This study evaluates the corrosion behavior of N80 production tubing steel under high-temperature, high-pressure (HTHP) conditions representative of CO₂-based geothermal exploitation in depleted hydrocarbon reservoirs. We developed a staged laboratory protocol that simulates (i) an early multiphase production window (oil + formation brine + supercritical CO₂), (ii) the same environment with the originally developed non-commercial inhibitor (INH), and (iii) a later stabilized stage dominated by near-anhydrous supercritical CO₂ (scCO₂) with trace brine and oil. Corrosion was quantified by gravimetric mass-loss, complemented by multi-scale surface characterization (2D/3D optical profilometry) and microscopic cross-section analysis. In the early multiphase scenario unprotected N80 experienced severe attack (mass-loss rate ≈ 0.67 mm·year⁻¹) with both uniform corrosion and incipient pitting beneath ferrous-carbonate deposits. Addition of an inhibitor at 5000 ppmv reduced mass loss by more than an order of magnitude (to ≈0.09 mm·year⁻¹, ≈97% inhibition) and substantially limited pitting. Under stabilized, near-dry scCO₂ conditions, corrosion was negligible (≈0.0016 mm·year⁻¹). Multi-scale imaging linked observed morphologies (porous FeCO₃ scales, under-deposit pits) to measured rates and supported stage-specific mitigation recommendations. The novelty of this work lies in the integrated, staged HTHP experimental approach and in providing quantitative, actionable inputs for material selection, inhibitor deployment, and monitoring strategies for CCS–EGS projects that reuse depleted hydrocarbon reservoirs.

Petroleum plasticisers are applied as softening additives in rubber vulcanisation processes and as components of rubber mixtures in the production and vulcanisation process. They contain polycyclic aromatic compounds exhibiting carcinogenic and mutagenic effects. Since 2010, the European Union has banned the use of high-aromatic DAE plasticisers. The petroleum industry and tyre manufacturers are developing new types of petroleum plasticisers. The best alternative to the DAE is the TDAE plasticisers, obtained mainly by selective solvent refining. The solvent dewaxing process of classic TDAE plasticisers was studied in order to improve the chemical composition as well as the rheological and low-temperature properties of deparafinate. This article presents the results of an examination of the TDAE plasticiser samples subjected to solvent dewaxing process on a laboratory scale with three types of solvents, MEK–TOL, MEK–MIBK and MEK–MTBE. It was demonstrated that solvent dewaxing of the TDAE plasticiser with positive pour points maintains good process selectivity and allows for a significant reduction of the plasticiser pour point, thus improving the rheological and low-temperature properties. In all dewaxing attempts, the pour point in the deparaffinate decreased significantly to the range −12 to −22°C, compared to the positive pour points of the raw materials. The application tests for two types of the TDAE plasticisers, used to produce oiled rubber and a standard rubber compound, meet the quality requirements for those products.

The European Union requirements related to the quality parameters for fatty acid methyl esters (FAMEs) are gathered in the standard EN 14214:2012 + A2:2019 that also includes reference to low-temperature properties. This paper presents studies on the obtaining of modified FAMEs, featuring improved low-temperature properties. Investigated fatty acid methyl esters (FAMEs) were subjected to a solvent dewaxing process with a methyl ethyl ketone and the mixture of methyl ethyl ketone—Toluene. It was found that the application of a process carried out under conditions similar to solvent dewaxing, used as a standard procedure for oils dewaxing and slack waxes of petroleum origin deoiling usually used in refinery industrial installations, allows us to achieve the intended goal. The modification of three different types of FAME by the dewaxing process with MEK-TOL and MEK solvents allows for the improvement of low-temperature properties of the obtained modified FAME, consistent in obtaining reduced cloud points, flow points and CFPP. The tests of fatty acid profiles show a clear increase in the content of glycerides of saturated acids in the separated sludge, as compared to the charges from the dewaxing process, which confirms that the selectivity of the dewaxing process is maintained for the atypical raw material, which are fatty acid methyl esters.