Laser-Enhanced Borehole Stability in Sand Formations During Horizontal Directional Drilling: Mechanism and Feasibility Investigation

Horizontal directional drilling (HDD) is a trenchless technology widely used for subsurface pipeline installation, but often suffers from borehole instability in sandy strata, leading to hole collapse and drill string sticking. This study investigates the feasibility of laser-enhanced borehole stabilization. Laboratory experiments demonstrate that high-power laser scanning induces localized sand melting, forming a continuous, hardened layer through laser sintering when sufficient thermal input is applied. A stability criterion for horizontal borehole walls is developed to evaluate the required thickness and strength of the wall to maintain integrity under overlying pressure. Stability evaluation of the sintered wall shows a safety factor of 3 for a 200 mm pilot hole drilled at a 2 m burial depth, which satisfies the requirements for typical HDD-based water pipe installations. Numerical simulations of laser–sand thermal interactions, validated by experimental data, show that laser process parameters directly control phase transformation and the final thickness of the sintered layer. A laser power-velocity (P-V) map is established for the experimental 0.4 mm spot laser system, defining thermal input windows to achieve target wall thicknesses. This study demonstrates that laser-enhanced borehole stability in sandy formations is feasible, offering a promising solution to stability challenges in HDD operations.