Abstract
Steam-assisted gravity drainage (SAGD) has been used to develop the “super heavy” oil reservoirs in Canada. The viscosity can reach more than 30,000 cp at 50°C. Moreover, owing to their continental deposit origin, the reservoirs have a low porosity and permeability. Because of these challenges, the conventional steam circulation start-up process takes 6 to 12 months before the well pair can be switched to production. Solvent has been used to start-up SAGD with success. But now, low price of oil and high cost of solvent make solvent-assisted start-up process limited. This paper applies experimental schemes, such as viscosity reduction rate evaluation, core flooding, and 3D physical simulation, tests solvent performance, optimizes process parameters, and designs process solutions. Apply numerical simulation to test solvent-assisted SAGD start-up effect and calculate the cost. This paper researches a unique low-cost solvent compare with xylene. The basic properties and core flood experiment show that the two solvents are similar with viscosity reduction rate, asphalt dissolution rate, and injection pressure, and the price of solvent is 18% lower. The 3D model experiment shows that the average start-up time is reduced by 15%, and steam injection volume is reduced by 21.4%. The numerical simulation results show that without solvent, it will take 180 d for start-up process, and with solvent, the time has reduced by 50% and takes 90 days. Cost calculation results show that the cost will reduce 18% by solvent compared to xylene. Moreover, the production rate has been improved in production stage. This paper applies a 3D physical model to simulate the solvent-assisted SAGD start-up process. Research conclusions show the start-up mechanism of solvent and the process of temperature change of steam chamber.
Highlights
Oil sands of NEXEN are rich in reserves and good reservoir properties, suitable for Steam-assisted gravity drainage (SAGD) technology development
After the solvent is transferred to the water flooding, the seepage channel formed by the solvent can improve the seepage capacity of the water phase and increase the heat convection capability of the steam and the reservoir
The effect of the preinjection solvent on the temperature is obvious, the average cycle time of the full-level section is reduced by 15%, and the steam injection amount can be reduced by 21.4%
Summary
Oil sands of NEXEN are rich in reserves and good reservoir properties, suitable for SAGD technology development. In the case of low oil prices, the high-cost problem is prominent [4]. The reservoir temperature is 6-8°C, the pressure is 750-950 kPa, and the crude oil viscosity is 6 × 107 cp at 10°C. It is a typical oil sand reservoir in Canada. This paper takes the SAGD start-up phase as a research entry point, and physical simulation and numerical simulation studies were carried out for a series of problems such as less oil production, large steam consumption, low energy utilization rate, and difficulty in handling the produced liquid during the SAGD warm-up start-up process. By adopting the solvent composite steam cycle method [6,7,8], the cycle of SAGD start-up phase is shortened, the steam injection amount is reduced, the mining cost is reduced, and the mining efficiency is improved [9,10,11]
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