Polymer salinity effect

Salinity is essential for all chemical processes. It directly affects polymer viscosity, and it determines the type of microemulsion a surfactant can form. Salinity effects in waterflooding, in both sandstone and carbonate reservoirs, have recently drawn research interest. This chapter briefly discusses sahnity and ion exchange. At the end of this chapter, the sahnity effects on waterflooding in sandstone and carbonate reservoirs are summarized. 

Figure 5.50 shows the salinity effect on the permeability reduction factor, Fkr, predicted from Eq. 5.36. This figure shows that F j decreases with salinity. However, Figure 5.40 shows that higher salinity leads to higher polymer adsorption. Therefore, the salinity effect on permeability reduction factor is different from that on polymer adsorption. In other words, because of the salinity effect, the permeability reduction based on Eqs. 5.36 and 5.37 does not... 

The preflush (or preliminary injection) is a slug applied to prepare the reservoir to help in protecting the surfactants and polymers against salinity effects and adsorption on the... 

Design procedures included laboratory tests on polymer rheology, relative permeability, shear degradation, screen factor, stability, and salinity effects. Computer simulations were performed to predict recoveries and to examine optimum polymer concentration. Field injectivity tests were conducted to examine injectivity behavior with time and to gain experience in surface handling of the polymer. Pressure-falloff tests were conducted in conjunction wiA the injectivity tests. Finally, the prqiamtion involved design of the polymer-injection plant and analysis of costs. 

This example describes a sequence of different phases of oil bank build-up and production. The polymer flood in West Block 2 was performed at a high salinity level without any fresh water preconditioning. The sharp oil bank developed confirms that the polymer solution effectively displaced reservoir brine and oil. There should be no significant reduction of polymer solution viscosity by mixing with reservoir brine or excessive retention. 

Although not designed to control filtration, HEC may be effective as a filtration control agent in combination with other organic polymers in waters having salinities up to saturation. 

The polymers exist in saline solution as tightly coiled chains and are readily adsorbed owing to relatively low solubiUty in hard water. Subsequent injection of soft, low salinity water uncoils the adsorbed polymer chains increasing water viscosity and reducing rock permeabiUty. This technology could also be used to reduce the permeabiUty of thief 2ones adjacent to injection wells. However, mechanical isolation of these 2ones may be necessary for cost-effective treatments. 

By 1980, research and development shifted from relatively inexpensive surfactants such as petroleum sulfonates to more cosdy but more effective surfactants tailored to reservoir and cmde oil properties. Critical surfactant issues are performance in saline injection waters, adsorption on reservoir rock, partitioning into reservoir cmde oil, chemical stabiUty in the reservoir, interactions with the mobiUty control polymer, and production problems caused by resultant emulsions. Reservoir heterogeneity can also greatly reduce process effectiveness. The decline in oil prices in the early 1980s halted much of the work because of the relatively high cost of micellar processes. 

Amoco developed polybutene olefin sulfonate for EOR (174). Exxon utilized a synthetic alcohol alkoxysulfate surfactant in a 104,000 ppm high brine Loudon, Illinois micellar polymer small field pilot test which was technically quite successful (175). This surfactant was selected because oil reservoirs have brine salinities varying from 0 to 200,000 ppm at temperatures between 10 and 100°C. Petroleum sulfonate apphcabdity is limited to about 70,000 ppm salinity reservoirs, even with the use of more soluble cosurfactants, unless an effective low salinity preflush is feasible. 

For Yiv > YPv> where y v and Ypv are the surface tensions of liquid and protein, respectively, AFads increases with increasing ysv, predicting decreasing polymer adsorption. An example of this is phosphate buffer saline where y]v = 72.9 mJ/m2 and Ypv is usually between 65 and 70mJ/m2 for most proteins [5]. Therefore, supports for gel-permeation and affinity chromatography should be as hydrophilic as possible in order to minimize undesirable adsorption effects. 

Perhaps the most important waterside problems relate to the likelihood of boiler surface deposits and their control. High concentrations of caustic or salines only occur if porous deposits are present. It is much better to remove the cause of deposition problems than to try to manage their effects, and modem iron and silica transport polymers, together with improved cleaning protocols, have done much to limit deposition in large boilers. 

Formation damage caused by clay migration may be observed when the injected brine replaces the connate water during operations such as water-flooding, chemical flooding including alkaline, and surfactant and polymer processes. These effects can be predicted by a physicochemical flow model based on cationic exchange reactions when the salinity decreases [1665]. Other models have also been presented [345,1245]. 

Salt Effects. In the low salinity region, the charge on the polymer determines the slope (Figure 6), and the acetate content changes the T by about 15 C per mole/repeat unit. We have obtained data for solutions of higher salinity. Not only have we looked at sodium chloride, but also salts such as calcium chloride and bromide which are used in heavy brines for drilling and workover operations. 

Results indicated that poly(DADMAC) will reduce damage caused by contact of low salinity fluid lost from the cement slurry with swelling clays present in the formation. An increase in poly (DADMAC) molecular weight from 600,000 to 2.6 X 10 daltons resulted in a decreased polymer effectiveness. The test columns were of relatively high permeability so the thickness of the adsorbed polymer layer, predicted to be greater for the higher molecular weight polymer, would have little effect on the observed flow rates. 

HPC exhibited a notable increase in adsorption with increasing NaCl concentration. Entrapment in the interlayer of recovered sodium montmorillonite did not vary with salinity the extent of entrapment was greater with the 4 M.S. HE and HP celluloses than either of the 2.0 M.S. polymers. Mixed ethers of HEC (2 M.S.) containing an anionic (carboxymethyl) or cationic (3-0-2-hydroxypropyltrimethylaramonium chloride) group at 0.4 M.S. levels did not adsorb from fresh water. Adsorption of these polar mixed ethers increased with increasing electrolyte until electrostatic and solvation effects were negated in 0.54N NaCl solutions and the adsorbed amounts typical of a 2 M.S. HEC were observed. Interlayer entrapments comparable to the equivalent M.S. HEC were observed at lower (0.18N) electrolyte concentrations. 

In the mucosal environment, effects of salt, pH, temperature, and lipids need to be taken into consideration for possible effects on viscosity and solubility. A pH range of 4-7 and a relatively constant temperature of 37°C can generally be expected. Observed solution properties as a function of salt and polymer concentration can be referred to as saline compatibility. Polyelectrolyte solution behavior [27] is generally dominated by ionic interactions, such as with other materials of like charge (repulsive), opposite charge (attractive), solvent ionic character (dielectric), and dissolved ions (i.e., salt). In general, at a constant polymer concentration, an increase in the salt concentration decreases the viscosity, due to decreasing the hydrodynamic volume of the polymer at a critical salt concentration precipitation may occur. 

A series of DCE-based formulations containing Igepal CO-630 Special (N9) and dextran sulfate (DS) were evaluated for in vitro contraceptive testing. Also included in the screening tests were placebos, N9, two commercial spermicidal products (Conceptrol and KY Plus), vaginal moisturizer products (KY Jelly and Replens ), and saline. Test results are summarized in Table 6. The N9-containing products exhibited similar spermicidal activity, as illustrated by the minimum effective concentration (MEC). Samples without N9 did not have spermicidal activity. DCE placebo vehicle inhibits sperm penetration into the cervical mucus, illustrated by the very low MOET values after 1 10 and 1 160 dilutions. This activity has not been reported for anionic or nonionic polymer vehicles. There are no striking differences... 

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