Upstream Oil and Gas Drilling Tubulars and Bits

In this lesson on tubulars and bits, we’ll discuss drill pipe, casing pipe, drill bits and different bit types.

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Tubulars

Drill Pipe

In simple terms, tubulars are the steel pipe that is used to drill the well, case the wellbore, and produce the reservoir fluids. They come in many varieties and are engineered for high strength and rigidity.

Tubulars are connected by independent couplings or screwed directly into each other by virtue of a box (female) end and a pin (male) end.

Drill pipe tubulars are commonly found in 30 ft lengths called joints and play a very important role in the overall drilling process.

There is a wide variety of equipment that either attaches to or runs through the drill pipe to aid in drilling. Mud flows through the center of the drill pipe. Special collars are attached to perform other tasks, such as aid in the well deviation process.

The bit is securely attached at the end of the drill string.

Casing & Tubing

The borehole is lined with steel casing to provide a conduit from the surface to the producing formation.

The casing lines the raw, open hole made by the bit as it travels through the formations. It keeps the borehole from caving in, and once cemented into place, keeps fluids in one formation from migrating to another.

Like drill pipe tubulars, casing is commonly found in 30 ft lengths (also called joints). Casing joints are also coupled together by independent threaded couplings.

Casing is manufactured around the world to API (American Petroleum Institute) specifications, in a wide variety of metallurgies, using either a seamless or ERW (Electric Resistance Welding) manufacturing process. Casing sizes range from 4-1/2″ to 13-3/8“.

Standard tubing sizes used to produce the reservoir fluids are 2 3/8”, 2 7/8” and 3 ½”

Drill Bits

A drill bit is a device attached to the end of the drill string that breaks apart, cuts or crushes the rock formations when drilling a well.

Everything on a drilling rig directly or indirectly assists the bit in cutting the rock. The bit is on the bottom of the drill string and must be changed when it becomes excessively dull or stops making progress. The term for this activity is “tripping pipe” and can take days on a deep well. Therefore, bits are designed to do their job in severe service for as long as possible.

Most bits work by scraping and/or crushing the rock as part of a rotational motion. Some bits, known as hammer bits, are activated by a downhole motor which pounds the rock vertically in much the same fashion as a construction site air hammer.

The drill bit is hollow and has jets to allow for the expulsion of the drilling fluid at high velocity and high pressure. This helps clean the bit and breaks apart the rock in softer formations.

Bit Types

Each bit type is custom-engineered for the expected formations. Three common types are the roller bit, the diamond bit, and the directional bit.

Roller Bits crush, chew, cut and gouge the rock formation. The configuration is dependant on hardness of rock. It can be used to drill any formations if the proper cutter, bearing, and nozzle are selected.

Diamond Bits are often called PDC bits for polycrystalline diamond cutting. These bits grind rock and is more durable than the roller rock bit. They are also used for core samples and designed to excavate hole by shearing the formation. They drill very quickly in soft to moderately hard formations such as sand, shale, clay and siltstone.

Directional Bits include a steerable motor mounted behind the drill bit which allows the ability to drill at an angle. They are used especially in offshore sites where a number of wells may be drilled from a single platform/borehole and in horizontal wells.