Environmental impact of the oil shale industry

Environmental considerations

Main article: Oil Shale Enviromental Effects

Surface-mining of oil shale deposits has all the environmental impacts of open-pit mining. In addition, the combustion and thermal processing generate waste material, which must be disposed of, and harmful atmospheric emissions, including carbon dioxide, a major greenhouse gas. Experimental in-situ conversion processes and carbon capture and storage technologies may reduce some of these concerns in future, but may raise others, such as the pollution of groundwater.

Surface mining & retorting

The waste material occupies after processing a greater volume than the material extracted, and therefore cannot be wholly disposed underground. Production of a barrel of shale oil can generate up to 1.5 tons of spent shale, which may occupy up to 25% greater volume than the original shale. The waste material may consists several pollutants including sulfates, heavy metals, and polycylic aromatic hydrocarbons (PAHs), some of which are toxic and carcinogenic. Therefore one environmental issue is to prevent noxious materials leaching from spent shale into the water supply.

In-situ processing

Currently, the in-situ process is the most attractive proposition due to the reduction in standard surface environmental problems. However, in-situ processes do involve possible significant environmental costs to aquifers, especially since current in-situ methods may require ice-capping or some other form of barrier to restrict the flow of the newly gained oil into the groundwater aquifers. However, after the removal of the freeze wall these methods can still cause groundwater contamination as the hydraulic conductivity of the remaining shale increases allowing groundwater to flow through and leach salts from the newly toxic aquifer.

Greenhouse gas emissions

Carbon dioxide emissions from the production of shale oil and shale gas are significantly higher than conventional oil production and a report for the European Union warns that 'increasing public concern about the adverse consequences of global warming may lead to opposition to oil shale development.'

Emissions arise from several sources. These include CO₂ released by the decomposition of the kerogen in the distillation process - which also releases some methane - the generation of the energy needed to heat the shale and in the other oil and gas processing operations, and the mining of the rock and the disposal of waste. As the varying mineral composition and calorific value of oil shale deposits varies widely, the actual values vary considerably. However even the more efficient in-situ conversion process uses the equivalent of 1/3 of the energy of the extracted shale oil in the production process.

At best, the direct combustion of oil shales produces carbon emissions similar to those from the lowest form of coal, lignite, at 2.15 moles CO₂/MJ, an energy source which is also politically contentious due to its high emission levels.

Other issues

Oil shale processing also requires water, which may be in short supply. In the United States around 3 barrels of water are needed for each barrel of shale oil produced.