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Gas Drilling Operations 161

in produced water with traces of H 2 S, corrosion is very difficult to control.
There have been local studies of corrosion control, but there is no single
study that covers worldwide operations or that profiles any significant
direction. Corrosion control, like misting agents, is a local issue.
Corrosion inhibition, misting, and foaming affect one another in a nega-
tive way. Increasing the conductivity of the electrolyte in a system (the
fluid) will cause corrosion to increase. Brine water will increase the conduc-
tivity and will act to destabilize the foam. As the foam begins to break
down, the amount of free water will increase. This further accelerates the
corrosion rate. As temperature increases, corrosion increases. Foams exposed
to higher temperatures also begin to break down, yielding additional free
water. This compounds the rate of corrosion. Oxygen is probably the worst
offender to foam with respect to corrosion. Any foam system generated
with air will be potentially corrosive if it is not well controlled. The two
types of corrosion inhibitors are anionic inhibitors, which are more compati-
ble with foaming agents, and cationic inhibitors, which tend to act contrary
to the foaming agent and have a destabilizing effect on the fluid system.

7.3.7 Safety
Safety issues in gas drilling mainly involve hydrogen sulfide (H 2 S) natural
gas, which is highly toxic and life threatening. Natural gas, either injected
as a drilling fluid or produced from a formation, can cause fires and
explosions at the surface if it is not handled correctly. Natural gas from
formations can also cause downhole fires and explosions when air is used
as the drilling fluid.
Hallman and colleagues (2007) reported on a case involving H 2 S
operations. Gas drilling operations where H 2 S may be present must
include warnings of hazards and the following measures:
• Adequate crew training
• Special safety equipment (sensors, alarms, respirators, etc.)
• Emergency contingency plan
• H 2 S-resistant materials and training
• Pressured surface separation vessels
• Auxiliary vacuum degassing equipment

Contingency plans must be carefully developed before the drilling opera-
tions begin. Casing programs, circulation designs, and onsite quality control
and monitoring are particularly important. Operational and equipment test-
ing procedures must be enforced and be well understood by all personnel.