Citation:
Presented by Maurice B Dusseault, Professor, Department of Earth and Environmental Sciences University of Waterloo, Waterloo Ontario, Canada
Abstract:
Rocks of intermediate depth (100-1000 m) and those in the deep (greater than 1 km) subsurface represent an environmental resource to aid the energy transition and to achieve improved environmental outcomes.
Porous and permeable sediments can be used to store fluid and solid wastes through processes of injection. Suitable porosity and permeability are needed for fluids disposal (CO2, waste water, acid gas), and slurried solids may be disposed in sediments through fracture injection, a process that has been taking place in the oil industry for over 40 years. Particular emphasise is placed on the potential for sedimentary rocks to accommodate injection and to dissipate pressures, but caution is warranted: the huge volumes of CO2 proposed for injection will exceed the sediments’ capacities in many areas, leading to regional pressurization and increased escape risks.
Biosolids injection leads to Carbon sequestration in solid form (a process of coalification), and in many jurisdictions this can be done as economically as current high quality treatment approaches. Using the example of South Tehran, a framework will be presented for more environmentally secure carbon sequestration combined with safer and economical urban biosolids treatment.
Energy storage in the subsurface may comprise HC storage, but also H2 storage, compressed air storage, heat storage, and pumped hydro. In Ontario, Canada, the first adiabatic compressed air storage facility in the world is operating, albeit at a pilot scale of 1.75 MW. The compressed air is stored in a repurposed salt cavern 420 m deep.
The usefulness of the subsurface to store low-grade heat for seasonal use in northern climates is being studied, and methods to cool subsurface repositories for sources of cooler air in warm months is technically feasible.
Intelligent use of the subsurface can, in many ways, help reduce the C-intensity of our energy sources while improving other environmental outcomes such as waste disposal and water clean-up.