Abstract

Thermal-based heavy oil recovery methods, which are exemplified by steam-assisted gravity drainage (SAGD), have been successfully used in a number of field applications to enhance heavy oil recovery over three decades. However, there are several major technical issues associated with the thermal-based methods, such as large energy and water consumptions, extensive heat losses and expensive water treatment, as well as considerable greenhouse gas emissions. Thus the thermal-based methods are not suitable for many heavy oil reservoirs with thin pay zones, bottom water, gas caps, and low rock thermal conductivities due to economic constraints and environmental concerns. Alternatively, the solvent-based heavy oil recovery methods are considered. This paper provides a critical review of several solvent-based methods by conducting a comprehensive literature search of over 100 most recent and significant technical publications. First, the basic idea and technical development of each solvent-based heavy oil recovery method are briefly introduced. The advantages of solvent-based methods are stressed. Second, solvent-based methods are classified and each method is described. Third, a large number of experimental, theoretical and numerical studies of solvent-based methods are reviewed, from physical and theoretical modeling to numerical simulations. In particular, the heavy oil recovery mechanisms, phase behaviour and mass transfer of the heavy oil–solvent systems are examined in detail. A few important factors or major phenomena as well as their effects on the solvent-based methods are analyzed, which include the operating conditions (i.e., pressure and temperature), well configuration, solvent-induced asphaltene precipitation, interfacial tension (IFT), and viscous fingering. Most importantly, a total of six pilot tests or field applications of solvent-based methods, such as vapour extraction (VAPEX), liquid addition to steam to enhance recovery (LASER), and other hybrid steam–solvent processes, are evaluated. Finally, several major technical recommendations are made accordingly for future studies and developments of solvent-based heavy oil recovery methods and their potential variations. This updated technical review will help to better understand the solvent-based heavy oil recovery processes and guide a heavy oil producer to better design a solvent-based heavy oil recovery project.

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