Understanding the impact of fluids injected into the subsurface is essential for a host of activities that have material benefits for society. For example, the extraction of geothermal energy, development of unconventional hydrocarbon resources, sequestration of carbon dioxide (CO2), clean-up of contaminated groundwater and storage of various types of fluids all require fluid injection into diverse types of subsurface systems. The long-term mission of the BES Geophysics Program at Berkeley Lab’s Energy Geosciences Division is to improve our ability to monitor and image in space and time where injected fluids migrate and what alterations they make to the Earth’s subsurface. We are resolving the numerous basic-science challenges involved with using different types of time-lapse geophysical data, including seismic, electromagnetic signals and strain information, to inform about the time-lapse changes to the subsurface.
Invading fluids change material properties through several mechanisms:
- the replacement of one fluid type with another alters any material property that depends on the fluid properties or on the emergent fluid structures (e.g., electrical conductivity, seismic velocity, seismic attenuation);
- the fluid pressure fronts alter the stress balance in the subsurface and can induce fracture and/or slip that results in seismicity that can be measured to track the front advancement; and
- such induced damage also alters the geophysical, hydrogeological and mechanical properties of the subsurface.
The basic-science questions are in how to model and understand the way that injected fluids alter rock properties, to simulate flow (miscible and immiscible) and transport of solute in highly heterogeneous materials and to simulate both the arrival of fluid-damage and how such damage alters rock properties. The approach in each of these cases is to develop new theoretical models that are informed and constrained by laboratory experiments. Further, new imaging techniques are developed that allow time-lapse geophysical data to be inverted to obtain the key material properties used in the forward-modeling simulators of the alteration process.
A Novel Laboratory Experiment
This novel laboratory experiment allows for the visualization of a fluid-induced fracture event as well as where the locally distributed cracking (acoustic emissions) takes place.