Divalents salinity affected

There are several factors that can affect a given surfactant s performance in a reservoir environment. First, the effect of inorganic ions is significant. Most oil reservoirs have an aqueous phase of saline brine that may vary in concentration from 0.5% to upwards of 15% NaCl. Also, there are divalent ions, such as Ca" "" " and Mg "" " present in significant concentrations. Most of the experimentation, which serves as the basis for this paper, was conducted utilizing a brine of 3% NaCl with 100 ppm (mg/1) of Ca" "" ". This composition is typical of many natural reservoir brines, and those surfactants that will perform well with this brine will also do well in the majority of reservoirs. 

A publication that specifically focuses on the screening criteria for chemical processes has not been seen in the literature. Screening criteria for broader EOR processes have been discussed by several researchers—for example, Taber et al. (1997a, 1997b), Al-Bahar et al. (2004), and Dickson et al. (2010). This section briefly summarizes several critical parameters regarding chemical EOR application conditions. Many parameters could affect chemical EOR processes however, the most critical parameters should be reservoir temperature, formation salinity and divalent contents, clay contents, and oil viscosity. Eor polymer flooding, permeability is another critical parameter. 

Variables identified as important in the achievement of the low IFT in a W/O/S/electrolyte system are the surfactant average MW and MW distribution, surfactant molecular structure, surfactant concentration, electrolyte concentration and type, oil phase average MW and structure, temperature, and the age of the system. Salager et al. (1979b) classified the variables that affect surfactant phase behavior in three groups (1) formulation variables those factors related to the components of the system-surfactant structure, oil carbon number, salinity, and alcohol type and concentration (2) external variables temperature and pressure (3) two-position variables surfactant concentration and water/oil ratio. Some of the factors affecting IFT-related parameters are briefly discussed in this section. Some other factors, such as cosolvent, salinity, and divalent, are discussed in Section 7.4 on phase behavior. Healy et al. (1976) presented experimental results on the effects of a number of parameters. 

Elffect of Salinity. The rheological behavior of polymer solutions also may be affected by salinity and divalent-ion content. The ef-... 

Compared with solutions of partially hydrolyzed polyacrylamides, viscosities of xanthan solutions are much less affected by changes in salinity or divalent-ion content. Figs. 5.17 and 5.1836 illustrate this by plotting the solution viscosity at various shear rates vs. salinity and divalent-ion content. 

Salinity also affects gel stability, and gels can synerese at very low or very high salt concentrations. Gels prepared in fresh water have been observed to synerese markedly when exposed to a brine. O However, the stability of gels prepared in brine has been noted to be relatively insensitive to change in salinity or to divalent-... 

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