Modification of a hybrid fluoro-surfactant containing double fluorocarbon chains on the carbonate and shale rocks for the wettability reduction of water and oil

An original hybrid fluoro-surfactant DHE with double fluorocarbon chains was synthesized. This surfactant aimed to reduce significantly the wettability of water and oil on the carbonate and shale rocks and adapt to the high salinities of the formation water. This could enhance the imbibition and injection of water in the matrix of carbonate reservoirs and the fracturing flowback in shale reservoirs. DHE showed good interface activities in saltfree and brine solutions, and remarkable water- and oil-wettability reduction on the two kinds of rocks. Moreover, its tolerant-NaCl concentrations were not below 80 g/L. The diameters of DHE mono-molecules were 1.5-4 nm and innumerable worm-like micelles were observed by TEM at the critical micelle concentration of 1.2 g/L in water. After being modified only using the 0.03 g/L DHE saline with 30 g/L NaCl for the carbonate rock, the surface energy was reduced substantially, so the primary water- and oil-wetting (0: 43-50.6 degrees) on the rock changed to nearly intermediate wetting (0: 85.0- 87.4 degrees), which was the most ideal wetting state for oil and gas production in reservoirs. Moreover, the modifying effect of DHE on the rocks became stronger with the DHE and salt concentrations in the DHE brines. Therefore, it was found that the capillary pressure could be changed to zero using very small amounts of hybrid fluoro-surfactants such as DHE because the rocks could be altered to intermediate wetting for water and oil phases. Consequently, the oil recovery in the water-flooding of carbonate reservoirs and the fracturing flowback in shale reservoirs would be improved significantly.