In Situ Emulsification By The Condensation Of Steam In Contact With Bitumen
Authors: Chung K.H. , Butler A.M. 
Published: March 2010

In a previous paper, low-pressure experiments on the steam assisted gravity drainage process using a scaled physical model showed more emulsification when the steam chamber was rising. This paper describes experimental results from an extended Investigation. Included are the confirmation of the previous results using a higher steam pressure, and studies of the effect of connate water and steam quality. The experiments were performed in two-dimensional reservoir models with Cold Lake bitumen. The injection steam pressure was varied from 153 to 3550 kPa (7.5 to 500 psig).

The results show that the primary mechanism for in situ water-oil emulsification involves the condensation of steam in contact with bitumen. Less emulsion is formed when the formation ontains connate water. The quality of the injected steam and the nature of the porous packing did not change the degree of in situ emulsification. The pressure of the injected steam had little effect on the emulsified water content on the produced fluid. As before, much more emulsion was formed when the steam chamber was rising. The retention of steam condensate n a formation initially completely filled with bitumen results in an irreducible water saturation. This irreducible water saturation was the same as that found in another experiment in which a water-filled reservoir was flooded with bitumen.

Introduction

In a previous paper(1), the content of water-oil emulsion in the produced fluid was monitored during the steam-assisted gravity drainage process using a low-pressure scaled reservoir model. It was found that when steam was injected near the base of formation, there was a meandering and counter-current flow of steam and heated heavy oil within the steam chamber which grew upward. This caused more emulsification. When steam was injected at the top of the formation, the steam chamber spread sideways and downward. A two-phase stratified flow of steam and heated heavy oil occurred in which steam flowed sideways to the interface, and heated heavy oil flowed down, below and along the interface. This resulted in less emulsification. Therefore, the degree of in situ emulsification can be changed by altering the geometry of the steam injection.

This paper extends the previous results from the low-pressure reservoir model to higher pressures. Other factors affecting in situ emulsification during steam-assisted gravity drainage process will be discussed. The change in water saturation of a depleted formation as a result of the retention of steam condensate during thermal recovery process has also been studied.

Experimental

The experiments were conducted using two-dimensional reservoir models with steam pressures varying from 153 kPa to 3.55 MP. (7.5 to 500 psig). The detailed description of the apparatus and experimental procedure for the low-pressure experiments have been described elsewhere(1, 2). The operating and sampling procedure used in the high-pressure experiments were similar to those in the low-pressure experiments, except for the method of handling high-pressure steam and the fabrication of the high pressure apparatus.

The schematic diagrams of the equipment for the high-pressure experiments are shown in Figure 1. The equipment consisted of a two-dimensional scaled reservoir model, a high-pressure vessel, a temperature monitoring system, and a flow line network for steam injection and oil production.