This technique typically sends carbon dioxide, nitrogen, or liquefied petroleum gas (LPG) into the reservoir--gases that are miscible (dissolve in the oil).A common first step is to inject a slug of a detergent-like surfactant that reduces the surface tension of the oil, which washes out of the rock pores and forms a micro-emulsion.Chemical flood This approach injects different chemicals--each serving a different purpose--into a depleted sandstone reservoir in separate batches, or slugs.