production. This effect is most likely associated with free gas coming out of solution.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado