АНАЛИЗ ГАЗОВОГО ВОЗДЕЙСТВИЯ НА УГЛЕВОДОРОДНЫЕ СМЕСИ МЕТОДОМ SWELLING TEST

This paper presents an algorithm for the implementation of a PVT Swelling Test aimed at evaluating changes in properties and phase behavior of hydrocarbon fluids during first contact with an injected gas. The experiment enables determination of key system characteristics, including swollen volume, gas–oil ratio, phase densities, and saturation pressure. The relevance of the study is associated with the expanding application of gas injection methods, including those related to decarbonization and CO₂ utilization, as well as with the need for rapid analysis of a large number of injection scenarios during the design of pressure maintenance and enhanced hydrocarbon recovery processes. The design of such technologies requires consideration of various injected gas compositions, since the efficiency of gas injection depends on the properties of the reservoir fluid, the composition of the injected agent, and pressure-temperature conditions. The developed algorithm is implemented in Python and is based on thermodynamic modeling using cubic equations of state. The methodology includes successive addition of the injected gas to reservoir fluid, determination of the saturation pressure, and subsequent evaluation of the Swelling Test parameters. This approach makes it possible to reproduce the sequence of the laboratory experiment in a digital form and to perform multiscenario calculations without modifying the computational workflow. The approach has been validated using oil and gas-condensate fluid samples with injection of carbon dioxide and various hydrocarbon gas compositions. The results demonstrate that the effect of the injected gas depends on both the fluid type and the objective of injection. For oil systems, carbon dioxide provides a pronounced swelling effect and may be considered a preferable displacement agent when its content in the injected mixture is optimized with due consideration of corrosion risks. In gas-condensate systems, CO₂ injection may be associated with a risk of hydrate formation, while the use of excessively dry gases can promote retrograde condensation; for this reason, an additional analysis of phase envelope was performed to identify scenarios accompanied by narrowing of the two-phase region.The developed digital Swelling Test significantly reduces the need for laboratory experiments, provides rapid assessment of multiple injection options, and can be integrated into domestic PVT simulators, thereby extending their functional capabilities.