Major engineering breakthrough of Well XA‐1, the deepest ten‐thousand‐meter well in a global sedimentary basin

Abstract

Ultra‐deep drilling in sedimentary basins provides rare direct evidence of how rocks, fluids, and pressure systems behave below 10 km. Well XA‐1 in the Junggar Basin was completed at a true vertical depth (TVD) of 11 156 m, the deepest predominantly vertical well drilled in a sedimentary basin. Drilling data show that clastic strata below 10 km retain strong lithological heterogeneity and compartmentalized overpressure, with formation‐pressure coefficients of 1.96–2.24. At approximately 9975 m, high‐pressure gas influx was followed by lost circulation, brine invasion, drilling‐fluid deterioration, and borehole collapse, during which drilling‐fluid density decreased from 2.12 to 1.42 g/cm ³ and the oil–water ratio declined from 90/10 to 50/50. Managed‐pressure drilling (MPD) subsequently expanded the controllable density window from 0.016 to 0.050 g/cm ³ and reduced a single round‐trip duration from 15.2 to 6.5 days. These observations indicate that ultra‐deep drilling risk arises from the coupled geological heterogeneity, pressure compartmentalization, active fluids, and wellbore instability, not engineering constraints alone.