## 3 Results and Discussion  
### Effects of Boundary Condition of the Top Water-Bearing Zone  
The SAGP simulation is carried out assuming 1 mol % of nitrogen, i.e., the SAGD operation injecting the nitrogen of which mole fraction to the steam amount is 1 mol %. The presence of the top water-bearing zone not only decreases the thermal efficiency, but also the oil productivity, regardless of the aquifer type. The performances of the SAGP process at the finite boundaries are more effective than those of the infinite case (refer to Figure 2). Figure 2 describes the production performances in accordance with the aquifer type, as follows: Figure 2a shows the trends of the oil production rate and Figure 2b depicts the water cut, i.e., the ratio of water produced compared to the volume of total liquids produced in the production well. Prior to the encounter between the steam chamber and the water-bearing thief zone, all of the performances are the same regardless of the boundary conditions; however, after the aquifer provides the effects on the chamber enlargement, different performances are observed according to the aquifer type. The oil sands deposit with the finite-sized water-bearing thief zone produces more oil and less water compared with the infinite condition. The water production increases by meeting the top water-bearing zone around 200 days, but the difference in oil production rates is not large, as shown in Figure 2b. After about 320 days, the significant decrement of the oil rate is observed, due to the boundary effect (see Figure 2a); furthermore, the water cut increases by supplying the groundwater for the case of infinite aquifer while, in the finite aquifer, the water is replaced with the injected fluids and thereby the trend of the decreasing oil production rate is slower than that of the finite-sized thief zone. The fluctuation from 300 days to 400 days, in the case of the infinite aquifer, explains a transient change, whereby the accumulation of the high pressure in the steam chamber does not respond to long-distance pressure boundaries. In the case of the infinite aquifer, it might take time to arrive at the equilibrium state. The detailed analyses related to the liquid production reveal that the infinite aquifer incurs more-problematic effects by continuously supplying a larger water influx amount. Since this simulation maintains a constant liquid production and injection volume, as shown in Table 3, the trajectories of the daily water cut can analogize the amount of the water influx from the top water-bearing zone. Figure 3 depicts the parameters related to the examination of energy (thermal) efficiency; the observations of the \(SOR\) (Figure 3a), the \(cSOR\) (Figure 3b), and the \(STEP\) (Figure 3c), respectively. The smaller the \(SOR\) and the \(cSOR\), and the larger \(STEP\), the more efficient the method of thermal process. Figure 3a shows that the \(SOR\) is sharply increased near 400 days and the slope of the \(SOR\) in the finite aquifer is smaller. At that time, the \(SOR\) value is about 8, whereby it would be assumed that the SAGP operation with negligible effects of aquifer has been until the \(SOR\) reaches 8, i.e., the \(cSOR\) is around 4 in Figure 3b. Figure 3c confirms that the SAGP in the presence of finite-sized heat thief zone is more profitable and more efficient that those of infinite case; furthermore, the finite aquifer shows the higher \(STEP\), as well as the longer arrival time at the maximum value. Figure 2: Comparison of liquid production performances with time: (**a**) oil production rate; and (**b**) water cut. Figure 3: Comparison of energy efficiency with time: (**a**) steam to oil ratio (_SOR_); (**b**) cumulative steam to oil ratio (_c_SOR_); and (**c**) simple thermal efficiency parameter (_STEP_). The flow characteristics of steam and nitrogen within the reservoir evaluate the effects of the nitrogen regarding the preservation of the proper growth of the steam chamber.