Improved oil recovery (IOR) techniques target the 60% of oil left behind by primary and secondary methods (those that utilise the natural energy of an oil reservoir). Air injection in situ combustion (ISC) is a thermal IOR technique used in general to increase the temperature in a reservoir and in turn reduce the viscosity of the oil. This increases the mobility of the oil and can lead to significant improvement in recovery factors. The process is complex and much work is needed to improve modeling capabilities essential for reservoir management.
To investigate high pressure air injection a combustion tube facility has been commissioned and four in situ combustion tube tests completed. This involved the development of data acquisition and control software (IscView) to fully automate the air injection facility. The ISC tests were carried out with a West Shetland Clair crude oil of 19.7°API and air injection fluxes between 12 and 70m³/m²hr and pressures between 50 and 100 bar. Post-mortem analysis of the burned cores showed 100% oil displacement in areas of core swept by the combustion front. In these areas the amount fuel burned varied between 4.6 and 15.3 %OOIP (original oil in place). The combustion front temperatures varied between 450°C and 730°C. It was found that combustion front temperature increased with air injection flux. The combustion front velocity varied between 10.4 and 22.2cm/hr. The combustion front velocity was observed to increase with pressure thus the combustion front velocity and hence propagation of the combustion front was shown to be reaction rate dependent.
History matching of the ISC tests was completed using the STARS simulator (Computer Modeling Group) a fully implicit non isothermal reservoir simulator. The simulations showed that when the grid size approached that of the actual reaction zone then the kinetics at different pressures did not change. Therefore, at this grid scale, the kinetic parameters used for a pseudo component representation of the oil can be applied as if it were a pure component, independent of pressure.
|Date of Award||29 Apr 1998|