The paper describes the modification conducted for the PAN carbon fiber surfaces in the solutions of nitric and sulphuric acids. The authors studied the impact of modification parameters such as temperature, acid concentration, time and ratio of the nitrosulphuric acid on the occurrence of reactive groups on the fiber surface. The authors revealed the presence of carboxylic and ketone reactive groups in the range of 1663-1798 and 1568 cm^-1 in the IR spectra of carbon fibers. The use of the nitrosulphuric acid did not identify sulfur-containing functional groups on the carbon fiber IR spectra. Preliminary acid treatment of the carbon fiber surface led to the formation of uniform continuous coating of a SiO₂ barrier being 127 ± 30 μm by a sol-gel method.

This paper presents the results of a study of silicon dioxide coating deposited on the surface of carbon fiber by the sol-gel method. The effect of the viscosity of the prepared sol-gel solution and the oxidizing properties at elevated temperatures obtained by SiO₂coatings were studied. It was found that the kinematic viscosity of the sol-gel solution does not change for 72 hours. An increase in viscosity leads to the formation of colloidal particles, which degrades the quality of the coatings.Studies have shown that in the temperature range 600-800 °C, the quality of uncoated fibers degrade, but the SiO₂coating well protects the fiber surface and significantly slows down the rate of destruction.

The challenge of water shutoff in carbonate reservoirs is complicated by the presence of fractures, which cannot be effectively blocked using conventional hydrogel screens designed for granular reservoirs. To reliably seal fractures, fibrous and dispersed fillers are added to hydrogels. These fillers must exhibit affinity for the matrix to ensure the composites can effectively isolate water. Given the wide variability in fracture apertures, it is evident that water shutoff composites should incorporate fibers and dispersed fillers of varying geometric sizes. This study presents a range of hydrogel composites reinforced with mono-, bi-, and tri-component fibers, as well as dispersed fillers, designed for water shutoff in fractured carbonate reservoirs with varying fracture apertures. Oscillation test results demonstrated a twofold increase in the elastic modulus (40–45 Pa) for compositions with various fillers compared to the base composition (23 Pa). Filtration studies revealed the effectiveness of the optimized compositions under different fracture apertures. Specifically, even at a fracture aperture of 650 μm, the residual resistance factor (RRF) reached 82.3 and 9.76 at water flow rates of 0.1 cm³/min and 0.5 cm³/min, respectively. The conducted rheological and filtration tests, along with field trials, confirmed the validity of the selected approach.

Well-killing operations in water-sensitive hydrophilic formations are often complicated by extended well clean-up periods and, in some cases, failure to restore the well’s production potential post-kill. Typical development targets exhibiting these properties include the Neocomian and Jurassic deposits of fields in Western Siberia and Western Kazakhstan. This paper proposes a well-killing method incorporating simultaneous near-wellbore treatment. In cases where heavy oil components (asphaltenes, resins, or paraffins) are deposited in the near-wellbore zone, their removal with a solvent results in post-operation flow rates that exceed pre-restoration levels. For wells not affected by asphaltene, resin, and paraffin deposits, killing is performed using a blocking pill of invert emulsion stabilized with an emulsifier and hydrophobic nanosilica. During filtration into the formation, this emulsion does not break but rather reforms according to the pore throat sizes. Flow rates in such wells typically match pre-restoration levels. The described engineering solution proves less effective when the well fluid water cut exceeds 60%. For wells exhibiting premature water breakthrough that have not yet produced their estimated oil volume, the water source is identified, and water shutoff operations are conducted. This involves polymer-gel systems crosslinked with resorcinol and paraform, reinforced with inorganic components such as chrysotile microdispersions, micro- and nanodispersions of shungite mineral, and gas black. Oscillation testing identified the optimal additive concentration range of 0.6–0.7 wt%, resulting in a complex modulus increase of up to 25.7%. The most effective polymer-inorganic composite developed by us, incorporating gas black, demonstrates high water shutoff capability (residual resistance factor ranges from 12.5 to 65.0 units within the permeability interval of 151.7 to 10.5 mD). Furthermore, the developed composites exhibit the ability to selectively reduce water permeability disproportionately more than oil permeability. Filtration tests confirmed that the residual permeability to oil after placing the blocking composition with graphene is 6.75 times higher than that to water. Consequently, such treatments reduce the well water cut. Field trials confirmed the effectiveness of the developed polymer-inorganic composite systems.

In this study to apply an oxide film to the surface of carbon fibers a sol-gel solution was used. Sol-gel solutions were prepared according to the described procedure from tetraethoxysilane (TEOS) and ethanol at various H2O concentrations. The molar ratio H2O/TEOS ratio was changed in the range from 2 to 20. After coating and drying, the surface morphology of carbon fibers was investigated. The relationship between the concentration of sol-gel solutions and the amount of deposited SiO2 on the surface of carbon fibers was analyzed.