Design and mechanical optimization of multidirectional pressure-preserved coring system for deep-earth resource exploration

Abstract

Pressure-preserved coring technologies are critical for deep-earth resource exploration but are constrained by the inability to achieve multidirectional coring, restricting exploration range while escalating costs and environmental impacts. We developed a multidirectional pressure-preserved coring system based on magnetic control for deep-earth environments up to 5000 m. The system integrates a magnetically controlled method and key pressure-preserved components to ensure precise self-triggering and self-sealing. It is supported by geometric control equations for optimizing structural stability. Their structure was verified and optimized through theoretical and numerical calculations to meet design objectives. To clarify the self-triggering mechanism in complex environments, a dynamic interference model was established, verifying stability during multidirectional coring. The prototype was fabricated, and functional tests confirmed that it met its design objectives. In a 300-meter-deep test inclined well, 10 coring operations were completed with a 100% pressure-preserved success rate, confirming the accuracy of the dynamic interference model analysis. Field trials in a 1970-meter-deep inclined petroleum well, representative of complex environments, demonstrated an in-situ pressure preservation efficiency of 92.18% at 22 MPa. This system innovatively expands the application scope of pressure-preserved coring, providing technical support for efficient and sustainable deep resources exploration and mining.

1. Introduction

The accelerating pace of globalization and industrialization has significantly increased global demand for energy and mineral resources [1,2]. As conventional shallow reserves are depleted, attention has shifted to deep-earth and deep-sea environments that harbor abundant oil, gas, mineral, and geothermal resources with considerable economic and strategic potential [3–5]. Exploiting these resources plays a critical strategic role in safeguarding national energy security and advancing sustainable economic growth, while also potentially guiding future energy transitions [6–8]. Despite its importance, deep resource exploration poses formidable challenges. Developing deep resources requires a comprehensive understanding of subsurface geological structures, rock mechanics, and reservoir properties [9,10]. However, as exploration extends deeper, rising temperatures, pressures, and geological risks increasingly challenge traditional methods of energy reserve assessment [11]. They impose high demands on the performance, durability, and reliability of exploration technology and equipment.

Moreover, as the physical and mechanical properties of deep-earth rocks become increasingly nonlinear, traditional approaches to studying rock mechanics behavior fail to adapt to deep environments [12,13]. In this context, acquiring in-situ environmental and rock physical–mechanical parameters is essential for reliable reservoir evaluation, rock stability prediction, and resource assessment. An effective approach is to obtain in-situ rock samples via coring for real-time tests and analysis to estimate energy reserves and rock mechanical properties [14,15]. Traditional coring techniques have been partially effective for shallow explorations but are inadequate for deep-earth applications. Conventional methods often release pressure during retrieval, compromising sample integrity and limiting the accuracy of subsequent analyses.