Residual resistance factors

The residual resistance factor is expected to be 30 to 100 in the high permeability streaks. 

Note Eq. 5.40 defines the term residual permeability reduction factor. In the literature (Jennings et al., 1971 Bondor et al., 1972 Sorbie, 1991 Green and Willhite, 1998 UTCHEM-9.0, 2000), the term residual resistance factor (Frr) is used to represent the residual permeability reduction factor (F]j ). Their residual resistance factor is defined as ... 

Resistance is related to mobility, which includes the effects of both permeability reduction and viscosity increase. Obviously, the viscosity effect is not included in the residual resistance factor defined in Eq. 5.41 because water viscosity is used before and after polymer flow. Such a name convention is confusing. Therefore, we suggest the terms permeability reduction factor and residual permeability reduction factor be used. If the process were considered reversible, there would be no need for the term of residual permeability reduction factor. To include both permeability reduction and viscosity increase, we define another parameter, resistance factor (F,) ... 

The chemical formnla in this pilot test was 1.25% NaaCOs + 0.3% B-lOO + 1200 ppm 1275A blended in fresh water. Table 13.10 shows the IFT values at different alkahne and surfactant concentrations. The table also shows that ultralow IFT of 10 mN/m was reached within a large range of concentrations, particularly near the designed injection concentrations. The chemical adsorption or consumption for alkah, surfactant, and polymer were 1.065,0.455,0.169 (mg/mL PV), respectively. The residual resistance factor in this test was 2.0695. The injection scheme was 0.32 PV ASP solution, then 600 mg/L polymer buffer solution, followed by water until the water cut reached 98%. 

From the pressure gradients determined for two flooding rates we are able to deduce the resistance factor RF, which serves as a measure of the flow resistance of the polymer solution in the pore space, as well as the residual resistance factor RRF. The factor RRF serves as a measure of the permeability reduction due to polymer material absorbed and retained in the pores. The values obtained for the VS/VA/AM-copolymers are particularly good. 

The results from a typical injectivity test are given in Figure 12 where resistance factor (RF) and residual resistance factor (RRF) are plotted versus the number of pore volumes of polymer and brine injected. Resistance factor is the mobility of brine (k/p) divided by the mobility of polymer and is a measure of the reduced Injection rate the polymer produces in a given reservoir rock. Residual resistance factor is the mobility of brine before polymer injection divided by the mobility of brine after polymer injection. Thus, a permeability reduction of 99 percent corresponds to an RRF of 100. 

The proper design of a profile modification treatment requires measurement of the permeability reduction caused by a given gel system. Core tests have shown that relative gel strength measurements with the capillary viscometer correlate with permeability reduction--Increasing gel strength develops higher residual resistance factors. 

Polyacrylamide El exhibits the highest active and residual resistance factors (45.6 and 32.2 respectively) of the polymers tested. Polyacrylamide El also exhibited the highest resistance factors in river water and in a mixture of river and formation waters. The transient resistance factor and normalized concentration curves as a function of pore volumes injected are illustrated... 

Polysaccharide G2 had an unusually high residual resistance factor (9.3) and retention (321 lbs/acre-foot) in an 80/20 mix of river/formation waters. The high retention and resistance factor resulted from mechanical entrapment of microgels (reversible complexes of divalent cations with polysaccharide molecules) formed in the 80/20 mixture of river and formation waters. Further testing in 100% formation water indicated higher retention (542 Ibs/acre-foot) in the reservoir cores. Correspondent increases in milli-pore filter ratios and filtration times were observed to occur with increase of univalent and divalent electrolytes. 

The difference between the two systems has been determined for each flow parameter, but Figures 15, 16 and 17 show data for resistance factors, residual resistance factor, apparent permeability and viscosity ratio only. In our figures the curves characterizing the water-wet cores are represented by solid lines, and those characterizing the oil-wet cores, by dotted ones. 

