Executive Summary-Characterization Of Reservoir Fluid Flow Properties

Abstract

The characterization of subsurface fluid flow is the key to exploration, production, and management of oil, gas, geothermal, and groundwater reservoirs. From a research perspective the question then becomes how can we measure or estimate the spatial variations in physical properties which control the flow of these fluids? Ideally we would like to be able to remotely identify fluid type and provide accurate estimates of in-situ porosity and permeability values in three dimensions. In some situations this may be possible, but in others such a goal may not be attainable. If accurate estimates of these physical properties cannot be achieved, there may still be important and useful related information available. For example, being able to provide accurate estimates of the direction of maximum fluid flow may be a very important piece of information for field development and drilling decisions. The Earth Resources Laboratory has focused on developing methods for using seismic waves to estimate fluid flow properties. Seismic waves provide higher resolution data than potential field measurements, can be polarized for anisotropy measurements, can be used in surface and borehole applications. and ERL has significant experience in the physics and modeling of wave propagation ill complex media. Our report this year provides results in three specific areas related to our overall goal of fluid flow characterization. The first. involves research into methods which utilize the actual motion, induced by seismic waves, of fluids ill porous rock. The passing of a seismic wave through a rock containing a viscous fluid results in relative motion between the fluid and the solid matrix. This mot.ion dissipates seismic energy resulting in the attenuation of the passing wave. The motion of the fluid, which contains ions, also creates an electrical field which can be measured. We present results in both of these areas in this report. A second research area is the measurement of flow directionality. The presence of open fractures with a preferred orientation will control the direction of fluid flow in a reservoir. Such fractures will also have a large effect on the elastic properties of the reservoir rock. The resulting elastic anisotropy may be observable in both surface seismic data as well as borehole acoustic logs. We present several papers on the effects of anisotropy on surface seismic data and AVO signatures, as well as on dipole sonic logs. Finally, because fluid flow is only one of the many factors which effect seismic waves, we must continue to improve our understanding of wave propagation in complex media. We present two such papers which look at scattering and scale dependent issues. The way in which property variations at different spatial scales affect seismic waves is an important research area that we will continue to investigate in the coming year. The following sections provide a more detailed summary of the results in each of these three broad areas.