Surfactant flooding interfacial tension effects

PH Krumkine, JS Falcone, TC Campbell. Surfactant flooding. 1 The effect of alkaline additives on interfacial tension, swfactant adsorption, and recovery efficiency. Soc Petrol Eng J 22 503, 1982. 

In the 1990s, the thmst of surfactant flooding work has been to develop surfactants which provide low interfacial tensions in saline media, particularly seawater require less cosurfactant are effective at low concentrations and exhibit lower adsorption on rock. Nonionic surfactants such as alcohol ethoxylates, alkylphenol ethoxylates (215) and propoxylates (216), and alcohol propoxylates (216) have been evaluated for this appHcation. More recently, anionic surfactants have been used (216—230). 

Acid flooding can be successful in formations that are dissolvable in the particular acid mixture, thus opening the pores. Hydrochloric acid is common, in a concentration of 6% to 30%, sometimes also with hydrofluoric acid and surfactants added (e.g., isononylphenol) [130,723]. The acidic environment has still another effect on surfactants. It converts the sulfonates into sulfonic acid, which has a lower interfacial tension with oil. Therefore a higher oil forcing-out efficiency than from neutral aqueous solution of sulfonates is obtained. Cyclic injection can be applied [4,494], and sulfuric acid has been described for acid treatment [25,26,1535]. Injecting additional aqueous lignosulfonate increases the efficiency of a sulfuric acid treatment [1798]. 

Effect of Ca2. In many reservoirs the connate waters ontain substantial quantities of divalent ions (mostly Ca . In alkaline flooding applications at low temperatures, the presence of divalent ions leads to a drastic increase in tensions r35,36]. Kumar et al. f371 also found that Ca and Mg ions are detrimental to the interfacial tensions of sulfonate surfactant systems. Detailed studies at elevated temperatures appear to be non-existent. 

The surfactant did not cause viscous forces to dominate during immiscible tertiary carbon dioxide injection. Apparently, the unmobilized oil reduced the foam stability while the surfactant reduced the interfacial tension and therefore the COj-brine capillary pressure sufficiently to allow gravity effects to dominate the flood.(9)... 

P7-28a An understanding of bacteria transport in porous media is vital to the efficient operation of the water flooding of petroleum reservoirs. Bacteria can have both beneficial and harmful effects on the reservoir. In enhanced microbial oil recovery, EMOR, bacteria are injected to secrete surfactants to reduce the interfacial tension at the oil-water interface so that the oil will flow out more easily. However, under some circumstances the bacteria can be harmful, by plugging the pore space and thereby block the flow of water and oil. One bacteria that has been studied, Leuconostoc mesenteroides, has the unusual behavior that when it is injected into a porous medium and fed sucrose, it greatly... 

Surfactant Mixing Rules. The petroleum soaps produced in alkaline flooding have an extremely low optimal salinity. For instance, most acidic crude oils will have optimal phase behavior at a sodium hydroxide concentration of approximately 0.05 wt% in distilled water. At that concentration (about pH 12) essentially all of the acidic components in the oil have reacted, and type HI phase behavior occurs. An increase in sodium hydroxide concentration increases the ionic strength and is equivalent to an increase in salinity because more petroleum soap is not produced. As salinity increases, the petroleum soaps become much less soluble in the aqueous phase than in the oil phase, and a shift to over-optimum or type H(+) behavior occurs. The water in most oil reservoirs contains significant quantities of dissolved solids, resulting in increased IFT. Interfacial tension is also increased because high concentrations of alkali are required to counter the effect of losses due to alkali-rock interactions. 

This method is also known as micellar flooding, microemulsion flooding, or low tension water fiooding. The primary effect of the use of surfactants is the lowering of the interfacial tension between the driving fluid and the oil. More formally the capillary number, Ac, is... 

A new dimensionless number called the trapping number has been defined it includes both gravity and viscous forces (UTCHEM-9.0, 2000). The dependence of residual saturations on interfacial tension is modeled in UTCHEM as a function of the trapping number. This is a formulation necessary to model the combined effect of viscous and buoyancy forces in three dimensions. Buoyancy forces are much less important under enhanced oil recovery conditions than under typical surfactant-enhanced aquifer remediation (SEAR) conditions therefore, it had not been carefully considered under three-dimensional surfactant flooding held conditions. 

Several micellar-polymer flooding models as applied to the EOR are discussed in [237]. It is noted that the co-solvent ordinarily used in this process considerably influences not only the microemulsion stabilisation, but also the removal of impurities in the pores of the medium. The idea of using an alkali in micellar-polymer flooding is discussed in [238] in detail. The alkali effect on the main oil components was studied aromatic hydrocarbons, saturated and unsaturated compounds, light and heavy resin compounds and asphaltenes. It is demonstrated that at pH 12 surfactants formed from resins allow to achieve an interfacial tension value close to zero. For asphaltenes, such results are achieved at pH 14. In the system alkali solution (concentration between 1300 to 9000 ppm)/crude oil at 1 1 volume ratio a zone of spontaneous emulsification appears, which is only possible at ultra-low interfacial tensions. 

