Heat injection process

Abstract

A method for heat injection into a subterranean formation is provided. The method utilizes flameless combustion. The absence of a flame eliminates the flame as a radiant heat source and results in a more even temperature distribution throughout the length of the burner. Flameless combustion is accomplished by preheating the fuel and the combustion air to a temperature above the autoignition temperature of the mixture. Preheating hydrocarbon fuel requires the inclusion of a carbon formation suppressant such as carbon dioxide or steam to prevent carbon formation.

I claim: 
     
       1. A method of heating a subterranean formation comprising at least one borehole providing communication from the surface to the subterranean formation to be heated, the method comprising: combining a hydrocarbon fuel gas with a carbon formation suppressant;   passing the fuel gas and carbon formation suppressant mixture through a fuel gas conduit to a mixing point within the borehole juxtapose to the formation to be heated;   passing a combustion air stream though an air conduit to the mixing point;   preheating either the fuel gas and carbon formation suppressant mixture, the combustion air stream or both such that the temperature of a mixture of the streams exceeds an autoignition temperature of the mixture of the streams;   combining the preheated combustion air and fuel gas and carbon formation suppressant at the mixing point resulting in autoignition forming combustion products;   passing the combustion products through the borehole from the mixing point to the surface, wherein the amount of the carbon formation suppressant combined with the fuel gas exceeds that which prevents carbon formation at the temperature of the preheated fuel gas and carbon suppressant mixture.     
     
     
       2. The method of claim 1 wherein the fuel gas and carbon formation suppressant mixture and the combustion air are both preheated by heat exchange with the combustion products flowing from the mixing point to the surface. 
     
     
       3. The method of claim 2 wherein additional preheated fuel gas and carbon formation suppressant is mixed with the combustion products in the borehole between the mixing point and the surface at points that are juxtapose to the formation to be heated. 
     
     
       4. The method of claim 2 wherein the fuel gas consists essentially of methane. 
     
     
       5. The method of claim 4 wherein the fuel gas and carbon formation suppressant mixture and the combustion air are both heated to a temperature above about 1000° F. 
     
     
       6. The method of claim 5 wherein the carbon formation suppressant comprises water and the mole ratio of water to carbon in the stream is greater than about 1. 
     
     
       7. The method of claim 5 wherein the carbon formation suppressant comprises carbon dioxide and the mole ratio of carbon dioxide to fuel gas carbon is greater than about 1. 
     
     
       8. The method of claim 5 wherein the carbon formation suppressant comprises a mixture of carbon dioxide and water. .Iadd. 
     
     
       9.  A method of supplying heat using a flameless combustor, the method comprising: combining a hydrocarbon fuel gas with a carbon formation suppressant;   passing the fuel gas and carbon formation suppressant mixture through a fuel gas conduit to a mixing point within the flameless combustor;   passing a combustion air stream though an air conduit to the mixing point;   preheating either the fuel gas and carbon formation suppressant mixture, the combustion air stream or both such that the temperature of a mixture of the streams exceeds an autoignition temperature of the mixture of the streams; and   combining the preheated combustion air and fuel gas and carbon formation suppressant at the mixing point resulting in autoignition forming combustion products, wherein the amount of the carbon formation suppressant combined with the fuel gas exceeds that which prevents carbon formation at the temperature of the preheated fuel gas and carbon suppressant mixture. .Iaddend.