The derrick (or mast) is the tall steel frame that rises over the well on a drilling rig. Its job is to support the weight of the drill string and the hoisting equipment, and to provide the vertical clearance needed to raise and lower pipe in and out of the hole. It is the most visible structure on any rig.
The tall steel structure positioned over the wellbore that supports the drill string and hoisting equipment and provides height to handle stands of pipe during tripping operations.
Derrick vs. mast
The terms are often used interchangeably, but there is a practical distinction. A derrick is typically a fixed, four-legged lattice tower assembled on site, common on large or offshore rigs. A mast is a portable structure that can be raised and lowered as a unit, common on land rigs that need to move between locations. Both perform the same fundamental role over the well.
The drawworks is the large winch at the rig that reels in and lets out the hoisting cable, allowing the derrick to raise and lower the drill string and casing.
Working with the hoisting system
The derrick is more than a static tower — it is the framework for the rig's hoisting system. The drawworks, a large winch, reels the hoisting cable that runs through the crown and traveling blocks at the top of the derrick. Together they raise and lower the drill string and casing. The derrick's height determines how long a "stand" of pipe can be handled at once, which directly affects how quickly the crew can trip pipe in and out of the hole.
As a core part of the rig system, the derrick or mast works in concert with the drawworks, rotary system and mud pumps to drill the well.
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Frequently asked
A derrick is typically a fixed lattice tower assembled on site, while a mast is a portable structure raised and lowered as a unit — common on land rigs that move between locations.
It supports the drill string and hoisting equipment and provides the vertical clearance needed to raise and lower pipe in and out of the well.
The drawworks is the large winch that reels the hoisting cable in and out, allowing the derrick to raise and lower the drill string and casing.