Optimisation of drainage performance of the thin-walled core barrel sealing technology for pressure preservation sampling

Pressure preservation sampling technology is a crucial method to assess natural gas hydrates. There are limitations to directly applying conventional pressure preservation technology for seafloor drills, such as large and complex structures. The working and design principle of the thin-walled core barrel sealing technique is introduced. To solve the problem of low core recovery percent during sediment drilling, the flow field characteristics of the valve spool in different working conditions are discussed. The area of the cross-section and the calculation method under the typical position are obtained. The valve spool structural parameters are determined and verified by a laboratory drilling test. The results show that: the larger the cone angle of the spool or the smaller the percentage of valve spool cone height to valve spool full cone height (the following is called P), the smaller the opening value when the cross-section area reaches a stable level. When the cone angle is 30, and the P is 20%, the cross-sectional area reaches stable after the opening is 4.5 mm. When the opening exceeds 3.0 mm, the flow rate changes little. When drilling in the sediment, the average coring recovery percent exceeds 70%. •The working principle of the thin-walled core barrel sealing technique is introduced.•The flow field characteristics of the valve spool are discussed.•The area of the cross-section and the calculation method are obtained.•The effects of the valve spool and the drilling speed on the flow field are studied.•When drilling in the sediment, the average coring recovery percent exceeds 70%.