Investigation of the Properties of Hydrocarbon Natural Gases Under Confinement in Tight Reservoirs Due to Critical Properties Shift

Abstract

Pure components exhibit different phase behavior and critical properties shift when confined, primarily due to increased molecules-pore wall interactions. While extensive research has focused on modeling this behavior for pure components, there is a need to extend these models to hydrocarbon gas mixtures in tight and shale reservoirs to understand the deviation of gas properties from bulk behavior. The study utilizes the Peng–Robinson equation of state to calculate gas properties, considering the shift in critical properties of pure components due to confinement in EOS parameter calculations. Trend analysis investigates the effect of pore size reduction on gas properties, introducing the concepts of the confinement impact factor and specific pore radius. Correlation analysis explores the relationships between variables. Nonlinear regression analysis leads to the development of a new correlation that accounts for confinement effects on gas properties. The findings reveal that the deviation from bulk properties depends on the pore radius, pressure, temperature, and gas composition. The magnitude of deviation ranges from negligible to exceeding 15% under specific conditions of high pressure, low temperature, small pore radius, and rich gas composition. Gas viscosity experiences the most significant alteration, followed by density, while the gas compressibility factor also displays a noticeable impact. The isothermal gas compressibility coefficient demonstrates minimal to no response to confinement. Decreasing pore radius increases the gas compressibility factor, while gas viscosity and density decrease. The obtained results are crucial for shale and tight reservoir engineering calculations, particularly in adjusting gas properties in reservoir simulation and production modeling software.