Abstract
The mechanical properties of deep rocks change nonlinearly in an in situ pressure environment, so standard cores cannot be used as real samples for deep rock mechanics research. Therefore, obtaining an in situ pressure core is essential. However, the existing pressure-maintaining cores cannot overcome the sealing capacity limit, largely due to the lack of consideration of sealing theory and experimental verifications of pressure-maintaining controllers. Therefore, this paper explores the sealing form and failure mechanism of pressure-maintaining controllers. The sealing state transition, pressure leakage, deformation failure theory, and test method for a pressure-maintaining controller are determined. Through theoretical analysis and experiments, (1) a seal-form discrimination method based on the chimeric curve is proposed to obtain the pressure seal conversion trend; (2) the leakage rate is exponentially related to the initial pressure, which confirms the pressure leakage principle of the pressure-maintaining controller; and (3) based on deformation failure theory for pressure-maintaining controllers, the failure mode and deformation trend are obtained through a destructive limit pressure experiment. The research results provide a theoretical basis and experimental support for improving pressure coring in deep rock and obtaining pressure cores at deep positions to construct a new conceptual system of deep in situ rock mechanics.
Highlights
Since the 20th century, large-scale exploitation has led to the depletion of shallow Earth resources, and the exploitation of resources from the deep Earth has become a significant strategic approach worldwide [1]
Kang et al performed a theoretical analysis of the support of coal roadways and found that when the roadway burial depth is deeper than 800 m, the secondary support mechanism based on traditional rock mechanics is invalid [6,7,8]
In situ pressure environment simulation experiments were conducted from the perspectives of seal-form conversion, the pressure leakage rate, and the ultimate pressure resistance capacity to preliminarily verify the proposed theory
Summary
Since the 20th century, large-scale exploitation has led to the depletion of shallow Earth resources, and the exploitation of resources from the deep Earth has become a significant strategic approach worldwide [1]. In 1983, the ODP organization in the United States developed the second-generation PCB coring device-PCS, which was sealed with a ball valve and had a working pressure close to 70 MPa [13]. This equipment has been used to extract pressure-maintaining combustible ice from the Blake Ridge [14]. In situ pressure environment simulation experiments were conducted from the perspectives of seal-form conversion, the pressure leakage rate, and the ultimate pressure resistance capacity to preliminarily verify the proposed theory. The results of this paper provide a theoretical basis and experimental support for improving the pressure capacity of deep rock coring systems and can be used to establish a technical means for obtaining deep in situ pressure cores
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