Oil and Gas at Your Door? (2005 Edition) - Earthworks

STAGES OF OIL & GAS DEVELOPMENT
FIGURE I-3. A DRILLING
RIG WITH ITS MAJOR
COMPONENTS AND
RELATED EQUIPMENT.
Kansas Geological
Survey 43
Spudding in: Spudding in refers to the first stage of the actual drilling operation. When a well
is spudded in, a large-diameter drill bit is used to drill a hole known as a well bore several hundreds
or thousands of feet deep.
A system of pipes, flexible hoses and pumps draw drilling fluid from nearby tanks or a mud
reserve pit. Drilling fluid, also known as mud, serves a number of purposes: 1) It is used to
lubricate and cool the drilling equipment; 2) it circulates through the drilling system and returns
to the surface, carrying drill cuttings, which are fragments of rock generated by the drill bit; 3)
it helps to prevent the fluids in the geological formations from entering the well prematurely;
and 4) the pressure of the drilling fluid prevents the uncased well bore from caving in. 44
Drilling fluids may be in the form of gases, foams or liquids. When drilling fluid is returned to the
surface, it is piped to a device called a shale shaker, which separates the drill cuttings and solid
materials from the drilling fluid. The fluid is usually returned to a mud tank or mud reserve pit
to be re-used. 45
Once the predetermined drilling depth is reached, the drill is removed from the well bore. The
well bore is then lined with a steel tube (known as casing), in order to stabilize the hole and prevent
caving. Casing should extend below the deepest freshwater zone, because another purpose
of the casing is to protect underground fresh water sources from contamination by oil, gas
or salty water that may flow through the well. Cement is pumped down into the space between
the outside of the casing and the well bore. This is to further ensure the protection of groundwater,
and to ensure that the casing is securely positioned.
A pressure test is then conducted on the casing and cement before drilling operations can be
resumed. Also, a blowout preventer is attached to the top of the surface casing. This device is
installed as safety measure to control the well if an abnormally high-pressure formation is
encountered. If a high-pressure zone is hit, the blowout preventer can be closed to prevent gas,
fluids and equipment from spewing out of the well bore. 46
Once the surface casing has been tested and the blowout preventer installed, drilling operations
can resume. The range in well depth is anywhere between 1,000 and 30,000 feet, with
an average depth of all U.S. wells drilled in 1997 of 5,601 feet. 47 I-9