## 5 Conclusions  
In this study, an in-situ simulation device for testing deep pressure-preserving coring tools under high-temperature and ultrahigh-pressure was developed, and the simulation principle and method for this extreme environment were expounded. Furthermore, the high-temperature and ultrahigh-pressure simulation test cabin and the driving module of the device were analyzed and experimentally studied. The main conclusions are as follows:  
(1) In this study, a simulated coring test system with a working pressure of 140 MPa and a temperature of 150 \({}^{\circ}\)C was established. On the basis of analyzing the stress state of rock in deep extreme environments, the principle and method of constructing the temperature and pressure conditions of the test cabin are proposed.  
(2) Based on the design standard of ultrahigh-pressure vessels, a segmented high-temperature and ultrahigh-pressure coring simulation test cabin was innovatively constructed. A pressure test was conducted on the cabin body by setting different pressure values. The results showed that the test cabin operated stably under the maximum pressure of 190 MPa (the effect of temperature of 150 \({}^{\circ}\)C has been translated into pressure for experiments), and there was no pressure or fluid leakage during the test. The test cabin exhibited good performance. Therefore, the design and manufacture of the cabin have high reliability, which has important reference value for the development of ultrahigh-pressure vessels for extreme environments.  
(3) The experimental study of the driving module showed that this module could run stably for 105 min under the conditions that the axis diameter is 50 mm, the test pressure is 140 MPa, and the rotation speed is 150 r/min (the highest tested), which provides a stable power source for the coring simulation. When the pressure is maintained at 140 MPa, the driving module can operate safely and stably by reducing the rotation speed of the rotating shaft. Therefore, after the completion of the test with the in-situ simulation device, the safe operation mode of reducing the speed first and then depressurizing the pressure can be adopted.  
(4) The in-situ simulation device innovatively developed in this study can realize the simulation of the in-situ extreme environment of deep rock occurrence. Further, it can be used for the research and development of deep pressure-preserving coring tools, which effectively avoids the problems of high risk and high cost in field testing of coring tools.  
Figure 17: Rotation speed vs. test pressure.  
**Author Contributions:** Conceptualization, W.H. and Z.Z.; data curation, Y.Y. and Y.L.; methodology, W.H. and Z.H.; supervision, H.X.; writing--original draft preparation, W.H.; writing--review and editing, J.L. and C.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Program for Guangdong Introducing Innovative and Entrepreneurial Teams (Grant No. 2019 ZT08G315) and the National Natural Science Foundation of China (Grant No. 51827901, U2013603).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors would like to thank the editors and reviewers for their valuable comments and constructive suggestions.  
**Conflicts of Interest:** The authors declare that there is no conflict of interest.