## 1 Introduction  
With the exhaustion of resources at shallow depths in the earth, the development of resources is gradually occurring at greater depths [1; 2; 3]. At present, the depth of coal mining exceeds 1500 m, metal mining has reached 4350 m, and oil and gas resource mining has reached 7500 m [4; 5; 6; 7]. The exploitation and utilization of deep resources require accurate knowledge of reservoir scale and properties. Coring is a vital method used in exploration; it can obtain core samples from subsurface formations. By analyzing core samples, reliable information about the rock and fluid properties can be obtained, and then the scale of the reservoir content can be identified [3; 8]. However, for conventional coring technology, the change in pressure during tripping can expel fluid and gas components from the core sample, resulting in a large error between the reserve assessment values and the real situation of the deep resource [9; 10; 11; 12; 13]. Field tests conducted by [PERSON] et al. have shown that for conventional coring technology, more than 50% of the fluid and gas can be lost from a sample due to fluid expulsion during tripping [14]. To overcome this issue, in situ pressure-preserved coring (IPP-Coring) technology has been introduced for deep exploration [15; 16; 17; 18; 19]. This technology avoids fluid expulsion by maintaining the core pressure at the bottom hole pressure, thereby making it possible to accurately assess the scale of the reservoir contents [20; 21; 22; 23]. At present, scholars around the world have performed much research on in situ pressure-preserved coring technology and developed many types of IPP-Coring equipment. For example, to obtain cores from offshore gas hydrates for research, the pressure core barrel (PCB), advanced piston core (APC), pressure core sampler (PCS), hydrate autoclave coring equipment system (HY-ACE), and pressure temperature core sampler (PTCS) have been developed by different countries and institutions in the past few years [24; 25; 26; 27; 28; 29; 30]. For onshore coring for deep oil and gas exploration, the GWY194-70 BB and GW-CP194-80A pressure coring systems are two typical types of IPP-Coring equipment; their pressure preservation capacities can reach 20 and 60 MPa, respectively [31; 32]. In current IPP-Coring devices, their pressure preservation principle is mainly the closure of a ball valve or flap valve to form a sealed chamber to maintain the in situ pressure of the core sample. The closure of the valves depends on the relative movement between the core (inner) pipe and the outer pipe through a mechanical device such as an overshot assembly or a hydrodynamic-pressure lifting device such as a differential motion assembly. In onshore deep oil and gas exploration, due to the small inner diameters of common oil drill pipes, tripping the mechanical device in the hole has been a problem; usually, it is necessary to use specialized drill pipes, which wastes considerable effort and cost. Therefore, relative movement between the core tube and outer tube often depends on the hydrodynamic-pressure lifting device in onshore deep oil and gas explorations, namely, the differential motion assembly in this study [32]. The working principle of the differential motion assembly used to realize the pressure preservation operation of the IPP-Coring system for onshore oil and gas explorations is shown in Figure 1. In the coring operation, the upper section of the IPP-Coring system is successively connected to the drill collars and drill pipes in the bottom hole assembly. When coring begins, the drilling fluid passes through the inside of the differential motion assembly, and the valve cover in the valve assembly stays open due to the constraint of the inner pipe. At the end of drilling, the rock core enters the in situ pressure-preserved core chamber. At this time, a steel ball is dropped into the hole and dropped onto the ball seat, which changes the drilling fluid path from the interior to the outer part of the differential motion assembly, as shown by the red arrow.