Oil from shale formation
Actually, shale formations do not have to be source rocks. Strictly speaking, shale oil comes from shale formations like source rocks and mud shale rocks; tight oil comes from low-permeability sandstones, silty sands, and carbonates. In practice there seems no clear or agreed difference between these two terms, and they are used synonymously. Oil shale must be mined using either underground- or surface-mining methods. After excavation, the oil shale must undergo retorting. This is when the mined rock is exposed to the process of pyrolysis -- applying extreme heat without the presence of oxygen to a substance, and producing a chemical change. Potential Green River Formation oil shale reserves based on 30 gallons per ton of rock are almost 20 billion barrels of oil. Shale Oil. So what is shale oil? It’s just that—ready-to-be refined oil produced from shale.