Abstract: Disclosed is a process for the recovery of oil from a subterranean oil reservoir by miscible displacement using a predominantly nitrogen-containing gaseous displacing fluid which may contain lesser quantities of carbon dioxide. The miscibility of the first portion of the gaseous displacing phase injected into the formation is greater than the miscibility of the subsequent portion, as a consequence of increased concentrations of carbon dioxide and/or normally liquid hydrocarbons for the purpose of decreasing the time and distance which the gaseous nitrogen-containing displacing fluid must travel into the reservoir before attaining a conditionally miscible transition zone at reservoir conditions of temperature and pressure. The concentration of carbon dioxide and/or normally liquid hydrocarbons may be decreased in a reverse taper function, after which essentially pure nitrogen or nitrogen containing only minimal amounts of more soluble components may be injected into the formation.

Abstract: Disclosed is a Process for the recovery of oil from a subterranean oil reservoir by miscible displacement. An initial light hydrocarbon slug is injected into the reservoir at a rate which results in fingering of the hydrocarbon through the reservoir oil to produce a light hydrocarbon-reservoir oil mixture. Thereafter, a predominantly nitrogen containing gas is injected into the reservoir at a rate resulting in a flow velocity which is less than the velocity of the previously injected light hydrocarbon. Injection of the nitrogen containing gas strips the previously injected light hydrocarbon from the oil to form a transition zone of conditional miscibility. The miscible zone is then displaced through the reservoir by injection of a suitable driving agent. By injecting the light hydrocarbon slug, the path length through the reservoir needed to establish the conditionally miscible transition zone at the reservoir conditions of temperature and pressure can be materially decreased.