Polymer flooding low-tension

The low-tension polymer flood technique consists of combining low levels of polymer-compatible surfactants and a polymer with a waterflood. This affects mobility control and reduces front-end and total costs. [929]. 

T. Austad, K. Veggeland, I. Fjelde, and K. Taugbol. Physicochemical principles of low tension polymer flood. In Proceedings Volume, volume 1, pages 208-219.7th Eapg Impr Oil Recovery Europe Symp (Moscow, Russia, 10/27-10/29), 1993. 

B. Kalpakci, T. G. Arf, D. M. Grist, S. B. Hyde, O. Vikane, and S. Es-pedal. A preliminary evaluation of an LTPF (low tension polymer flood) process for Stat ord Field, Norway. In Proceedings Volume,... 

K. Taugbol, H. H. Zhou, and T. Austad. Low tension polymer flood the influence of surfactant-polymer interaction. In Proceedings Volume, pages 281-294. Rec Adv Oilfield Chem, 5th Royal Soc Chem Int Symp (Ambleside, England, 4/13-4/15), 1994. 

Kalpakci et al. [13] introduced the concept Low Tension Polymer Flood , LTPF. The flood was conducted by coinjection of surfactant and polymer and, due to chromatographic effects, the polymer moved ahead of the surfactant. In such an application, mobility of the water at the front will be reduced and the activity of the surfactant will be enhanced. The LTPF system should, according to Kalpakci, exhibit type III/II( —) (slightly under optimum) phase behavior at the injection. Ethoxylated... 

An alternative to this process is low (<10 N/m (10 dynes /cm)) tension polymer flooding where lower concentrations of surfactant are used compared to micellar polymer flooding. Chemical adsorption is reduced compared to micellar polymer flooding. Increases in oil production compared to waterflooding have been observed in laboratory tests. The physical chemistry of this process has been reviewed (247). Among the surfactants used in this process are alcohol propoxyethoxy sulfonates, the stmcture of which can be adjusted to the salinity of the injection water (248). 

A more recent study [70] examined the effects of the polymer on surfactant adsorption in a low tension polymer water flood (LTPWF). The surfactant was alkylpropoxyethoxy sulfate, Ci2-i5-(PO)4-(EO)2-0S03 Na, and the polymers were xanthan and a copolymer of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate (AN 125 from Floerger). The solid materials were sandstone cores from a North Sea oil reservoir, Berea, and Bentheim cores. For these systems the xanthan caused a 20% reduction in the adsorption of the surfactant. It was also observed that surfactant adsorption appeared to increase as the water... 

The flooding performance is termed Low Tension Polymer Water Flood, LTPWF, or low surfactant concentration enhanced water flood, and illustrated in Figure 3. 

Low Tension Polymer Water Flood. In oil reservoirs, where the critical capillary number is relatively low, a significant amount of waterflooded residual oil can be displaced by surfactants of high efficiency even at two-phase flood conditions. This was demonstrated by the snccessfnl second Ripley surfactant flood pilot test in the Loudon field where approximately 68% of waterflooded residual oil was recovered by injecting a 0.3 PV microemulsion bank [63]. The microemulsion bank was followed by I.O PV of higher viscosity polymer drive. The chemical formnlation consisted of a blend of two PO-EO sulfates. 

Obviously, it is documented in the literature that it is technically possible to perform a low tension water flood at low surfactant concentration by using polymer to control the mobility. Efforts should be made to establish good routines to synthesize PO-EO sulfonates in a reproducible and cost effective way. Mobility control is very important, and routines for preparing low cost polymers are important as well. 

A second field evaluation of the ASP process has been initiated in Wyoming. Additionally, an ASP field project has been designed for the Peoples Repubhc of China. The appHcability of the ASP process to a variety of reservoirs has yet to be fully determined. AppHcation of alkali and alkali polymer flooding has been limited to cmde oils having discernible acid numbers, wherein the alkali produced cmde oil soaps which in combination with alkali resulted in providing low interfacial tensions. The ASP process appears to be suitable for cmde oils with nil acid numbers (177), and hence should have broad apphcabdity. 

Morgan J.C., Schechter, R.S. and Wade, W.H. (1977) Recent advances in the study of low interfacial tensions. In D.O. Shah and R.S. Schechter (eds), Improved Oil Recovery by Surfactant and Polymer Flooding. Academic Press, New York, pp. 101-118. 

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. 

Recently we have carried out laboratory tests (17, 18, 19) in which the sodium silicate was added directly to a dilute surfactant solution to recover oil. Such a process would be akin to alkaline flooding processes where a dilute surfactant is formed in-situ. In this case however the crude is lighter and does not contain the natural acids necessary to form surfactants in-situ. Therefore surfactant is injected and protected or enhanced by the sodium silicate such that a low tension waterflood is assured. Such a system is less complex and therefore more widely applicable than micellar/polymer techniques thus filling the void between the alkaline and micellar/polymer EOR processes. 

Low tension waterflooding is a method intermediate between alkaline and micellar/polymer technology. The LTWF employs a dilute surfactant to reduce IFT and mobilize residual oil. A few field trials (26-29) of this process have been tried with mixed success. None of these trials however employed sodium silicates in any part of the flood design. Instead, other alkalis such as sodium carbonate and sodium tripoly- phosphate were used. Some of the reasons proposed for the limited success in these trials were 1) high consumption of the sacrificial agents, leaving the surfactant unprotected, 2) poor sweep of the pay zone, 3) limited mobility control and lower than expected displacement efficiency. Recent work published and obtained in our laboratories has shown that sodium silicates may help to overcome some of these problems better than other alkalis. 

Because of the cost and the time factors involved, oil displacement studies are always preceded by certain test tube screening procedures. Specifically, the interfacial tension (IFT) of less than 0.01 dyne/cm is recognized to be the necessary but not the sufficient criterion for selection of a surfactant system. Many investigators (10-15) have shown that ultralow IFT of less than 0.001 dyne/cm can be achieved with less than 0.1 wt. % surfactant solution. Since this low surfactant concentration system is several hundred times more dilute than the ones used in a typical surfactant-polymer flooding process, the economics dictates that the oil displacement by such low surfactant concentration solution should be explored. Moreover, it should be established that the... 

Flooding of oilfields is another example where interfacial reactions lead to changes of the Interfaclal tension. The issue is essentially a wetting problem the oil in the pores of the shales should be displaced by the fluid applied, which may be (caustic) water, a polymer solution, steam, or still something else, depending on the demands of the system, including the relative water- or oil-wettability of the rock. Under conditions where the interfacial tension is, or becomes, very low not only does the tension itself become relevant but cdso the bending moduli. 

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