Under conditions prevailing in many oil reservoirs, gas-oil displacement has higher microscopic sweep efficiency than water-oil displacement. However, the mobility ratio between injected gas and the displaced oil bank is typically unfavourable because the relatively low viscosity of the injected phase. A technique developed to overcome this problem is to inject slugs of water and gas alternately (WAG process). Simultaneous flow of the two fluids results in a reduction of the mobility of each phase, and thus the mobility of the process is improved.
This paper an experimental study of immiscible WAG (water alternating gas) injection is presented. Core flooding experiments were performed using a homogeneous sandstone core rock. Multi-step core flooding procedure was performed with brine, nitrogen and viscous oil. Comparison of phase cycling sequences has been investigated. The results showed that alternating the injection of water and gas additional oil was recovered. The final oil recovery was higher in the cycles where the sequence was initiated by water injection before the immiscible gas.
Numerical simulations of the experiments were performed and microscopic sweep efficiency was investigated. Matching the oil production and the pressure drop during the displacements, water-oil and gas-oil relative permeability curves have been obtained.
