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PREPARATION OF SITE
An all weather access to the Entrance and Exit sites for the HDD must be constructed and a level hard standing area for the drilling operation prepared at each of these points as follows:
1. Entrance or Rig Site
A rectangular area has to be prepared that is approximately 150-200 feet long by approximately 100 feet wide. The longer side must be parallel to the proposed drilling direction with the mid-point of the shorter side facing the drilling direction at the Entrance to the proposed drill hole. Reference LDD-005 for a typical entrance side set-up.
Access to the Entrance should be either an "all weather" board road capable of withstanding heavily loaded transporters, or by floating equipment adequate to move the equipment to and from the Entrance. The hard stand should be either clay filling with a cover of laterite, wooden mats or steel plates. (On most sites, mats of steel plates are sufficient and no filling is required.)
The clean water (not salt water) requirements will be met by either a reliable pumped supply, able to meet the requirements of that particular drill, or an actual storage pond, sufficient to meet the requirements. (Allowance for water trucks to resupply the pond during the operation must be made.)
The bentonite pit must be of sufficient capacity to accommodate the used slurry/cuttings mixture. Further disposal of the used bentonite during the operation must be possible using other means. The pit will only be prepared when the rig is on site.
Note: If the client requires a complete mud cleaning system, than much larger areas, at least double size, must be prepared at the Entrance and the Exit.
A. Dead Man
The Dead Man comes with the rig. It is 3 feet deep by 30 feet long by four feet wide. The hole for the Dead Man must be excavated accurately and the top of the Dead Man must be flush with the ground. If additional anchorage is needed then the mud tanks can be hooked onto the rear of the rig and if this is still not sufficient, anchor piles will be driven.
The most important point is that the anchorage must be rigid and must not pivot. When operating from floating equipment anchorage is provided by spudding or anchoring the platform to achieve the same effect.
B. The Support Equipment required is:
(1) 25 ton capacity, rubber tire, hydraulic all terrain crane or equivalent
(1) Hydraulic tracked backhoe, 20 ton capacity or equivalent
(1) Hydraulic Backhoe either rubber tire or track with 20 ton capacity or equivalent
(1) four inch electric driven water pump with generator
(1) Fuel storage, capacity approximately 1,300 gallons
(1) Vacuum truck fitted with booster pumps
(1) Mud cleaning and recirculating system (optional)
(1) Haul truck, 5 ton capacity or equivalent
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2. Exit End
A rectangular area, approximately 100-175 feet long by 50-100 feet wide, of dry, flat hard stand is to be prepared as per LDD-006. The hard stand should be constructed in a similar manner to the Entrance. A similar access, as constructed for the Entrance should be provided.
A bentonite pit will be constructed to collect any bentonite/slurry discharged from the drill hole. The pit will be similar to that excavated for the Entrance.
Note: If the bentonite/slurry is to be cleaned, then either a second mud cleaning unit has to be installed or the bentonite/slurry must be pumped or transported to the first mud cleaning unit near the Entrance.
Equipment required for the Exit is one tracked hydraulic backhoe or equivalent.
The client must also provide either a tracked excavator or bulldozer fitted with side booms and sufficient rollers to support the pipeline when it is being pulled in.
Alternatively, a floatation ditch can be constructed, in which the pipe can either be floated on floats (smaller pipe diameter) or floated under its own buoyancy (larger pipe diameters).
In the cases where the equipment is mounted on floating equipment (i.e. where the Entrance and/or Exit is under water), then the deck area of the barge or platform must be sufficient for all equipment to operate safely. Additional barges can be used for storage of materials, etc.
In case where the client asks for assistance in pulling into place the "overbend" at the Exit point, or where a flotation ditch is to be used to float the pipe prior to the pull back operation, then the area at the Exit must be expanded to suit the diameter of the pipe to be handled and installed. The pulling in of the overbend for the client is usually done at the clients' risk, but eliminates the need for constructing a pit for the tie-in at the Exit end. This is most beneficial for the client in the case of large diameter pipes (i.e. 24 inch and above ).
3. Survey
3.1 To layout the TruTracker or control wires, the surveyors must have "Line of Sight".
3.2 The distance between the TruTracker wires,which are laid on the surface, should be
approximately the same distance in width as the depth of the drilling at that
particular point.
3.3 The TruTracker wires should be nearly equidistant from the drilling centerline,
when viewed in a plan.
3.4 The TruTracker wires do not have to be continuous (i.e. when a river has to be
crossed). During a river crossing, the driller will rely on information relayed
from the magnetometer and accelerometer.
3.5 The drilling accuracy is directly related to the layout of the TruTracker wires.
HDD Drilling Operation
A complete directional drilling rig consists of the following major components:
(1) Drilling unit
(1) Rig power unit
(1) Generator
Water pumps
Mud tanks
(1) TEE mud pump skid mounted
Drill pipe and racks
(1) Control cabin
(1) TruTracker guidance system
Secondary mud cleaning systems (Optional)
Miscellaneous tools
1. 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.
2. 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. (An "as"-built drawing is issued.)
3. 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 with the drill profile drawing. The rig is then
anchored in position.
4. The drilling operation begins by drilling a pilot hole using the drill bit, the steering tool and the high pressure
injection of bentonite slurry. The drilling is carried out continuously in intervals of 30 feet, equivalent to one
length of drill pipe. A new length of drill pipe is added at the end of each interval.
Figure 1.
5. Guidance of the drill bit is monitored using a TruTracker 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 coordinates 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. The operator also has additional information from the magnetometer and accelerometer
readings.
6. 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 about 12 inches larger in diameter than the pipe to be installed, is attached to the drill string.
Depending on the diameter of the pipe to be installed, several reamings with progressively larger diameter
reamers may be necessary (i.e. with a 36 inch diameter pipe, the first reaming could be with an 18 inch reamer,
the second reaming with a 36 inch reamer and the third reaming with a 48 inch reamer).
Figure No.2. During
the reaming process, bentonite drilling mud is pumped, under high pressure, through the drill string to the
reamer as the reamer is pulled back by the drill rig, drillpipe is attached continuously behind the reamer for the
subsequent swabbing and pipe pulling operations.
7. When the reaming of the hole is completed, a swab, through which high pressure drilling mud is pumped, is
pulled through the hole. This prepares the hole for the pipe to be pulled in.
Figure No.3. Once the driller is
satisfied that the hole is clear and ready for the pipe, the pullhead is connected, to the drill string via a swivel.
The swivel prevents the client's pipe from rotation during the pullback. Figure No.4.
In the case of pipes of diameter 28 inches and greater, PVC or HDPE pipes are inserted into the clients pipe
from the end farthest from the drill rig, prior to the pullback commencing. When the pullback has commenced
and when the pulling force begins to increase, clean fresh water is pumped into the clients pipe at a controlled
rate to ensure that the portion of the clients pipe in the drill hole is kept full. This is to counteract the buoyancy
of the clients pipe in the bentonite slurry.
8. 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 a single length. The length being equivalent to or greater than the length
of the drilled hole.
9. The client's pipe is then pull back toward the Entrance area by the drill rig. The drill rig is then moved to the
next drill site.
Figure No.4. In cases where the client wants the overbend pulled in, pull in is stopped just short
of completion to allow the overbend section of pipe to be welded onto the new or existing line pipe, field
coated, and tested.
10. Once the pipe has been fully pulled in, it is usually hydrostatically tested again by the client.
LEAVING THE SITE
The site will be left clean and tidy and basically in a similar condition as it was prior to the drilling commencing. |
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