Mechanistic Modelling for Field Trial of Enhanced Water-Alternating-Gas (EWAG) Injection in Malaysian Oilfields

Abstract

Application of gas injection to displace crude oil for pressure maintenance and improving oil recovery often suffer from severe viscous fingering and gravity override. As such, Water-Alternating-Gas (WAG) injection mode is usually promoted, in order to improve macroscopic and microscopic displacements. The improvement in oil recovery due to WAG injection is attributed to the contact of the unswept zones and modification of residual oil saturations, targeting the attic oil. Hysteretic effects which changes saturation paths, due to sequential injection of water and gas, additionally improve the recovery. The gas flow may, however, still develop preferential paths that bypass many unswept regions because of its inherent viscosity and density differences against water. Foam as gas mobility controller has been studied and introduced to enhance WAG displacement process. It acts as a blocking agent in high-permeability zones and diverts the gas flow to the other oil-trapped regions. Foam is a discontinuous phase which consists of liquid lamella and foam gas. Having intermediate behaviours between water and gas, its stability is strongly dependent on the component saturation, strength, size, gas quality etc. As a result, it poses a great challenge to simulate these complex mechanisms and behaviours, not to mention the pertaining effects in the porous media. At present, foam mechanisms are widely modelled via simple quasi-equilibrium approach using interpolation parameters, such as oil saturation, capillary number etc. to correlate the corresponding Mobility Reduction Factor (MRF). This paper presents the foam model results which intend to predict the foam injectivity at wellbore conditions, subsequently developing an injection proposal scheme for the field trial of EWAG process in Malaysia oilfields. In turn, the field trial results later will be history-matched, aiming to improve the prediction model for successive full-field modelling. The mechanistic modelling approach employed in this study takes into account of changes of lamella densities, allowing foam degradation and regeneration via stoichiometric reaction expressions. The mobility control is modelled throughinterpolation of relative permeability using foam gas concentration as interpolator andpermeability blockage in the presence of trapped lamella in solid form.