Fossil fuels are formed the gradual accumulation of organic remains on the sea floor. As the accumulation rate increases, the organic remains are subjected to heat and pressure, which leads to fossil-fuel formation.
When the sea floor is stagnant, the formation of fossil fuels , such as oil and gas, can begin by accumulating organic remains into a sediment pile. The sea floor is considered stagnant when there is no oxygen present, and it is devoid of organisms to feed on the organic material resting on the ocean floor. The organic remains can be buried faster with the help of a high sediment accumulation rate. Burying the material prevents the action of decay from occurring. At a certain depth of sedimentation, heat and pressure is applied and causes the formation of oil and gas. Before getting too hot, the hydrocarbons must migrate to a reservoir rock to be extracted. Porous sandstone is a preferred type of reservoir rock. To prevent the hydrocarbons from escaping to the surface of the Earth, the reservoir rock must be covered by a cap-rock, such as clay. Fossil fuels are generally used as a source of energy. These fuels are burned in the form of heat.