HDD Rig Selection Guide Based on Different Formations

1. Clay Formation

Clay is the most ideal stratum for HDD construction. It features uniform texture, good self-stability and low collapse risk. Conventional small and medium-sized HDD rigs can achieve high working efficiency. Standard drill bits and low-viscosity drilling mud are sufficient for lubrication and cooling. This formation requires low construction cost and brings little equipment loss, suitable for conventional pipeline crossing projects.

2. Sand and Silty Sand Formation

Sand and silty sand are typical unstable strata with loose structure. They easily lead to hole collapse, slag deposition and stuck drill pipes during drilling and reaming. It is recommended to adopt HDD rigs with stable hydraulic systems and high-flow mud pumps. High-viscosity mud with anti-collapse and wall-protection additives is necessary. Long-time shutdown is prohibited during operation to avoid buried drilling tools.

3. Quick Sand and Silt Soil Formation

Distributed in river beaches and wetland areas, this stratum is featured by high water content and extremely poor hole stability. It faces high risks of hole collapse, track deviation and excessive pullback resistance. Heavy-duty HDD rigs with sufficient pullback torque and upgraded mud circulation systems are required. Multi-stage gradual reaming and constant borehole pressure maintenance are essential to ensure smooth pipe pullback.

4. Cobble and Gravel Interlayer Formation

Cobble and gravel strata have high hardness and strong abrasiveness, bringing severe impact load to drilling equipment. Ordinary soil-type rigs cannot adapt to such working conditions. High-torque rigid HDD rigs, carbide-reinforced drill bits and professional rock reamers are required. Construction shall adopt low-speed and stable propulsion to prevent track deviation and tool damage.

5. Weathered Soft Rock Formation

Weathered soft rock brings continuous and high drilling resistance. Only professional rock-type HDD rigs are applicable, which are equipped with high continuous torque output and efficient heat dissipation systems. Matching rock breaking drill tools and step-by-step reaming technology are adopted to improve drilling efficiency and reduce equipment overload failure.

There is no universal HDD rig for all geological conditions. Construction parties shall select rig models and supporting tools strictly according to geological survey results. Matching standard rigs for clay, high-performance mud systems for sand, and high-torque rock rigs for pebble and rock strata can effectively reduce construction risks, avoid rework and control overall project costs.