Page 188 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 164

[ ] Well Programming
2.3.2

When a survey barrel is run or dropped into the UBHO sub with
an orientating muleshoe, the tool rotates as it enters and aligns itself
with the key. This is how the toolface azimuth can be determined.
Inclination-only surface readout sub (vertical wells). When
drilling a vertical well, surveys still have to be taken to ensure that
downhole events have not forced the bit to build angle. Circumstances
could include setting high bitweights on insufficiently stabilized
assemblies, faults, changes in dip, or boulders.
The Anderdrift Inclination Indicator is a sub run in the drill col-
lars. It is mechanical only and it gives a set of pressure pulses, visible
on the standpipe, depending on the inclination. A survey takes a cou-
ple of minutes (almost independently of depth), and the tool elimi-
nates the risks associated with wireline surveys. It can be very cost
effective for drilling vertical holes, especially with a high daily rate
operation. A Totco ring can be placed above it so that Totco surveys (or
single shots, if monels are run) can still be run on wireline.
Totco surveys (vertical wells). A Totco tool consists of an outer
barrel that houses the working parts of the tool. The measurement part
consists of a timer unit, an inclinometer, a punching mechanism, and
a disk holder.
When a measurement is taken, the inclinometer reading is
punched through a marked paper disk with a pin. The paper disk is
then rotated 180˚ and another pinhole is made.
After recovering the tool, the paper disk is removed from the holder
and examined. The two pinholes should both give the same reading and
be 180˚ apart; if they do not give the same reading or are not directly
opposite, then either the survey barrel was moving during the survey
period or the tool itself is faulty. It is easy to check the tool on surface; load
it, set the timer for a couple of minutes, and stand it almost upright some-
where so it will not move. Check the paper disk after the survey is taken.
The Totco tool can be run and recovered on wireline. Alternatively,
it can be dropped down the string and recovered later, either by wire-
line or when the BHA reaches surface. It is a good idea to drop the tool
whenever the bit is tripped out because this gives a survey with virtu-
ally no time impact. There is room past the tool for circulation so cir-
culation is possible. However, if there are any potential problems when
tripping out, it is better not to drop it for later recovery.

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