# An Innovative System of Deep In Situ Environment Reconstruction and Core Transfer
## 7 Experiment Results and Discussion
### Experiment of the Temperature and Pressure Decoupling Control  
In the process of initial environment reconstruction, the water in the storage chamber was heated from 25 \({}^{\circ}\)C and 0.1 MPa to 95 \({}^{\circ}\)C and 70 MPa. As shown in Figure 16, the decoupling control path ABCDE consists of four steps:  
Step 1. Iso-thermal pressurizing from A (25 \({}^{\circ}\)C, 0.1 MPa) to B (25 \({}^{\circ}\)C, 10 MPa). During the heating process from 25 \({}^{\circ}\)C to 95 \({}^{\circ}\)C, the water pressure reduction caused by the expansion of the chamber is about 6 MPa. Therefore, in order to reduce the possible water supplement operation during the reconstruction, the system was pressurized to 10 MPa in advance.  
Step 2. Iso-mass heating from B (25 \({}^{\circ}\)C, 10 MPa) to C (60 \({}^{\circ}\)C, 40.3 MPa).  
Step 3. Iso-thermal depressurizing from C(60 \({}^{\circ}\)C, 40.3 MPa) to D(60 \({}^{\circ}\)C, 22.7 MPa).  
Step 4. Iso-mass heating from D (60 \({}^{\circ}\)C, 22.7 MPa) to E (95 \({}^{\circ}\)C, 70 MPa).  
Where C and D were planned by B and E, respectively, according to Equation (7).  
Figure 17a shows the temperature and the pressure curves during the process and Figure 17b shows the P-T curve, in which B\({}^{\prime}\), C\({}^{\prime}\), D\({}^{\prime}\) and E\({}^{\prime}\) were the real values of target points B, C, D and E, respectively. When the system was stable at points B\({}^{\prime}\), C\({}^{\prime}\) and D\({}^{\prime}\), the temperature and pressure values were B\({}^{\prime}\)(25 \({}^{\circ}\)C, 10.1 MPa), C\({}^{\prime}\)(60.2 \({}^{\circ}\)C, 38.2 MPa), D\({}^{\prime}\)(60.2 \({}^{\circ}\)C, 22.6 MPa) and E\({}^{\prime}\)(95.2 \({}^{\circ}\)C, 68.4 MPa), respectively. It can be seen that there were errors on the control points. Besides the accuracy of the control algorithm, there were many others factors that might cause these steady-state errors; for example, the physical characteristics of water might change under different pressures and temperatures, the non-uniformity of the temperature field in the chamber might have an impact on the relationship between temperature and pressure and the actual thermal deformation of the chamber might be different from the theoretical one. To improve the accuracy of the system, after the reconstruction process reached point E\({}^{\prime}\), an iso-thermal pressure fine-tuning was carried out to ensure that the system is stable at E(94.9 \({}^{\circ}\)C, 70.1 MPa).  
In the process of P-T preservation, the pressure and temperature changes during the push rod pushing out and retracting were examined. With the internal volume of the storage chamber being 35.33 L and the diameter of the push rod being 50 mm, according to Equation (9) when the push rod moves 10 mm each time, the pressure fluctuation can be controlled within 1.5 MPa, less than 2%. The speed of the push rod was 0.5 mm/s. The test steps were as follows: (1) let the push rod move out by 10 mm; (2) stopped the push rod and waited till the system got stable; (3) then pulled the push rod back by 10 mm; (4) stopped the push rod and waited till the system got stable again. The test was repeated 10 times. Figure 18 shows the curve obtained by averaging the pressure values of the 10 tests at 85 \({}^{\circ}\)C. It can be seen that the pressure fluctuation was controlled within 1.5 MPa.  
Figure 16: The planning of the P-T decoupling control path.  
There were always temperature fluctuations when the push rod moved, but these fluctuations had no obvious regularity. This might be related to the disturbance of the push rod movement to the uniformity of the temperature field, or to the change of the temperature conduction characteristics in the chamber due to the movement of the metal push rod. However, because of the preheating mode adopted by the SERCT, even in the process of water replenishment, the water temperature in the chamber did not change significantly, and the temperature errors were controlled within 1%.