Phase Behaviour and Physical Property Measurements for VAPEX Solvents: Part II. Propane, Carbon Dioxide and Athabasca Bitumen

Abstract

The solubility of pure carbon dioxide in Athabasca bitumen was measured and compared with the literature data. Multiple liquid phases were observed at carbon dioxide contents above approximately 12 wt%. A correlation based on Henry's law was found to fit the saturation pressures at carbon dioxide contents below 12 wt%. The saturation pressure and solubility of carbon dioxide and propane in Athabasca bitumen, as well as the liquid phase densities and viscosities, were measured for three ternary mixtures at temperatures from 10 to 25 °C. Two liquid phases (carbon dioxide-rich and bitumen-rich) were observed at 13 wt% carbon dioxide and 19 wt% propane. Only liquid and vapour-liquid regions were observed for the other two mixtures (13.5 wt% propane and 11.0 wt% carbon dioxide; 24.0 wt% propane and 6.2 wt% carbon dioxide). The saturation pressures for the latter mixtures were predicted using the correlation for the carbon dioxide partial pressure and a previously developed correlation for the propane partial pressure. The mixture viscosities were predicted with the Lobe mixing rule. Introduction In Part I of this work(1), mixtures of carbon dioxide and propane were identified as a potential solvent for the VAPEX process. At typical heavy oil reservoir conditions (pressure of ~1.2 MPa and temperature of ~10 °C), propane and butane have sufficient solubility to reduce the oil viscosity to a level where gravity drainage can occur in an economic time scale. However, propane and butane are expensive solvents and the success of the process depends on how much solvent can be recovered. As well, the VAPEX process operates below the saturation pressure of the solvent and, therefore, propane and butane cannot be used at higher reservoir pressures where they exist only in the liquid phase. Methane can be added to achieve the desired pressures(2). However, carbon dioxide may also be a better VAPEX solvent than methane because it is more soluble in heavy oil and significantly reduces the viscosity(3). Mixtures of carbon dioxide and propane may achieve the desired reduction in viscosity while minimizing the required propane volumes. Hence, there is an incentive to evaluate mixtures of carbon dioxide and propane as a VAPEX solvent. VAPEX performance depends on the viscosity and density of the liquid phase that forms at the edge of the vapour chamber. In order to design and optimize VAPEX and other solvent-based processes, it is critical to be able to determine the diffusivity of the solvent in the heavy oil, identify the phases that form in the solvent and heavy oil mixtures at various temperatures and pressures, and determine the density and viscosity of the liquid phase. Other solvent-based processes (steam and solvent injection for heavy oil recovery and solvent extraction of oil sands) require similar data. In Part I of this work(1), saturation pressures and liquid phase densities and viscosities were measured for propane and Athabasca bitumen. There are also considerable data in the literature for mixtures of carbon dioxide and crude oils. Simon and Graue(4) measured the solubility, swelling and viscosity of mixtures of carbon dioxide and nine different oils.

Rheology and Phase Behavior of Carbon Dioxide and Crude Oil Mixtures

“…An example is Chuang et al, where the CO2 solubility, oil swelling factor and viscosity for 4 different CO2 saturated heavy crude oils were measured and correlated at different temperatures and pressures [4]. Similar studies can also be found in [5][6][7][8][9][10][11]. In addition, the viscosity of CO2 and alkane diluted crude oil was reported by Li et al [12].…”

“…Moreover, as reported by many papers [6][7][8][9]15], CO2 solubility in crude oil normally increases with increasing pressure but decreases with increasing temperature. The pressure sensitivity of the CO2 solubility at high pressures depends on the phase of CO2: when CO2 is in the liquid phase, the solubility is least sensitive to pressure [4,7].…”

“…The pressure sensitivity of the CO2 solubility at high pressures depends on the phase of CO2: when CO2 is in the liquid phase, the solubility is least sensitive to pressure [4,7]. On the other hand, there are two determining factors on crude oil density: the compression effect of pressure and the swelling effect of dissolved CO2 [4,6,7,9]. Therefore, the crude oil density changes resulting from changes in CO2 pressure depend on the nature of the crude oil and the operational conditions.…”

Experimental and Theoretical Determination of Equilibrium Interfacial Tension for the Solvent(s)–CO2–Heavy Oil Systems

“…PR EOS Model. Because of its wide application in the petroleum and chemical industries, the PR EOS 19 is chosen as the EOS for describing the phase behavior of 0.786 C 39 1.583 C 10 0.844 C 40 1.600 C 11 1.037 C 41 0.750 C 12 1.267 C 42 0.830 C 13 1.817 C 43 1.380 C 14 1.950 C 44 0.929 C 15 2.300 C 45 0.929 C 16 2.143 C 46 0.700 C 17 2.286 C 47 0.833 C 18 2.238 C 48 0.792 C 19 2.048 C 49 0.792 C 20 1.857 C 50 0.733 C 21 2.071 C 51 0.750 C 22 1.329 C 52 0.717 C 23 1.743 C 53 0.717 C 24 1.571 C 54 0.683 C 25 1.714 C 55 0.650 C 26 1.600 C 56 0.650 C 27 1.583 C 57 0.667 C 28 1.650 C 58 0.667 C 29 1.452 C 59 0.667 C 30 1.281 C 60+ 36.164 …”

“…6 Although some laboratory efforts have been conducted to study the mechanisms for enhancing heavy oil recovery by CO 2 injection, 5,7−12 few attempts have been made to evaluate the IFT performance of the solvent(s)−CO 2 −heavy oil systems under sub-and supercritical conditions. 13,14 Therefore, it is of fundamental and practical importance to study the interfacial behavior of the solvent(s)−CO 2 −heavy oil systems under reservoir conditions.…”