EXPLORATION, RECOVERY, AND TRANSPORTATION 73
When the pre-set depth is reached, the casing pipe section are run
into the hole and cemented to prevent the hole from collapsing. The
casing pipe has spacers around the outside to keep it centered in the
hole. The cement is pumped down the casing pipe using a bottom
plug, a cement slurry, a top plug, and drilling mud. The pressure
from the drilling mud causes the cement slurry to move through the
casing and fill the space between the outside of the casing and the
hole. Finally, the cement is allowed to harden and then tested for
such properties as hardness, alignment, and a proper seal.
Drilling continues in stages and when the rock cuttings from the
mud reveal the oil sand from the reservoir rock, the final depth may
have been reached. At this point, the drilling apparatus is removed
from the hole and tests are preformed to confirm that the final depth
has been reached.
New methods to drill for oil are continually being sought, including directional or horizontal drilling techniques, to reach oil under
ecologically sensitive areas, and using lasers to drill oil wells.
Directional drilling is also used to reach formations and targets
not directly below the penetration point or drilling from shore to
locations under water. A controlled deviation may also be used
from a selected depth in an existing hole to attain economy in drilling costs. Various types of tools are used in directional drilling
along with instruments to help orient their position and measure
the degree and direction of deviation; two such tools are the whipstock and the knuckle joint. The whipstock is a gradually tapered
wedge with a chisel-shaped base that prevents rotation after it
has been forced into the bottom of an open hole. As the bit moves
down, it is deflected by the taper about 5° from the alignment of the
existing hole.
Drilling does not end when production commences and continues after a field enters production. Extension wells must be drilled
to define the boundaries of the crude oil pool. In-field wells are
necessary to increase recovery rates, and service wells are used to
reopen wells that have become clogged. Additionally, wells are
often drilled at the same location but to different depths, to test
other geological structures for the presence of crude oil.
3.2.4 Well Completion
Once the final depth has been reached, the well is completed
to allow oil to flow into the casing in a controlled manner.
When the pre-set depth is reached, the casing pipe section are run
into the hole and cemented to prevent the hole from collapsing. The
casing pipe has spacers around the outside to keep it centered in the
hole. The cement is pumped down the casing pipe using a bottom
plug, a cement slurry, a top plug, and drilling mud. The pressure
from the drilling mud causes the cement slurry to move through the
casing and fill the space between the outside of the casing and the
hole. Finally, the cement is allowed to harden and then tested for
such properties as hardness, alignment, and a proper seal.
Drilling continues in stages and when the rock cuttings from the
mud reveal the oil sand from the reservoir rock, the final depth may
have been reached. At this point, the drilling apparatus is removed
from the hole and tests are preformed to confirm that the final depth
has been reached.
New methods to drill for oil are continually being sought, including directional or horizontal drilling techniques, to reach oil under
ecologically sensitive areas, and using lasers to drill oil wells.
Directional drilling is also used to reach formations and targets
not directly below the penetration point or drilling from shore to
locations under water. A controlled deviation may also be used
from a selected depth in an existing hole to attain economy in drilling costs. Various types of tools are used in directional drilling
along with instruments to help orient their position and measure
the degree and direction of deviation; two such tools are the whipstock and the knuckle joint. The whipstock is a gradually tapered
wedge with a chisel-shaped base that prevents rotation after it
has been forced into the bottom of an open hole. As the bit moves
down, it is deflected by the taper about 5° from the alignment of the
existing hole.
Drilling does not end when production commences and continues after a field enters production. Extension wells must be drilled
to define the boundaries of the crude oil pool. In-field wells are
necessary to increase recovery rates, and service wells are used to
reopen wells that have become clogged. Additionally, wells are
often drilled at the same location but to different depths, to test
other geological structures for the presence of crude oil.
3.2.4 Well Completion
Once the final depth has been reached, the well is completed
to allow oil to flow into the casing in a controlled manner.