For the last few decades, the development of heavy oil has kept attention of petroleum companies around the world. However, in spite of its enormous in-place, the development of heavy oil has not been conducted actively. There are some reasons for it, the biggest one is its high viscosity.
To solve this problem, various steam injection methods have been applied to increase reservoir temperature, to decrease oil viscosity and hence to recover heavy oil. However, the generation of steam is expensive and involves the emission of large amounts of carbon dioxide. Therefore, to reduce the consumption of steam in heavy oil recovery, co-injection of solvent with steam, which is called “solvent assisted steam injection”, has been recently proposed. “ES-SAGD” (Expanding Solvent-Steam Assisted Gravity Drainage) is one of such examples. In ES-SAGD, high-temperature steam containing a solvent is injected from an upper horizontal well to reduce the viscosity of heavy oil, and this less viscous oil flows downward and is produced from a lower horizontal well. In this research, we have developed a three-dimensional, equation of state (EOS) based multi-component, thermal flow simulator, expecting that this simulator could predict heavy oil reservoir performances, especially solvent assisted steam injection performances, more accurately than existing thermal simulators adopting pseudo-multi-component system.
For developing this simulator, a total of 9 flow equations and EOS based phase equilibrium equations were derived as governing equations. These equations were then discretized to be reduced to the system of 9 non-linear equations. This simulator solves this equation system for 9 primary unknowns of pressure, temperature, global composition and equilibrium constants of each component by the Newton-Raphson method in each time step. After developing this simulator, the results calculated by this simulator were compared with those simulated by a commercial pseudo-compositional thermal simulator. As a result, it was revealed that the calculation results by this simulator was more accurate than those by the above commercial simulator in terms of phase equilibrium/behavior.
Then, the sensitivity studies were conducted to examine which reservoir properties and operation conditions affected the heavy oil production in SAGD and ES-SAGD. Finally, the pros and cons of SAGD and CSS (Cyclic Steam Stimulation) as well as the effectiveness of solvent co-injection in these methods were discussed through case studies.