Polymer slug size

Figure 7. Comparison of Oil Recoveries (at 5% oil cut) for Various Alkali/Surfactant/Polymer Slug Sizes...

Absolute polymer retention values showed an almost linear dependency upon polymer concentration. The effect of polymer slug size on absolute polymer retention is also discussed. 

There are two other constants in Equation (1) and f2 Values of F and f 2 depend on the pore structure, fluid saturations, type of polymer, salt environment, polymer slug size, and perhaps on the injection rate. 

Figure 19 illustrates the effect of injected concentration on the effluent polymer concentration curve when a 0.4 PV polymer slug size was applied. 

The viscosity of the polymer slug (at injection concentration). The polymer slug size. 

Therefore, the minimum polymer slug size to satisfy retention is Dp PV. Ideally, when Dp PV s are injected, the polymer flood front will just reach the end of the linear system but no polymer will be produced. 

Fig. 5.71 —Effect of polymer slug size on oil recovery In a five-spot pattern with a single layer.

Usually, the polymer slug size used in field application is less than 0.5 PV. However, in the laboratory, much larger slugs are used to achieve irreducible oil saturations, which are needed to establish the relative permeability cnrve. The core was previously waterflooded to simulate field conditions i.e., the pilot area was already prodncing 50- 0 % water cuts. 

The polymer breakthrough and its concentration profile in the produced fluid depend on various parameters, such as well distance, drainage area, rate distribution, polymer slug size, and retention. 

Micellar/polymer (MP) chemical enhanced oil recovery systems have demonstrated the greatest potential of all of the recovery systems under study (170) and equivalent oil recovery for mahogany and first-intent petroleum sulfonates has been shown (171). Many somewhat different sulfonate, ie, slug, formulations, slug sizes (pore volumes), and recovery design systems were employed. Most of these field tests were deemed technically successful, but uneconomical based on prevailing oil market prices (172,173). 

Based on Cases krl to kr4, we change the surfactant slug size from 0.1 PV to 0.2 PV, and the concentration from 3% to 1.5%. We also move 0.2 PV polymer into the surfactant slug. The resulting cases are II to 14. In these cases, we start... 

To investigate the effect of the amounts of polymer and surfactant injected, we use different concentrations and slug sizes and compare the incremental oil recovery factors and chemical costs (chemical Ib/bbl incremental oil) for different amounts of polymer and surfactant injection. The amount of surfactant injected is commonly presented in concentration (%) PV(%), and the amount of polymer is commonly presented in mg/L PV(fraction). Note that the unit PV is in fraction of pore volume. This section presents both polymer and surfactant in concentration (%) PV(%). The relationship between these two units is mg/L PV(fraction) = 100 concentration (%) PV(%). Figures 9.5 and 9.6 show the results. From these two figures, we can see that the more chemicals injected, the more incremental oil is recovered. However, in general, the chemical cost per barrel of incremental oil is also increased. Apparently, when a low load of chemicals is injected, the chemical cost per barrel of incremental oil is not sensitive to the amount of chemical injected. This observation is seen for both polymer and surfactant. 

A new technique using C02-activated plugs of sodium orthosilicate is used to plug fractures in sandstone cores. This is followed by injection of chemical slugs, such as alkali/surfactant and polymer/alkali/surfactant. A series of experimental runs were conducted on artificially fractured Berea sandstone cores. It is shown that recovery as high as 75% of the oil In place is possible with the novel treatment as compared to less than 10% recovery with waterfloods. Results are presented for various slug sizes. 

Figure 6. Comparison of Oil Recoveries for Various Slug Sizes of Alkali/Surfactant/Polymer...

The visible ROS ring was located next to the zone which was totally cleaned out of oil near the injection sand face. Thickness of the ROS ring appears to be a direct function of the slug size of the alkaline/polymer blend solution. 

Nasr-El-Din, H., K. A. Green and L. L. Schramm, The Alkali/Surfactant/ Polymer Process Effects of Slug Size, Core Length and a Chase Polymer, Revue de I lnstitut Frangais du Pitrole 49, 359-377 (1994). 

Polymer concentrations in the produced water in polymerflooding tests were studied using various polymer concentrations, slug sizes, salt concentrations, and different permeability sands. In general, high polymer concentrations were noted in the breakthrough water. 

Figures 14,15 and 16 illustrate the effect of slug size on produced water polymer concentration at selected injection polymer concentrations in the 173 md permeability sand. When the polymer solution was continuously injected, the effluent concentration did not attain the injection concentration level.

Figure 17 compares the effluent polymer concentration curves for different salinity waters. In one test the polymer was dissolved in brine and followed by brine while in the other test, the polymer was dissolved in tap water and then followed by fresh water. Although, the same polymer concentration and slug size were applied in both tests, considerably less polymer appeared in the produced water immediately after the water breakthrough when tap water was used. After about 0.3 PV of produced water, this situation was reversed. 

Fig. 14. The effect of slug size on polymer concentration in produced water during oil recovery.

When a larger (0.4 PV) slug size is applied, the flow resistance increases in the main flow channels whereby more polymer enters the small pores. Therefore, the leveling off section of the retention versus concentration curve begins at higher polymer concentrations. 

The role of slug size is evident from Curves 1,2,3, and 4 in Figure 25. These curves show that as the polymer slug passes a given location, the polymer retention becomes nearly completed. An increase in slug size from 0.2 PV to 0.4 PV results in only a slight change in the polymer retention. 

Alcohol-free chemical floods using an equimolar blend of an olefin sulfonate and a petroleum sulfonate were reported to give a final oU recovery of 94% with a 13% of PV slug size using 3 vol.% surfactant concentration. When the slug size was reduced to 3% of PV, the oil recovery was still 80% [J7]. The mobility was controlled by adding polymer so the minimum slug viseosity, Hs, was at least equal to the reciproeal value of the water mobility at residual oil saturation, Sor Rw is viseosity of water and fcrw is relative permeability of water, i.e. ... 

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