Ignition process for downhole gas generator

Claim 1

A process of operating a system for use for recovering hydrocarbons or other materials from underground formations penetrated by a borehole, said system including a gas generator located in the borehole, said gas generator comprising: a housing forming a chamber and having an upper inlet end for receiving fuel and an oxidizing fluid, said chamber defining a combustion zone, and a restricted lower outlet for the passage of heated gases, said system comprising: fuel conduit means extending from the surface to said inlet end for supplying fuel from the surface into said chamber, oxidizing fluid conduit means extending from the surface to said inlet end for supplying oxidizing fluid into said chamber, first valve means located in the borehole near said gas generator and coupled to said fuel conduit means, second valve means located in the borehole near said gas generator and coupled to said oxidizing fluid conduit means, and control means located at the surface for controlling said first and second valve means, said process comprising the steps of: while said first valve means is closed injecting a given fuel into said fuel fuel conduit means for flow to the level of said first valve means, while said second valve means is closed injecting a given oxidizing fluid into said oxidizing fluid conduit means for flow to the level of said second valve means, said given fuel being characterized such that it ignites spontaneously when exposed to said given oxidizing fluid, injecting a second fuel into said fuel conduit means behind said given fuel, operating said control means to open said first and second valve means for allowing said given fuel and said given oxidizing fluid to flow into said chamber for ignition of said given fuel, and flowing said second fuel and an oxidizing fluid into said chamber to form a combustible mixture which is ignited by the ignition of said given fuel.