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main functions of core barrels

Core barrels are cutting devices used to collect the core of the drilled rock. The circular device has an open center portion that retains rock core samples from drilling operations. Core barrels are typically used to cut through extremely hard surfaces, such as rock bottomed sea floors and steel reinforced concrete. Their length varies from 1m to 3m. Core barrels are used when conventional augers are less effective or in conjunction with tapered rock augers for very hard rock drilling. The core barrel is designed with a thin cutting edge to maximize the penetration rate through less contact surface area having to be cut and removed. The main functions of core barrels are to collect sub-surface samples in the shape of core and accompanying sludge material in order to study their mineral assemblage, chemical composition, rock structure, and physical strength for various purposes. 

How Do Core Barrels Function
Core barrels are mounted to stabilizing equipment, such as a drilling rig or a truck rig, which can be operated by fewer workers and used for smaller cores. The barrel itself is made from a variety of hardened materials, like steel and titanium that are designed to withstand large amounts of pressure, and features a row of cutting teeth along the bottom edge. The teeth are usually made from similar materials as the drill itself and are often reinforced with additional metals for heavy duty jobs. These drills are manufactured in a variety of sizes and can be designed to the specifications of the purchasing company.

Rotating Core Barrels
These barrels are two part drill systems that are comprised of a spinning drill bit which moves around a non-rotating inner core. These core barrels are often used to penetrate the hard, crusty rock at the bottom of the ocean, and are frequently found in use on off shore oil rigs for drilling wells. The drill rests on the surface of the rock and begins spinning down into the hardened sediment. The interior non-rotating core can be inserted periodically to take samples of the rock for analyzing. The stationary core can be removed at any time and replaced with a secondary rotating drill for added force.

Diamond Core Barrels
They are similar to the rotating core barrels, and employ an inner and outer core to obtain rock and mineral samples during the drill process. The diamond bit is used when the material is too hard for a standard rotating barrel to penetrate. The diamond core bit may be inserted into the existing well, and then rotate the outer barrel around the inner barrel to cut away the sample. This technique is beneficial in preventing any exterior water from entering the core sample during the extraction process, which is a primary concern when drilling in the ocean. 

There are three types of core barrels:
· Single tube core barrel
· Double tube core barrel
· Triple tube core barrel.

Functions Of Single Tube Core Barrels
Single tube core barrels consist of a head section, core recovery tube, reamer shell and a cutting bit. The main functions of these core barrels are they are often used as a starter barrel during the beginning of core operations. They are used in coring homogeneous hard rock formations, where the core does not wash away or crumble easily, and a solid core can be taken without risk of blockage in the barrel. They are also suitable for penetrating rock layers above the strata, where high core recovery is not essential. They are not recommended for drilling friable or easily eroded formation since the core is continually washed by the drilling fluid. 

Functions Of Double Tube Core Barrels
These are the standard core barrels with an outer barrel that rotates with the cutting bit and an inner barrel that is either fixed or swivel type with bearings. This inner barrel retains the core sample. They are used in a wide range of core drilling conditions, and due to their narrow kerf bit, they will give good performance and core recovery in medium hard to extremely hard formations. 

Functions Of Triple Core Barrels
These core barrels are ideal for obtaining core samples in fractured rock and highly weathered rocks. The outer core barrel initializes the cut, the second barrel cuts the surface to finer size and the third barrel retains the cored samples. Triple core barrels reduce frictional heat that may damage samples.

The main functions of core barrels are to penetrate rock layers, cemented gravel and encountering boulders, so they are typically utilized by industrial construction companies and geological survey teams.