Composition of Drilling Core Barrel Assembly

The composition of a drilling core barrel assembly is the key to coring success. The assembly consists of a core-retaining inner barrel, a catcher, and several boxes.

Choosing the proper catcher depends on the type of inner barrel expected and the lithology of the rock. A split ring or slip catcher improves core recovery in unconsolidated sandstone, while a full-closure catcher is used for shale and other hard rock.

Inner Barrel

The inner barrel is a crucial component of the drilling core barrel assembly and contains the sample that will be cut. The inner barrel is made of steel, aluminum, or fiberglass. The materials are lightweight and provide a low coefficient of friction that makes the inner barrel easier to handle and maintain.

Cores are drilled from various surfaces, including cement, wood, rock and ice. Different drills are used for each surface type. The core barrel assembly is designed to accommodate a variety of core drilling tools.

Normally, the outer barrel is attached to the core bit and a string of rotary drill pipe. This string is connected to a wireline. The inner barrel is lowered through the drill string, locked in place for coring and then retrieved by wireline.

A core barrel with a retrievable inner barrel offers a substantial time saving over conventional coring. This is especially useful in the case where a longer formation interval than the 90 ft maximum allowed by a standard core barrel needs to be cut.

This can be achieved by dropping a diamond drilling plug into the core hole and then lowering the retrieveable inner barrel to the well bottom, locking it in place, and then pulling it back through the drill string to surface on a wireline. A replacement inner barrel is then lowered down to the bottom and coring can resume without delay.

Another option for coring unconsolidated or conglomeritic formations is a rubber sleeve core barrel and BWcasing pipe. This core barrel is unique in that the top of the inner barrel does not move relative to the core as it is progressively encased in the rubber sleeve.

The system works best from fixed drilling platforms, but can be operated on floating rigs as long as rig movement is minimal. The sponge liner is pumped off the core by hydraulic pressure and the core is broken off and placed in PVC handling tubes for transport to a core analysis laboratory.

The telescoping outer tube of the JamBuster anti-jamming system automatically telescopes if a core jams in the inner barrel, preventing unscheduled trips out of the well. The core barrel can hold up to four jams before it has to be tripped out of the well.

Core Catcher

The core catcher of a drilling core barrel assembly is an essential component of the drilling operation. It protects the core sample from the effects of fluid flushing and helps retain the sample after it has been broken.

A core catcher can be made of steel, bronze or stainless steel and will normally withstand thousands of core samples. However, it is important to note that it can rust or break if left untreated for long periods of time.

As a result, it is crucial to check it on a regular basis and to grease it before deploying the head. This can help extend the life of the head and prevent serious downhole problems from occurring.

An alternative approach to this problem is to use a disposable inner core barrel. This allows the driller to replace it when necessary without compromising the integrity of the core.

In addition, the low coefficient of friction between the core barrel and the sample tube can improve both the quality of the core and its recovery rate. It also minimizes the amount of core that gets lost during tripping operations.

Another advantage of a core catcher is that it can be used with various types of sample tubes, including plastic, metal or glass ones. The catcher will hold and preserve the sample as it is retrieved, while also allowing the driller to catalogue and document the contents of the tube.

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This is particularly helpful for geologists who are involved in evaluating the potential of a future mine site. They can then compare a mine's core with other similar ones to determine the best location for a new mine with steel drill rod.

The inner tube of a drilling core barrel is connected to the outer - tube via locking couplings and adapter couplings. The locking coupling threads into the drill rod string and provides a hardened mating surface that the inner tube assembly latches to while drilling. The locking coupling also provides directional control for the inner tube through wear resistant stabilizing pads that abrade against the drill hole wall.

The head assembly is attached to the inner tube through an overshot device and is secured into place by the locking couplings. As the inner tube assembly is lowered into the drill string, it is secured by the landing shoulder on the head assembly, which collides with the Landing Ring located in the upper-end of the outer-tube. The head assembly then secures the inner tube to the drill string and allows it to be retrieved from the bottom of the drill hole for further processing.

Core Boxes

A drilling core barrel is a large metal box that contains a segmented core inserted by the coring crew during coring. This core encapsulates the unconsolidated reservoir rock within its surface layer and is protected from further damage during shipping or storage in the laboratory.

The inner portion of the box is covered with plastic materials for HDD drill pipe (e.g., SaranTM wrap) to prevent leakage of oil or water during transport. The box should also be marked for well name, depth, and top or bottom. The boxes are then sealed with caps furnished by the coring company.

For rubber sleeve and fiberglass cores, waterproof material is used to mark the top and bottom of the sleeve and cap and to seal the joint. Tape should be wrapped around the sleeve-cap joint to ensure air tightness.

In some cases, a core gamma log is run on the sleeve to help select sample points in thinly laminated sands. These gamma logs are sometimes X-rayed to locate bedding planes and sand stringers suitable for sampling.

These cores are then reboxed in boxes that are approximately 6 inches in height and 3 feet long. The boxes should be stacked in a safe area to be visited by geologists who will be responsible for inspecting and processing the cores.

Typically, boxes are numbered according to the order in which the cores come out of the barrel, so that samples from the oldest sediments are in the first box, and the youngest are in the last box. This is to reflect the age progression of the rocks sampled, which will vary from well to well.

This is a relatively simple process, but can be complicated depending on the nature of the drilling and the size of the cores being processed. The boxes should be carefully labeled, and a core tally sheet is produced for each section of the core.

After the cores have been processed and packaged, they are retrieved from the core barrels in a manner that minimizes frictional heat. The outer core barrel is used to cut an initial segment of the core, and then a second or third barrel is used to cut finer sections of the core. This reduces the jarring effect of rotation and allows the drilled core to be reinserted into the inner barrel in a safe and controlled manner.

Core Tally Sheet

A core tally sheet is an important tool for recording and analyzing results of a drilling project. It helps track data measurements such as the number of holes drilled, the type of bit used, the diameter of the hole and the depth of the core.

The core tally sheet also includes information about the rig location, drilling date and time, number of cores retrieved, the type of fluid and its slug content and more. The chart can be customized to fit the needs of your team and is a great way to keep track of a project's progress.

There are several types of core barrels available for use in different applications. These include:

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Wireline Double Core Barrel

This wireline system eliminates the need to pull the drill string each time a core sample is retrieved. This reduces the cost of drilling because it does not require the use of a drill rod or casing.

It is ideal for coring in soft and hard formations, using water flushing or polymer fluid with HQ3Core Barrel Assembly. Its thin walls allow fast penetration and a larger core sample.

They come in standard and basket types. They can be case hardened upon request for added wear resistance.

The inner tube and outer-tube of a core barrel are manufactured from cold drawn seamless steel tubes with high tensile strength and straightness. They are heat treated to prevent corrosion and extend the life of the product.

Another component of the core barrel is the head assembly, which is essential to the system's operation. It features latching and pivoting spearpoint mechanisms, a bearing assembly that allows the inner tube to remain stationary while drilling and fluid pressure operating indications.

All of these features ensure the integrity of the core barrel's internal components and help to prevent downhole problems. Additionally, the head assembly can be greased to increase its life.

The core lifter or core retainer mates to the outer tube and acts as a push fit between the core tube and the core bit when the bit is pushed down into the rock strata. The core lifter or core retainer can be split ring or basket type, depending on the application and the rock strata.