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

摘要

In many light or moderately viscous oil reservoirs inrnSaskatchewan and Alberta, a high water saturation zonernovarying thickness and extent ("bottom-water zone") occurs inrncommunication with the oil zone above. As a result, thernprimary production period is short, and water coning occursrnvery early in the life of the reservoir. Later, during thernsecondary recovery stage, such a zone can have an adverserneffect on the waterflood efficiency. This research addressesrnthe problem of waterflooding such reservoirs.rnThis study was directed towards reducing water mobility inrnthe bottom-water zone for more efficient oil displacement.rnPolymer in various concentrations was used as a blockingrnagent in the bottom-water zone and as a mobility control agentrnin the oil zone. Different strategies were investigated tornreduce the water mobility in the bottom-water zone andrnimprove the vertical sweep efficiency. The variablesrnexamined were: relative water-oil layer thickness, oilrnviscosity, polymer concentration, injection rate and injectionrnpoint, as well as the effect of vertical and horizontal injectionrnand production wells.rnThe results showed that oil recovery could be increased byrnminimizing crossflow between layers by blocking the bottom-waterrnzone completely. It was also found that for anrnunfavourable mobility ratio, as the injection rate increases thernultimate oil recovery increases. The injection of a polymerrnsolution had a favourable impact on waterflood performance.rnMoreover, the worse the conventional waterflood performancernwas, the more effective the polymer was as a mobility andrnblocking control agent. The use of horizontal wells showed slightly better oil recovery over vertical wells in arnconventional waterflood of reservoirs under bottom-waterrnconditions. In addition, some certain well combinationsrn(horizontal production and vertical injection) gave better oilrnrecovery due to the increase in the swept area.