Distribution of retained polymer

Distribution of retained polymer in sandpacks showed an exponential function of the distance. The dynamic polymer retention values in short packs showed higher values than the static polymer adsorption values due to mechanical entrapment. 

The effect of residual oil saturation on polymer retention and the polymer retention during the displacement of oil from porous media has not been reported. Although some phenomena [1-11] indicated that more polymer is retained in the first segment of a porous media, the literature lacks quantitative data on the distribution of retained polymer in porous media. The mechanism of polymer retention during unsteady-state flow [11] has not been adequately described. 

An attempt will be made to clearly separate the two basic retention phenomena mechanical entrapment of molecules and physical adsorptioa Factors influencing these retention mechanisms will be discussed in detail The resultant distribution of retained polymer in porous media will be given. 

The first member of the right hand side of Equation (1) represents the distribution of retained polymer due to mechanical entrapment. The second member is constant, and the value of it depends on whether Equation (1) is applied for steady-state polymer flow or after sufficient brine flush to establish residual polymer retention. 

It was earlier pointed out that after the first invasion of a porous body with a polymer solution, the retained polymer shows a characteristic distribution. If, for the first invasion the flow parameters are chosen in such a manner that finally a steady-state flow is attained, this characteristic distribution of retained polymer will not change with time. This function determines a distribution of resistance factors. Then, if the flow rate is increased to a value above the critical velocity, the initial distribution of the resistance factors at this increased velocity shows also a characteristic distribution. Further analysis of the initial resistance factor distribution during unsteady-state flow is given in Appendix B. 

Figure 29 demonstrates the role of pore structure on distribution of retained polymer. The exact shape of the curves in unknown since one has to know the retained polymer minimum at three locations to determine the constants in Equation (1). It should be noted that because of the C t,constant on the right-hand side of Equation (1), a... 

Figure 30 shows the distribution of retained polymer in two sandpacks. Preceding a 0.2 PV polymer slug in brine, a 0.4 PV brine slug was injected. After the polymer slug, five pore volumes of brine were injected. 

Fig. 29. Distribution of retained polymer in sandpacks after several pore volumes of injected polymer during oil recovery and thereafter, several pore volumes of injected brine.

The factors determining the distribution of retained polymer in porous media are as follows ... 

FIGURE 5.36 Distribution of retained HPAM along a sand pack after a polymer flood. Source Szabo (1975). 

So far, the only living processes industrially available are anionic and cationic polymerization [50, 51], which generally suffer little or no termination. In these processes, the initiation step is very fast compared to the process time and, hence, all the chains start growing almost simultaneously. The degree of polymerization, DP, increases linearly with monomer conversion and is inversely proportional to the initiator concentration. At the same time, Poisson-like distributions of the polymer chain length are obtained with final polydispersity values dose to the ideal value of (1 -I- 1/DP). Finally, the polymer retains the ionic end groups till the end of the polymerization and the reaction is simply restarted by further addition of monomer. However, this kind of polymerization is often impractical from the industrial viewpoint, since the main requirements are high purity of all the reactants, very low temperatures, and the use of solvents. Moreover, it does not work with several widely used monomers, such as styrene. 

Figure 5.2. Distribution of retained HPAM along a sandpack after a polymer flood. Conditions 0.4 pv brine, 0.2 pv polymer, continuous brine injection, k— 1200md, t = 6ft/day (after Szabo, 1975).

Thus we may retain the root-mean-square end-to-end distance as a measure of the size of the random-coiling polymer chain, and the parameter jS required to characterize the spatial distribution of polymer segments (not to be confused with the end-to-end distribution) can be calculated from It should be noted that the r used here... 

The ionization of a molecule and the rupture of a chemical bond by ionizing radiation necessarily result in the pairwise formation of radical species. The pairwise correlation of radical species will be more or less retained in solid polymers where the radical migration is restricted. This heterogeneity of spatial distribution of radical species affects the radiation chemistry of polymers. Another source of spatial heterogeneity is the heterogeneous deposition of radiation energy [6, 7]. Low LET radiations such as y-rays produce an ensemble of isolated spurs. Each spur is composed of a few ion-pairs and/or radical... 

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