Abstract

The Alberta all sand deposits contain a vast amount of bitumen, most of which will have to be recovered by in situ steam injection methods. To improve the efficiency of these methods, studies from this laboratory have focused on the development of steam-surfactant systems. In this paper, we describe a core-size test facility for evaluating chemical additives to steam. The test facility features a production station for the visualization of the production fluids at run conditions. The additives investigated include NeOH/NaCl mixture, Thermoflood 808 (a micellar formulation of thin film spreading agents) and Sun Tech IV (a sulfonate surfactant). Numerical simulation studies complemented and aided in the interpretation of the experimental results. Steam/water flow experiments in an oil-free sand pack demonstrated the existence of pressure drops in the presence of surfactant over and above that due to biphasic flow in the absence of surfactant. It was shown that high bitumen recovery is most likely associated with the formation of a foam block in the steam swept zone of the core.

Introduction

There is now a great deal of interest: in the use of surfactants and alkali reagents to improve the efficiency of steam based processes. This interest stems from a number of claims of successful field performances, mainly in California heavy oil reservoirs, for additives such as Sun Tech IV 1–4 thin film spreading agents (TFSA) 5–7 and alkali reagents 8,9. A large number of laboratory studies have also been reported on the evaluation of surfactants and caustic for high temperature application including thermal stability, consumption, interfacial activity and displacement efficiency 10–18. Despite the increasing interest, little is known about how surfactants and caustic function to improve recovery under steamflood conditions.

Over the past number of years, investigations from this laboratory have focused on the development of asteam-surfactant system for use in Alberta's oil sand reservoirs. To this end, the crumble test was developed and used as a low temperature method for rapid evaluation of surfactant performance21.Experiments on thermal stability were carried out to investigate the degradation kinetics of surfactants with sulfonate moieties. This work demonstrated that the decomposition process can be suppressed, making commercial sulfonate surfactants good candidates for high temperature application 22. Interfacial tension studies were conducted to examine methods of chieving low interfacial tensions at elevated temperature22,23. Experiments in both core-size cells (hoc water injection) and large scale test beds(steam injection) showed a very substantial increase in bitumen displacement efficiency in the presence of surfactants22,24. A study to visualize the displacement process under adverse mobility conditions using a novel "xeroradiographic" system was recently described 25.

One of the main purposes of this study was to develop a core-size apparatus for evaluating chemical additives to steam, which would permit a "mechanistic" interpretation of recovery data and at the ame time be amenable to numerical simulation. The test facility features a production station for the visualization of the produced fluids at run conditions.

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