Feasibility Evaluation of Warm Solvent Assisted Gravity Drainage Process in Low-Carbon Developing Super-Heavy Oil or Oil Sands Project

Abstract

It is very difficult to realize good economy returns using conventional SAGD process in many oil sands projects due to large CPF investment, massive steam injection, expensive surface diluent adding and increasing carbon emission tax. By contrast, warm solvent assisted gravity drainage process (WSAGD) is a promising low-carbon technology to deal with these SAGD challenges. This paper conducted feasibility evaluation by combined with Nsolv Best pilot analysis and a series of physical simulations. From 2014 to 2017, WSAGD pilot was successfully carried out by injecting butane at 60℃ in Suncor Dover oil sands. Its reservoir geological characteristics, physical properties, development technology policy and production performance were systematically analyzed. Combined with 4D seismic interpretation, RST and observation well data, the size and growth rate of solvent chamber were monitored and analyzed. Considering great uncertainty in numerical simulations influenced by many factors including grid size, solvent diffusion coefficient, interfacial tension and capillary force, a series of experimental tests and physical simulations were conducted. The behavior of viscosity reduction, interfacial tension reduction and microscopic oil displacement related to different solvents were systematically tested including propane, butane, pentane and hexane. Particularly, the performance of SAGD and WSAGD process were evaluated by 2D and 3D visual physical simulations. In Nsolv Best pilot, the target reservoir is low pressure, thin and shallow buried. The oil rate reached 250-300 barrels per day under 300 m horizontal section, and API degree of produced oil was upgraded to 13-16 from original 8. After 3 years of tests, the width of solvent chamber is 40-60m, lateral and vertical 1.56 m and 0.96 m per month, and horizontal conformance is 67%. The experiments results show that viscosity reduction trend will flatten out when the solvent concentration exceeds 10 vol% due to partial asphaltene precipitation. Both sweep efficiency and displacement efficiency of hot water, steam, gaseous and liquid hexane are increasing with temperature increase. Compared with other medium, sweep efficiency and displacement efficiency of gaseous hexane are higher due to greater dissolving ability and speed in bitumen. Both 2D and 3D experimental results indicate that WSAGD process achieves faster vertical solvent chamber and higher recovery factor than conventional SAGD process. Besides, gaseous pentane has significant upgrading effect considering substantial reduction of asphaltene and resin in the produced oil, which is not available in conventional SAGD process. This paper first systematically compares the mechanisms and performance of warm solvent assisted gravity drainage (WSAGD) process with SAGD process by physical simulations. It presents a promising low-carbon technology to enhance oil recovery, partially upgrade the produced oil and reduce carbon dioxide emissions in developing super-heavy oil or oil sands project.