<title>Subsurface fluid flow properties from time-lapse elastic wave reflection data</title>

Abstract

Time-lapse (4D) seismic is a procedure where a reservoir is imaged with reflected seismic energy at several time steps while being depleted. This technology is successful when changes in dynamic reservoir properties, such as pressure, saturation of fluids and temperature produce an observable change in the seismic impedance contrast of the medium in 3D space. A careful analysis combining rock physics measurements, reservoir simulation and forward seismic modeling is required to identify if changes in reservoir properties can produce seismically observable impedance changes, and if so, how they are related to dynamic fluid flow in the reservoir. In current industry practice, angle- averaged (or stacked) P-to-P wave reflection seismic images, approximating P-wave impedance changes, are used in time- lapse seismic analysis. Introduction of angle dependency in P-to-P wave reflection data allows us to estimate both P- wave and S-wave impedance changes over the reservoir. Utilizing multi-parameter images from angle-dependent elastic time-lapse seismic surveys, or 4D AVO (amplitude variation with offset) attributes, we demonstrate the potential to invert for multiple reservoir properties such as changes in saturation of fluids and pressure. Estimates of saturation and pressure changes allow integration of time-lapse seismic with reservoir engineering models to improve reservoir fluid-flow prediction and enhance reservoir management decisions.