Research and Field Testing of Horizontal Wellbore Reconstruction and Efficient Volumetric Re-Fracturing Technology for Changqing Tight Oil Reservoirs

Horizontal well development has become a cornerstone for sustained production in the Changqing Oilfield. However, early horizontal wells-constrained by outdated frac design and stimulation technologies-exhibit low stimulation intensity, and after long-term production, suffer from declining well productivity, and low EURs. These challenges severely restrict the high-quality development of tight oil reservoirs. This study aims to overcome these limitations by reconstructing horizontal wellbores and establishing an integrated re-fracturing design to maximize stimulated reservoir volume and recovery efficiency. Building on prior research into "three-field" (energy, fracture network, and seepage field) reconstruction, this work focuses on 5.5-inch horizontal wellbores. Key enabling technologies include deployment of 4.5-inch liners within the larger wellbore, resin-based unsaturated polyester (UPR) narrow-gap cementing, and dual-casing perforation to reconstruct new horizontal wellbores. On this basis, refracturing was conducted to redevelop energy field and hydraulic fracture network. forming a complete technical package for efficient volumetric re-fracturing in reconstructed horizontal wells. Field implementation in more than 50 wells has demonstrated significant improvements. For the first time domestically, efficient volumetric re-fracturing was achieved by deploying 4.5-inch liners within 5.5-inch horizontal wellbores. Operational efficiency improved markedly, with pump rates reaching 12 m³/min and treatment efficiency exceeding three stages per day. Post-stimulation results show stimulated reservoir volume exceeding four times that of the initial fracturing, while single-well production increased to more than five times the pre-refracturing level. These results confirm that wellbore reconstruction combined with efficient volumetric re-fracturing provides a practical pathway for revitalizing underperforming horizontal wells. This study pioneers a comprehensive horizontal wellbore reconstruction approach that integrates energy, fracture, and seepage field optimization with innovative completion and stimulation technologies. The combination of 4.5-inch liner reconstruction, resin UPR cementing, dual-casing perforation, and novel fracturing fluid systems represents the first successful field application of such a method in 5.5-inch horizontal wells worldwide. The outcomes provide a new technical framework for the secondary, high-efficiency development of tight oil reservoirs and offer broad applicability to similar unconventional reservoirs.