Drill String Components: Ahmed AYAD Hassan DHIAA Hameed Hussein Hawra Jawad
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AHMEDDrill String Components: Ahmed AYAD Hassan DHIAA Hameed Hussein Hawra Jawad
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DRILL STRING COMPONENTS
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Ahmed AYAD
Hassan DHIAA
HAMEED HUSSEIN
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HAWRA JAWAD
Date: 2018/11/11
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Drill String Components
The drillstring means the tubulars and the accessories used to run the drill
bit to the bottom. The drill string is composed of drill pipe, heavy weight drill
pipe, drill collars and other components like stabilizers and drilling jars.
1- Drillpipe: The drill pipe constitutes the majority of the drill string length.
It is seamless with threaded connections. The drill pipe has two tool
joints, one female is called a box and the other male is called pin. The
outer diameter of the tool joint is larger than the body of the drill pipe to
accommodate the threads. One drill pipe is called a single or a joint.
The dimensions of the drill pipe are specified by the API (American
petroleum Institute).
2- Heavy weight drill pipe (HWDP): A type of drillpipe whose walls are thicker
and collars are longer than conventional drillpipe. HWDP tends to be
stronger and has higher tensile strength than conventional drillpipe, so it is
placed near the top of a long drillstring for additional support.
3-Drill collars: A component of a drillstring that provides weight on bit for
drilling. Drill collars are thick-walled tubular pieces machined from solid
bars of steel, usually plain carbon steel but sometimes of nonmagnetic
nickel-copper alloy or other nonmagnetic premium alloys. The outside
diameter of the steel bars may be machined slightly to ensure roundness,
and in some cases may be machined with helical grooves ("spiral collars").
Last, threaded connections, male on one end and female.
4-bottomhole assembly: The lower portion of the drillstring, consisting of
(from the bottom up in a vertical well) the bit, bit sub, a mud motor (in
certain cases), stabilizers, drill collar, heavy-weight drillpipe, jarring devices
("jars") and crossovers for various threadforms. The bottomhole assembly
must provide force for the bit to break the rock (weight on bit), survive a
hostile mechanical environment and provide the driller with directional
control of the well.
5-Tool Joint: The tool joints provide screw threads in order to connect drill pipes
together. The seal is guaranteed by the shoulder/shoulder connections between
pin and box. Hard facing material is welded on the surface to protect the tool
joint from abrasive wear when rotating drill string in the borehole or when
making connection by rig tongs. The internal diameter of the tool joint is less than
the internal diameter of main body.
Other drill string components:
1- Stabilizers: Stabilizers are piece of pipe with blades machined on the
external surface. The blades can be spiral or straight, normally they are 3
blades. They have many functions
- Reducing bending and buckling stresses on drill collars
- Remaining the string in concentric position which allows higher WOB.
- Preventing stuck by differential sticking.
2- Shock sub: A shock sub is used to dampen the vibration caused by the
bit while drilling hard formation. it is normally located above the drilling bit to
minimize stresses due to bit bouncing.
The shock sub absorbs the vertical vibrations using a steel spring.
Reducing bit bouncing has many advantages:
- Extending bit life by reducing impact on teeth
- Avoid string failures
- Reduce damage to surface equipment
3-Subs: They are short joints of pipe used as crossovers. The main
function is adapting the threads, the size, or both of them to connect
different joints of string components.
4- Drilling jars: It is a very important piece of equipment which has to be
used in any drill string. It is used to free the string if any stuck pipe is faced.
They are activated by a straight pull and provide an upward blow. The
sharp motion or blow can shake the string and free it. The drilling jar is
placed above the drill collars and it is not recommended to work in
compression.