Measurements of Mobile Water Saturation in Oil Sands

ABSTRACT

The presence of mobile water saturation in heavy oil and bitumen systems is of considerable importance when understanding how different reservoir recovery methods will work. In non-thermal heavy oil production, the presence of mobile water saturation has extreme significance to the production of cold heavy oil (CHOPS) wells. Some wells are able to produce oil under relatively low and constant water cuts, while other wells produce significant water and quickly need to be shut in due to high production water cuts. In this study, an NMR and core analysis approach is used to shed some light into the properties of oil sand with or without mobile water present. Specifically, tests were run in order to study if mobile water is a localized pore scale phenomenon or if it can be understood through a more macroscopic view of the reservoir.

Samples of core are taken from two heavy oil producing wells: one that experienced very high production water cuts, and the other that produced mainly heavy oil with minimal water. The samples (containing heavy oil and connate water) are flooded with water in order to measure effective permeability to water. NMR spectra are also obtained after flooding and after cleaning of the cores, in order to understand the pore-scale location of water in different effective permeability samples. The outcome of this study is insight into what is the difference in core properties between wells with vs. without mobile water. The key conclusion reached is that wells behave similarly at the pore/core scale, but differences are observed macroscopically. The well with high historical water contains thin zones of high water saturation (high water effective permeability) which were missed at the resolution of the logs. Water production may be due to the presence of these heterogeneous zones.

A full version of this paper is available on SCAWEB Online.