Petroleum
The word Petroleum is derived from two Latin words: Petra (meaning rock) and Oleum (meaning oil). Therefore, it literally translates to “rock oil” because it is extracted from the rocks deep beneath the Earth’s surface.
In its natural, unrefined state extracted from the ground, it is a dark, thick, viscous, and foul-smelling liquid commonly known as Crude Oil. Chemically, it is a highly complex mixture of various hydrocarbons (compounds made entirely of carbon and hydrogen), along with small amounts of water, salt, and earth particles.
Economic Significance: Petroleum is the most important liquid fuel in the world today. Due to its immense commercial value and its wide range of everyday applications—from running vehicles and airplanes to manufacturing plastics, lubricants, and synthetic fibers—petroleum is frequently referred to as “Black Gold”.
Origin and Formation of Petroleum
Like coal, petroleum is a fossil fuel. However, while coal was primarily formed from the remains of dense land forests, petroleum was formed from the remains of tiny plants and animals that lived in ancient seas and oceans.
The formation of petroleum is a slow geological process that occurred over millions of years. The step-by-step process is as follows:
- Marine Life Accumulation: Millions of years ago, microscopic marine plants and animals (like plankton and algae) lived in the oceans. When these organisms died, their bodies sank and settled at the bottom of the seabed.
- Burial and Deposition: Over thousands of years, these dead organic remains were covered by thick, heavy layers of sand, mud, and clay.
- Anaerobic Conditions: As they were buried deeper and deeper under the ocean floor, they were completely cut off from the oxygen supply (an anaerobic environment).
- Action of Heat and Pressure: The massive weight of the overlying sediments created intense pressure, while the internal heat of the Earth significantly raised the temperature. Under these extreme conditions of high temperature and high pressure, the dead organic matter was slowly chemically transformed into petroleum and natural gas.
Occurrence in the Earth's Crust
Because petroleum is a liquid and natural gas is a gas, they are lighter than water. Over time, they slowly squeezed through porous rocks (like sandstone) and migrated upwards.
However, they eventually reached a layer of hard, non-porous rocks (impermeable rocks) which blocked their upward movement. As a result, the petroleum and natural gas became permanently trapped underground between these rock layers. These geological traps are usually found within sedimentary rocks.
When a well is drilled into the Earth’s crust, natural gas is usually found forming a layer just above the petroleum, and both float above the heavier underground salt water without mixing with it.
