Abstract: A steam flooding method for recovering oil from an underground formation penetrated by an injection and at least one production well is modified by initially lowering the permeability of the lower vertical portion of the formation, e.g., by plugging thereof with gravel sand pack, capped by a plaster of paris or cement, thereafter continuing to inject the steam into the injection well and maintaining high level of production from the production well until thermal breakthrough is achieved in the production well. Subsequently, the initial permeability of the lower vertical portion of the formation is restored, e.g., by removing the gravel sand pack, and oil is recovered from the production well. In a preferred embodiment, the permeability of substantially the entire initial completed interval of the production well is decreased in the aforementioned manner, the well is recompleted higher in the formation and steam is continuously injected into the injection well.

Abstract: The combustion front in an in situ combustion oil recovery operation is stabilized by cyclically varying the injection rate of the gaseous oxidant which is injected through the injection well. Periodic reduction in the injection rate of the oxidant halts the advance of the combustion front through the formation and permits the formation fluids to flow in a reverse direction back towards the front so that burned through fingers or streaks collapse and any overriding tendencies of the front are corrected. In this way, the vertical conformance of the front is increased to improve the sweep efficiency of the process. The process is most effective in externally pressured formations.

Abstract: A method for operating a production well during an oxygen driven in-situ combustion oil recovery process comprising continuously injecting an inert gas such as nitrogen or carbon dioxide into the bottom of the production well at a predetermined low injection rate, preferably 0.1 to 2 MSCF/day, and continuously monitoring the oxygen concentration of the produced effluent gas and the bottomhole temperature of the production well. In the event that the oxygen content of the effluent gas increases to a value within the range of 5 to 20 volume percent or the bottomhole temperature of the production well increases to a value within the range of 200.degree. to 300.degree. F., the injection rate of the inert gas into the bottom of the production well is increased to a maximum rate until the oxygen concentration of the effluent gas and the bottomhole temperature are reduced to a safe level.

Abstract: An injection well used in an in-situ combustion oil recovery process using a high oxygen concentration gas is completed with dual tubing strings to conduct the oxygen-containing gas and nitrogen separately down the well. The gases are mixed after they leave their separate tubing strings and enter the formation through perforations in the casing. If the bottomhole temperature of the well increases to a specific level, injection of the oxygen-containing gas is terminated and injection of the nitrogen is increased to a maximum amount until the bottomhole temperature decreases to a desired level for resuming in-situ combustion. In addition, injection of water into the bottom of the well is available as a back-up in the event that injection of the nitrogen does not lower the bottomhole temperature to the desired level. The use of the separate tubing strings for nitrogen and oxygen flow permits a faster bottomhole response to be obtained if undesired temperature increases take place downhole.

Abstract: A well completion for an injection well includes continuous tubing disposed within a tubing string. Oxygen is supplied to a fire flood process through the continuous tubing and water is supplied through the tubing string. The tubing string and continuous tubing are valved and seated in a manner which provides for safe injection of high purity oxygen into the subsurface formation.

Abstract: Apparatus for mixing a gas, e.g., oxygen, and a liquid, e.g., leach solution, at a downhole location in a well for treating a formation, e.g., in situ leaching of uranium. The apparatus comprises a mixing means which is adapted to be affixed to the lower end of the gas supply conduit and is lowered into and raised out of the well by means of the conduit. The mixing means is comprised of a solid, noncorrosive plate having a central opening into which the gas conduit is secured. The plate has a plurality of additional openings surrounding the central opening and has a gasket thereon to form a seal between the plate and the well bore. Liquid is flowed down the well and passes through the additional openings in the plate. At the same time, gas is supplied through the conduit and flows through the central opening in the plate. Due to the increased velocity of the liquid caused by the liquid as it flows through the additional openings in the plate, the gas is trapped to form a gas pocket below the plate.