Injection-Production Strategies for Reservoirs Having a Bottomwater Zone

Abstract The major oil sands deposits of Alberta are estimated to contain 197 billion cubic meters (1.23 × 1012 bbls) of heavy oil. In situ, thermal recovery techniques must be used to recover the vast majority of this resource. These techniques are complicated by the fact that about 25% of the deposits have a high water saturation zone underlying the formation. The extent of this bottom water zone varies from a few meters to tens of meters under a payzone averaging between 10–25 meters depending on the particular reservoir. In designing a suitable thermal recovery method for these deposits, the presence of bottomwater is likely to have two important but competing effects. First, it may serve the purpose of providing initial injectivity in the highly viscous oil sand deposits. The second effect, however, is that this zone may act as a heat sink and significantly reduce the efficiency of heating oil sand above. The magnitude of these effects will depend on a variety of factors, notably oil viscosity, vertical permeability, injection rates, and oil saturation in the water sand, if any. Thus it is evident that for most reservoirs, the injection-production strategy must be "tailor-made" to optimize recovery. This paper presents the results of numerical simulation studies undertaken to evaluate the effectiveness of steam and steam-additive processes to recover heavy oil from deposits with bottom water zone. It is concluded that additives such as carbon dioxide and permeability blocking agents do not improve recovery in many cases. However, it is shown that suitable injection-production strategies can be developed to improve oil recovery by using steam-additive processes.