Drill String Length

The drill string length is the total length of all the components in a drilling string used in oil and gas drilling operations.  The drill string is a column of drill pipes and associated tools that transmits drilling fluid (mud) and rotational power from the surface to the drill bit at the bottom of the wellbore.  Most components in a drill string are manufactured in 31 foot lengths (range 2) although they can also be manufactured in 46 foot lengths (range 3).  Each 31 foot component is referred to as a joint.  Typically 2, 3 or 4 joints are joined together to make a stand. 

Drill String Length Consists of Various Elements

Bottom Hole Assembly (BHA)  -  Comprises a drilling bit for breaking up rock formations and heavy drill collars that exerts weight on the drill bit during oil well drilling.  BHA also comprises reamers, jars, shock subs, and drill string stabilizers.
Transition Pipes  -  A transition pipe is a heavy-weight drill pipe (HWDP).  It may be 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.
Drill Pipes  -  A drill pipe comprises most of a drill string from the bottom of an oil well to the surface.  Every drill pipe has a long tubular section with a specific outside diameter.  Each end of a drill pipe tubular has tool joint connections.

The length of the drill string is cumulative, based on the lengths of all these components put together to reach the target depth.  For instance, if the target depth is 10,000 feet, the drill string length would be slightly more than 10,000 feet to account for all components and their connections.