Optimization of Fast-steam-assisted gravity drainage for the energy-efficient operations at a heterogeneous oil-sands reservoir

This paper discusses the energy-efficient operation of Fast-steam-assisted gravity drainage wellpad system in the presence of reservoir heterogeneity, different well constraints, and lateral flux communication between adjacent steam chambers. Fast-steam-assisted gravity drainage incorporates cyclic steam stimulation in an unrecovered area between steam-assisted gravity drainage wellpairs, and the well constraints of the wellpad system (including the injection pressure and steam injection rate at the injectors, bottom hole pressure, surface liquid rate, and steam rate at the producers) are simultaneously optimized to accomplish the minimum cumulative steam-to-oil ratio for a given bitumen recovery constraint. The higher injection pressures of the cyclic steam stimulation can result in greater efficiency by pushing the diluted fluid mixture to the steam-assisted gravity drainage producers through the cross-over zone between the steam chambers. At an early stage, a greater amount of steam should be injected through the cyclic steam stimulation work, and at the late stage, a lower injection pressure is needed to use the latent heat. The positive effects of the cyclic steam stimulation at the edges of the steam-assisted gravity drainage steam chambers are concentrated at localized flow paths where the lateral flux transport occurs due to spatial heterogeneity. A sensitivity analysis shows that the injection pressure and the steam rate produced for the steam-assisted gravity drainage wellpairs influence the energy efficiency of the entire thermal operation when compared to other configurations.