A drill string on an oil rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and rotational power (via the kelly drive or top drive) to the drill bit. An oil platform or oil rig is a large structure used to house workers and machinery needed to drill and/or extract oil and Natural gas through wells Drilling a very deep hole is a very costly business The hole size is kept very small as the drilled depth increases because it is to cased and cemented after wards Kelly Drive is a winding four-mile road along the Schuylkill River from the Philadelphia Museum of Art to the neighborhood of East Falls Philadelphia where it connects with For the ficitonal character see Drill Bit (Transformers. Drill bits are cutting tools used to create cylindrical holes The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit. The drill string is hollow so that Drilling fluid can be pumped down through it and circulated back up the annulus (void between the drill string and the formation). Drilling a very deep hole is a very costly business The hole size is kept very small as the drilled depth increases because it is to cased and cemented after wards The annulus (yellow area in diagram of an oil well refers to any void between any piping tubing or casing and the piping tubing or casing immediately surrounding
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Drill string components
The drill string is typically made up of 4 sections:
- Bottom hole assembly (BHA)
- Transition pipe (Often HWDP - Heavy Weight Drill Pipe)
- Drill Pipe
- Drill Stem subs
Each section is made up of several components and joined together using special threaded connections known as tool joints.
Bottom hole assembly (BHA)
The BHA is made up of a drill bit which is used to break-up the rock formations, drill collars which are heavy, thick-walled tubulars used to apply weight to the drill bit, and stabilizers which keep the drilling assembly centered in the hole. For the ficitonal character see Drill Bit (Transformers. Drill bits are cutting tools used to create cylindrical holes The BHA may also contain other components such as a downhole motor, Rotary Steerable System, measurement while drilling (MWD), and logging while drilling (LWD) tools. Measurement while drilling is a tool that transmits information in real time from the tool located near the drill bit to the surface Logging while drilling (LWD is a technique of measuring Geologic formation properties in real-time while drilling an Oil well.
Transition pipe
Heavyweight drill pipe (HWDP) is used to make the transition between the drill collars and drill pipe. The function of the HWDP is to provide a flexible transition between the drill collars and the drill pipe. This helps to reduce the number of fatigue failures seen directly above the BHA. A secondary use of HWDP is to add additional weight to the drill bit.
Drill pipe
Drill pipe makes up the majority of a drill string. A drill string is typically about 15,000 feet in length for an oil or gas well vertically drilled onshore in the United States and may extend to over 30,000 feet for an offshore deviated well.
Drill Stem Subs
Drill stem subs are used to connect drill string elements.
Running a drill string
Most components in a drill string are manufactured in 31 foot lengths (range 2) although they can also be manufactured in 45 foot lengths (range 3). Each 31 foot component is referred to as a joint. Typically 2 or 3 joints are joined together to make a stand.
Pulling the drill string out of or running the drill string into the hole is referred to as tripping. Drill pipe, HWDP and collars are typically tripped in stands to save time.
Stuck drill string
A stuck drill string can be caused by many situations.
- Packing-off due to cuttings settling back into the wellbore when circulation is stopped.
- Differentially when the formation pressure is too low, the wellbore pressure is too high or both, essentially pushing the pipe onto the wall of the wellbore.
- Keyhole sticking occurs mechanically as a result of pulling up into doglegs when tripping.
- Adhesion due to not moving it for a significant amount of time.
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