Causes, Treatment and Pre-control Measures of Stuck Drill Accidents in Horizontal Directional Drilling

Horizontal directional drilling is the mainstream trenchless construction technology for pipeline engineering. Stuck drill is the most common downhole fault that hinders construction progress and causes economic losses, which mainly occurs during hole reaming and pipeline pullback. Focusing solely on stuck drill issues, this paper analyzes the hazards, root causes, on-site identification methods, emergency solutions and pre-construction prevention measures, providing practical references for field construction and management.

1. A stuck drill in horizontal directional drilling means drill rods, reamers, drill bits and other downhole tools cannot rotate or move axially, and may be completely locked in severe cases. The long and narrow horizontal borehole makes slag removal and stuck drill releasing far more difficult than vertical drilling. Minor stuck drills accelerate equipment wear and waste mud materials; moderate faults suspend construction and lead to pipeline pullback failure; severe buried drills require excavation for tool recovery, damaging road surfaces and existing underground pipelines, resulting in high costs for construction delays and maintenance, and even safety accidents such as pipeline rupture. Stuck drill accidents frequently occur in miscellaneous fill layers, water-rich sand layers and broken weathered rock layers, with the highest incidence during reaming.

2.There are four major triggers for stuck drill accidents on construction sites: geological conditions, underground obstacles, unqualified mud performance and irregular operation. Hole wall instability is the primary cause. Silt, sand and expansive clay are prone to hole collapse and hole shrinkage, with soil deposits wrapping drilling tools to cause jamming. Construction in urban areas often encounters sudden jamming from construction waste, large boulders and offset old pipelines without early warning. Improper mud viscosity, specific gravity, pump pressure and flow prevent drill cuttings from circulating out, forming slag accumulation jams.

3.Types of stuck drills can be quickly distinguished through drilling rig data and borehole conditions. Hole collapse jamming features gradually rising torque, reduced mud cuttings output and slight ground settlement. Obstacle jamming brings abrupt torque surge and rig stall while mud circulation remains normal. Slag accumulation jamming shows steady torque growth with almost no cuttings discharged. Adhesion jamming caused by improper operation stalls the rig immediately after restart, with all mud operating parameters remaining normal.

4.Stuck drills shall be treated by severity grading, and violent pulling of drill rods is prohibited to avoid fracture. For minor jamming where tools rotate but cannot be pulled out, increase mud flow rate, perform forward and backward reaming repeatedly, and move tools slowly to clear accumulated slag. For moderate fully locked jamming with unobstructed mud circulation, circulate lubricating mud continuously to soak the borehole and reduce friction before releasing the drill. For severe buried drills with blocked mud circulation, stabilize the hole wall first to prevent secondary collapse, then use jacks for auxiliary pushing. Targeted small-scale excavation for tool recovery is adopted if all above measures fail.

5.Pre-construction prevention is the most efficient way to reduce stuck drill risks. Complete underground pipeline detection and geological survey before construction, and design borehole routes to avoid unfavorable strata and underground obstacles. Prepare special wall-protecting drilling mud matched with formation conditions. Standardize construction procedures by progressive staged reaming, control drilling speed and borehole curvature, and minimize intermediate shutdowns. Monitor drilling torque, pump pressure and mud discharge throughout construction, and shut down equipment for inspection immediately if abnormal parameters appear to fundamentally reduce stuck drill accidents.

Vanessa，GOODENG Machinery

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