SAGD well orientation in point bar oil sand deposit affects performance

Abstract

The creation and evolution of point bar reservoir systems are well understood in meandering river deposits. A large fraction of Athabasca oil sand deposits are ancient point bar systems characterized by bedded, sandstone-dominated strata with interbedded siltstone layers. The recovery process of choice for these deposits is the Steam-Assisted Gravity Drainage (SAGD) process due to the high viscosity of the oil, low solution-gas ratio, and often caps rock not sufficient to withstand injection pressures of Cyclic Steam Stimulation (CSS). However, because of the presence of siltstone interbeds, these reservoirs commonly have lateral and vertical lithological heterogeneity which interfere with the formation of uniform steam chambers along SAGD wellpairs. Other units in point bar deposits that impact SAGD chamber development within the formation include remnant channel succession and channel lag. The objective of this research is to construct a detailed three-dimensional point bar model to determine how its heterogeneity impacts SAGD performance. Here, the point bar model is based on the Lower Cretaceous Middle McMurray Formation in the Athabasca oil sand deposit in Alberta, Canada. Single SAGD wellpair submodels at different locations and orientations were extracted from the detailed point bar model. The results of the reservoir model simulation suggest that attention must be paid to SAGD wellpair placement in point bar systems.