| 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 |
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. |
