Oil Shale and Tar Sands

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Oil Shale and Tar Sands Two potentially rich sources of fossil fuel are oil shale (or shale oil) and tar sands (or oil sands). Oil shale is actually a misnomer. It is not shale, but a rock, and it doesn’t contain oil, but rather a solid organic compound kerogen, which is tightly packed in clay, mud, and silt. Tar sands are grains of sand containing thick, viscous, soluble organic liquid called bitumen (Figure 7-18). Th e United States has two-thirds of the entire world’s oil shale (along shores of Green River in Wyoming, Colorado, and Utah), and Canada has the largest percentage of tar sands in the world (in Alberta). In fact, if tar sand reserves are included, Canada would have the second largest Figure 7-17 Shale oil can potentially meet a great portion of the future energy demand. 164 amount of petroleum reserves in the world aft er Saudi Arabia.28 Russia and Brazil are also rich in oil shale, whereas Venezuela has the second largest deposits of tar sands (aft er Canada). Worldwide resources of tar sands are estimated at around two trillion barrels.29 An additional 2.8-3.3 trillion barrels of oil can be recovered from oil shale.30 Mining operations are very energy intensive; oil shale resides deeply underground and must be heated to high temperatures (around 400-500oC) before it releases any oil. In fact, the oil extract is not petroleum, but liquid kerogen. Steam is needed to hydrogenate kerogen into hydrocarbons that may then be refi ned into gasoline and other petroleum products. Tar sands must also undergo a similar process. Heating them to high temperatures causes the viscosity of the bitumen to drop, making it fl ow more easily out of the sand. Various petroleum products, such as kerosene can be manufactured by distilling the kerogen and bitumen oils. In addition to their low yield (50-100 liters per ton of rock), oil shale and tar sands are not clean. Th ese resources are rich in sulfur and nitrogen which can contribute signifi cantly to the acid rain problem. Another environmental concern is the disposal of residues, called tailing, which occupy many times the volume of crude they produce. Th ese problems have hindered widespread use of oil shale and tar sands. Canada is pursuing mining tar sand deposits aggressively; Estonia, Brazil, and China use oil shale to produce electricity and in production of cements. As the price of petroleum rise, these resources will fi nd a more prominent role to meet our energy needs.

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