Investigation of Asphaltenes Precipitation Under Immiscible Interaction of Reservoir Heavy Oil and Liquid Carbon Dioxide

Abstract

A new method for assessing the stability of the asphaltene phase in reservoir fluids using a high-pressure microscope is presented. The new method is based on the observation of the asphaltene particles sedimentation in a vertically oriented sapphire cell. This determines the size of sedimentation particles, their number and sedimentation rate. Experimental results are used as input parameters for calculating solid particles sedimentation of using the Stokes law equation. It makes possible to calculate the density and weight percent of the solid phase, evaluate the aggregative and kinetic stability of the fluid with respect to solid particles depending on thermodynamic parameters (pressure, temperature, reagent concentration). The proposed method was tested in the single-contact study of high-viscosity reservoir oil and liquid carbon dioxide and was compared with the results of asphaltene precipitation gravimetric test. According to the results analysis, were conclusions about the applicability of the new method and the mechanism of asphaltenes precipitation in high-viscosity oil when it contact with carbon dioxide. It is shown that the combination of gravimetric and visual analyzes allows to investigate the asphaltenes precipitaion separately in two processes: reduction of pressure and vaporization of fluids. This makes it possible to assess the likelihood of formation and the effectiveness of reagents for combating solid deposits in the entire process chain of oil production. Concluded that the asphaltenes precipitation in the contact of carbon dioxide and high-viscosity oil occurs according to the complex mechanism and includes intensification due to a drop in oil viscosity and damping due to mass transfer between carbon dioxide and oil phases. From this, inhibitors selection criteria are derived and the using of deasphalted oil as a stabilizer of asphaltenes is proposed.