Petroleum (crude oil) was initially formed from the remains of ancient marine organisms that died and sunk to the bottom of sea thus mixing with other sediments. Petroleum is formed when various hydrocarbons combine with certain minerals such as Sulphur, and this formation occurs under extreme pressure over hundreds of millions of years. When sea organisms die and sink to the seafloor, they mix with sand and silt hence causing decomposition and a tiny bacteria function to clear the remains of Phosphorus, Oxygen, and Nitrogen . Only carbon and hydrogen are left in the decomposed leaves and the raw materials for creating petroleum is formed. As these sediment piles, they turn into Kerogen (a waxy solid that is used to make oil).
Kerogen is formed through a process referred to as diagenesis which involves the breakdown of organic compounds into simple elements such as carbonates and hydrocarbons. The said reaction takes place as follows: Fulvic acids + humin acids + humin = H2O +CO2 + ammonia + geopolymers. As heat and pressure break down the compounds in the sediments, kerogen is made. Thus, the process of petroleum formation is simplified, and the final material of diagenesis is then transformed into refined petroleum and gas. Montmorillonite plays a major role in catalyzing the reactions in the process of decarboxylation off various fatty acids to create a long chain of alkanes . The longer chains are later broken down into short and simple chains of alkanes that contain similar molecules to those of petroleum. The rate of reaction at this stage is estimated at 36kcal/mole for decarboxylation and 44.6 kcal per mole for the cracking of the hydrocarbons. It is important to note that as the petroleum is formed, it remains in the form of hydrocarbon pyrolysis which is irreversible and exists in liquid form. Thus, once the oil is formed, it remains liquid below the surface of the earth and can stay for millions of years without turning into gas or solid form. This is the reason as to why oil deposits petroleum is mined in liquid form and refined into the desired products.