## 3 Results  
### Three-Tube Coreflooding Experiment Performance  
#### 3.1.1 Production Dynamics  
From the oil and liquid rate curves of each sandpack with time (Figures 3 and 4), the total steam displacement can be divided into three phases: early stage (the first stage), pressure and fluid communication establishment stage (the second stage), and steam breakthrough stage (the third stage).  
At the early stage, oil was produced from each sandpack under the pressure difference of the initial sandpack pressure and back pressure at the outlet, which is also called the pressure depletion stage, during which the displacement pressure did not reach the outlet and the production drive force is from the pressure differential between back pressure and initial pressure in the coreholder. The oil production of the three cores was 8.1 mL, 3.5 mL, and 1.4 mL. As the pressure in the sandpack depleted rapidly, the pressure difference could not maintain a high production rate, which led to a fast decline in production rate of each sandpack.  
During the pressure and fluid communication establishment stage, the displacement pressure transferred from inlet to outlet steadily, which can be validated by the slow enhancement of the liquid rate. Another evident characteristic is that during pressure advancement, the high-permeability coreholder achieved the pressure communication first, while the other two coreholders with lower permeability were yet to be pressure communicated, which resulted in the massive rise of liquid and oil rate in the high-permeability coreholder and the increasing difficulty of steam into the other two low-permeability coreholders, and the liquid and oil rate in these two coreholders declined accordingly. In the medium-permeability coreholder particularly, the change of production rate was evident, the fundamental reason is that different permeability corresponds to a different pressure advancement rate and communication time, which leads to different injection capacity and production rate.  
During the third stage, which is characterized as steam breakthrough in the high-permeability coreholder, the steam displacement performance was the best in this coreholder, while in this steam channeling route, the steam which was supposed to drive oil in the other two coreholders, entered into this route, causing massive enhancement of the liquid rate and a rapid decline of the oil rate. Meanwhile, as steam surpassed the medium-permeability coreholder, the liquid rate declined rapidly and there was almost no liquid output at the displacement end, which is similar to the field production performance.  
The steam injection into each sandpack was 17.11 PV, 1.73 PV and 0.12 PV, which was calculated according to the liquid production in each coreholder. The cumulative oil of the three coreholders was 44.1 mL, 13.9 mL, and 6.2 mL. The corresponding oil displacement efficiency was 84.9%, 17.26%, and 13.55%. It should be noted that the previous steam absorbing coreholder became unabsorbed after the steam breakthrough in the high-permeability coreholder, while the low-permeability coreholder did not absorb steam at all [2].  
The watercut dynamics also witnessed different watercut rises in coreholders (Figure 5). The earliest water output time and highest watercut rise rate in the high-permeability coreholder means during commoning steam injection in the field, the primary displacement target was the high-permeability zone. The watercut in the medium-permeability coreholder rose relatively slow while it also reached over 90%, which means that the steam injected during the first stage reached the outlet under the pressure difference, while a small, condensed water rate could hardly drive the oil out.