Abstract
Tight sands are abundant in nanopores leading to a high capillary pressure and normally a low fluid injectivity. As such, spontaneous imbibition might be an effective mechanism for improving oil recovery from tight sands after fracturing. The chemical agents added to the injected water can alter the interfacial properties, which could help further enhance the oil recovery by spontaneous imbibition. This study explores the possibility of using novel chemicals to enhance oil recovery from tight sands via spontaneous imbibition. We experimentally examine the effects of more than ten different chemical agents on spontaneous imbibition, including a cationic surfactant (C12TAB), two anionic surfactants (O242 and O342), an ionic liquid (BMMIM BF4), a high pH solution (NaBO2), and a series of house-made deep eutectic solvents (DES3–7, 9, 11, and 14). The interfacial tensions (IFT) between oil phase and some chemical solutions are also determined. Experimental results indicate that both the ionic liquid and cationic surfactant used in this study are detrimental to spontaneous imbibition and decrease the oil recovery from tight sands, even though cationic surfactant significantly decreases the oil–water IFT while ionic liquid does not. The high pH NaBO2 solution does not demonstrate significant effect on oil recovery improvement and IFT reduction. The anionic surfactants (O242 and O342) are effective in enhancing oil recovery from tight sands through oil–water IFT reduction and emulsification effects. The DESs drive the rock surface to be more water-wet, and a specific formulation (DES9) leads to much improvement on oil recovery under counter-current imbibition condition. This preliminary study would provide some knowledge about how to optimize the selection of chemicals for improving oil recovery from tight reservoirs.
Highlights
Spontaneous imbibition is a common phenomenon encountered in subsurface reservoirs (Hatiboglu and Babadagli 2010)
interfacial tensions (IFT) alteration between surfactant solutions and crude oil is recognized as a crucial mechanism for enhancing oil recovery
This study tested the IFTs between the light crude oil and the solutions of NaCl, NaBO2, ionic liquid, O342, DES6, DES14, and C12TAB with different concentrations, respectively
Summary
Spontaneous imbibition is a common phenomenon encountered in subsurface reservoirs (Hatiboglu and Babadagli 2010). In the reservoirs with weakly water-wet or neutral wet state, the gravity plays a more important role in producing oil and a lower IFT contributes to the oil recovery enhancement (Mohammed and Babadagli 2015). Other factors such as oil properties, temperature, boundary condition, and flow type (such as co-current and countercurrent flow) remarkably control the imbibition rate and oil recovery (Babadagli 2001a; Fischer and Morrow 2005; Behbahani et al 2006). For oil-wet tight reservoirs, spontaneous imbibition will occur only after wettability alteration while maintaining high oil–water IFT (Sheng 2017)
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