Water and surfactant flooding at different wettability conditions

Master's thesis in Petroleum engineeringIn a surfactant flooding of oil reservoirs, surfactant products are added to the injected water to reduce the oil-water interfacial tension (IFT) and thereby mobilize capillary trapped oil. The theory in classic surfactant floods is based on water-wet sandstone reservoirs. It is now known that the wettability of sandstone reservoirs is often characterized as mixed-wet. The classic theory for surfactant flooding cannot be applied. This thesis characterizes water flooding and surfactant flooding at different wettability conditions in Berea rock. Different wettability conditions (water-, oil- and mixed-wetting) are established by the chemical product Quilon L. Three experiments will be carried out in the laboratory. In the first experiment (static), the wettability of treated and untreated minerals and crushed rock is characterized to evaluate the wettability alteration by the chemical Quilon L. Then, in the second experiment (stability test), water and surfactant flooding is performed in treated and untreated Berea core plugs to study the stability of the wettability alteration. Finally, in the third experiment, water flooding and surfactant flooding is applied at multiple rates to Berea core plugs at different wettability conditions to observe the characteristics in each type of rock. Results obtained in these experiments show that water flooding is more effective in strongly oil-wet and mixed-wet rocks reducing remaining oil saturation to very low values or close to zero. Conversely, surfactant flooding is more effective in strongly water wet rocks due to high remaining oil saturation after water flooding. Also, capillary number in water flooding ranges from 10 -8 and 10 -6 whereas in surfactant flooding 10 -6 and 10 -4 in all cases