BAKER HUGHES - Drilling Fluids Reference Manual

TABLE OF CONTENTS
HYDRATE FORMATION DURING WELL CONTROL INCIDENTS
Hydrate formation may be accelerated during the drilling operations as a result of gas influx (kick).
A critical situation, in respect to gas hydrate formation, may arise during well control incidents when
the well is shut in.
A typical kick is detected at 10 bbl of pit gain. By the time the well is shut-in, the kick volume could
reach 50-60 bbl. Depending on the hole and drill pipe size, the kick could reach a height of 1500 –
2000 ft. (457 - 610m.) Although the kick fluid leaves the formation at a high temperature, with an
extended shut-in period it can cool to sea bed temperature. With high enough mud hydrostatic
pressure at the mudline, hydrates could form in the BOP stack, choke and kill lines.
Two procedures are used by the industry to shut-in wells during a gas kick: the soft shut-in and the
hard shut-in procedures. In the soft shut-in, the hydraulically operated choke line valve is opened, the
annular BOP is closed, and finally the adjustable choke is slowly closed. This procedure is applied
with the intention of reducing shock loads on the casing shoe.
Figure 13 - 6
Typical BOP Riser
Arrangement
The hard shut-in procedure
requires opening the hydraulically
operated choke line valve and
then closing the ram, with the
adjustable choke remaining closed
at all time. This procedure takes
considerably less time and thus
allows less influx into the well,
reducing wellbore pressures
during killing operations.
However, because of the concern
over possible shock loads, the soft
shut-in method has historically
been preferred by the operators.
To achieve successful kick
containment, the Blowout
Preventor (BOP) must operate
properly and the choke and kill
lines must remain clear for
circulation. Consequently, and as
a safety precaution, the drilling
fluid must have good hydrate
inhibition properties.
The risers on deep water drilling
rigs are partially insulated with
the floatation material attached to
them. The BOP and choke and
kill lines are normally exposed to sea water. Insulation will help reduce the rate of heat transfer
during lengthy shut-in periods. In very deep water situations insulation may not provide adequate
protection even after long circulation periods.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 13-16