Screening and Uncertainty Assessment of Foam-Assisted Water-Alternate Gas Injection
H. Groot, J. Groenenboom, N.I. Kechut, N.M. Rahayu Razali, S. Vincent-Bonnieu and A. Mar-Or
Event name: IOR 2019 – 20th European Symposium on Improved Oil Recovery
Session: Modelling Foams
Publication date: 08 April 2019
Info: Extended abstract, PDF ( 2Mb )
Price: € 20
In a Foam-Assisted Water-Alternate Gas injection (FAWAG) process, surfactant is used to reduce the mobility of the gas by creating foam in the reservoir. This process potentially improves the performance of a Water-Alternate Gas injection (WAG) process. The effective dynamic behaviour of FAWAG can be highly complex and often stands in contrast to the behaviour of WAG. This paper presents insights in the effective dynamic behaviour of FAWAG and a comparative study of its sensitivity to uncertainties, reservoir conditions, field design and modelling assumptions, which is important for risk mitigation, opportunity realisation and process optimisation. In this paper the FAWAG process is modelled from the assumption of local equilibrium of foam creation and coalescence using an Implicit Texture model. Sensitivities to uncertainties, pattern design and reservoir screening parameters are studied to identify and analyse the key parameters impacting the FAWAG process as opposed to a WAG process and quantify the reliability of production forecasts with FAWAG. A box reservoir model is used for the study that represents a line drive pattern and can mimic a wide range of different reservoir conditions, injection strategies and pattern designs. A ranking is made of the sensitivity parameters according to their ultimate impact on oil recovery. The results are compared with the literature. From the sensitivity study it is concluded that FAWAG is mostly sensitive to permeability and well-spacing because of the relatively low throughput rate, while in contrast WAG is mostly sensitive to reservoir heterogeneity and oil viscosity as the process requires high displacement stability. In addition, FAWAG requires high throughput rate or project duration to overcome high heterogeneity and oil viscosity in the long run. It shows that the optimal conditions for a successful FAWAG are high permeability, small well-spacing, high layer connectivity and favourable conditions for injectivity. Furthermore, FAWAG can still be expected to perform well in a reservoir with high heterogeneity and reasonably high oil viscosity, which could turn out to be detrimental conditions for iWAG. Finally, a successful FAWAG project requires optimal conditions for foam generation in the reservoir, which means foam strong enough to improve mobility control, yet not too strong to impair injectivity. However, the optimal conditions for foam at field scale often prove to be highly uncertain in practice and should be determined from field pilots or injectivity tests.