Asphaltene Precipitation from a Heavy Crude Oil with CO2 and Solubility of Crude Oil/CO2 Mixtures

Abstract

Carbon dioxide (CO2) flooding by immiscible gas drive is being increasingly used for Enhanced Oil Recovery (EOR) operations to address the challenging recovery of heavy crude oils. CO2 may trigger the precipitation and deposition of asphaltene, which may lead to a decrease in the crude oil recovery efficiency due to reduced permeability and porosity of the reservoir rock. Asphaltene deposition is currently one of the costliest technical challenges in the petroleum industry. Further research is required on identifying the conditions that will cause the onset of asphaltene precipitation with CO2 and the subsequent amount of asphaltene precipitated. In our work we have investigated the relationship between the mass of precipitated asphaltene from a heavy crude oil (API = 9.3) and the mass of a precipitant in crude oil/hydrocarbon and crude oil/supercritical CO2 systems. The experiments were carried out in a high pressure/high temperature filtration cell, filled with crude oil and the precipitant CO2. The use of a filtration cell is a precise method to determine the amount of precipitated asphaltene by any precipitant. The solubility of CO2 in the crude oil was measured at various pressures at 50 °C using a high-pressure mixing vessel connected to a syringe pump. The onset point was quantified in terms of the Hildebrand solubility parameter, which has previously been shown[1] to reconcile the behaviour of different hydrocarbon precipitants for an oil/hydrocarbon system. Precipitation induced by CO2 has a quantitatively different behaviour from precipitation induced by hydrocarbon systems; however, for the first time we were able to interpret the data by measuring the solubility of CO2 in oil and thereby estimate the system solubility parameter. This approach can then be used to predict the amount of precipitated asphaltene for various mixtures. The results will help to understand asphaltene behaviour in EOR operations in more detail as it is yet not fully identified how heavy crude oil asphaltene behave in reservoir rocks under precipitating conditions. [1] Wang J. and Buckley J. S. (2003) Energy and Fuels, 17, 1445-1451.