Experimental Investigation of In Situ Combustion at Low Air Fluxes

Abstract

Abstract The oil industry has inherited a mixed history of success and failure of application of air injection as an enhanced oil recovery method. Close scrutiny of these projects shows that in order to conduct a successful in situ combustion oil recovery project, sustained propagation of the combustion front within the reservoirs is a must. Sufficient air must be supplied to maintain the propagating combustion front in the desired bond scission (carbon oxide forming) mode otherwise unfavorable oxygen addition i.e. Low Temperature Oxidation (LTO) reactions will consume oxygen and not mobilize oil. When this happens, the combustion process is deemed to be exhausted. Quantification of the minimum air flux required for sustaining combustion zone propagation is needed to properly match the capacity of the air injection facility to the volume of reservoir which is to be swept by the thermal zone. Undersizing of the air injection capacity causes the in situ combustion process to become inefficient when only a small portion of the reservoir has been "burned". One-dimensional combustion tubes (CTs) are conventionally used to obtain important combustion parameters required for designing an air injection project. Due to the high heat capacity of laboratory equipment designed for elevated temperature and pressure operation, oxygen addition or LTO reactions are promoted by the heat transfer through the core holder walls when the laboratory tests are performed at low air injection rates. Therefore, when operated at elevated pressures, the CTs are unable to operate at the low air fluxes required to establish the minimum possible air injection flux while maintaining the combustion reactions in an effective mode. To address this issue, a state of the art combustion cell was conceived and utilized as a way of addressing the above mentioned constraints associated with high pressure one-dimensional combustion tubes. A conical combustion cell design was built as it enables continuous air flux reductions without having to adjust the air injection rate. The heater control strategy was also modified in order to address the lag-lead operation often used for one-dimensional combustion tubes. To date, the unit has operated at air fluxes down to 3 sm3/m2∙h. This experimental work described in this paper provides insight into the limitations in laboratory investigations of in situ combustion as well as the expected behavior of field applications of the in situ combustion process.