Research on a high-precision measurement system for in-situ core length in downhole coring operations

Downhole coring operations are critical for reservoir evaluation in oil and gas exploration, yet the monitoring of in-situ core length is severely hindered by radial space constraints, dynamic seal failures, and measurement inaccuracies in extreme environments. To address these limitations, a high-precision measurement system based on contact draw-wire displacement sensing and non-contact magnetic coupling electromechanical encoding is proposed in this study. To resolve the design contradiction between narrow spatial constraints and the requirements for a large measurement range and high precision, a multi-objective optimization of the winding mechanism is conducted utilizing the NSGA-II algorithm. Furthermore, a novel topological architecture of “winding in a high-pressure open area and encoding in an atmospheric isolated area” is implemented, by which dynamic sealing structures are eliminated and downhole pressure balance is realized. The system’s environmental adaptability is enhanced through the integration of precise wire arrangement, torsional decoupling, multi-stage sand-control structures, non-magnetic pressure-resistant PEEK encapsulation, and a passive thermal management strategy. The prototype was manufactured and multi-condition testing indicates that the prototype achieves a large measurement range and high accuracy. Reasonable stability was observed across the tested well inclination angles, high-temperature and high-pressure environments, and complex drilling fluid conditions. This study presents a prototype-level approach to in-situ core length measurement, and may provide technical support for the further development of digital closed-loop control of well coring.