Petroleum Base Oils Petroleum was formed many millions of years ago. It is believed to originate from the remains of tiny aquatic animals and plants that settled with mud and silt to the bottoms of ancient seas. As successive layers built up, the deposits were subjected to high pressures and temperatures and, as a result, underwent chemical transformations, leading to the formation of the hydrocarbons and other constituents of crude oil. In many areas, the crude oil migrated and accumulated in porous rocks overlaid by impervious rock that prevented further movement. Usually, a layer of concentrated salt water underlies the oil pool.
Crude oil is recovered by drilling holes as deep as five miles into the earth's crust.
The crude oil frequently comes to the surface under great pressure and in combination with large volumes of gas. The dry gas is sold as fuel or recycled back to the underground formations to maintain pressure in the oil pool and, thus, increase crude oil recovery. All of these materials can cause problems in refining or subsequent product applications. Their reduction or removal increases refining cost appreciably. The first step in petroleum refining is usually a desalting operation, followed by heating in a furnace where the oil is partially vaporized.