## 2 Materials and Methods
According to the results of hydrodynamic studies of the target oil producing well of 15 June 2019, the value of the skin factor was determined as equal to 1.1. The authors calculated the reduction of flow resistance in the near-wellbore zone using the above technique, which allowed to further calculate the increase in the target well flow rate after acid treatment on the hydrodynamic model. Before acid treatment of the productive formation, in order to eliminate undesirable consequences, it was expedient to carry out laboratory research on the compatibility of AC with fluids inflowing from the target facility. The study of their interaction plays an important role in the design of hydrochloric acid treatment, since in case of poor compatibility, there is a possibility of a high-viscosity emulsion, clots, flakes, and precipitation that result in damage of void space. For this purpose, testing with 15 different ratios of oil, water, and acid composition was performed under laboratory conditions. In the beginning, stable water-oil emulsion from the selected samples of oil and water from the target well under study was obtained; after that, the acid composition under test was added to the obtained emulsion. As a result, the state of the obtained mixture was assessed visually for precipitation and phase immiscibility at several-minute exposure; the obtained mixture was filtered through a 100-mesh sieve with registration of presence/absence of nonfilterable residue. Table 2 illustrates some of the laboratory findings on the compatibility of the acid composition under test with the fluids collected from the target well. As a result of laboratory research on compatibility of formation fluids with acid composition, it can be concluded that formation fluids and acid composition are well compatible, as in all cases, there were no signs of residue formation during filtration of the obtained mixtures. Therefore, FLUXOCORE-210 composition can be considered applicable to these conditions by the nature of interaction with the fluids. To determine the predicted change in the skin factor from Equation (10), a number of laboratory studies to obtain the initial data for the calculation were conducted. The mass fractions of calcite and dolomite contained in the rock were found to be 89.7 and 1.2%, respectively, which are typical of the Tournaisian stage in Perm Krai. The viscosity value of FLUXOCORE-210 acid composition, determined as the average of several experiments, was \(1.37\times 10^{-3}\) Pa-s. The radius of the diffusing AC particle, as determined with Mikmed-5 microscope, was \(1.0\times 10^{-6}\) m. This radius is defined as the average of several radii of the particles under study, their values changing within a small range. Figure 5 shows the image of AC particles under microscope as obtained by the authors during the research in the scientific laboratory. \begin{table}
\begin{tabular}{l} \hline \hline
**Prepared Mixture** & **Composition of Interacting Products** \\ \hline Water—25\% & Oil—25\% \\ AC—50\% & AC—50\% \\ \hline Water—33.3\% & Oil—33.33\% \\ AC—33.34\% & \\ \hline Water—0\% & Oil—50\% \\ AC—50\% & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of study of compatibility of formation fluids collected from the target well, with the acid composition under test. Data on reservoir pressure provides an understanding of the required rate of acid injection into the formation. The HAT process was often carried out using AzINMASH-30 pumping unit. Its technical characteristics are given in Table 3 ([PERSON] and [PERSON], 2018 [20]; [PERSON], 2003 [21]). According to Table 3, the acid composition pumping rate was determined as \(6.5\times 10^{-3}\) m\({}^{3}\)/s. Bottom-hole temperature was 28 \({}^{\circ}\)C, as determined from telemetry data. The well diameter was \(146\times 10^{-3}\) m.  
According to geophysical and hydrodynamic studies, the formation operated by the target oil production well is characterized by strong heterogeneity and low permeability.