Environmental effects of oil shale industry

Environmental effects of oil shale industry consist issues of land use, waste management, and water and air pollution. 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.^[1]

Surface mining and retorting

Land use and waste management

Surface mining and in-situ processing requires extensive land use. Mines should avoid high density population areas. Oil shale stockpiles, crushing and loading units cause noise and dust spreading. After mining the land has to be reclaimed.^[2] Disposal of mining wastes, spent shale (semicoke) and combustion ashes needs additional land use.

According to the study of the European Parliament, the waste material occupies after processing a greater volume than the material extracted, and therefore cannot be wholly disposed underground. According to this, production of a barrel of shale oil can generate up to 1.5 tons of semicoke, which may occupy up to 25 % greater volume than the original shale.^[3] This is not confirmed by the results of the Estonia's oil shale industry. The mining and processing of 1000 million tons of oil shale in Estonia has created about 360-370 million tons of solid waste, of which 90 million tons is a mining waste, 70–80 million tons is a semicoke, and 200 million tons are combustion ashes.^[4]

The waste material may consist of several pollutants including sulfates, heavy metals, and polycylic aromatic hydrocarbons (PAHs), some of which are toxic and carcinogenic.^[5][6] To avoid contamination of the groundwater, the solid waste from the thermal treatment process is disposed in an open dump (landfill or "heaps"), not underground. As semicoke consists, in addition to minerals, up to 10 % organics that may pose hazard to the environment due to leaching of toxic compounds as well as due to the self-ignition.^[4]

Water management

Thermal processing of oil shale needs large amounts of water, which may be in short supply. In the United States around 1 to 3 barrels of water are needed for each barrel of shale oil produced.^[1][7] At the same time in other places the mining requires the lowering of groundwater levels below the level of the oil shale strata, which may have harmful effects on the surrounding arable land and forest. In Estonia for each cubic meter of oil shale mined, 25 cubic meters of water must be pumped.^[8]

Water represents the major vector of transfer of oil shale industry pollutants. One environmental issue is to prevent noxious materials leaching from spent shale into the water supply.^[3] The oil shale extraction process is accompanied by the formation of large amounts of different process waters and waste waters containing phenols, tar and several other products, heavily separable and toxic to the environment.^[4]

Air pollution management

Main air pollution is caused by the oil shale-fired power plants, which provide the atmospheric emissions of gaseous products (SO₂, NO_x, CO₂) and the airborne particulate matter (fly ash). It includes particles of different types (carbonaceous, inorganic ones) and different sizes.^[9]

Open deposition of semicoke causes distribution of pollutants in addition to aqueous vectors also via air (dust).^[4]

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.^[1][3]

Emissions arise from several sources. These include CO₂ released by the decomposition of the kerogen in the extraction 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.^[3][10] As the varying mineral composition and calorific value of oil shale deposits varies widely, the actual values vary considerably.^[3] 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,^[3] an energy source which is also politically contentious due to its high emission levels.^[11][12]

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 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.^[13][14]

See also

• Oil shale
• Oil shale geology
• Oil shale reserves
• Oil shale industry
• Oil shale extraction
• Oil shale economics

References

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