Pre-drilling

A detailed geotechnical survey helps make the right choice of drilling rig, fluid composition, tools and techniques.  Identifying challenging conditions like geological faults and gravel is crucial to the successful engineering of any HDD project.  Lucas can engineer a drillhole through almost any material from sand to solid rock as long as conditions are properly identified before drilling. 

The drill path is engineered using computer-aided design and sophisticated mechanical and stress engineering software which will model in 4D to suit the pipeline material, geographical conditions and any underground obstacles, such as sewer mains, railway tunnels or natural hazards.

This is also the stage where Lucas works with government authorities and communities to ensure all legal, environmental and community issues have been identified and addressed.  HDD flexibility makes it easy to avoid damage to vulnerable areas like wildlife, habitat, archaeological sites, Aboriginal sites and other culturally sensitive sites.

Pilot hole drilling

With the rig accurately aligned to the drill path, drilling fluid is pumped down the drill pipes.  This provides high pressure fluid to jet nozzles for drilling the softer materials, or power to a downhole motor which drives a roller-cone bit in rock.  The fluid is normally a mix of bentonite (an environmentally safe natural clay) and water.  As well as providing drilling power, the mud helps to consolidate the walls of the drillhole, acts as a lubricant and carries spoil out of the hole.  As the cuttings laden fluid travels back up  the drillhole, it is captured, the cuttings removed and recycled, so the fluid can be pumped back around the drilling loop. 

The downhole drilling assembly is guided by electronic steering instrumentation that transmits data in real time to a surface-based computer that allows the driller to precisely locate the drilling assembly and guide it along the pre-determined drill path. 

Complex 3D paths can be followed to avoid underground obstacles if required. 

Pilot hole reaming

The drilling assembly is replaced with a reamer which is pulled back or pushed forward to enlarge the pilot hole to the size needed for the product pipe.  Depending on the material and final size, several reaming passes may be needed. The hole is reamed to a size that's defined by the geology, pipe type and diameter among other factors.

HDD is generally suited to pipe diameters in the range of 4” (100mm) – 56” (1422mm).

Product pipe installing and testing

After the last reaming pass and a final pre-pull and gauging pass, the product pipe is drawn back behind the reamer.  Pipes can be high density polyethylene (HDPE) or steel. Steel pipes are usually coated externally with a corrosion protection layer which is in turn protected by an erosion protection layer. Once installed, the pipe is hydrostatically tested to ensure its integrity.