Unconventional fossil fuels are hydrocarbon reserves that cannot be accessed through traditional vertical drilling and pumping methods. These resources, which include oil sands, shale gas and oil, and deepwater deposits, are trapped in complex geological formations, such as low-permeability shale rock or highly viscous bitumen deposits. Accessing these sources requires advanced, energy-intensive techniques like hydraulic fracturing and steam injection, which introduces a distinct set of environmental, climate, and structural concerns that differ substantially from conventional energy production. This article explores the specific risks associated with utilizing these challenging hydrocarbon sources.
Environmental Degradation and Water Consumption
The extraction of unconventional fossil fuels creates profound, localized environmental impacts, with water consumption and contamination being major concerns. Hydraulic fracturing (“fracking”), used to extract shale gas and tight oil, demands massive volumes of water—often millions of gallons per well—to fracture the rock and release hydrocarbons. Oil sands operations, such as Steam-Assisted Gravity Drainage (SAGD), involve injecting high-pressure steam deep underground to mobilize thick bitumen, requiring significant quantities of freshwater.
This massive water demand stresses local and regional water supplies, especially in arid areas. Once used, the water returns to the surface as highly contaminated flowback and produced water. This wastewater contains a complex mixture of fracturing chemicals and naturally occurring substances mobilized from the deep earth.
These mobilized contaminants include high concentrations of salts, heavy metals, and naturally occurring radioactive materials (NORM). The disposal or accidental release of this toxic flowback water poses a significant threat to soil and groundwater resources. Surface mining used for shallow oil sands bitumen leads to large-scale habitat destruction and leaves behind immense tailings ponds of toxic wastewater. These disturbances permanently alter landscapes and require extensive reclamation efforts.
Elevated Energy Intensity and Lifecycle Emissions
Unconventional resources require significantly greater energy inputs for their extraction and processing compared to traditional crude oil and natural gas. This higher energy demand stems from the difficulty of liberating hydrocarbons from tight rock formations or viscous deposits. For example, producing bitumen from oil sands often necessitates generating large amounts of steam or mechanical power for mining and upgrading.
This difference in energy input is reflected in the Energy Return on Energy Invested (EROEI), which is lower for unconventional sources. A lower EROEI means that more energy must be expended to produce a usable unit of fuel. This high energy intensity results in elevated lifecycle greenhouse gas (GHG) emissions.
Lifecycle assessments indicate that oil sands crude can have lifecycle emissions approximately 17% higher than average refined conventional crude. Furthermore, shale gas extraction is associated with the risk of methane leakage, or fugitive emissions, from wells and infrastructure. Methane is a potent greenhouse gas, and studies show that these emissions from some unconventional gas operations have been underestimated, contributing substantially to climate change.
Geologic Instability and Infrastructure Vulnerability
The complex methods employed for unconventional extraction introduce risks of geological instability and heighten the vulnerability of transportation infrastructure. The disposal of massive volumes of wastewater generated by hydraulic fracturing often involves injecting it deep underground into porous rock layers. This high-pressure injection has been linked to increased induced seismicity, triggering man-made earthquakes in regions with little historical seismic activity.
For deepwater drilling, the extreme operating environment presents a significant technical challenge and risk of structural failure. Operating at great depths involves immense hydrostatic pressure and high temperatures, which can compromise drilling equipment and well casings. Failure of pressure control systems can lead to catastrophic blowouts and oil spills, as demonstrated by past deepwater incidents.
The transportation of unconventional products, which are often volatile or highly viscous, poses distinct logistical risks. Shale oil, such as Bakken crude, is notably volatile and has a high propensity to ignite or explode during rail transport accidents.
Oil sands bitumen is typically diluted into “dilbit” to flow through pipelines, but this corrosive mixture requires higher operating temperatures and pressures, increasing the risk of pipeline corrosion and ruptures. When transported by rail, the diluents in dilbit can make the material just as flammable as volatile shale oil, leading to intense fires following derailments.