Analysis of impact of thermal and permeability heterogeneity on SAGD performance using a semi-analytical approach

Due to the presence of heterogenic shale lenses within oil sands, engineers implementing the SAGD process are often forced to run time-consuming computer simulations before developing even a basic idea of reservoir feasibility. Therefore, there is a need for a robust analytical expression for the oil rate that can be quickly used to assess the sensitivity of the performance of a SAGD well pair to various combinations of reservoir and fluid parameters. This paper will shed some additional insights into the effect of both thermal conductivity and permeability heterogeneity on SAGD performance. Numerical simulation results for several cases of reservoir heterogeneity will be analyzed using a semi-analytical equation developed by Azom et al. that modifies the fundamental equation for SAGD performance by Butler. Using SISIM, a geostatiscal reservoir building software, several base correlations were modeled, each correlation representing a given set of lens parameters and dimensions. The numerous realizations produced from each correlation were simulated using CMG STARS and a relationship between the heterogenic properties and adherence to Azom's model has been developed. Our results show that naturally occurring low permeability barriers caused the steam chamber to have a shape quite different from that assumed in the literature for proxy model development and severally limited the growth of the steam chamber. As expected, variations in permeability more significantly impacted the steam chamber than corresponding thermal conductivity variations. Modifications to the semi-analytical model are required to make it a viable proxy model for fast SAGD simulations/history matching.