Petroleum

Origins

The formation of petroleum can be traced back hundreds of millions of years to ancient microscopic plants and bacteria. These living organisms were able to convert the energy from the sun directly for their own sustenance. These organisms, residing in the ancient seas that covered the earth, sank to the sea floor upon death. Over time, sedimentary layers of silt trapped the nondecayed organic matter in what would later become source rock. Sedimentary layers accumulated above the organic materials, and combined with the weight of the ocean, exerted great pressure and heat. Over time, this pressure and heat transformed the organic source material into the hydrocarbon we now know as petroleum. This process is similar to the formation of natural gas, which is a reason why petroleum and natural gas are often found at similar locations in the earth's crust today.

Over time and under extreme pressure, petroleum was squeezed into the crevices of relatively porous sandstone or limestone, called reservoir rock. Subsequent deformation of the earth's crust acted to trap petroleum into pockets under dense, impenetrable cap rock like marble or granite. The three main geologic forces trapping petroleum into pockets within the earth's crust are folding, faulting, and pinching out. Folding results from horizontal pressure being exerted on the cap rock, forming a fold (or anticline). The resulting bell-shaped fold in the cap rock serves to trap petroleum. Faulting represents a fissure in the cap rock, with a large section of cap rock slipping down, forming a petroleum-trapping cavity. In the pinching out process, impenetrable rock is forced upward into the reservoir rock, resulting in petroleum-trapping pockets. Each of these geologic formations has the potential to hold reservoirs of petroleum, allowing geologists today to predict the possible locations of underground reserves.

As with other natural resources, petroleum's status as a resource began with its recognized use and value to human populations. Ancient civilizations located petroleum seeping to the surface of rivers and lakes. Over time, medicinal uses for petroleum, such as for skin ailments, were realized, and petroleum was used to waterproof canoes and water buckets and provide a base for paint.

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