An experimental and theoretical investigation of asphaltene precipitation in a crude oil from the Brazilian pre-salt layer under CO_2 injection

摘要

The asphaltene onset pressure (AOP) is a key parameter to determine the flow assurance of oils. In this work we performed an experimental study of the PVT (pressure-volume-temperature) properties of a crude oil from the Brazilian pre-salt layer. First, dead-oil was recombined with natural gas at the reservoir gas-oil ratio (GOR). Then, different techniques (volumetric, visual, light-scattering and filtration) were used to measure the AOP and bubble pressure (BP) at temperatures in the range of (293.15 to 348.15) K. The effect of CO2 injection on both properties was also evaluated at reservoir temperature. Additional data of mass density was measured at reservoir pressure and temperature. The experimental data were used to fit the adjustable parameters of the Peng-Robinson equation of state (PR-EoS) and the calculated results are compatible with the experimental data. The PR-EoS calculates a decrease in the AOP and an increase in the BP as temperature rises. PR-EoS correctly predicts the qualitative effect of gas injection on the studied properties: all evaluated properties increase as CO2 is injected in the recombined oil.