Abstract
Pore geometry and wettability are fundamentally the most important parameters that control the miscible displacement efficiency of oil reservoirs. Understanding the physics of solvent flooding process in micro scale can result in significant improvement to better describing the miscible processes observed in laboratory and in the field. However, displacement behavior of a co-solvent at different wettability conditions under the influence of pore geometry in five-spot models remains a topic of debate in the literature. Here, miscible solvent injection experiments performed on several one-quarter five spot glass micromodels. Network patterns with different pore geometries along with those obtained from thin sections of sandstone and carbonate rocks were used in the experiments. Wettability of the micromodels was altered towards strongly water-wet and oil-wet conditions by applying a new chemical procedure. Influence of four different groups of chemicals and their mixtures as co-solvents as well as the effect of pore geometry parameters, on microscopic and macroscopic displacement efficiency in both strongly wetted media have been investigated. Precise analyses of the high quality pictures provided continuously during experiments were used to explore the solvents' displacement behavior. An optimum mixture of co-solvents with greatest sweep efficiency was determined. The results showed that the displacement efficiency of the solvents is generally higher in strongly water-wet medium, but its extent is dependent on pore geometrical factors. Star-shape pores with higher coordination number and lower pore-throat size ratio showed maximum displacement efficiency. In addition, the sweep efficiency in heterogeneous patterns was in the range of the data obtained from network patters with similar geometrical parameters. The microscopic observations confirmed that the presence of connate water in strongly water-wet medium could improve the final recovery, while the recovery factor in absence of connate water was not affected majorly by surface wettability.
