Page 16 - A Primer of Oilwell Drilling, 7th Edition

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nce the formation evaluation is done, the operator must decide
Oif the well should be completed as a producing oil or gas well.
Petroleum Extension-The University of Texas at Austin
if the well does not contain hydrocarbons, or not enough to pay for
the completion, the well will be plugged and abandoned (P&A).

PLUggINg aNd aBaNdONINg a WELL
To P&A a well, the drilling rig pumps several cement plugs through the Completing
drill pipe. The cement plugs are used to isolate and seal unprofitable
hydrocarbon zones from nonhydrocarbon-bearing zones and to seal the Well
freshwater zones from saltwater-bearing zones. The intervals between
cement plugs are left full of drilling mud. At this time, it might be pos-
sible to cut off and recover some of the intermediate casing string (if
one is present) for use in other wells. The surface casing string is always
left in place and sealed at the bottom and top by either cement plugs
or a combination of mechanical and cement plugs. The surface casing
will be cut off below the ground level or mud line and a cap placed on
the stub. if the well is on land, the well site will be environmentally
restored after the drilling rig has been moved off the location.

COMPLETINg a PROdUCINg WELL

The drilling rig is used to run and cement production casing as
described previously. The blowout preventers are removed and a
production wellhead is attached to the top of the casing. The pro-
duction wellhead seals the tops of the various casing strings in the
well, provides a place to suspend and seal production tubing as needed,
and provides the valves that control fow out of the well. Figure 209
shows a typical land wellhead or Christmas tree.

Figure 209. This collection
of valves and fttings is a
Christmas tree.

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