CCS and Power Systems
Carbon Storage - Monitoring, Verification, Accounting, and Assessment
Advanced Technologies for Monitoring CO2 Saturation and Pore Pressure in Geologic Formations: Linking the Chemical and Physical Effects to Elastic and Transport Properties
Performer: Stanford University
Project No: FE0001159
This four-year project—performed by Stanford University’s Stanford Rock Physics Laboratory in partnership with ExxonMobil and Ingrain, Inc.—is providing robust methodologies for using seismic data to quantitatively map the movement, presence, and permanence of CO2 relative to its intended storage location. Optimized rock-fluid models incorporate the seismic signatures of (1) saturation scales and free vs. dissolved gas in a CO2-water mixture, (2) pore pressure changes, and (3) CO2-induced chemical changes to the host rock (Figure 1). Work products from this project include an innovative dataset, methodologies, and algorithms for predicting the seismic response of multiphase and reactive fluids in CO2 storage programs.
In spite of advanced techniques for geophysical imaging, current methods for interpreting CO2 saturation from seismic data can be fundamentally improved. Until now, Gassmann’s equations, which relate pore fluid compressibility and the rock frame to overall elastic properties, have been the primary tool for interpreting CO2 plumes from time-lapse seismic data. Gassmann’s model is purely mechanical, and is best suited for conditions of single-phase fluid saturation in relatively inert systems. Yet, CO2-rich fluid-rock systems can be chemically reactive, altering the rock frame via dissolution, precipitation, and mineral replacement. Furthermore, CO2 systems are multiphase, with uncertainties in scales of phase mixing in the pore space and solution of one phase in another. Errors from ignoring the physicochemical factors during CO2 injection can affect predicted seismic velocity changes, resulting in compromised estimates of saturation and pressure of CO2-rich fluids.