MANUAL – REFLEX EZ-TRAC™ | 77
7. Gently lift the survey system from the hole.
8. Place the survey system in a safe position away from the
borehole and unthread the running gear.
11.2.2 Through drill string - tripping out
Surveying through the drill string while tripping out is most commonly
used for Multi Shot surveys.
The instrument is run down the drill string, through the drill bit and into
the open hole. A landing collar is needed to prevent the survey
system from passing out of the drill string completely. There has to be
an opening at the drill bit, large enough for the instrument to pass
through, but small enough for the landing collar to stop.
For boreholes with inclinations up to 45 degrees from vertical, gravity
is used to lower the survey system down the drill string. Wireline may
be used for extra safety. For boreholes that are not inclined enough
or are directed upwards, the survey system must be pumped in while
attached to the core tube.
The survey is performed while tripping out. This is best done when
the drill string has to be recovered for a change of drill bit, for
example. Surveys may also be performed on subsequent drill bit
changes. In that case, survey coverage would extend back to the
start of the previous survey. All these survey sections may be merged
together. Alternatively, the hole is completed and the drill rig is to be
moved on. The survey should then be performed while recovering the
rods.
The survey system for surveying through the drill string while tripping
out consists of the
REFLEX EZ-TRAC™ instrument, three aluminium
extension rods and a landing collar or core adapter.
11.2.2.1 Gravity
Gravity may be used to lower the survey system down the hole.
Naturally, this is only possible for inclined boreholes, with inclinations
up to 45 degrees from vertical.
When lowering the survey system using gravity, a pin spear type or a
box type of landing collar can be used. Note, the landing collar box
type must not be threaded onto the overshot assembly as it is
impossible to release it at the bottom of the hole.
Lower with gravity
1. Before lowering the survey system down the drill string, ensure
that the drill rods are raised from the bottom a minimum of seven
meters.
2. Gently place the survey system – including a landing collar of
appropriate size – at the collar of the hole and let it go. Gravity will
lower the system to the bottom. If the borehole is filled with water,
allow sufficient time to reach the bottom.
3. When the survey system has reached the drill bit, the landing
collar will rest in the bit with the instrument extending 4.5 m/15 ft
past the bit.
4. Continue to the section Tripping out below.
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