Polymer permeability reduction caused

Permeability reduction caused by polymer retention and the viscosity increase resulting from polymer concentration were the primary contributions to the resistance factor at a velocity of 3.2 ft/D. 

Starch is also used for fluid loss control. It does not provide carrying capacity therefore other polymers are required. Although starch is relatively cheap, it has two serious limitations (1) starch is subject to fermentation, and (2) it causes significant permeability reduction due to plugging. 

Polyacrylates are often added to drilling fluids to increase viscosity and limit formation damage. The filter-cake is critical in preventing reservoir invasion by mud filtrate. Polymer invasion of the reservoir has been shown to have a great impact on permeability reduction [98]. The invasion of filtrate and solids in drilling in fluid can cause serious reservoir damage. 

Permeability reduction, or pore blocking, is caused by polymer adsorption. Therefore, rock permeability is reduced when a polymer solution is flowing through it, compared with the permeability when water is flowing. This permeability reduction is defined by the permeability reduction factor (Fkr) ... 

Bondor et al. (1972) assumed that the permeability reduction is caused by polymer adsorption, and the adsorption process is irreversible. They further assumed the maximum permeability reduction corresponds to the polymer adsorptive capacity on the rock, AdC. The permeability reduction factor is linearly interpolated based on the ratio of the amount of polymer adsorbed to the adsorptive capacity ... 

If we assume that the permeability reduction is caused by polymer adsorp-tion/retention, let us check whether the prediction from the previous equations is consistent with some observations on polymer adsorption/retention discussed earlier in Section 5.4.2. 

For oil and water relative permeability curves after polymer injection, Huang and Yn (2002), and Chen and Cheng (2002) reported their observations, which were similar to residnal permeability reduction after polymer flooding. Compared with the relative permeability curves before polymer flooding, the relative permeability curves had the following three characteristics (1) k was reduced at the same water saturation, and corresponding to the same k, , water saturation was larger (2) immobile water saturation was increased and (3) residual oil saturation was reduced. It is believed this result was caused by polymer adsorption, which made a rock surface more water-wet. 

Retention of xanthan biopolymer is relatively small when bacterial debris are removed by filtration. The permeability to brine after contact with polymer may be reduced from 10% to 30%.Table 5.6 compares the brine permeability before and after contact of Berea sandstone and unconsolidated sandpacks with xanthan biopolymer. Compared with xanthans, polyacrylamides usually cause larger reductions in brine permeability. At high salinities or divalent-ion content, permeability reduction is decreased. Table 5.7 contains typical permeability data before and after contact of porous rocks with polyacrylamides. 

Consider the effect of adding sufficient polymer to the injected water so that the apparent viscosity of the polymer solution is 4 cp. Assume that no reduction in water relative permeability is caused by the polymer. The mobility ratio, Mg, would be expected to decrease by a factor of four to about 0.54, which is clearly favorable. In Example 3.5, the displacement performance of a polymer flood was estimated for a polymer solution containing 300 ppm polymer with an apparent viscosity of 4.0 cp. Retention is 17.5 /tg/g at 300 ppm, so that Dp =0.424. Effective inaccessible PV for this system is estimated to be 0.25. Thus, —< g+Z>p =0.174. 

The effect of orientation on oxygen permeability of the medium and high barrier resins is seen to be dependent upon the morphological nature of the barrier resin prior to orientation. A plot of the oxygen transmission rates as a function of the overall draw ratio (figure 3) illustrates this clearly. While the semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6, show little change in the permeability with moderate amounts of orientation in the solid state, orientation of the amorphous polymers SELAR PA 3426 and XHTA-50A causes reduction in the permeability by 5-30% in both resins, depending upon the overall level of orientation. 

Support for the idea of a percolated structure connected by solid bridges may be found in the Frisk and Laurent [ 1996] patent on the reduction of permeability through a polyester wall container reduction by a factor of 100 was reported after addition of w = 5 wt% clay (aspect ratio p = 1000 to 1500). This large effect cannot be explained by the standard mechanism of tortuosity [see Utracki, 2004, vol. 2], but it is logical if combined with the intrinsie reduction of matrix permeability caused by solidification of polymer on clay platelets that form a continuous barrier to CO2 fiux. 

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