HORIZONTAL DIRECTIONAL DRILLING
|HDD HORIZONTAL DIRECTIONAL DRILLING|
HDD is a valuable tool in today’s networks construction where unexpected obstacles can have a critical effect on the line construction.
A complete directional drilling process consists of the following major components:
- Water pumps
- Mud tanks
- Mud pump skid mounted
- Drill pipe and racks
- Locating guidance system
- Miscellaneous tools
The steps of HDD process are as follows:
- Before the drilling operation begins, the drill site is surveyed and a drill plan and profile is established. A cross-section drawing is made of the drill hole. At the field site, the Entrance and Exit stakes are put in place.
- The drill profile drawing establishes the Entrance and Exit angles and the radius of the method curvature, to achieve the depth and length of the drill.
- The drill unit is placed at the Entrance where the drill will enter at exactly the correct location. The drill unit is then elevated at the rear so that the Entrance angle conforms to the drill profile drawing. The rig is then anchored in position.
- The drilling operation begins by drilling a pilot hole using the drill bit, the steering tool and the high-pressure injection of betonies slurry. The drilling is carried out continuously in intervals equivalent to one length of drill pipe. A new length of drill pipe is added at the end of each interval.
- Guidance of the drill bit is monitored using a Locating guidance system, where the sensing unit is fixed to the rear of the steering tool. The sensing unit transmits the location of the drill bit back to the operator in the control cabin. From this information the operator knows the location of the drill bit at all times. The operator verifies the accuracy of the drilling by comparing the co-ordinates of the actual location of the drill bit against the planned drill profile. If there is a major difference between the actual and planned location of the drill bit, the operator is able to correct the actual profile by pulling back to a correct position of the planned profile and begin re-drilling. The more readings taken during the drilling increases the accuracy of the drilling along the planned profile.
- Once the drill bit exits the other end of the drill hole, (the Exit), the drill bit, steering tool, etc. are detached and a reamer, which is larger in diameter than the pipe to be installed and attached to the drill string. Depending on the diameter of the pipe to be installed, several reamers with progressively larger diameter reamers may be necessary during the reaming process, betonies drilling mud is pumped, under high pressure. Through the drill string to the reamer as the reamer is pulled back by the drill rig, drill pipe is attached continuously behind the reamer for the subsequent swabbing and pipe pulling operation.
- When the reaming of the hole is completed, once the driller is satisfied that the hole is ready for the pipe, the pull-head is connected, to the drill string via a swivel. The swivel prevents the client’s pipe from rotation during the pull back.
- Prior to the pull back, the client’s pipe has had a pull head welded on to it, has been prepared and hydrostatically tested by the client in single length. The length is being equivalent to or greater than the length of the drilled hole.
- The client’s pipe is the pulled back toward the Entrance area by the drill rig. The drill rig is the moved to the next drill site. In cases where the client wants the Over-bend pulled in, pull-in is stopped just short of completion to allow the Over- bend section of pipe to be welded onto the new or existing line pipe, field coated, and tested.
- Once the pipe has been fully pulled in, it is usually hydrostatically tested again by the client.