Simulation to Seismic Fluid Substitution Modeling at the Illinois Basin – Decatur Project

Abstract:

The Illinois Basin – Decatur Project (IBDP) is one of the most advanced US Department of Energy-funded carbon dioxide (CO₂) sequestration projects. The goal of injecting 1 million tonnes of CO₂ over a three year period was reached in November 2014 and the project is now in the post injection site closure (PISC) phase. A number of seismic methods are being utilized in the IBDP PISC plume monitoring program. These include time lapse three-dimensional (3D) vertical seismic profile (VSP) surveys, time-lapse surface seismic surveys, and passive seismic monitoring.

While each seismic monitoring method has inherent spatial resolution and imaging footprint characteristics, all fundamentally rely on variation of reservoir elastic properties in response to injection induced changes in saturation and pressure conditions. These variations in elastic properties, and the resulting time-lapse seismic response, are often subtle and non-unique with respect to saturation and pressure effects. Elastic properties of saturated porous media may be estimated using rock physics theory and fluid substitution methods; however, the complexity of typical reservoir rock and fluid systems under injection conditions, and the subtlety of the resulting changes in elastic properties, dictate the need for representative estimates of the reservoir geologic framework, reservoir rock physics, and the anticipated plume geometry.

At IBDP a “simulation-to-seismic” workflow has been used to develop accurate estimates of 3D time-lapse elastic property and seismic signal responses for CO₂ plumes generated using a calibrated compositional flow simulation model. The anticipated time-lapse response for the IBDP surface and VSP time-lapse surveys have been estimated using ranges of rock physics parameters derived from geophysical logs. These investigations highlight the importance of geologic controls on plume geometry in monitoring program design as well as during model-based interpretation of time-lapse seismic data.