How is oil removed from layers of rock?

Answer 1

Petroleum oil is seldom found as pools in layers between rocks, rather it is normally in the pores of the rocks. Usually there is considerable pressure from the layers of rocks above the oily rock layers so if there is a crack in the rock layers, the oil will seep into the crack - sometimes resulting in oil pooling on the surface as it is squeezed up through the crack to the surface. Mostly however, oil is recovered from the deep layers of oily rock by sinking a shaft into the oily layer and pumping the oil to the surface. Once the oil that will naturally flow into the drilled shaft has been recovered, secondary and tertiary oil recovery methods are used. Some of these include pumping water into the area around where the oil is trapped in the rock to displace the oil with the water. Carbon dioxide may be pumped into the rock from wells drilled around the oil field. The carbon dioxide mixes with the oil and reduces the viscosity to help it flow better, Surfactants may be added to the fluid pumped into the wells to get the oil to not stick to the pores so much and flow to where the well has been drilled. In Hydraulic fracturing (also fracking, fraccing, hydrofracturing or hydrofracking) fluid is pumped under pressure into the well to cause the rocks to fracture in order to make it easier to recover the oil by providing cracks that the oil can flow through instead of having to migrate solely through the pores of the rocks. Most of the time, however fracking is used to assist gas recovery rather than oil recovery.