AAPG Latin America and Caribbean Region Geoscience Technology Workshop

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Analysis of 3-phase Behavior in WAG Injections for Various Wettabilities

Abstract

WAG increments are known to be quite variable, both in the field and in the simulations, and are often analysed by splitting the WAG applications between miscible and immiscible cases. The authors are quite convinced that the more complex theory combining wettability and interfacial tensions, predicting the wetting order at pore scale, is relevant at core scale and field scale, and that it could explain some surprisingly good results of immiscible WAG in oil-wet reservoirs, and some disappointing results of miscible WAG in water-wet conditions. In coherence with this existing theory, we have adapted our wetting model, and extended the Larsen- Skauge model to allow water trapping as well as gas trapping. It allows to reproduce quite well the serious water injectivity limitations for WAG in rather water-wet reservoirs, as well as the absence of this issue in oil-wet operations. We also believe that the 3-phase relative permeability corrections which are applied to the 2-phase inputs need to be consistent with that pore occupancy scheme, and have explained notionally how the parameters should vary with wettability. Naturally, further work is needed to consolidate these findings, but some suggestions are already made to estimate the new parameters to use with extended 3-phase hysteresis model. Useful representations on ternary diagrams and injectivity plots are proposed, and the link to wettability is discussed. WAG increments are known to be quite variable, both in the field and in the simulations, and are often analysed by splitting the WAG applications between miscible and immiscible cases. The authors are quite convinced that the more complex theory combining wettability and interfacial tensions, predicting the wetting order at pore scale, is relevant at core scale and field scale, and that it could explain some surprisingly good results of immiscible WAG in oil-wet reservoirs, and some disappointing results of miscible WAG in water-wet conditions. In coherence with this existing theory, we have adapted our wetting model, and extended the Larsen- Skauge model to allow water trapping as well as gas trapping. It allows to reproduce quite well the serious water injectivity limitations for WAG in rather water-wet reservoirs, as well as the absence of this issue in oil-wet operations. We also believe that the 3-phase relative permeability corrections which are applied to the 2-phase inputs need to be consistent with that pore occupancy scheme, and have explained notionally how the parameters should vary with wettability. Naturally, further work is needed to consolidate these findings, but some suggestions are already made to estimate the new parameters to use with extended 3-phase hysteresis model. Useful representations on ternary diagrams and injectivity plots are proposed, and the link to wettability is discussed. WAG increments are known to be quite variable, both in the field and in the simulations, and are often analysed by splitting the WAG applications between miscible and immiscible cases. The authors are quite convinced that the more complex theory combining wettability and interfacial tensions, predicting the wetting order at pore scale, is relevant at core scale and field scale, and that it could explain some surprisingly good results of immiscible WAG in oil-wet reservoirs, and some disappointing results of miscible WAG in water-wet conditions. In coherence with this existing theory, we have adapted our wetting model, and extended the Larsen- Skauge model to allow water trapping as well as gas trapping. It allows to reproduce quite well the serious water injectivity limitations for WAG in rather water-wet reservoirs, as well as the absence of this issue in oil-wet operations. We also believe that the 3-phase relative permeability corrections which are applied to the 2-phase inputs need to be consistent with that pore occupancy scheme, and have explained notionally how the parameters should vary with wettability. Naturally, further work is needed to consolidate these findings, but some suggestions are already made to estimate the new parameters to use with extended 3-phase hysteresis model. Useful representations on ternary diagrams and injectivity plots are proposed, and the link to wettability is discussed.