Precise Guidance Drilling Technology for Horizontal Well Clusters in Shale Oil In-Situ Conversion

Abstract

The economic recovery of low-grade, deep-buried shale oil and heavy oil resources via in-situ conversion processing (ICP) requires deploying closely spaced, high-density horizontal well clusters with exceptional precision. Maximizing reservoir contact and ensuring uniform heat distribution demand drilling multiple laterals within tight spatial tolerances (on the order of metres) from a single surface location at depths exceeding one kilometre. This study presents the development and field validation of an integrated precision drilling system designed to address these challenges. The methodology comprises three sequential phases: first, establishing a geological–engineering benchmark using a pilot well logged with high-precision measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools to construct a high-fidelity three-dimensional geological model; second, deploying a magnetic ranging system in which a high-sensitivity probe in the reference well and a magnetic short sub in the drilling bottom-hole assembly (BHA) enable real-time, centimetre-level inversion of the relative three-dimensional coordinates for targeted geosteering; and third, a closed-loop trajectory optimization system that fuses the geological model, real-time MWD data, and magnetic ranging information to automatically steer the rotary steerable system (RSS), ensuring strict anti-collision compliance. The technology was successfully demonstrated in the Chang 73 of the Ordos Basin, a continental shale-oil play of ultra-low permeability. The project achieved a globally unprecedented milestone: the precise deployment of a kilometre-deep horizontal well cluster of an eight-well design (one producer, four heaters, three monitors), of which the first batch of six wells (five horizontal and one directional) was drilled in this study. Operational results significantly exceeded design specifications, with a vertical spacing accuracy of 3 m ± 0.3 m, a horizontal spacing within 4 m ± 0.5 m, and successful navigation of a 6 m × 8 m target window. This level of precision directly resolves the core technical bottlenecks of ICP development, including dense well-pattern deployment, accurate target entry, and collision avoidance. The novelty of this work lies in its system-level integration and the successful application of a complete precision drilling workflow at true vertical depths exceeding 1,000 m, representing a world-first achievement. By integrating high-precision formation evaluation, unique inter-well magnetic positioning, and intelligent closed-loop control, the system substantially enhances operational efficiency, reduces non-productive time (NPT), and minimizes the risk of well collision. These findings confirm that the technology is not merely an incremental improvement but a foundational capability enabling the industrial-scale, commercially viable development of in-situ conversion for challenging unconventional resources,providing a robust technical foundation for unlocking vast low-grade oil reserves with broad global applicability.