Directional drilling is the practice of drilling non-vertical wells. This was invented in the 1920s when it was originally used in the oil fields to increase oil production. In the earlier 1990's the technology was adapted for utility installations. Directional bores have been installed for pipelines carrying things such as oil, natural gas, petrochemicals, water, sewerage and other products. Besides crossing under highways, railroads, airport runways and areas with a lot of building congestion, installations have been made under rivers and waterways and protected wetlands.
There are three stages to go through when installing directional borings. The first stage is called Pilot Hole. A pilot hole is horizontal drilling that continues under and across an obstacle. An electronic transmitter sends a signal to the surface which is read by the receiver. This then transmits the information back to the drill rig operator. The driller can then steer the bore path in any direction needed.
The second stage is called Pre-ream. Once the pilot hole is complete, the hole must be enlarged to a suitable diameter to safely install the product lines. This is accomplished by "pre-reaming" the hole to a larger diameter. A reamer is pulled back and rotated while drilling fluid is pumped to cut and remove solids in the hole. Usually, the reamer is attached to the drill string on the opposite end of the borehole and pulled back into the pilot hole.
Lastly, the third stage is called Pullback. Once the drilled hole is enlarged, the conduit can be pulled through it. A reamer is attached to the drill string and then connected to the product by a swivel. The swivel allows the reamer to turn without turning the product with it. The drilling rig then begins the pullback operation, rotating and pulling on the drill string as well as circulating the drilling fluids.
The use of directional drilling is growing rapidly and is expected to continue to grow in popularity in the future.