Alkali plays a unique role in the alkaline/surfactant/ polymer (ASP) flood processes. It has been well recognized that the injected alkali can generate the surfactants in situ by reacting with the organic acids in the crude oil. Such generated surfactants will reduce the interfacial tension (IFT) and mobilize the residual oil in a reservoir. On the other hand, the reservoir rock surface will become more negatively charged at higher hydroxyl ion concentrations. These ions adsorbed onto the rock surface not only deter the adsorption of anionic chemicals, such as anionic surfactants and polymers, but also alter its wettability. In this paper, an experimental study is conducted on the interactions of alkaline solutions with oil-brine-rock systems in ASP flood processes. First, the total alkaline loss is determined by measuring the alkaline concentration change. Physically, alkaline loss is caused by the pair interactions of alkalioil, alkali-brine, and alkali-rock, respectively. The alkaline loss due to the alkali-oil chemical reactions mainly depends on the acid number of the crude oil. The alkaline loss also occurs when alkali reacts with the divalent cations in the brine, such as Ca2+ and Mg2+. The adsorption of alkali onto the rock surface is usually considered as the largest portion of the total alkaline loss, given the enormous rock surface area available in a reservoir. In addition, the silicon dissolution caused by the alkali-rock chemical reactions is quantified in terms of sand loss. Secondly, the IFT is measured as a function of alkaline concentration by using the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case. Thirdly, the interactions among alkali, surfactant and polymer are studied. Furthermore, the coreflood tests of alkaline flood are performed and the detailed coreflood results show that alkaline flood can enhance oil recovery up to 12.7%. It is also found that the alkali remaining in the produced fluids can be effectively reused for further enhancing oil recovery.
It is well known that a typical oil recovery for waterflooding is usually around 30-40%. Thus, there is still 60-70% original oil in place (OOIP) left in the reservoir in the form of oil ganglia. This residual oil is trapped mainly due to high capillary pressure, i.e., high IFT at the oil-brine interface. Further oil recovery can be enhanced by increasing the oil displacement efficiency and the sweep efficiency simultaneously (1–4). ASP flood is a promising EOR technique applied to recover the residual oil. The major EOR mechanisms of ASP flood are described as follows. In conjunction with the added surfactant, the surfactants generated in situ by the chemical reactions between the injected alkali and the natural organic acids in the crude oil can result in ultralow IFT. The ultra-low IFT at the oil-brine interface helps to emulsify and mobilize the residual oil in a reservoir. In addition, the reservoir rock surface becomes more negatively charged at higher hydroxyl ion concentrations. These negatively charged ions not only prevent the adsorption of anionic chemicals, such as anionic surfactants and polymers, but also change the wettability of the rock surface (5–6)
