Key challenges in drilling under high-temperature and high-pressure environments in ultra-deep wells exceeding 10000 m

Abstract:

To address the challenges encountered during drilling in ultra-deep wells exceeding 10000 m， including low rate of penetration， frequent drilling tool failures， and elevated drilling risks under high-temperature and high-pressure （HTHP） conditions， this paper systematically discusses the major technical difficulties from five aspects： rock brittleness-ductility transition， accelerated bit wear， power transmission attenuation， trajectory control inaccuracy， and high-temperature drilling fluid failure. The results indicate that HTHP conditions in ultra-deep wells alter rock-breaking mechanisms， causing the failure mode to gradually shift from predominantly brittle fracture to coupled brittle-plastic deformation， thereby increasing rock-breaking difficulty. Meanwhile， drill bits are subjected to severe wear and a higher risk of failure under elevated temperatures， heavy loads， and highly abrasive formations， resulting in a shortened service life. Friction and vibration of long drillstring reduce the surface power transmission efficiency， and the performance and operational reliability of downhole motors decline due to the degradation of seals， bearings， and elastomeric components. Vertical drilling tools may experience trajectory control inaccuracies because of performance drift or failure of electronic components under HTHP conditions. In addition， high temperatures can deteriorate the rheological properties of drilling fluids and reduce their filtration performance and stability， thereby weakening their functions in cuttings transport， cooling， and wellbore stabilization. The challenges of drilling ultra-deep wells are characterized by significant multi-factor coupling， and fundamentally arise from the synergistic failure of drilling tool systems and drilling fluids under extreme downhole conditions， particularly the HTHP environments encountered in deep formations. Therefore， further research is needed on multi-physics coupled rock-breaking mechanisms， high-temperature-resistant materials and structural designs for drilling tools， and intelligent drilling fluid systems to support the optimization of drilling processes and tool development for ultra-deep wells.