Prediction of asphaltenes deposition in the Russian oilfield: Laboratory investigations and modeling

Abstract

The purpose of this study is to investigate the asphaltenes precipitation in oil and their deposition in the pore volume, as well as to model the possible production scenario in case of asphaltenes deposition in the near wellbore area of the Russian oil field.The study of asphaltene envelope in reservoir oil was carried out using light-scattering and microscopy under high-pressure methods. Three experiments were carried out in the isothermal pressure reduction mode at three different temperatures (70.3, 60 and 50 °C). Pressure decreased from 28.87 to 14.0 MPa in each experiment with rate of 0.2 MPa/min. Asphaltenes envelop is generated from laboratory experiments. In addition, potential areas of asphaltenes deposition along the tubing were identified using the pressure and temperature profiles along the wellbore of the producer.The effect of asphaltenes deposition in the pore volume on permeability was studied on three core samples. Filtration of reservoir oil was carried out in the mode of step-by-step backpressure reduction from 28.87 to 14 MPa by maintaining constant confining pressure and reservoir temperature. The results showed that there is a sharp decrease in core permeability due to the asphaltenes deposition when Asphaltenes Onset Pressure (AOP) is reached. The maximum decrease in permeability corresponds to 68.3% at 17 MPa.It is noted that a number of producers of the Russian oil field operated with high oil rates, so areas of low pressure (drawdown pressure cone) in the near wellbore areas were formed, contributing to the aggravation of the issue. Based on the laboratory results, the calculation of the permeability decrease in near wellbore area due to the asphaltenes deposition was provided for three cases (drawdown pressure cone 20, 100 and 500 m). Results show that gradual expansion of drawdown pressure cone deep into the reservoir during field operation will be accompanied by an increase in the skin factor from 9.7 to 12.5 (for 969 days of well operation). The prevention and remediation methods of the organic-scales formation in the field are proposed.