Macroemulsion and Microemulsion Flooding If a suitable surfactant is injected into the reservoir, it can form macroemulsions and/or microemulsions with the reservoir oil depending on the composition and reservoir conditions. Several articles have been published on the recovery of oil by microemulsion and macroemulsion flooding processes.Among various factors, the most important factor of surfactant flooding in the form of an emulsion is the lowering of the interfacial tension (IFT) at the oil/water interface. Microemulsions are more effective in oil displacement as compared to macroemulsions because microemulsions can provide low IFT systems. 

The data from these tests show that sodium orthosilicate is more effective than sodium hydroxide in recovering residual oil under the conditions studied, both for continuous flooding and when 0.5 PV of alkali was injected. The mechanisms through which sodium orthosilicate produced better recovery than sodium hydroxide in this system have not been completely elucidated. Reduction in interfacial tension is similar for both chemicals, so other factors must play a more important role. Somasundaran (26) has shown that sodium silicates are more effective than other alkaline chemicals in reducing surfactant adsorption on rock surfaces. Wasan (27,28) has indicated that there are differences in coalescence behavior and emulsion stability which favor sodium orthosilicate over sodium hydroxide. Further work is being done in this area in an attempt to define the limits of physically measurable parameters which can be used for screening potential alkaline flooding candidates. 

The equilibrated and nonequilibrated oil/brine/surfactant systems differed in their oil displacement efficiency. The equilibrated oil rather than the equilibrated aqueous phase of the surfactant solution is responsible for the high oil displacement efficiency of dilute surfactant systems containing no alcohol. The oil soluble fraction of petroleum sulfonate is more effective in lowering the interfacial tension and in promoting the flattening of oil drops. Almost 94% oil recovery was achieved in sandpacks by a low concentration ( 0.1%) surfactant plus alcohol formulation when used in place of brine flooding. 

Low interfacial tensions and minimal surfactant loss due to interactions with reservoir solids are two of the most important conditions for effective oil recovery by displacement fluids in chemical flooding. These two requirements are, of course, related surfactant adsorption from a microemulsion whose properties have been carefully designed leads to changes in the composition and therefore in the interfacial behavior of the microemulsion. 

These examples indicate a need for very careful examination of surfactant adsorption data in terms of the adsorption of individual components of surfactant mixtures. Also, if only one surfactant in the mixture produces ultralow interfacial tensions, then its own isotherm may have a more important effect on the results of a surfactant flood than the overall isotherm. 

The salinity of poljmier solution can influence four major parameters of surfactant-pol)mi r flooding process, namely, interfacial tension, mobility control, surfactant loss and phase behavior. When polymer solution of various salinities are equilibrated with surfactant solution in oil, the formation of lower, middle and upper phase microemulsion has been observed (1) similar to the effect of increasing connate water salinity (2,3). In general, there is an optimal salinity (2) which produces minimum interfacial tension and maximal oil recovery (1,4). On the basis of interfacial tension alone, the salinity of polymer solution should then be designed at or near the optimal salinity of the preceding surfactant formulation. 

This causes an increase in the microemulsion/brine interfacial tension. In a core flood this may lead to trapping of a microemulsion phase and thus to high surfactant losses. Polymer may also cause a drastic increase in the viscosity of the microemulsion (perhaps a non-equilibrium effect), which is an additional factor hampering the displacement efficiency and thus increasing surfactant loss. 

Cmc values are important in virtually all of the petroleum industry surfactant applications. For example, a number of improved or enhanced oil recovery processes involve the use of surfactants including micellar, alkali/surfactant/polymer (A/S/P) and gas (hydrocarbon, N2, CO2 or steam) flooding. In these processes, surfactant must usually be present at a concentration higher than the cmc because the greatest effect of the surfactant, whether in interfacial tension lowering [30] or in promoting foam stability [3J], is achieved when a significant concentration of micelles is present. The cmc is also of interest because at concentrations... 

Recently, Wellington and Richardson [J5] presented an interesting paper discussing the mechanism of low surfactant concentration enhanced water flood. The surfactant system consisted of alkyl-PO-EO glyceryl sulfonate with small amounts of an ethoxylated cationic surfactant to control phase behavior, interfacial activity, and surfactant loss. The surfactant systems had the ability to reduce their cloud point and interfacial tension when diluted, which was regarded as very useful for an effective flood performance. A surfactant concentration of about 0.4% removed essentially all the residual oil from sand packs in just over f PV with a surfactant loss of less than O.f PV. Mobility control by polymer was strongly required for good displacement and sweep efficiency and to reduce surfactant loss. 

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