The article presents the laboratory studies results of enzyme-based complexes. It has been shown that to prevent a decrease in enzyme activity in reservoir conditions due to high salinity and temperature, it is necessary to include chelate compounds to limit the effect of metal ions. The results of the EDTA-chelate experiment showed that at EDTA concentrations between 2 and 0.8%, the turbidity of the enzyme solution decreased during the testing time, demonstrating the positive effect of using EDTA with enzymes in a salt water environment. On the basis of experiment the optimal enzyme solutions and surfactants concentration for the minimum surface tension value has been clarified. The optimal effect of the minimum surface tension value is 1.735 mN/m with components was obtained at the enzyme:surfactant ratio equal to 0.477:0.3. The thermal stability of the enzyme complex study results showed that the interfacial tension between the enzyme complex solution and kerosene is much less than the interfacial tension between sea water and kerosene (21.75 mN/m), and this is proof of the enzyme complex thermal stability at the reservoir temperature. Keywords: enzyme solution; thermal stability; wettability; oil recovery stimulation; surfactant.

The article presents the laboratory tests results of enzyme solutions application on the model of the White Tiger Miocene deposits. It has been established that the enzyme solutions application makes it possible to increase the oil displacement efficiency in the range of 7.23–10.59%. The values variation is associated with different core samples characteristics in terms of porosity, permeability, initial oil saturation, and in terms of lithological composition as well. After enzyme solution treatment the differential pressure decreases, which indicates a change in the oil with oil-bearing rock wettability. Keywords: Enzyme solution; reservoir model; oil displacement efficiency; wettability; bottomhole formation zone.

The possibility and expediency of using reservoir and oilfield wastewater in areas of depleted and exhausted deposits in oil production for the preparation of liquids used for well killing, cement slurry mixing; table salt suitable as a food product producing. Based on laboratory studies, it has been found out that from one ton of water, on average, 180–210 kg of well killing fluid and 140–150 kg of common salt can be obtained, and dilution of heavy brine with fresh technical water can significantly increase the cement stone strength when fixing wells. The carried out simulation tests indicate that there is no deterioration in the reservoir properties of productive formations when they come into contact with heavy brines and the possibility of using such brines as a well killing fluid. A method has been developed for well-killing fluid and sodium chloride obtaining from oil field formation waters, including the initial formation water of calcium chloride type purification from mechanical impurities, oil residues, bringing its density to the concentration of calcium chloride, at which sodium chloride precipitates. Keywords: reservoir water; well killing fluid; table salt; cement stone strength; sodium chloride salting.

The paper shows that the liquid obtained as a result of reservoir water desalination has a reduced magnesium ions content. Using such a liquid, it is possible to increase the mechanical strength of cement stone, its impermeability, adhesion to casing pipes and the well wall, as well as reduce magnesia corrosion. Keywords: reservoir water; cement stone; construction lime; cement stone strength.

The article shows that in the conditions of Vietnamese fields to prevent a decrease in the enzymes activity in reservoir conditions due to high salinity and temperature, it is necessary to include chelate compounds limiting the metal ions influence. The results of the EDTA-chelate experiment showed that at EDTA concentrations from 2.0 to 0.8%, the turbidity of the enzyme solution decreased during the testing time, demonstrating the positive effect of EDTA with enzymes in a salt water environment. The results of a study comparing changes in the enzyme and surfactant solutions surface tension showed that the addition of 1% stabilizer EDTA, 1% surfactant alpha-olefinsulfonate to the enzyme solution increases the activity of the system. Based on the experimental data obtained using the Modde 5.0 software, the optimal concentrations of enzyme and surfactant solutions for the minimum value of surface tension were determined. The optimal effect of the minimum surface tension value is 1.735 mN/m with components was obtained at a ratio of components enzyme:surfactant=0.477:0.3. Based on the results of optimization, the component composition of the system was obtained: microbial product of enzyme origin is 50%; Surfactant is 30%; stabilizer is 1.0%; microorganisms inhibitor is 0.5%. Keywords: enzyme; surfactants; bottomhole formation zone; chelate compounds; surface tension.