Enhanced recovery of medium crude oil in heterogeneous reservoirs using air injection/in situ combustion-horizontal well technology

A simple 3-D physical model has been developed to investigate the use of in-situ combustion in heterogeneous reservoirs. Gas over-ride phenomena is one of the major causes of instability of combustion process; gas override results in poor sweep efficiency with subsequent low oil recovery. However, the use of horizontal wells in direct line drive arrangement has shown a great deal of combustion stability and propagation by means of controlling gas override This paper has extended the scope of using horizontal wells in direct line drive configuration in heterogeneous reservoirs. Three cases of reservoir heterogeneity were investigated in this study. In the first case, a dual-layer permeability of sand was used (a high permeability layer on top and a low permeability layer on bottom); in the second case, placement of the aforementioned layers was swapped, and in the third case, a high permeability streak was sandwiched between two low permeability layers of fine sand. The results indicated that a stable combustion front has been achieved in the first two cases with a high oil recovery, however the performance of the combustion process markedly deteriorated when a high permeability streak layer was utilised as a result of a severe low temperature oxidation due to oxygen channelling through the streak, with subsequent poor sweep efficiency and in turn low oil recovery. The use of horizontal wells as producers and injectors in a line drive configuration is beneficial and effective for minimising the effect of reservoir heterogeneity to some extent.