Page 348 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 324

[ ] Practical Wellsite Operations
3.1.5

For sour service the complete high-pressure BOP system is to be of
metals resistant to sulfide stress cracking. Refer to the current issue of the
National Association of Corrosion Engineers, NACE Standard MR-01-75.
Dedicated kill lines are to be a minimum of 2 in nominal ID and
are to have two valves and a non-return valve (NRV) between the line
and the BOP stack. Choke lines or dual-purpose choke/kill lines are
to be at least 3 in nominal ID and should have two valves from the
BOP, the outer of which should be hydraulically operated. For
drilling and workover operations, blind/shear rams are required that
can shear the drillpipe/tubing under no-load conditions and subse-
quently seal the well.
Any measuring instrument needs to be regularly checked and cal-
ibrated to ensure accuracy. On many rigs, pressure gauges stay in place
for years without getting checked; they go through rig moves, weather,
exposure to hot drilling fluids, physical knocks, vibration, etc. Yet
when it comes to a well kill situation the safety of the people on the rig
and the rig itself can depend on those gauges reading accurately. Check
that they have valid test or calibration certificates—preferably not more
than six months old and never more than a year old. If necessary,
demand that they be replaced with recently certified gauges.
Diverters: general considerations. A diverter is installed to allow
time to evacuate the wellsite in the event of shallow gas. Current sys-
tems are not designed to handle a sustained erosive flow from the well.
A diverter must be installed on a well when both of these condi-
tions apply:

1. There is a possibility of losing primary control
2. The conductor or casing shoe is not strong enough to close in
the well with a BOP, which would cause fracturing to surface if
the well were closed in

The diverter lines must be designed so that produced fluids and
solids can be taken clear of the rig with the minimum back pressure
and without eroding or plugging off. The lines should be of minimum
12 in ID, and they should be as straight as possible without flow
restrictions or bends that would induce turbulence and increase ero-
sion. Minimum pressure rating for the diverter is 500 psi, but a higher
rating may be necessary if the anticipated surface pressure is greater.

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