Shale Oil - Extraction Process

Extraction Process

Shale oil is extracted by pyrolysis, hydrogenation, or thermal dissolution of oil shale. The pyrolysis of the rock is performed in a retort, situated either above ground or within the rock formation itself. As of 2008, most oil shale industries perform the shale oil extraction process after the rock is mined, crushed, and transported to a retorting facility, although several experimental technologies perform the process in place (in-situ). The temperature at which the kerogen decomposes into usable hydrocarbons varies with the time-scale of the process; in the above-ground retorting process decomposition begins at 300 °C (570 °F), but proceeds more rapidly and completely at higher temperatures. Decomposition takes place most quickly at a temperature between 480 and 520 °C (900 and 970 °F).

Hydrogenation and thermal dissolution (reactive fluid processes) extract the oil using hydrogen donors, solvents, or a combination of these. Thermal dissolution involves the application of solvents at elevated temperatures and pressures, increasing oil output by cracking the dissolved organic matter. Different methods produce shale oil with different properties.

A critical measure of the viability of extraction of shale oil lies in the ratio of the energy produced by the oil shale to the energy used in its mining and processing, a ratio known as "Energy Returned on Energy Invested" (EROEI). A 1984 study estimated the EROEI of the various known oil-shale deposits as varying between 0.7–13.3. More recent studies estimates the EROEI of oil shales to be 1–2:1 or 2–16:1 – depending when self-energy is counted as a cost or internal energy is exclude and only purchased energy is counted as input. Royal Dutch Shell reported an EROEI of three to four in 2006 on its in situ development in the "Mahogany Research Project."

The amount of oil that can be recovered during retorting varies with the oil shale and the technology used. About one sixth of the oil shales in the Green River Formation have a relatively high yield of 25 to 100 US gallons (95 to 380 l; 21 to 83 imp gal) of shale oil per ton of oil shale; about one third yield from 10 to 25 US gallons (38 to 95 l; 8.3 to 21 imp gal) per ton. (Ten US gal/ton is approximately 3.4 tons of oil per 100 tons of shale.) About half of the oil shales in the Green River Formation yield less than 10 US gal/ton.

The major global shale oil producers have published their yields for their commercial operations. Fushun Mining Group reports producing 300,000 tons per year of shale oil from 6.6 million tons of shale, a yield of 4.5% by weight. VKG Oil claims to produce 250,000 tons of oil per year from 2 million tons of shale, a yield of 13%. Petrobras produces in their Petrosix plant 550 tons of oil per day from 6,200 tons of shale, a yield of 9%.