Evaluation of Diffusion of Light Hydrocarbon Solvents in Bitumen

Abstract

Solvent-based processes are often used as potential recovery agents in bitumen systems, with and without the addition of heat to the solvent. Solvents can sometimes be applied as a liquid phase, during SAGD start-up operations or processes aimed at developing injectivity into the oil. Light hydrocarbon liquids are traditionally tested for this application. Solvent injection may also occur in a vapour state and its objective is to reduce oil viscosity and improve mobility of bitumen under low temperatures Ͻ100°C. In general, hydrocarbon solvents such as propane are often used for this application. The objective of this study is to conduct CT-based measurement of static mixing of bitumen and both liquid and vapour phase solvents, and to quantify some of the time-dependent changes that occur during solvent mixing with bitumen.Diffusion experiments have been conducted with propane and DME (vapour phase) and with propane, DME, pentane and toluene (liquid phase) solvent systems. Solvents are mixed with medium viscosity Peace River bitumen and high viscosity Grosmont bitumen. The Tests are run under constant pressure and temperature, and Computer-Assisted Tomography (CT) is used to monitor mass transfer of solvent into oil as a function of time. The outcome of this study is measurements of mass transfer rates of solvent into oil, and the degree of oil phase swelling during the tests.During solvent injection processes in the field, the rate of mixing is a key parameter that will help in deciding which solvent is optimal for different processes. This study focuses on the rate of solvent mixing with oil. In vapour phase solvent systems, the analysis of the CT images allows for an understanding of the impact of oil phase swelling on the effective rate of penetration of solvent into oil. Overall, the test data provided in this work demonstrates that DME mixes into oil faster than other solvents, and leads to more swelling in a vapour solvent-bitumen system. The analysis of CT data provides an understanding of concentration-dependent diffusion coefficients and limitations from predicting mass transfer using constant coefficients in liquid and vapour solvent systems.

Thermophysical properties of dimethyl ether/Athabasca bitumen system

“…The major concern about using solvents for bitumen and heavy oil recovery is their cost. Alternatives to the hydrocarbon solvents that have similar mass transfer rate and solubility in bitumen and heavy oil has to be considered . Recently, DME has been proposed as a non‐hydrocarbon solvent for recovery of bitumen and heavy oil.…”

“…DME, which is often referred as “synthetic LPG,” can be produced directly from fossil fuel like natural gas or from renewable sources such as waste, wood, and agricultural products . Propane can be produced from liquefied petroleum gas (LPG) or natural gas condensate.…”

Heavy Oil Recovery via Combination of Radio-Frequency Heating With Solvent Injection

“…While the theoretical definition of the solvent diffusion coefficient relates it to mixture viscosity (cf. Hayduk andCheng 1971, Das andButler 1996) the recent CT-tomography based measurements done both for gaseous and liquid hydrocarbon solvents demonstrated different behavior (Diedro et al 2015). The systematic study of the diffusion coefficients in bitumen carried out during last ten years at the U. of Calgary indicates that in many cases the coefficient remains nearly constant up to certain (typically high enough) solvent concentration and then changes rapidly to significantly higher value.…”

“…Recognizing the importance of solvent mass transfer to HO, several different experimental techniques have been used previously for measurements of diffusion coefficients for light hydrocarbon solvents (cf. Das and Butler 1996, Creux et al 2005, Diedro et al 2015. These solvents diffusion process is generally concentration, temperature and pressure dependent, the latter being important mainly for the case of gaseous (non-condensible at working GC conditions) solvent.…”

“…The specified in Das and Butler (1996) mixture-viscosity based formulation with power value ␤ recommended by these authors and constant value of coefficient corresponding to numerous reported mesurements (see eg. Creux et al 2005, Diedro et al 2015 and other publications of the group on http://perminc.com/). The value used in simulations is 0.46 (cf.…”