What Is Directional Drilling And Why Is It Used?

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.

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Directional Drilling

An oil well is a general term for any boring through the Earth's surface designed to find and produce petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil, and a well designed to produce mainly or only gas may be termed a gas well.

The earliest oil wells were drilled percussively by hammering a cable tool into the earth. Soon after, cable tools were replaced with rotary drilling, which could drill boreholes to much greater depths and in less time. The record-depth Kola Borehole used non-rotary mud motor drilling to achieve a depth of over 12 000 meters (38,000 ft). Until the 1970s, most oil wells were vertical (although different lithology and mechanical imperfections cause most wells to deviate at least slightly from true vertical). However, modern directional drilling technologies allow for strongly deviated wells which can, given sufficient depth and with the proper tools, actually become horizontal. This is of great value as the reservoir rocks which contain hydrocarbons are usually horizontal, or sub-horizontal; a horizontal wellbore placed in a production zone has more surface area in the production zone than a vertical well, resulting in a higher production rate. The use of deviated and horizontal drilling has also made it possible to reach reservoirs several kilometers or miles away from the drilling location (extended reach drilling), allowing for the production of hydrocarbons located below locations that are either difficult to place a drilling rig on, environmentally sensitive, or populated.