The first step
for most wells in Canada is the installation of production casing. The casingtubular steel pipe connected by threads and couplingslines the total length
of the wellbore to ensure safe control of production, to prevent water entering
the wellbore and to keep rock formations from "sloughing" into the wellbore. Production casing is cemented in place by pumping a cement mixture
into the casing and forcing the cement back up the annulus, between the casing
and wellbore. The task must be done quickly but carefully because a poor cement
job can adversely affect the finished wellbore.
Once the cement
has set, the drilling rig is usually moved, and a smaller, truck-mounted service
rig is brought in to complete the well. There are about 600 service rigs in
Canada. They also return to wells periodically to perform maintenance, replace
equipment or enhance production.
The second step
is the installation of the production tubing. Production tubing is steel pipe
smaller in diameter than the production casing. It is lowered into the casing and
held in place by packers which also isolate the producing layers of rock. The
tubing hangs from a surface installation called the wellhead. The wellhead
includes valves, chokes and pressure gauges, and makes it possible to regulate
production from the well.
Petroleum Communication Foundation. Our Petroleum Challenge: Exploring Canada's Oil and Gas Industry, Sixth Edition. Calgary: Petroleum Communication Foundation, 1999. With permission from the Centre for Energy.