Once a site has been selected, it must
be surveyed to determine its boundaries, and environmental
impact assessments (EIAs) are completed. Lease agreements,
titles and right-of-way accesses for the land must be obtained
and evaluated legally.
When legal issues have been settled, the
land is cleared and leveled, and access roads may be built.
The Drill Rig and necessary equipment can
then be trucked to the drill site. Once the equipment
is at the site, the rig is set up.
The crew sets up the rig (see
diagram) and
starts the drilling operations. First, from the starter hole,
they drill a surface hole down to a pre-set depth, which
is somewhere above where they think the oil trap is located.
There are five basic steps to drilling the surface hole:
- Place the drill bit, collar and drill pipe in the hole.
- Attach the kelly and turntable and begin drilling.
- As drilling progresses, circulate mud through the pipe
and out of the bit to float the rock cuttings out of the
hole.
- Add new sections (joints) of drill pipes as the hole
gets deeper.
- Remove (trip out) the drill pipe, collar and bit when
the pre-set depth (anywhere from a few hundred to a couple-thousand
feet) is reached.
|
|
The drill bit
cuts through the rock formation |
The Rotary Table
drives the rotating motion |
|
|
As drilling goes
deeper,
new sections of drill pipe are added to the drill
string |
Drilling
is a 24 Hour Operation |
Cementing |
Once they reach the pre-set depth, they must run
and cement the casing -- place casing-pipe sections
into the hole to prevent it from collapsing in on itself.
The casing pipe has spacers around the outside to keep
it centered in the hole.
The casing crew puts the casing pipe in the
hole. The cement crew pumps cement down the casing pipe using
a bottom plug, a cement slurry, a top plug and drill mud.
The pressure from the drill 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: They drill, then run
and cement new casings, then drill again. If the rock cuttings
from the mud reveal the oil sand from the reservoir rock,
they may have reached the final depth. At this point, they
remove the drilling apparatus from the hole and perform several
tests to confirm this finding:
- Well logging - lowering electrical and
gas sensors into the hole to take measurements of the rock
formations there
- Drill-stem testing - lowering a device
into the hole to measure the pressures, which will reveal
whether reservoir rock has been reached
- Core samples - taking samples of rock
to look for characteristics of reservoir rock
Christmas Tree |
Once they have reached the final depth, the crew completes
the well to allow oil to flow into the casing in a controlled
manner.
First, they lower a perforating gun into
the well to the production depth. The gun has explosive
charges to create holes in the casing through which oil
can flow. After the casing has been perforated, they run
a small-diameter pipe (tubing) into the
hole as a conduit for oil and gas to flow up the well.
A device called a packer is
run down the outside of the tubing. When the packer is
set at the production level, it is expanded to form a seal
around the outside of the tubing. Finally, they connect
a multi-valved structure called a Christmas tree to
the top of the tubing and cement it to the top of the casing.
The Christmas tree allows them to control the flow of oil
from the well.
http://science.howstuffworks.com/oil-drilling4.htm
