No abstract

Modification of CO2 mobility to prevent premature breakthrough and poor sweep efficiency is a major step for improving oil recovery in CO2 injection. Water-alternating-CO2, foam, and direct viscosification are the main proposed methods to limit CO2 mobility and improve the sweep efficiency. CO2 direct viscosification is the most desirable option. Control of the process is very simple. In this work, an engineered molecule is introduced to increase CO2 viscosity and improve oil displacement efficiency in CO2 flooding as a secondary recovery technique. An engineered oligomer of 1-decene (P1D) with the approximate molecular weight of 2950 g/mol is used to viscosify supercritical CO2. A mixture of 1.5 wt% P1D in supercritical CO2 with the relative viscosity of 5.2 at the temperature of 140 ˚F and pressure of 3500 displace the oil in most of our experiments. A set of coreflood experiments in sandstone and carbonate rock samples are carried out to evaluate and compare oil recovery performance by neat and thickened CO2. Hexadecane, with viscosity of 1.7 cp and density of 0.745 kg/m3, and a dead crude oil sample, with viscosity of 4.1 cp and density of 0.843 kg/m3, at the pressure of 3500 psi and temperature of 140 ˚F are displaced by neat and viscosified CO2. Breakthrough time, breakthrough recovery, and recovery at 1 pore volume injection in the horizontal orientation are the key measurements. At the experimental conditions, CO2 breakthrough is delayed by an average of 2 times and oil recovery is increased by an average of about 20 % upon CO2 viscosification. These results reveal the effectiveness of the engineered oligomer in viscosification and improved oil recovery performance. There is no permeability loss detected in core flooding experiments. This work sets the stage for CO2 viscosification as a viable approach as an improved oil recovery method. The process, is relatively simple and has many advantages over alternatives such as CO2-foam or water-altenative-CO2.