Pressure-Induced Viscoelastic Strengthening in Heavy Crude Oils: Experimental Quantification Under Reservoir-Relevant Conditions

Heavy crude oils exhibit complex rheological behavior governed by the interplay between temperature, pressure, and colloidal microstructure. In this work, the coupled influence of pressure and temperature on the viscoelastic response of five Mexican heavy crude oils was experimentally investigated under reservoir-relevant conditions. Steady and oscillatory shear measurements were performed at temperatures between 10 and 30 °C and at pressures ranging from atmospheric to 10.034 MPa. The results revealed pronounced shear-thinning behavior for all samples, with viscosity increasing systematically with pressure and decreasing strongly with temperature. Pressure effects were particularly significant at low temperatures, where enhanced elastic behavior and longer characteristic relaxation times were observed. Oscillatory measurements showed that pressurization shifted the viscoelastic crossover toward lower frequencies, indicating pressure-induced reinforcement of internal structures and reduced molecular mobility. The viscoelastic response was interpreted using a pressure-modified Arrhenius model, which successfully described the dependence of characteristic relaxation time on temperature and pressure. The fitted activation energies and activation volumes revealed systematic differences associated with crude oil composition and colloidal stability. Samples with lower resin-to-asphaltene ratios exhibited stronger pressure sensitivity and higher structural rigidity. The results demonstrate that pressure and temperature jointly control the relaxation dynamics and structural organization of heavy crude oils. These findings provide useful insights into flow assurance, transport, and production operations involving heavy crude systems under thermobaric conditions.