The article discusses researches performed in the Well Drilling Department of the St. Petersburg Mining University. The directions of development of the department are shown. Special attention in this article is paid to research in the field of developing drilling fluids for drilling wells in various mining and geological conditions. It is shown that the gas-liquid mixtures studied by the department will be effective for under balanced drilling under conditions of abnormally low reservoir pressures when using a binary mixture of sodium lauryl sulfate 0.5% + linear sodium alkyl benzene sulfate 0.5% as a surfactant and polyacrylamide FP complex 107 (0.05%) as a forming and stabilizing additive + carboxymethyl starch BUR-2 (1%). Studies in the field of development of inhibitory fluids have shown that an increase in the concentration of polar compounds in the drilling fluid compared to their concentration in the rock Cp> Cn by 0.25 mol/L makes it possible to increase the stability of the rocks around the wellbore compared to the initial conditions. Studies of lubricating additives showed that introducing 1.5–2.0% of FRW additive reduces the friction coefficient of the metal– metal pair in a clay solution by 70–75% and in an aqueous solution up to 65%. The findings suggest that drilling fluids developed at the Well Drilling Department of the St. Petersburg Mining University have a high potential for their application in oil and gas fields in order to improve the efficiency of drilling and completion of wells. It is also noted that the scientific and technical potential of the department allows for input control of reagents in drilling fluids, as well as the development and research of various compositions not only for drilling and completion of wells, but also for development and repair, which are applicable in real field conditions.10.5829/ije.2020.33.04a.22

The aim of the work is to increase the well completion efficiency when using oil-based drilling fluids. In this study, the effect of the aqueous phase content on the change in the rheological parameters of the solutions and the effect of the type of asphalt on the structural-rheological and filtration parameters of the oil-based solution was conducted. Studies have shown the effectiveness of various types of asphalt in OBM systems, the obtained dependencies on the effect of the Oil-water ratio can be used in production to select the optimal ratio for the selection of specific properties of solutions.

The boring log in the Eastern Siberia regions is characterized by the presence of frozen rocks, which causes a number of specific drilling problems. In such conditions, magnesia materials characterized by high expanding capacity are widely used for cementing wells. These materials improve well cementing quality by increasing the areas of complete contact at the rock-cement and cement-casing boundaries. For their effective use, it is important to evaluate the cementing parameters in comparison with the traditionally used Portland cement-based plugging materials. The high quality of the magnesia cement compositions in comparison with Portland cement was justified based on the data obtained from laboratory analysis.

In this paper water cut of well products problem is considered. To solve this problem it is proposed to use a technology of water inflows isolation during the drilling process developed by the authors. Not only does our approach stimulates the production of hard-to-recover hydrocarbons but it also protects local water and undisturbed geological formations against the impact of hydraulic fracturing operations. This approach also enables higher well potential due to a longer service life of the wellbore. The use of a device-pressure regulator with synchronous injection of the developed blocking fluid is presented. Mathematical modeling of the experiment was performed, aimed at determining the dependence of the change in pressure drop in the annular space of the well on the flow conditions of the blocking composition with a device installed in the bottom hole assembly that will effectively apply the controller device, taking into account the drilling parameters of a particular well. The novelty of this approach lies in the fact that this work offers an aquifer isolation technology, which suggests applying a pressure regulating device, and provides a layout of a blocking viscoelastic system.

The most significant change in the structure of Portland cement at temperatures above 110°C is a decrease in strength. There are several additives that enhance the cement's resistance to structural failure at high temperatures, such as metallurgical slags, quartz, and carbon nanomaterials. One of the emerging approaches is the utilization of mineral wool impregnated with carbon nanotubes. The relatively small particle size of mineral wool enables the filling of capillary micropores with carbon nanotubes, thereby increasing the overall structural integrity of the cement. This study investigates the impact of adding mineral wool saturated with carbon nanotubes (25%) to Saudi G-class cement. Six cement paste specimens were prepared with mineral wool contents ranging from 0 to 25%. The chemical composition of the cement was analyzed using X-ray fluorescence, the physical composition was evaluated via X-ray diffraction, testing of the cement slurry samples was conducted in accordance with ISO 10426-2:2003, tensile strength testing of the specimens was performed using the Brazilian method as per ASTM D 3967-08, and permeability testing was carried out according to ISO 10426-2:2003. The properties were assessed under elevated thermal conditions of 300°C. After curing for 7 and 28 days, these cement stones underwent testing over a temperature range from 25 to 300°C. The research findings indicate that the optimal content is 10-15% mineral wool containing 25% carbon nanotubes (resulting in a carbon nanotube concentration in the cement matrix of 2.5-3.75%). Results obtained after 28 days show high compressive strength values exceeding 50 MPa, which is 5-23% higher than that of the additive-free cement at 25°C and 5.7-6.2 times higher at 300°C. Additionally, tensile strength values are higher, being 1.4 times greater than the additive-free cement at 25°C and 3.7-3.9 times higher at 300°C. Moreover, low permeability values of the cementitious material were achieved, with permeability ranging from 2 to 3 mD*10-3 for mineral wool concentrations of 5 to 15%, representing a 2-2.5 times reduction compared to critical values, thereby ensuring good inter-column insulation.

Relevance. Strength decrease is a phenomenon that becomes more pronounced as the temperature rises above 110°C. It is characterized by significant chemical and microstructural changes that Portland cement undergoes at high temperatures. Adding silica particles (SiO2) to cement can significantly increase cement resistance to strength reduction when the temperature exceeds 110°C. Nanoclays are currently used in the cement industry to increase the strength of the cement matrix due to their ability to fill capillary micropores and due to their relatively small particle size. Aim. To investigate the effect of adding nanoparticles (nanoclay) to Saudi grade G cement on compressive and tensile strength, and cement stone permeability under high temperature conditions (300°С). Objects. Six samples of cement mortars with different concentrations of nanoclay, cement stones from, tested after 7 and 28 days of hardening at 25 and 300°C. Methods. Cement chemical composition was evaluated by the X-ray fluorescence method with the WORKSTN-V Olympus Vanta X-ray fluorescence analyzer. Cement physical composition was evaluated by the method of ray diffraction on the Mastersizer 2000 laser particle size analyzer. The test of the grouting stone samples was carried out in accordance with ISO 10426-2:2003 on a hydraulic press 65-L1132. The tensile strength of the samples by the Brazilian method was tested in accordance with ASTM D 3967-08 standard on a hydraulic press 65-L1132. The permeability of the samples was determined by single-phase stationary filtration at a facility for studying the filtration and capacitance properties of the PIK-OFP-UCH core in accordance with ISO 10426-2:2003. Results. The data obtained showed that cement destruction at extremely high temperatures can be avoided by using nanoclay (up to 3% by weight of cement). The microstructure of the cement matrix was significantly affected due to the aggregation of nanoparticles when more than 3% of nanoclay was added. All rheological characteristics of the cement slurry were improved by the addition of nanoclay particles.