Abstract

Experiments and numerical simulations on initial stages of the steam-assisted gravity drainage (SAGD) process were carried out. Experimental studies used two-dimensional scaled reservoir models to investigate fluids flow characteristics in the steam chamber and production fluids. The rise and growth of the initial steam chamber were observed and visualization of micro-phenomena at inclined interface on the side of the steam chamber with a high-resolution optical-fiber scope was carried out. Very fine water droplets of 0.01 mm order in size were observed at the interface between steam and heavy oil phases. These droplets entered into heavy oil phase and created emulsion together with the heated oil, which floweddown and was produced from the production well. It was successfully demonstrated that these micro phenomena has an influence on chamber expansion rate in horizontal direction and oil production rate.

The numerical simulation of the SAGD process was also performed. The thermal simulator, CMG's STARS™, was used to simulate the experimental steam chamber growth at the initial stage. The simulation used the two-components (water and heavy oil) black oil, three-phase (water, heavy oil and steam) and three-dimensional numerical model for the physical model. The results from the history-matched numerical simulation were found to be in good agreement with those of the experiments for oil production and steam chamber shape by using the Intermediate3-Stone1 wettability model represents fluids behavior cumulating the microscopic phenomena at the chamber interface. Furthermore, a new process named Surfactant-SAGD injecting a surfactant before starting steam injection to enhance the communication between two wells and mobility of the production fluids was tested.

Introduction

Production of bitumen and heavy oil efficiently and economically remains a formidable challenge. However, as shown in the reports of the UTF projects (phases A and B) in Canada, the steam assisted gravity drainage (SAGD) process for bitumen has proven to be a superior process compared to other recovery processes due to its high recovery factor1–4. The process was first developed, and refined by Butler and his co-workers5–14. The underlying idea for SAGD was to overcome the problems associated with the flow of highly viscous bitumen by gravity drainage in steam chambers generated by displacement of heavy oil (Figure 1).

Recently, the SAGD process involving surface-drilled horizontal wells at the UTF was tested and shown to be more economical (Komery et al.15 and Bauquis16). Many field test projects have been started. The Japan Canada Oil Sands Ltd. (JACOS) has also successfully produced bitumen from seven horizontal well pairs from the surface at Hangingstone, Alberta (Ito et al. 17).

It is pointed out that in this work, conventional SAGD process refers to the process involving injection of steam through the upper horizontal injector, and production from the lower horizontal producer, such as the original configuration used by Butler et al.13, and the well configuration at the UTF project. Previous experiments by Sasaki etal.18,19 showed the rate of vertical rise of the steam chamber was less than that predicted by the conventional SAGD numerical model. Also, the lead-time required to generate a steam chamber in near breakthrough condition between two wells prior to the vertical expansion of the steam chamber was long. It was hypothesized that the conventional SAGD process could be modified to first shorten the time period prior to the vertical rise of the steam chamber, and second enhance the expansion rate of the steam chamber in consideration of fluids phenomena at the chamber interface.

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