Enhancement of residual oil recovery using a mixture of nitrogen or methane diluted with carbon dioxide in a single-well injection process

摘要

A method for recovering oil from a subterranean formation penetrated by a well is provided, comprising the steps of injecting via the well a gas mixture into the formation, the gas mixture comprising carbon dioxide and a gas selected from the group consisting of methane, nitrogen, or mixtures thereof; wherein the gas mixture is injected in an amount sufficient to establish in the vicinity of the well a zone of oil in contact with the gas mixture; and wherein the carbon dioxide comprises about 5 percent to about 50 percent by volume at reservoir conditions of the gas mixture; shutting in the well for a predetermined period of time; and producing the well and recovering the residual oil from the formation. Alternatively, an amount of carbon dioxide may first be injected, followed by a slug of gas to form a gas mixture with the carbon dioxide, wherein the gas is methane, nitrogen, or mixtures thereof; and wherein the carbon dioxide comprises about 5 percent to about 50 percent by volume at reservoir conditions of the gas mixture. The steps in either of the above processes are cyclically repeated until further production of oil from the formation becomes uneconomical.