Produced Fluid Changes During A Fireflood

Abstract The Cities Service-U.S. DOE Bodcau In-Situ Combustion Project in Bellevue Field, Bessier Parish, Louisiana, has been in progress since 1976. During this fireflood, oil, gas and water produced at 37 wells were analyzed five times to measure changes in the fluids resulting from the fireflood. One analysis was done during the dry burn phase of the project and four were done during the simultaneous water-air injection phase. Temperatures as high as 800 deg. C are reached in the dry burn phase and as high as 550 deg. C in the wet combustion phase. Burning of coke and oil at these high temperatures results in complicated chemical and physical changes of the fluids. Hydrothermolysis of the crude oil by the fireflood resulted in a lower sulfur content, a shift in the distillation curve toward increased amounts of lighter components and a slight increase in the API gravity and a decrease in viscosity. The methane concentration in the produced gas increased during the fireflood. Evidence indicates that this methane increase was produced by coke gasification reactions rather than thermal degradation of the crude oil. Introduction The Bellevue Field is located in Bessier Parish, Louisiana, east of Shreveport. The field was discovered in the 1920's, but due to the high oil viscosity, the wells produced at very slow rates. Pilot fireflooding began in the late 1960's. The Pilot fireflooding began in the late 1960's. The pilot firefloods were successful and the DOE project pilot firefloods were successful and the DOE project expansion began in 19761. Air injection in the five project patterns began in August-September 1976. project patterns began in August-September 1976. In March 1977, water injection into the upper part of the oil formation began. The produced fluids were analyzed five times from 1976–1979. One analysis was done during the dry-burn phase and four have been done during the wet phase and four have been done during the wet combustion phase. The oil analyses were done to determine any changes in the oil properties during the fireflooding project. Viscosity, boiling-point curves, gravity, project. Viscosity, boiling-point curves, gravity, percent sulfur, acid number and percent emulsified percent sulfur, acid number and percent emulsified water were measured. Viscosities were measured at three temperatures (37.8 deg. C, 48.9 deg. C and 60 deg. C) and at various shear rates on a Brookfield variable shear viscometer. In the May 1979 analyses, viscosity measurements were done on the oil-water emulsion and on the oil after removing emulsified water. The combustion gases were analyzed to monitor the progress of the fireflood. Percent oxygen, carbon progress of the fireflood. Percent oxygen, carbon dioxide, carbon monoxide nitrogen and hydrocarbons were measured by gas chromatography. Hydrogen sulfide analyses were done by the Tutweiler method and by the Cadium Sulfate Iodometric Procedure. In addition to these complete gas analyses, oxygen, carbon dioxide and carbon monoxide concentrations were measured twice monthly by field personnel using the Orsat procedure. The hydrocarbon and hydrogen sulfide concentrations were monitored to detect hydrothermolysis of oil or other chemical changes due to the fireflood. The sulfur content of the crude oil was reduced from the native oil concentration, showing that sulfur in oils was converted to hydrogen sulfide. Methane concentrations increased during the wet combustion phase of the fireflood. P. 277