Handling and Implications of Downhole Fishing Incidents in Hot Dry Rock Wells: Case Study of GH-X Well in Gonghe Basin

Hot dry rock (HDR) drilling operations face frequent downhole complexities that jeopardize project efficiency and cost control. This study examines fishing incident resolution strategies through the critical case of GH-X well in China’s Gonghe Basin—the pivotal well in the nation’s first HDR pilot development project. Operating under extreme conditions (formation temperatures > 180 °C, pore pressures exceeding 85 MPa), the well encountered multiple fishing incidents during extended leak-off testing. Investigation revealed that such incidents primarily stem from fractured formations, fatigue failure of drilling tools, and insufficient adjustment of drilling parameters. Notably, the expansion of formation fractures and borehole instability led to repeated occurrences of stuck pipe and tool joint failures, resulting in dropped drill bits and broken tools. Multiple remediation techniques were employed, including high-strength magnetic fishing, milling operations, and sidetracking to bypass obstructions. These methods effectively recovered some of the lost tools and enabled continued drilling using high-temperature, hard-rock directional drilling technologies. Through a detailed analysis of the incident and response measures, this study identifies the mechanisms behind downhole accidents in HDR drilling and proposes targeted mitigation strategies. These include accurately predicting formation pressure changes following offset-well fracturing, enhancing the quality of drilling tools, optimizing drilling parameters, and strengthening real-time monitoring. The findings offer valuable insights for the prevention and control of downhole accidents in HDR development and provide technical guidance for future geothermal projects.