1. Overview of Derrick

The derrick is one of the most prominent symbols in the petroleum industry. It is used to mount lifting equipment and tools such as the crown block, traveling block, and hook, and to bear the load generated during operations like raising and lowering drilling tools and casing. It provides height and space for lifting and storing the drill string. The structure is typically a tower-style steel frame.

2. Classification of Derricks

Derricks can be classified into the following four types based on their structural characteristics:

Tower Derrick

A-type Derrick

Mast Derrick

K-type Derrick (i.e., front-opening derrick)

1) Tower Derrick

The tower derrick is a four-cornered conical space structure, typically with a square cross-section. This type of derrick is usually assembled from single vertical rods, making installation and dismantling time-consuming and requiring high-altitude work. However, it has a wide base support, an enclosed overall structure, and excellent stability with high load-bearing capacity. Tower derricks are an important structural form for offshore drilling rigs.

2) A-type Derrick

This derrick consists of two large legs, a crown block, additional upper guy wires, and a two-story platform, forming an "A" shape space structure. The legs' cross-section may be rectangular or triangular. This type of derrick offers better load-bearing capacity and overall stability. The sections are connected with pins, and the derrick is installed at a lower level. It is open at the front and rear, providing a good field of vision for the driller, hence it is called the “full-vision derrick.”

3) Mast Derrick

Mast derricks are primarily used in truck-mounted drilling rigs and workover rigs. They are made from a single or several grid or tubular legs, forming a space structure. When in use, the mast tilts towards the wellhead at an angle of 3° to 8° and requires guy ropes to maintain structural stability. Mast derricks are available in telescopic and non-telescopic forms, with truck-mounted rigs and workover rigs typically using the telescopic type.

4) K-type Derrick

The K-type derrick is a front-opening derrick with an open front, and the cross-section is a "П" shaped space truss structure. The two sides are welded in segments or blocks into several sections, while the back is a truss rod system. Each section and component is connected using pins or bolts, allowing for low-position installation and the option for lifting using winch power or hydraulic cylinder thrust. The K-type derrick also features good overall rigidity. This derrick can also be made into a telescopic type.

3. Main Structure of the Derrick (using K-type Non-Guy Rope Derrick as an Example)

Derrick Main Body: Typically divided into 4 to 5 sections, these sections are connected with pins. The upper section is a closed square structure, and the remaining sections are front-opening L-shaped structures. The rear frame and diagonal braces are removable.

Two-Story Platform: Composed of the platform body, operating platform, directional beams, and inner and outer guardrails.

Cage Ladder: Installed on both sides of the derrick for operators to ascend and descend to the crane and the two-story platform.

Lifting Equipment: Includes the lifting frame, buffer tank, lifting ropes, and various lifting pulleys.

Derrick Accessories: Includes the standpipe control station, casing centralizer platform, large tongs counterweight, etc.

4. Substructure

The substructure is used to install drilling equipment (winch, rotary table, transmission device, diesel engine, etc.), store drill pipes and drill collars, and mount the derrick. It provides space for the installation of wellhead equipment and serves as an operational platform. The substructure bears the drilling work load, derrick lifting load, and the self-weight of the equipment, distributing these loads to the foundation and ground.