Contamination gas is a byproduct that is produced during the drilling process. When drilling mud is injected into the wellbore and gas is introduced into it via other trajectory, the gas combines with mud and ends up being contaminated. It is only formed when the drilling fluid or drilling mud is an oil-based mud system, involving explosive liquids such as diesel fuel. Apart from the oil base in the drilling fluid, the gas can get contaminated due to the presence of other lubricants or additives present in the mud.
During drilling procedures, drilling mud of three kinds is employed to induce fractures in the formation. When an oil-based mud system is brought into use on wells that are difficult to drill, gas is also introduced in the wellbore from another source, such as a trajectory so as to increase pressure. When this gas combines with volatile materials, such as diesel fuel, additives and proppants in the oil-based drilling fluid, it reacts and gets contaminated. As a result of this chemical reaction under the wellbore, the contamination gas is produced.