Page 448 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 424

[ ] Practical Wellsite Operations
3.7.3

if problems occur while pulling out of the hole. There is a better alter-
native, however.
If a keyseat is possible, run a string reamer in the drillpipe, if avail-
able. Position it at the top of the dogleg section with the bit on bottom.
1
Size it greater than the DC OD and smaller than the bit; /2 in under-
gauge is usually about right. As drilling progresses, the reamer dresses
out the inside of the dogleg section, wiping out any keyseat. This pre-
vents having to backream, which can be quite time consuming without
a top-drive system. Run the reamer every two or three trips as neces-
sary. No extra time is taken since it works while drilling.

3.7.3. Directional Jetting—Practical Considerations

For an explanation of this technique, see the “Kickoff by Jetting”
in section 2.3.3. The directional driller on site should be experienced
in jetting to kick off, since jetting can create very severe doglegs if not
carefully controlled.
Run a mill tooth bit - near bit stab (bored for and complete with
float) - float sub (if no float in the NBS) - UBHO sub - monels - rest of
BHA. Align the UBHO with the large nozzle for orientation. Set up the
stabilizers for building angle (see “Design of rotary BHAs for building or
dropping angle” in Section 3.7.1). Run in, take a single shot survey,
mark the pipe, and align with the required azimuth after making up the
kelly. Lock the table, bring the pumps up to speed and jet down the dis-
tance from the bit to the top NB stab blades. Pick up, ream through, and
drill ahead for the rest of the single. Take another survey after adding a
single and repeat the process if necessary. If the formation will not wash
with just weight on bit and pump rate, the bit can be spudded.
Spudding the bit involves picking up the string a meter or two and
dropping it until the bit reaches bottom (mark the string), then applying
the main brake hard. The inertia of the string allows the bit to hammer
into the formation, helping to exceed the mechanical formation strength.
This precludes the use of any bit type except a steel mill tooth bit.
Jet only a small amount at a time, otherwise extremely high dogleg
severities can result. In the right application, jetting saves the cost of
using motors for kicking off and saves tripping time to bring out the
motor and run a build assembly.

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