Generally,
more than one well is required to produce the
recoverable gas from a reservoir. Multiple wells are
drilled in a gas field. When natural gas is located,
the next step is to install a casing. This is a
tubular steel pipe that lines the hole; it prevents water and rock from entering
and controls the removal of materials. The casing is sealed to the
well with cement being pumped both inside and
outside of the casting. The next step in completing a
gas well is to perforate the casing so gas can flow
into the production tubing. This is done by lowering
a perforating gun, a device with many explosive
charges that fire metal rods through the casing and
into the producing reservoir. A steel production
tubing is then installed to remove the gas.
Stimulation may be needed if the natural gas flow
is stopping. This can be done either as part of the
completion process or later on in the life of the
well. Stimulation processes are acidizing or
fracturing a well. Acids are pumped into the
producing reservoir under pressure to dissolve
reservoir rock to increase the number and size of
channels carrying gas to the well bore. Fracturing
is where fluids such as water or carbon dioxide are
pumped into the reservoir at sufficient pressure to
break the rock. To prevent the breaks from closing,
proppant is then introduced into the reservoir.
Proppant includes sand, ceramic beads, or resin coated
material that props open the new fractures and
enhance gas flow. Natural gas from coal, tight gas
sands, gas shales and gas hydrates are often
referred to as unconventional gas resources. Methane
is the main component of unconventional natural gas,
but other parts vary and may have to be removed to
produce sales grade natural gas. Unconventional gas
is the same as conventional natural gas except it
has different reservoir characteristics.
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