Changes
Drilling technology
'''Petroleum''', named for "rock oil", is a [[fossil fuel]] usually found deep within the [[earth]], although some deposits are very close to the surface.
It is a heavy dark [[liquid]], consisting of many different [[hydrocarbon]] [[chemical compound|compound]]s. Crude Wells are drilled deep in to the ground, and the crude oil is extracted from the ground and [[distillation|fractionated]] into its components by volatility in an oil refinery. Recent advances in drilling technology have enabled deeper and more difficult wells to be succesfully drilled, allowing previously inaccessable reserves to be tapped. Some of the main products distilled from crude oil are:
The following table<ref>Stainforth, J., Nourse, R. & Nosiara, M., 2007, ''Basin Oriented Geology - Petroleum Systems Module Course Manual''.</ref> compares the qualities of various types of petroleum:
