Drilling ever deeper, and thus in increasingly difficult conditions, is associated with restrictive requirements that must be met by cement slurries. This implies the need to use advanced, innovative measures that will significantly improve the performance parameters of the cement slurry and cement stone. Due to its unique properties, an admixture of nanosilica improves the properties of the cement stone and allows for appropriate zone insulation. The article presents the results of strength tests of cement stone samples with the addition of silica nanoparticles deposited in an environment of increased temperature of 90 °C. In all three cases of modification with an admixture of nanosilica (type 1, 2 and 3, concentration 0.5%, 1% and 5%), the cement stone shows an improvement in mechanical properties, which is manifested by an increase in compressive strength. The most homogeneous results of strength measurements are for cement slurries with an admixture of type 3 nanosilica (the highest average strength: 132–149% in relation to the base sample). They show the smallest stretch marks and deviations from the average. The highest average increase in strength is for the sample with the addition of 1% nanosilica (on average 124% in relation to the base sample). This amount causes the greatest increase in strength with no significant deterioration of rheological parameters.

Purpose. Development of effective composite plugging systems for reliable fastening of oil and gas wells in difficult mining-geological conditions of deposits of Ukraine. Methods. The proposed research is based on an analytical and industrial study of the problems of the well construction and fastening in the conditions of chemogenic deposit occurrence when applying the analysis of geophysical research materials. The research of tamponage solutions and buffer liquids was carried out using standard devices and methods that meet the set of requirements for testing cements and technological systems for well construction. Processing of research results was carried out in MATHSAD and EXCEL. Composite cement CEM V according to the European standard EN 197-1, tamponage cement 1-G, krents - high-basic C2F CaSO4 and low-basic 3(CF) CaSO4 calcium sulfoferites were used for the research. Findings. It was established that the basic plugging material, as well as technological solutions for fastening wells in difficult mining-geological conditions, do not ensure compliance of the well as an engineering structure with operational reliability indicators. As a result, violations in the fastening system are quite often recorded, which require significant time and financial costs for their elimination, and sometimes lead to well liquidation. In order to increase the reliability of fastening wells, it is necessary to use multi-component tamponade systems modified by krents. Calcium sulfoferrite admixtures have been proved to accelerate the kinetics of early strength and contribute to the formation of cement stone with improved characteristics. The need to use effective buffer systems to improve the quality of fastening is substantiated. Originality. On the basis of assessment, systematization and detailed study of geophysical material and features of well fastening under the conditions of exposure to chemogenic sediments, the necessity of using composite plugging material was established. The conducted studies have proved that to ensure reliable fastening of wells in difficult mining-geological conditions, it is necessary to use multicomponent composite plugging material modified by calcium sulfoferites with accelerated kinetics of early strength, which form cement stone with a densely packed structure. Practical implications. Based on the industrial material evaluation and detailed laboratory studies, technological solutions have been developed to increase the reliability of well fastening due to the introduction of multi-component composite plugging material modified by krents and buffer liquids.

The object of research in the work is a mathematical model of the operation of a hydrodynamic well generator of the spring-valve type. The existing problem lies in the fact that vibrating wave swabbing differs from known methods of vibrating wave influence on the near-breakout zone of the formation in its ease of execution and, as a result, a much smaller range of equipment. At the same time, its effectiveness should not be inferior to known methods because the treatment of the formation is carried out by elastic low-frequency pressure fluctuations against the background of depression on the formation. Since the swab generator valve is, in fact, a hydrodynamic well generator (HWG) of the spring-valve type, the processes of pressure fluctuations in the considered devices will be similar. However, because of the review of HWG designs, the presence of a mathematical model describing the operation of rotor-type devices, and not valve type, was revealed. Despite the fact that the mathematical model takes into account all the main factors that determine the process of the HWG piston movement, this model cannot be used to describe the operation process of the swab generator valve. Due to the absence of a pulsating flow created at the wellhead by pumping units. Taking this fact into account, as well as taking into account the compressibility of the liquid passing through the valve, a new mathematical model was developed. It describes both the process of operation of a spring-valve type HWG operating in a well on pump-compressor pipes, and the operation of a swab generator valve that is lowered into a well on a rope. Thanks to this, it is possible to obtain the parameters of the oscillating system: geometric dimensions, inertial mass of moving parts, stiffness of the spring, coefficient of viscous friction between the piston and the valve body, as well as parameters of the working fluid: pressure, flow and its rheological properties. In comparison with the similarly known technology of vibration wave impact on a formation with known HWG, it provides such advantages as a higher speed of movement and frequency of oscillations of the moving end of the spring from the identified essential parameters of the oscillating system and the working fluid of the spring (100–1000 N/mm), consumption of working liquid (10–130 m3/h), valve opening pressure (1–7 MPa). This will make it possible to calculate a helical cylindrical compression spring made of round steel for its operation in the valve of the swab generator without collision of turns.

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informuj?ce swoich czytelnik?w o najnowszych osi?gni?ciach naukowych i nowoczesnych rozwi?zaniach technicznych w Polsce i na ?wiecie, popularyzuje problemy techniczne oraz poszerza wiedz? i kultur? techniczn?.

An overview and actuality of oil and gas production are provided. The article reviews the mining and geological features of the Verkhnyomaslovetske field of PJSC “Ukrnafta”. It is established that this field belongs to the category of fields with hard-to-recover hydrocarbon reserves. It is shown that the main complication in well drilling is the absorption of drilling mud. Attention is focused on the tasks and implemented solutions for well production casing. It has been established that the lack of necessary and inconsistency plugging materials to cementing conditions causes absorption of the grouting mortar, resulting in defects in the work and the need for additional time and financial costs to eliminate them. At the same time, it is difficult to estimate the extremely negative impact of grouting mortar absorption on the filtration and capacitance characteristics of the formation. The main parameters of the grouting mortar that caused its absorption are analysed. A new lightweight plugging material with a cement batter density of 1.25 g/cm3 was developed. The main parameters of the grouting mortar and stone based on the developed plugging material were investigated and tested in accordance with the thermobaric and technological conditions of cementing a typical well of the Verkhnyomaslovetske field. The obtained results of research make it possible to improve the quality of casing support under abnormally low reservoir pressures (ALRP) conditions at the Verkhnyomaslovetske field, as well as, in the future, at other fields with related mining and geological conditions.