Flooding viscosity’ control flood

Screening criterion Heterogeneity Viscosity control control polymer polymer flood flood Comment... 

If the polymer application is for viscosity control, then the simple model may be a 2-D areal or simple layered five-spot pattern the well locations will be known, and any faults that are known should be included using transmissibility modifiers. In this areal system, the key features in the calculation are that the oil viscosity is correct and reasonable estimates of the reservoir relative permeabilities are available. For a heterogeneity control flood, a multilayer cross-section similar to the eight-layer system described in Chapter 8 may be selected. Here, the most important factor is to get the layering structure and layer permeabilities correct, especially the permeability contrast between the high-permeability layer(s) and the position of this layer. The value of the kjk ratio may also be very important in this type of polymer flood, but it may be sufficient to know that it is > 0.05 for example (see Chapter 8). In such an application, the mobility ratio may be close to... 

The mobility-control surfactant increased the apparent viscosity of CO2 sufficiently to prevent gravity override and viscous fingering. The bulk CO2 phase passed through the core in a piston-like manner. Oil and most of the brine were displaced from the core ahead of the bulk-phase CO2. Differential pressure measurement across the length of the core indicated an average gradient, 1.3 psi/ft, similar to that observed during the brine flood. 

Fiori and Farouq Ali (73) proposed the emulsion flooding of heavy-oil reservoirs as a secondary recovery technique. This process is of interest for Saskatchewan heavy-oil reservoirs, where primary recovery is typically 2-8%. Water-flooding in these fields produces only an additional 2-5% of the original oil in place because of the highly viscous nature of the oil. In laboratory experiments, a water-in-oil emulsion of the produced oil is created by using a sodium hydroxide solution. The viscous emulsion formed is injected into the reservoir. Its high viscosity provides a more favorable mobility ratio and results in improved sweep of the reservoir. Important parameters include emulsion stability and control of emulsion 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. 

Salt Sensitivity. The viscosity of mobility control polymers is a strong function of their environment. The ionic composition of a petroleum reservoir determines the conformation that the polymer chains assume in it. This very fact is one of two reasons why the salt sensitivity of the polymer solutions need to be studied. The second incentive for an investigation of this kind is the possibility of using the water produced from a flooded field in making the new polymer solution. Since the produced water contains many salts and minerals, knowing how the viscosity changes as a function of ion concentration is important. 

Instead of relying completely on theory for the determination of mobility, most researchers also performed experimental measurements of the quantities of interest. Many of the first experiments on foam were performed with water and gas with the outlet at ambient pressure, and many were simply gas floods of packs or cores saturated with surfactant solution. Although for many such transient experiments, the published data were insufficient for the estimation of the steady-state mobilities required for the estimation of mobility-control effectiveness, this was not true for some of them. Calculated values of mobility and relative mobility were derived by Heller et al. (22), from the data published in six different papers (23—28). The values they found, given in terms of relative mobilities, ranged from 0.001 to 0.6 cP-1, or in terms of effective viscosities from 1000 down to 1.6 cP (1 to 0.0016 Pa-s). Not enough information was available to trace all of the relevant parameters that may have caused these differences. 

Dyes (36) and Blackwell et al. (37) as a mobility-control method to be used with light hydrocarbon solvent floods. Although the original suggestions were for simultaneous injection of water and solvent, field practicalities changed this to alternation. Because of the low viscosity of C02, WAG has become the standard for use in these floods as well, with the only variables being the WAG ratio (volumetric water rate C02 rate) and the WAG cycle time. Most of the C02 floods now being operated are WAG floods, often with a cycle time of 1 year and a WAG ratio of 1 1 or 2 1. 

Polymers are used for mobility control in chemical flooding processes such as micellar-polymer and caustic-polymer flooding and in polymer augmented waterflooding. Selection of a polymer for mobility control is a complex process because it is not possible to predict the behavior of a polymer in porous rock from rheological measurements such as viscosity/ shear rate curves. Polymers used for mobility control are non-Newtonian fluids. Flow characteristics are controlled by the shear field to which the polymer is subjected. Properties of polymers can be measured under steady shear in rheometers. However, in porous rock, it is difficult to define the shear environment a polymer experiences as it flows through tortuous pores. 

Figure 1 shows the usual relationship between specific viscosity and overlap parameter. This figure shows that for EOR polymer solutions, which must have specific viscosity between 5 and 10 for mobility control during flooding, the overlap parameter must be about 3. Also, economics dictates that EOR polymer flooding solution concentrations must be 1000 ppm or less. Therefore a polymer must have an intrinsic viscosity of about 30 dl/g to be an effective and economical EOR candidate. 

The viscosity stability of water-soluble polymer solutions is critical to their performance in many application areas this is particularly true in petroleum recovery processes. The importance of viscosity stability in mobility control buffer applications (i.e., in polymer augmented water flooding and as a low cost viscosifying medium behind more expensive chemical slugs in EOR) has been highlighted by Chang(l) and in drilling by Thomas(2). Maerker(3) has cited the... 

Surfactants and polymers are the principal components used in chemical flooding. The surfactant lowers the interfacial tension (IFT) between the reservoir oil and the injected water, while the polymer will create favourable viscosity conditions and good mobility control for the surfactant slug. The oil is then displaced by the viscous forces acting on the oil by the flowing water. For this reason, chemical flooding is also denoted as ... 

A large percentage (80%) of Canadian enhanced oil production comes from hydrocarbon miscible flooding [1], The low density and viscosity of the injected fluids cause hydrocarbon miscible EOR processes to suffer from poor sweep efficiency, due to viscous fingering and gravity override. Mobility control foams provide a means for improving the sweep efficiency and could significantly increase oil production from Canadian reservoirs. 

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