Scaled physical experiments on drainage mechanisms of solvent-expanded SAGD in super-heavy oil reservoirs

Abstract

In view of high oil viscosity at high temperatures, slow steam chamber expansion rate, low oil rate, and low oil/steam ratio of domestic super heavy oil blocks developed with dual-horizontal well steam assisted gravity drainage (SAGD), the solvent-aided oil viscosity reduction tests were carried out, based on which the analytical equations and similarity laws of solvent-expanded SAGD (ES-SAGD) were deduced. The large 2-D ES-SAGD scaled physical simulation experiments were conducted to compare the SAGD performances of the conventional steam and two formulas of solvent-steam system. The experimental results show that the light hydrocarbon solvents have good viscosity reduction effects to oil, and the oil reduction ratio can reach 96.5% by adding 5% N-hexane at 50 °C. Moreover, adding light hydrocarbon solvent (10% in the experiments) into the steam can bring the oil viscosity reduction effect of solvent and high temperature steam into play, speed up the lateral steam chamber expansion rate, increase the oil drainage rate and enhance the oil recovery degree. Adding 1% of xylene into the steam-solvent system can dissolve the asphalt to reduce asphalt precipitation, reduce the porous flow resistance and further enhance the oil recovery factor. The ES-SAGD recovery by reusing the solvents can realize replacement of the steam with small amount of solvents. Although currently higher in cost, the technology has the advantages of higher oil drainage rate, reduced production period, and enhanced oil recovery. The ES-SAGD theoretical model by modifying the SAGD model based on the oil viscosity reduction characteristics of solvents has been validated by the experiments and can be applied in ES-SAGD production predictions.

Keywords

• SAGD
• solvent-expanded SAGD
• oil viscosity reduction characteristics
• asphalt dissolution
• production dynamics
• EOR