Low Temperature Carbon Dioxide Injection in High Temperature Oil Reservoirs
Authors: Hamdi Zakaria , Bt. Awang Mariyamni , Moradi Babak 
Published: May 2016

Abstract
Carbon dioxide injection has been used as a successful tertiary recovery method for the past decades. The main advantage of CO2 is its miscibility with the crude oil which can lead to higher recovery. Large quantity of CO2 exploration is often explored as gas or supercritical phase; but, low temperature CO2 is produced in some downstream facilities such as cryogenic separation units. This low temperature CO2 opens a novel opportunity to evaluate the potential of low temperature CO2 injection for both storage and enhanced oil recovery methods.
In this study, a non-isothermal compositional simulation was conducted using a commercial simulator to examine the performance of low temperature CO2 injection process in a high temperature reservoir. The results showed that, after 24 years of production, 8.73% increase of total oil recovery by liquid CO2 is expected in comparison with supercritical CO2 injection in isothermal mode (200 °F). It also shows the high storage capability of CO2 in this method. The storage of CO2 increased by 11.2% in compare with isothermal mode. The results of this study proved a significant advantage for low temperature CO2 injection to improve oil recovery as well as storage capability that can be implemented in the field.

Introduction
For the past decades, CO2 flooding has proven to be an acceptable tertiary recovery in enhanced oil recovery (EOR) (Lake 1989, Green, Willhite et al. 1998, Moritis 2004). CO2 causes a massive viscosity reduction due to component exchange between oil and CO2 (Latil 1980, Holm 1982, Holm and Josendal 1982, Orr and Taber 1984, Lake 1989, Blunt, Fayers et al. 1993, Green and Willhite 1998); it is reported that the addition of CO2 in the crude oil may reduce the crude oil viscosity by a factor of 10 even for heavy crude oils (Rojas, Zhu et al. 1991, Quraini, Sohrabi et al. 2007). Besides that, dissolution of CO2 in the oil results in oil swelling, solution gas drive, and oil extraction which those mechanisms can help to increase oil recovery (Holm 1982, Holm and Josendal 1982, Orr and Taber 1984, Bondor 1992, Blunt, Fayers et al. 1993). But the major benefit of CO2 flooding is miscibility with the oil. The minimum miscibility pressure (MMP) of CO2 and crude oil is lower than other gases such as methane, nitrogen etc. But low viscosity and low density of CO2 may lead to gravity override (Orr and Taber 1981, Stalkup 1983).
Whilst increasing oil production, EOR by CO2 can also facilitate the storage of CO2 in the oil reservoir (Kovscek 2002, Gozalpour, Ren et al. 2005, Kovscek and Cakici 2005, Rackley 2009, Ren, Niu et al. 2011) As a result, it may provide some economic benefits (Espie 2005).
Carbon dioxide is known as greenhouse gas that contribute in global warming (Kongsjorden, Kårstad et al. 1998, Hepple and Benson 2005, Rackley 2009, Schrag 2009). CO2 emitted into the atmosphere is the main cause for global warming (Jeong, Sato et al. 2010). Injection of CO2 in the oil reservoir is one of the possible solutions in the reduction of CO2 in the atmosphere (Kovscek 2002, Gozalpour, Ren et al. 2005, Kovscek and Cakici 2005, Ren, Niu et al. 2011).
CO2 is a colorless odorless gas in standard condition but its phase is highly dependent on the temperature and pressure as shown in Figure 1.