In-situ pressure-preserved coring for deep oil and gas exploration: Design scheme for a coring tool and research on the in-situ pressure-preserving mechanism

To accurately assess onshore deep oil and gas resources, this study proposed a design scheme for a new in-situ pressure-preserved coring (IPP-Coring) tool with a pressure-preserving capacity of 70 MPa and extensively elucidated its pressure-preserving mechanism. This tool can complete the pressure-preserving operation using the hydraulic lifting force of the drilling fluid. The pressure-preserving mechanism of this tool was attributed to the combined action of the fixed sealing structure, separate sealing structure, and pressure controller sealing structure. Using theoretical calculations and CFD simulations, the structural parameters and operation technology of this tool were elaborately determined. To demonstrate the IPP-Coring performance, laboratory and field tests were conducted. Four core samples 0.6 m, 0.92 m, 0.3 m, and 0.8 m long were obtained during laboratory coring experiments, and the average recovery of the core was 75 %. Notably, the IPP-Coring tool formed a stable sealing chamber that could maintain pressure at 70 MPa for at least 2 h in a downhole drilling fluid environment. In addition, an in-situ core sample of 1.4 m was obtained at 9 MPa in a real drilling field. This study offers a theoretical framework and design standards for the creation of analogous pressure coring technologies.