Method and apparatus for injecting a gaseous stream into a subterranean zone

In a method for injecting a free oxygen-containing gaseous stream into a subterranean zone in processes wherein elevated temperatures occur in said subterranean zone;

• said method consisting essentially of:
• (a) Positioning a casing means in fluid communication with said subterranean zone and the surface, the lower end of said casing being positioned near the bottom of said subterranean zone;
• (b) Injecting said gaseous stream into said subterranean zone through said lower end of said casing;
• an improvement comprising:
• (c) Reducing the diameter of a lower portion of said casing so that the reduced diameter lower portion of said casing has a cross-sectional area from about 5 to about 50 percent of the cross-sectional area of said casing, said lower portion extending upwardly from said lower end of said casing through said subterranean zone for a distance above said subterranean zone sufficient to protect said casing from elevated temperatures in said subterranean zone;
• (d) Positioning insulation selected from the group consisting of aluminum oxide and refractory fibers having a meeting point in excess of about 3500.degree. F. about the outer circumference of said lower portion;
• (e) Cementing said casing including said lower portion in place, said cement being positioned about the outer circumference of at least a portion of said insulation;
• and
• (f) injecting said gaseous stream into said subterranean zone through said casing, said lower portion and said lower end of said casing at a rate sufficient to maintain the casing temperature below about 900.degree. F. when elevated temperatures occur in said subterranean zone.