Fig. 15. Dependence of resistance factor and residual resistance factor on the fluid volume injected into porous media. (1, polymer solution (0.5 gdm" ) 2, connate water 3, distilled water.)...

The residual resistance factors at residual oil saturations were computed from the equation below ... 

Figure 10 shows the polymer flow and residual resistance factor curve related to the experiments described in Figure 8. As can be seen, the polymer flow resistance factors stabilized at both 100% water saturation, and at residual oil saturation. The small differences in polymer flow resistance factors in these two experiments are probably due to small differences in pore structure from one pack to another.

Fig. 10. The effect of residual oil saturation on polymer flow and residual resistance factors.

Abstract. This article describes a hydrodynamic model of collaborative flnids (oil, water) flow in porons media for enhanced oil recovery, which takes into account the influence of temperature, polymer and surfactant concentration changes on water and oil viscosity. For the mathematical description of oil displacement process by polymer and surfactant injection in a porous medium, we used the balance equations for the oil and water phase, the transport equation of the polymer/surfactant/salt and heat transfer equation. Also, consider the change of permeabihty for an aqueous phase, depending on the polymer adsorption and residual resistance factor. Results of the numerical investigation on three-dimensional domain are presented in this article and distributions of pressure, saturation, concentrations of poly mer/surfactant/salt and temperature are determined. The results of polymer/surfactant flooding are verified by comparing with the results obtained from ECLIPSE 100 (Black Oil). The aim of this work is to study the mathematical model of non-isothermal oil displacement by polymer/surfactant flooding, and to show the efficiency of the combined method for oil-recovery. 

The water mobility, may be further affected by the pore-blocking behaviour of the adsorbed polymer. This resistance to flow is thought only to affect the aqueous phase (White etal, 1973). It is related to a residual resistance factor (Jennings etal, 1971), RRF, corresponding to a final adsorbed level of polymer, Qf. The resistance factor, R, corresponding to a given adsorption level, Cg, may be given by a semi-empirical equation such as that used by Bondor etal (1972) ... 

Polymer adsorption isotherms and residual resistance factors differ between rock types and are given in Sorbie etal. (1982)... 

Figure 8.35. Correlation of polymer retention levels and residual resistance factors with rock permeability (Sorbie et al., 1982).

In order to make pore blocking an effective oil recovery mechanism, the residual resistance factors must be greater in the high-permeability zone than those estimated for the biopolymer. However, if the residual resistance factors... 

It is convenient to describe the permeability reduction in terms of the initial brine permeability. In practice, this is done by defining the residual resistance factor (Eq. 5.12) as the ratio of the brine mobility before contact with polymer, to the brine mobility after aU mobile polymer has been displaced from the pore space. 

The permeability reduction usually persists for a large number of PV s of fluid throughput. In laboratory tests with relatively low fluid throughput, little change in brine permeability occurs, as shown in Table 5.8, However, prolonged fluid inyection eventually erodes the permeability reduction, as indicated in Fig. 5.29, where the residual resistance factor declines markedly with PV s throughput. 

Although excluded-volume effects are well-accepted in polymer chromatography, the preceding arguments are not without controversy in the petroleum literature because of the way that the apparent polymer viscosity in porous media was determined. In our work, we simply report the resistance factor (i.e., the brine mobility before polymer injection divided by the polymer-solution mobility). This is a well-defined parameter that derives directly from the Darcy equation and measurements of pressure drops and flow rates. Advocates of the depletion-layer effects use a different method to determine apparent polymer viscosity in porous media. Specifically, they flush water through the core after polymer injection to determine the permeability reduction or residual resistance factor. The resistance factor during polymer injection is then divided by the residual resistance factor to determine the apparent polymer viscosity in porous media. Unfortunately, several experimental factors can lead to incorrect measurement of high residual resistance factors, which, in turn, lead to calculation of unexpectedly low apparent polymer viscosities in porous media. 

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