Wettability alteration

Key mechanisms important for improved oil mobilization by microbial formulations have been identified, including wettability alteration, emulsification, oil solubilization, alteration in interfacial forces, lowering of mobility ratio, and permeability modification. Aggregation of the bacteria at the oil-water-rock interface may produce localized high concentrations of metabolic chemical products that result in oil mobilization. A decrease in relative permeability to water and an increase in relative permeability to oil was usually observed in microbial-flooded cores, causing an apparent curve shift toward a more water-wet condition. Cores preflushed with sodium bicarbonate showed increased oil-recovery efficiency [355]. 

J. Chen, G. J. Hirasaki, M. Flaum 2004, Study of Wettability Alteration from NMR Effect of OBM on Wettability and NMR Responses, paper presented at the 8th International Symposium on Reservoir Wettability, Houston, TX, May 16-18,... 

It may also be beneficial to alter the wettability (see Section 3.5.3) of the reservoir rock, particularly in order to shift oil-wetting regions towards neutral wetting, which is probably about the optimum for improved oil recovery [158]. Figure 3.23 (see Section 3.5.3) shows how surfactant adsorption can alter wettability, but not always in a simple manner. Such surfactant-induced wettability alteration might be considered for predominantly oil-wetting reservoirs such as chalk reservoirs in the North Sea. 

The large Canadian oil-sands surface-mining and water-based flotation processing operations involve a number of kinds of emulsions and foams in a variety of process steps. Whereas mineral ore flotation relies on wettability alteration and bubble attachment, oil and bitumen flotation rely more on attachment and filming to create an oleic foam. 

Spinier, E.A. Baldwin, B.A. Surfactant Induced Wettability Alteration in Porous Media in Surfactants, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), Cambridge University Press Cambridge, UK, 2000, pp. 159-202. 

The wettability of reservoir rocks can be altered by the adsorption of polar compounds or the deposition of organic material such as asphaltenes in the crude oil. Wettability alteration is determined by the interaction of oil constituents, mineral surface, and brine chemistry including ionic composition and pH. Any extraneous substance such as artificial surfactants that changes the mineral surface will change the wettability of the rock and consequently the flow of fluids inside the reservoir. 

Wettability Alteration by Seawater Injection into Chalk Formation... 

The following may be snmmarized about wettability alteration from what is shown in Fignre 3.5 ... 

The higher the reservoir temperature, the better the wettability alteration. 

FIGURE 3.6 Schematic model of the suggested mechanism for the wettability alteration induced by seawater, (a) represents the mechanism when Ca and SO/ are active at lower temperature and (b) represents the mechanism when Mg and S04 " are active at a higher temperature. Source Zhang et al. (2007a). 

A 0.1% selected surfactant was then added to the injection water. The core flood experiments showed that injection pressure was reduced by 26.6%, and that the oil recovery was increased by 6.7%. This effect was a result of wettability alteration to more water-wet, reduced immobile water and oil saturations, and increased oil and water relative permeabilities. The data are shown in Table 7.11. 

Chang (1976) showed that use of a polyphosphate, which is a buffer, improved recovery. Sodium tripolyphosphate (STPP) was used in laboratory tests for Cretaceous Upper Edwards reservoir (Central Texas). STPP was proposed to minimize divalent precipitation, for wettability alteration and emulsification (Olsen et al., 1990). Generally, it is not used as a primary alkali to generate soap for purposes of IFT reduction. Instead, it is used together with other alkalis such as sodium carbonate when divalents could be a problem (Harry Chang, Chemor Tech International, Plano, Texas, personal communication on June 16, 2009). 

Castor et al. (1981b) observed that the IFT in the alkaline flooding was on the order of 0.1 mN/m. Their capillary numbers of alkaline floods are presented in Figure 10.18. The capillary number of alkaline floods was about 100 times higher than the capillary numbers in waterfloods. The alkaline flooding results from Castor et al. show that the recovery efficiencies could be better correlated with the stability of emulsions and wettability alteration than with IFT of the systems. 

Standnes, D.C., Austad, T., 2000. Wettability alteration in chalk 2. Mechanism for wettability alteration from oil-wet to water-wet using surfactants. J. Pet. Sci. Eng. 28, 123-143. 

Strand, S., Hpgnesen, E.J., Austad, T., 2006. Wettability alteration of carbonates—effects of potential determining ions (Ca and SO/ ) and temperature. Colloids and Surfaces A Physicochemical and Engineering Aspects 275 (2006), 1-10. 

Tang, G.-Q., Firoozabadi, A., 2002. Relative permeability modification in gas/liquid systems through wettability alteration to intermediate gas wetting. SPEREE 5 (6), 427-436. 

Zhang, P., Tweheyo, M.T., Austad, T., 2007a. Wettability alteration and improved oil recovery by spontaneous imbibition of seawater into chalk Impact of the potential determining ions Ca % Mg, and SO/. Colloids and Surfaces A Physicochemical Engineering Aspects 301, 199-208. 

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