Mobility Control by Polymers Under Bottom-Water Conditions, Experimental Approach

Abstract

Abstract In many light or moderately viscous oil reservoirs in Saskatchewan and Alberta, a high water saturation zone ovarying thickness and extent ("bottom-water zone") occurs in communication with the oil zone above. As a result, the primary production period is short, and water coning occurs very early in the life of the reservoir. Later, during the secondary recovery stage, such a zone can have an adverse effect on the waterflood efficiency. This research addresses the problem of waterflooding such reservoirs. This study was directed towards reducing water mobility in the bottom-water zone for more efficient oil displacement. Polymer in various concentrations was used as a blocking agent in the bottom-water zone and as a mobility control agent in the oil zone. Different strategies were investigated to reduce the water mobility in the bottom-water zone and improve the vertical sweep efficiency. The variables examined were: relative water-oil layer thickness, oil viscosity, polymer concentration, injection rate and injection point, as well as the effect of vertical and horizontal injection and production wells. The results showed that oil recovery could be increased by minimizing crossflow between layers by blocking the bottom- water zone completely. It was also found that for an unfavourable mobility ratio, as the injection rate increases the ultimate oil recovery increases. The injection of a polymer solution had a favourable impact on waterflood performance. Moreover, the worse the conventional waterflood performance was, the more effective the polymer was as a mobility and blocking control agent. The use of horizontal wells showed slightly better oil recovery over vertical wells in a conventional waterflood of reservoirs under bottom-water conditions. In addition, some certain well combinations (horizontal production and vertical injection) gave better oil recovery due to the increase in the swept area.