Polymer concentrations, injected-water viscosity

Linear and radial core flood tests were conducted to determine the polymer concentration for mobility control requirement. Figure 13.39 shows Brookfield (UL adapter) viscosity properties for the Alcoflood 1275A polymer in injection water and in an alkaline-surfactant solution. Note that the AS dramatically decreased the viscosity, and a higher polymer concentration was required to provide the same viscosity. 

When dissolved in more saline waters, xanthan gum produces a higher apparent viscosity than the same concentration of polyacrylamide (292). Prehydration of xanthan in fresh water followed by dilution in the saline injection water has been reported to provide higher viscosity than direct polymer dissolution in the same injection water. Optical rotation and intrinsic viscosity dependence on temperature indicate xanthan exists in a more ordered conformation in brine than in fresh water (293). 

The polymer injection was started in May and ended in December 2002. A 0.248 PV polymer solution with 1248 mg/L concentration (total 310 mg/L PV) was injected the injection solution viscosity was 54.8 mPa s. In November 2002, the injection pressure was 9.5 MPa compared with 5.4 MPa before injection. The increase was 0.6 MPa lower than that in the compared area where a polymer solution mixed with fresh water was injected. The water cut decreased by 38.6%, 9.4% more than that in the compared area. During the polymer injection period, the incremental oil recovery factor was 6%. The produced water was injected in other areas of the Lamadian field. Thus no produced water was disposed. 

Before PF, 0.1153 PV water had been injected from October 1996 to August 1997. A total polymer injection of 597.64 mg/L PV was started on August 28, 1997, and ended in October 2002. The average injected polymer concentration was 892 mg/L, and the injection PV was 0.67. The viscosity at the injection wellhead was 20 mPa s. In this case, the incremental oil recovery factor was 8.55%. 

As we know, adding alkali in a polymer solution will reduce the polymer solution s viscosity. We may take advantage of this fact in low-injectivity wells. Initially, the polymer solution with alkali has a low viscosity. As the alkah is consumed by reacting with formation water and rocks, the polymer solution s viscosity will become higher than the initial value. Thus, initially the injectivity and later the sweep efficiency will be improved. Note that the polymer concentration will also be reduced by adsorption. The final effect is determined by the balance between the two effects of the reduced alkaline and polymer concentrations. 

The variations of reduced polymer concentration C/Co and intrinsic viscosity [ulr = [ul/[ul, where Cq and [ri] are the values at the inlet, are plotted in Fig. 1 to 5 as a function of the volume of polymer solution injected Vp, and of water volume injected Vw. both expressed in terms of pore volume PV. 

The requirements for the presentation of the general flow characteristics of polymer solutions were best met by high molecular mass (3.5 10 ) hydrolyzed (40%) polymer. Concentration of the polymer was 100 ppm, viscosity of the solution under laboratory conditions (24 C) was 3.05 mPas. Taking into consideration the rock s permeability (59 10 and 62 10" ym ) and the equivalent diameter of the random coils (2600A), the polymer-rock system may be regarded as compatible. In the course of the experiments, comparison is made between the flow phenomena observed in the porous cores considered to be water wet and oil wet, respectively. When the permeability was determined by "connate water" (2% sodium chloride solution), the injection sequence of the fluids was as follows 1) polymer solution, 2) connate water, and 3) distilled... 

Figure la shows the permeabihty distribution. It can be noted, that for calculation of distribution of the main parameters used heterogeneous field. In opposite corners of the selected area are two wells injection and production. These wells are set bottom hole pressure Pinj or Pprod)- Figure lb shows the results of calculating the distribution of pressure in domain. Distribution of water saturation, polymer and surfactant concentrations, which are pumped through injection well, presented in Figures 2, 3 and 4. It is considered that the salinity of injection water is equal to zero (Figure 5). In these calculations, the solution is pumped into the reservoir over the reservoir temperature, the distribution of which is shown in Figure 6. Thus, the problem is solved numerically in a simple formulation, i.e. not taken into accoimt changes in viscosity of the concentration of the reagents and temperature, polymer adsorption was not affected by the...

A number of parameters of the system were varied to study their effect on cross-flow and oil production. These included reservoir properties such as the ratio of vertical to horizontal permeability kjk % the ratio of horizontal permeabilities between the layers (khighAiowX the relative thickness (Azhigh/Az,o ) of the high- and low-permeability layers. The ratio of oil to water viscosity (jUo// w) the relative viscosity of polymer solution at injection concentration (jUp//iw) tso varied. For the base case, the thickness of the low-permeability layer was twice that of the high-permeability layer, and the values (/c //cj = 0.1, (khighAiow) = 10. (/ o w) = 3.4 and... 

Coreflood temperature 68°F, crude oil viscosity 7.3 cP, produced water containing 3.3% total dissolved solids (of which 2700 ppm Ca + + Mg +) surfactant concentration range in ASP slug 0.1-0.2 wt.% polyacrylamide concentration in ASP and polymer slugs-550 mg/L injection sequence - 3 pore volumes (Vp) produced water, 0.3 Vp ASP slug, 0.3 Vp polymer slug, 3 Vp injection water. 

The polymer used in the Vernon pilot exhibits the property of unusually high resistance to flow through porous media. " A small concentration in injected water effects a mobility reduction considerably beyond that predicted from increases in bulk viscosity as measured in a capillary or rotating cup viscosimeter. Water mobility in the subject flood is reduced by a factor of 7.55 with the addition of 500 ppm Pusher chemical to... 

Fig. 12 shows the effects of Kelzan M concentration and shear-rate on polymer water viscosity. The effect of shear rate was determined by varying spindle speed on an LVT Brookfield viscosimeter with the U.L. attachment. The decrease in viscosity at high shear rates is desirable from an injectivity standpoint. It is conceivable that polymers having strong friction reducing properties might show higher injectivities than water alone. 

Contrary to expectation, analysis of the water produced in the polymer floods showed all but the first small increment to contain some polymer. The concentration did remain quite low (less than 15 percent of feed) until a volume of water equal to all the connate water plus about 0.12 PV had been produced. This appearance of polymer in the first water produced indicates a far less efficient displacement of the less viscous connate water than repotted by Brown in his experiments where injection water and connate water were of the same viscosity. 

Properties for the oU/water are identical to the 2D cases presented previously, except that the injected polymer concentration was reduced to 0.5 kg/m. For the polymer simulations, only the water viscosity is modified as a function of dissolved polymer. We did not include adsorption effects or shear-thinning effects, to avoid including two effects that could cancel each other out. By only using water viscosity increases caused by the polymer we ensured a clear production signal that could be compared between the two simulators. 

Further problems arise with the technique by the lack of availability of suitable primary calibration standards and the high viscosity of the synthetic polymers in water, resulting in much lower sample concentrations being used for injection (as low as 0.01%). 

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