A Water-Based Analogue Model for Foamy Oil Experiments

Abstract

Foamy oil is a phenomenon that is not yet fully understood. Studies often involve high pressure equipment that make experiments slow, expensive, and the equipment difficult to clean. A simple suggestion of wallpaper paste solution (carboxyl-methyl cellulose and water) and antacid mixture could be used to determine a number of the physical processes and properties needed to further understand foamy oil. The wallpaper paste solution when combined with antacid behaves similarly to that of foamy oil, but experiments can be conducted without the inconvenience of using the oil. Such experimental studies would be easier, low cost, and cleaner, and could be precursors to experiments on actual foamy oil. Introduction Certain heavy oil reservoirs under solution gas drive exhibit production rates in terms of well productivity and quantities greater than anticipated by normal material balance calculations, and at the surface there is a rapid shrinking of the oil volume over a couple of days. The term foamy oil is often used to distinguish this type of reservoir fluid from that of "normal" heavy oil - the difference is in the manner of gas release and on the volume of oil recovered. The phenomena have not yet been fully explained, although some attempts have been made since 1990, when the first reports were made. Good reviews have been published(1–4), and their reference lists can guide the reader to many more. Additionally, other work certainly remains within the restricted access of internal company reports or conference proceedings with limited circulation, so are not in full public domain. However none have yet given the definitive reasoning of how best to produce heavy oil by solution gas drive. A sound understanding is needed of the current theory, current best practice, and current new ideas on how to predict, diagnose, and use to advantage the properties of foamy oil. Foamy Oil Experiments Generally, it is believed that foamy oil flow occurs with some heavy oils below the bubble point, i.e., gas is being released under the solution gas drive, but that the gas is entrapped in the oil as bubbles. The bubbles are slow to coalesce within the oil, which itself is a high viscosity, often non-Newtonian, fluid. The coalescence processes require that the oil films between the gas bubbles becomes thin and then rupture. The thinning process is highly dependent on the oil film viscosity and the defoaming effects of particles accumulated at the gas/oil interface (e.g., asphaltenes, rock debris, etc.)(5,6). If foamy flow can be induced or maintained, the recovery from that reservoir and the productivity of wells may be enhanced. At surface conditions the interface science of foam breakage is important and, again, the high non-Newtonian characteristics of the oil are very significant in the gas release. Researchers continue to study foamy oil from microscopic to macroscopic behaviour in order to identify the mechanisms involved(1–4). The purpose is that this understanding could lead to new directions for a more optimised plan of heavy oil recovery from a reservoir, particularly cold primary production by solution gas drive.