## 2 Design of WPCS
### Working Mechanism  
The WPCS is structured into three principal subassemblies (Figure 1). (1) The upper barrel assembly encompasses the running and retrieving tools. (2) Situated centrally is the pressure control assembly, housing a pressurized reservoir. (3) At the base lies the lower barrel assembly, designed for the sample autoclave.  
This configuration facilitates efficient operation and ensures the integrity of core samples during retrieval. Each subassembly plays a crucial role in maintaining operational stability and preserving the quality of recovered geological samples. The integration of a pressurized reservoir within the middle assembly enhances the system's capability to manage pressure differentials encountered during coring operations.  
In practical operation, the WPCS is deployed using a wireline running tool which is lowered through the drill string to engage with the BHA. Once the WPCS is securely latched onto the BHA at the bottom of the borehole, the connection between the wireline running tool and the WPCS can be automatically disengaged. Subsequently, upon retrieval of the wireline running tool on the deck, the WPCS undergoes rotation facilitated by the top drive mechanism, utilizing the latch and BHA drill string. Throughout the coring operation, the drilling mud is circulated down the drill string by the drilling mud pump. This serves the dual purposes of maintaining borehole stability and facilitating cooling and lubrication of the coring drill bit. To safeguard the integrity of the gas hydrate cores, a plastic core liner is employed. This liner is supported by a core liner bearing within the inner barrel assembly, ensuring both the core liner and core catcher remain stationary. This approach minimizes any potential disturbance to the core samples during retrieval.  
After completing the coring process, the wireline retrieving tool was deployed to engage the WPCS, initiating the release of the outer latch releasing sleeve. Upon lifting the sleeve, several sequential actions were observed. Firstly, the wireline tension caused the release of the inner latch, allowing the inner barrel to ascend. Secondly, the lower ball valve of the pressure chamber promptly closed upon the plastic core liner being drawn into the autoclave section, driven by the thrust spring force of the valve (Figure 2). Subsequently, the outer latch was disengaged, followed by the closure of the upper seal of the pressure chamber. (4) Finally, the retrieval of the WPCS proceeded similarly to other wireline coring tools, as shown in Figure 3. These procedures ensure the systematic retrieval of geological core samples while maintaining the integrity of the samples for subsequent analysis.  
Figure 1: The structure of WPCS.  
Figure 3: The physical diagram of section connection of the WPCS: (**a**) the upper barrel assembly of WPCS; (**b**) the lower barrel assembly of WPCS.  
Figure 2: The position and schematic diagram of the ball valve: (**a**) the comparison of ball valve before and after turning; (**b**) the process of turn-over sealing of the downward motion unit.  
Upon recovery of the WPCS onto the deck, the pressure chamber was detached from the WPCS via the quick link system. Subsequently, it was connected to the newly designed PCATS for transfer and analysis of pressure cores without releasing pressure (Figure 4). Throughout the coring recovery process, pressure and temperature data were continuously recorded by the pressure/temperature recorder positioned atop the core liner with the pressure chamber system.