Composition for recovering hydrocarbons

#1. Field of the Invention

#This invention relates to a method of recovering hydrocarbons from a subterranean hydrocarbon-bearing formation. More particularly, this invention relates to a method of recovering hydrocarbons in which in situ combustion is first conducted in the formation after which a mixture of hydrogen and carbon monoxide is injected into the formation where reaction of the injected carbon monoxide and steam generated from the formation water takes place thus generating additional hydrogen and carbon dioxide and hydrocarbons are recovered from the formation via a production well.

#2. Prior Art and Background

#The in situ combustion step in the process of my invention is carried out by a conventional manner using known techniques. For example, a combustion supporting gas such as oxygen as contained in air or a mixture of air and oxygen, for example, is injected into the injection well or wells and is forced through the formation to the production wells. Next, ignition of reservoir hydrocarbons and the oxygen or air and oxygen mixture is initiated by conventional methods and once combustion is attained the combustion front is propagated through the formation toward the production wells. As this in situ combustion operation proceeds, the heat from the operation lowers the viscosity of the inplace hydrocarbons which are moved toward the production wells where they are produced.

#After the first step in the process of this invention, i.e., the in situ combustion step has been operated for a period of about 30 to about 120 days or more and after the combustion zone has propagated for some distance away from the well bore, i.e., from 10 to about 100 ft. or more, injection of the combustion-supporting gas, which can be air, an air and oxygen mixture, etc. is terminated and, if desired, the unconsumed combustion-supporting gas behind the combustion zone is displaced by injection into the formation via the injection well of an inert gas such as nitrogen, carbon dioxide, etc. The temperature of the formation at the conclusion of the in situ combustion step will be about 80.degree. to about 1500.degree. F. or more.

#In the next step of the process of this invention a mixture of hydrogen and carbon monoxide, for example, as obtained from a synthesis gas generator is injected into the formation via the injection well. If a hydrogen-carbon monoxide mixture obtained from a synthesis gas generator is employed, the ratio of hydrogen to carbon monoxide by volume will depend on the type of fuel employed as feed for the generator. During the step in which the hydrogen-carbon monoxide mixture is injected, additional hydrogen and carbon dioxide are formed by reaction between the carbon monoxide and the in place steam generated from the formation water during the in situ combustion step. The advantages of carbon dioxide in recovering oil from hydrocarbon bearing formations are well known and its use as a displacement medium has been demonstrated. Carbon dioxide having a high solubility in oil causes the oil to swell and substantially reduces the oil viscosity. If desired, saturated steam, wet steam or superheated steam in an amount of from about 5 to 50 percent by volume based on the volume of the carbon monoxide-hydrogen mixture may be introduced into the formation along with the carbon monoxide-hydrogen mixture. The step of in situ combustion in which a combustion-supporting gas alone is injected into the formation and the step in which a mixture of hydrogen and carbon monoxide is injected into the formation may be repeated in a cyclic manner, as desired, in operating the process of this invention.