Geological storage is one method of reducing the amount of carbon dioxide (CO2) released into the atmosphere to reduce global warming trends. The CO2 is stored in the pore spaces of suitable geological formations in a porous rock, such as sandstone, and sealed in place with an impermeable caprock, such as shale.
The process of injecting the CO2 into the storage space increases pressure and modifies stress conditions in rocks. This can potentially lead to slippage along pre-existing faults and fractures or the development of fractures in rocks which in turn can release stored elastic energy in the form of small- or large-scale seismicity. The Center for Geologic Storage of CO2, a U.S. Department of Energy-funded Energy Frontier Research Center, has been investigating the mechanisms of injection-induced microseismicity and whether microseismicity can be predicted and controlled.
As part of this effort, Schlumberger scientists designed a laboratory simulation of injection-induced seismicity in collaboration with the Illinois State Geological Survey (ISGS), Norsar, Sintef, University of Illinois, Los Alamos National Laboratory, National Energy Technology Laboratory, University of Notre Dame, and Texas Tech.
In the simulation, a cubic-meter block of Castlegate sandstone was sawn in half obliquely to mimic a fault. The halves were fastened together and fluid was injected at high rates using stepwise increments (pore pressures about 3.5MPa) to induce slippage along the “fault.”
After the experiment, ISGS has thoroughly characterized, sampled, and further tested the sandstone block to extract parameters. ISGS scientists are using this data to develop dynamic three-dimensional computer models and better understand the evolution of pressure, stress, strain, and displacement during fluid injection. This effort will provide comprehensive information that could be linked with recorded acoustic emissions during the experiment. The experiment has produced a unique and rich data-set that has provided considerable insight into fundamental mechanisms associated with small-scale seismicity.