Low-Temperature Oxidation of viscous crude oils

During in-situ combustion, oxygen can bypass the flame front and react with oil temperatures that are relatively low compared with those in combustion. These reactions, called low temperature oxidation (LTO), can adversely affect the crude's physical and chemical properties and result in lower oil recovery. This paper presents laboratory study results on the LTO of four oils, ranging from 31.1 to 10.1{degrees} API and from 14 to 54,300 cp dead-oil viscosity at 85{degrees}F. They include two biodegraded oils, a mature crude and an immature heavy oil. The LTO of these oils is reported as a function of reaction time, oxygen partial pressure, and temperature. LTO increased oil viscosity and density. For the 31.1{degrees} API oil, these increases are minor and should have insignificant effects on process performance. For the heavier oils, however, the viscosity of the oxidized oils increases exponentially with increasing extent of oxidation, X{sub O{sub 2}}. relatively minor oxidation (40mg O{sub 2}/g oil) results in a six-fold increase in viscosity. The rate of viscosity increase depends on an oil's API gravity, origin, and composition. Compositional changes accompanying LTO are also discussed.