# A Computational Study of Polymer Solutions Flow Regimes during Oil Recovery from a Fractured Model
## 1 Introduction  
Currently, acrylamide-based synthetic polymers have been widely used in oilfield development to enhance oil recovery. Today polymer flooding is one of the most efficient oil-recovery enhancement methods [1; 2; 3]. In most cases, partially hydrolyzed polyacrylamide is used for this process, since this is a relatively inexpensive and accessible reagent. In addition to its availability, other important advantages of polyacrylamide are their good solubility in water, due to which the viscosity of solutions quickly changes, the ability to easily filter in rock, and, also, environmental safety. However, these polymers have low stability in reservoir conditions, which are characterized by high temperature and increased salinity. An increase in temperature in the rock reservoir leads to the hydrolysis of polyacrylamide [4]. Another important problem with the use of polymer flooding with polyacrylamide solutions is their high sensitivity to the formation of water salinity. Anionic activity in the polymer chain in the presence of divalent calcium and magnesium cations leads to a decrease in the viscosity characteristics of the solution [5]. In addition, the problem of polymer adsorbing by rock walls is well known. Therefore, a large number of laboratory tests are now being carried out to increase the efficiency of polymer flooding. Therefore, the search for new, more thermally stable, polymer compounds is currently continuing. For example, experiments on the polymer flooding of a one-dimensional sandstone model using an aqueous solution high-molecular-weight hydrophobic-associated polyacrylamide copolymer (HAPAM) were conducted by [PERSON] et al. [6]. The rheological properties and thermal stability of HAPAM were investigated in detail. It was found that HAPAM has satisfactory thermal and salt resistance. This copolymer exhibits pseudoplastic behavior and is also capable of reducing the interfacial tension between the crude oil and the brine solution at room temperature, resulting in increased mobility of residual crude oil. The process of injecting partially hydrolyzed polyacrylamide polymer (PHPA) into a rock model was experimentally investigated by [PERSON] et al. [7]. A sandy bulk model was used in the experiments. The experiments have shown that polymer behavior is influenced by polymer concentration, pH of the solution, and salinity. Increasing polymer concentration enhances oil recovery. [PERSON] et al. [8] synthesized a synthetic water-soluble sulfonated polyacrylamide copolymer (SPAM), based on acrylamide with sulphonic acid groups and quaternary ammonium groups. A comparative analysis of the synthetic copolymer with the partially hydrolyzed polyacrylamide polymer (HPAM) was carried out. The synthetic copolymer has shown better thermal stability at high salt-ion concentrations, as well as demonstrating salt tolerance and shear stability. In core-flooding experiments, the oil-recovery factor (ORF) was higher when using SPAM as compared to that for HPAM. In addition to synthetic polymers, xanthan gum is also used in the oil industry in large quantities, since it can be utilized in high-salinity solutions. In addition, it is also compatible with a great number of surfactants and other additives used for injection into the bed [9]. Using a xanthan gum solution as a polymer-flooding fluid was studied by [PERSON] et al. [10]. The authors studied the rheological properties of xanthan gum solutions; the rheology was accurately described by the Herschel-Bulkley and Ostwald models. In addition, the modification of conventional polymer solutions by adding various-size nanoparticles and compositions is currently being investigated intensively [11; 12; 13]. In fact, this is a new area in oil-recovery enhancement methods. However, the use of nanoparticles and the evaluation of the effect of additives on oil recovery have not been sufficiently studied. In this connection, active research is being carried out in this direction.