As the exploration and production of conventional reservoirs have passed their peak, the development of unconventional reservoirs including heavy oil are increasingly important. A 3D preliminary numerical model to simulate thermal recovery of oil through mass and heat injection in SAGD technology is developed based on the programs of TOUGH2 as well as its inclusive phase equilibrium library EOS8. The instantaneous distributions of temperature and oil saturation were figured out and the fundamental process of SAGD was studied. It demonstrated that TOUGH2 source codes are potential to model thermal recovery of heavy oil through secondary development.
Steam Assisted Gravity Drainage (SAGD) is an enhanced oil recovery technology (Williams, 2003; Moritis, 2004), which has been widely used in Alberta because of its richest reserves of heavy oil and asphalt sands. In fact, the use of SAGD in the world is also growing not only just in Canada, but also in such as the US and China. It can be seen that SAGD technology has a wide range of application prospects.
To briefly summarize SAGD's development history, a large amount of literature has been reviewed. From 1979 to 1997 was the first stage: In early 1979, the systematic Lindrain theory firstly started to be published. The gravity drainage equation by percolation mechanics and numerical heat transfer was derivated (Butler and McNab, 1981). Soon after its clear principle, a method named SAGD with up-injection and down-production double horizontal wells (Butler, 1991), which is currently the most commonly used technology in heavy oil recovery, was proposed. In the same period, Tandrain Theory, similarity criteria and Linear Model Theory were proposed successively (Reis, 1992; Butler &; Stephens, 1981; Chung &; Butler, 1989). The second phase is from 1997 to the present: A technology named SAGP (Steam and Gas Push) for recovery oil from thin oil reservoir was developed by Bulter research team (Butler, 1997). In 2000, the FAST-SAGD technology was developed to recovery oil from super heavy oil reservoir. It had been proved that compared with traditional dual horizontal wells it can improve oil-steam ratio and recovery factor (CyrCoates and Polikar, 2001; PolikarCyr and Coates, 2000). In general, the success of steam-assisted gravity drainage has been demonstrated by both field and laboratory studies (Chen, 2009).
Numerical simulation, as an important research method, is also widely used in the field of oil recovery. In this article, firstly, the multi-field and multiphase mechanism in dynamic non-isothermal process during steam injection is elucidated, a non-isothermal three-phase flow model is described based on the mathematical theories of reservoir flow. Secondly, a numerical model of SAGD was established based on TOUGH2 for analyzing the steam injection process. Meanwhile, the parameter sensitivity was analyzed. Lastly, the corresponding summary and outlook are given.