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AVO as a Fluid Indicator: A Physical Modeling Study

Wandler, Aaron V. 1, Brian J. Evans2, Curtis A. Link3 (1) formerly Montana Tech, Billings, MT (2) Curtin University of Technology, Perth, Australia (3) Montana Tech, Butte, MT

 

Changes in seismic amplitude variation with offset (AVO) from a producing reservoir could optimize production, especially when used in a time-lapse mode. To this end, we designed a scaled physical model experiment to investigate the AVO response of fluid-only models under varying pressures and with different combinations of fluids. We analyzed the AVO response from common midpoint seismic data recorded over fluid models containing mixtures of water, brine, oil and carbon dioxide at pressures of 0 MPa, 1 MPa, and 2 MPa.

 

The small changes in density and velocity for each fluid due to increasing pressure was not detectable and was assumed to lie within the error of the experiment. However, AVO analysis was able to detect changes in the elastic properties between fluids that contained oil and those that did not. When the AVO response was plotted in the AVO intercept-gradient domain, fluids containing oil were clearly separated from fluids not containing oil. This was observed in the AVO response from both the top and base of the fluids in the physical model.

 

We then compared the measured AVO response with the theoretical AVO response given by the Zoeppritz equations. The measured and theoretical AVO intercept responses for the top fluid reflection agree well although the AVO gradients disagree slightly. For the fluid base reflection, the measured and theoretical responses are in close agreement.

 

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana