Page 446 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 422

[ ] Practical Wellsite Operations
3.7.1

Use a nearbit stabilizer, bored for a float, and run it with a float in
place. This gives extra protection in the event of a kick, when tripping,
or if there is a leak on the standpipe or pump when the well is shut in.
It is safer to routinely run one float when drilling with a diverter or on
top hole with no secondary well control equipment.
Float valves sometimes have a small hole to allow the string to fill
up while RIH and to allow Pdp to be read when the well is shut in.
The ported float provides protection against strong backflow or flow
through the drillstring. Although it does not stop flow completely,
the small port only allows a relatively small flow through it and there-
fore still performs a useful function in reducing backflow to a man-
ageable level.
For the maximum anticipated WOB, calculate the number of drill
collars and HWDP needed to provide this, in mud, at the relevant
hole angle. The HWDP can be run in compression providing a short-
er, lighter DC section to reduce hook loads, drags, and sticking. The
drillpipe can also be run in slight compression so it is not necessary
to pick up excess weight on the BHA. For calculating the axial force
exerted by a steel pipe in an inclined wellbore, refer to “Tension due
to weight in a deviated wellbore” in Section 1.4.13, “Calculating,
Axial Loads.”
Design of rotary BHAs for drilling straight. Position full gauge
stabilizers above bit, 10-15 m above the NB stab and another at 10-15
m above that. (Bit - NB Stab [Full Gauge] - DC - Stab [Full Gauge] -
DC - Stab [Full Gauge] - rest of BHA.) Position undergauge stabilizers
one per stand above the top full gauge stabilizer, to hold the drill col-
lars off the wall to reduce sticking. More or less can be run if field expe-
rience shows this to be necessary. Run a Totco ring above the NB sta-
bilizer; if a magnetic single shot is run then a monel drill collar is need-
ed above the NB stab. Calculate the drill collars and HWDP for weight
as outlined in this section.
This BHA will minimize the likelihood of sticking and allow
greater overpull than a heavier BHA. Since it is well locked up, maxi-
mum WOB can be run on the bit without causing directional problems
and bit life should be maximized by reducing wear and whirl. Drags
will be kept lower as dogleg severities are kept at a minimum, espe-
cially if each kelly is reamed while circulating the cuttings above the
BHA before each connection, as recommended.

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