Carbon Dioxide For The Recovery Of Crude Oil
Authors: Doscher T.M. , Kuuskraa V.A. 
Published: December 2007

Abstract
The history of the proposed use of carbon dioxide is briefly reviewed with particular concern as to the evidence for the need for frontal displacement to occur for successful recovery of crude.
In the absence of frontal displacement, recovery is achieved by solution, oil phase expansion, and its displacement by the dense, gaseous carbon dioxide.
Material balance in an idealized non-frontal displacement reveals the efficiency of carbon dioxide to depend upon initial oil saturation, oil formation volume factor, and the solubility of the carbon dioxide in the crude under reservoir conditions.
Frontal displacement, however, would improve performance but special conditions are required for performance but special conditions are required for achieving it which apparently were not sought in field tests conducted to date. Even without frontal displacement, wide-spread economic recovery of oil by CO2 may ultimately be achieved if carbon dioxide can be re-used by recirculation into a trend of reservoirs.

Introduction
In this age of competitively scarce energy resources, it is the responsibility of the oil recovery technologist to inquire whether there is any potential for improving a particular recovery process potential for improving a particular recovery process to the point where it may become economically successful.
Identification of such potential, or its lack, could help channel appropriate fruitful research and development activities.
The purpose of this paper is to examine the competitive potential of carbon dioxide as a recovery fluid for residual oil.

HISTORICAL NOTES ABOUT CARBON DIOXIDE IN OIL RECOVERY

a. Background
Carbon dioxide for oil recovery was first mentioned in the technical literature in a United States patent issued in 1951. The patent presents a clear and concise statement of the manner in which carbon dioxide was claimed to function in improving oil recovery.
"As injected carbon dioxide gas (at pressures in excess of 1000 psi.) contacts the oil some of the oil evaporates into the carbon dioxide and simultaneously some of the carbon dioxide dissolves in the oil whereby the viscosities of the fluids approach one another. As the viscosities of the two fluids become more nearly equal the oil production approaches the condition of displacement of a fluid by a fluid of the same composition which would result in complete displacement of the contacted fluid originally in place." place." Figure 1, reproduced from the patent, clearly indicates the beneficial effect of high pressure and carbon dioxide purity of laboratory displacements.
In 1959 the concept that carbon dioxide would extract a fraction of the oil and develop a solvent slug that would frontally displace crude was introduced.

b. Discussion of Oil Displacement
The technical literature often states that carbon dioxide is miscible with crude oil. However, miscible means soluble in all proportions. Carbon dioxide is not soluble in all proportions in black crude oils as the earliest attempts to show pertinent phase equilibria indicated. The phase envelope phase equilibria indicated. The phase envelope that exists at high molar carbon dioxide concentrations in the system does shrink with increased pressure, see Figure 2, but there is no evidence that it disappears at any practical reservoir pressure.