Directional drilling was invented in the 1920 and the technology was originally used in the oil field to increase oil production. In the earlier 1990's the technology was adapted for utility installations. Directional bores have been installed for pipelines carrying oil, natural gas, petrochemicals, water, sewerage and other products. Also, conduits have been installed to carry electric and fiber optic cable. Besides crossing under highways, railroads, airport runways, shore approaches, traffic islands, areas congested with buildings; installations have been made under rivers and waterways, pipeline corridors and protected wetlands.
Directional borings have the least environmental impact of any alternate method. The technology also allows conduit placement under obstacles and provides maximum protection and minimizes maintenance costs. During installation normal business operations are not interrupted. Directional borings have a predictable and short construction schedule.
1st Stage - Pilot Hole
A pilot hole is drilled horizontally and continues under and across the obstacle along a predetermined design path. An electronic transmitter is placed in a housing which is directly behind the cutting head. The transmitter sends a signal to the surface which is read by the receiver, which then transmits the information back to the drill rig operator. The driller then, by using the relayed information, can steer the bore path in any desired direction.
2nd Stage - Pre-ream
Once the pilot hole is complete, the hole must be enlarged to a suitable diameter for the product pipeline. This is accomplished by 'prereaming' the hole to successively larger diameters. Generally, the reamer is attached to the drill string on the opposite end of the borehole from the drill and pulled back into the pilot hole. Slurry is pumped into the hole to maintain the integrity of the hole and to flush out cuttings.
3rd Stage - Pullback
Once the drilled hole is enlarged, the conduit can be pulled through it. The pipeline is prefabricated at the end of the bore opposite the drill rig. A reamer is attached to the drill string, and then connected to the product by a pulling head and swivel. The swivel allows for the reamer to turn without the product turning. The drilling rig then begins the pullback operation, rotating and pulling on the drill string as well as circulating drilling fluids. The pullback continues until the reamer exits the bore path by the drill rig and the pipeline is in place.
Some of the benefits of directionally drilled pipe installation include:
- Continuation of normal operation
- Avoidance of identified infrastructure installations
- Maintain integrity of roadways, buildings, and natural features
- Little or no disturbance to wetlands or nature conservators.
- Minimum site restoration
Directionally drilled utility conduits are protected from ambient environmental conditions during installation as well as long-term use. In addition to the construction benefits, directionally installed lines have a useful life expectance and service requirement similar to that of trenched lines and superior to that of exposed lines.
The price of the project is determined by several factors, such as the length and size of the installed product, the expected ground conditions, and the ongoing operation. If the expected ground conditions are bedrock, or other hard to drill conditions, horizontal installation may be cost prohibitive.
Every site is unique and every installation method should be selected to draw on the experience of the engineer and contractor as well as meet the needs of the client and address the characteristics of the site. With this as a caveat, the following Rules of Thumb have been described by directional boring designers and constructors:
- Under good conditions a driller can install 200- 300 ft of pipe per day
- A setback is needed for entrance and exit points and must be included in the length of the borehole. Setbacks range from 3 to 5 feet for each foot below grade of the installation. For example, for a placement 5 feet below grade, include 15 to 25 feet of boring on each side of the installation for the set backs.
- Accuracy of monitoring and placement of bore holes less than 30 feet below grade is measured in inches.
- Mobilization and set up usually takes less than an hour
- Cobbles are the nemesis of directional drills and can deflect drill strings. Difficult-to-penetrate conditions will increase the time needed to complete a project and increase the cost.
In addition to the horizontal drilling rigs, Directional Technologies supports each project with a self-contained fluid management vehicle, vacuum truck to remove drilling fluids and well-development water, and a support vehicle equipped with welding gear, tools, and parts.
Horizontal Directional Drilling Rigs
Directional Technologies, Inc. owns and maintains a fleet of state-of-the-art horizontal drill rigs. The D80 X 100 is manufactured by Vermeer in Pella, Iowa. The JT 2720 and JT 4020 are manufactured by The Charles Machine Works, Perry Oklahoma that carry Ditch Witch brand. The range of capacity in these rigs provides the opportunity to match the equipment to a wide range of field conditions.
Our fleet includes:
D80 x 100 Directional Drill
JT 4020 Heavy Duty Directional Drill
JT 2720 Medium Duty Directional Drill
Directional Technologies, Inc. uses several of the most widely used locating system for mid-sized drilling operations. This includes the DigiTrak Eclipse system and the TruTracker.
The DigiTrak Eclipse system is a walkover locating system that relies on a transmitter or sonde that is placed in a housing located behind the drill bit. The sonde sends a signal to the surface and is picked up by a receiver held by the locator. The locator is able to monitor the path of the bore by reading and analyzing the data provided by the receiver, the information includes 'tool face' and 'pitch', a depth reading is calculated by using signal strength. The receiver is calibrated prior to beginning the bore. The drilling rig equipped with a remote receiver that also allows the driller to receive, analyze, and record the locating data.
Magnetic Guidance System (MGS)
This is an industry standard for both the HDD and Oil industries. The basic theory behind these tools is they use a tri-axial magnetometer package which provides azimuth/bearing and a tri-axial accelerometer package with provides inclination and tool face. The data is transmitted up a wire line which is placed inside the drill pipe during drilling operations; the data is then displayed in a format the directional driller uses to provide the required steering commands to the driller so the bore can stay on it's pre-planed course.
TruTracker is a secondary form of locating an MGS steering tool. An MGS steering tool provides its left and right measurements by an azimuth just like a compass. So, just like a compass, when placed near steel or magnetic object, the directional information is distorted. TruTracker allows the operator to create a magnetic field, or coil, of known origin in relation to the proposed drill path. The computer receives input of the coil position. When the MGS probe is positioned underneath the coil, a TruTracker survey can be taken.