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What is Wireline Core Drilling?
Wireline core drilling is a special kind of drilling process that allows the core barrel to be removed from the base of the hole without taking out the drill rod. With wireline coring, the drill rod only has to be withdrawn up to the surface when the drill bit needs to be changed. This type of core drilling can be used for drilling boreholes that are over 1000 meters deep with a 76 mm diameter, especially in deep mining of solid minerals and in oil and gas exploration.

The Working Principle of Wireline Coring
Wireline core drilling uses wire lined retrievable core bits with a slim hole as well as a downhole shock absorber and a core barrel. The main objective of this technology is to reduce the amount of time spent in retrieving and lowering the drill pipe to take out a core sample. With the conventional method of drilling, the whole drillstring must be taken out of the bore hole along with the core barrel and core sample after drilling for about 3 meters. Thus, more time is spent in hoisting and lowering the core barrel than in actually drilling the hole.

However, with wireline drilling, anytime the driller needs to remove the core, an overshot – positioned at the end of the wireline, attaches itself to the outer part of the core barrel's inner tube. Then the inner tube disengages from the barrel as the wireline is pulled back. When the drill bit needs to be changed, the retrievable core bits are pulled out through the drillstring. This makes it easier and faster to change the drill bits in response to changing geological conditions.

Benefits of Using Wireline Coring

1. Time Savings: Wireline drilling provides a time savings of about 25% or more. This is due to the greater depth that can be drilled before retrieving the core barrel to the surface. Also, the use of the best drill bit for each geological formation makes cutting more efficient and reduces the time required to complete each drilling project.

2. Higher Penetration Rates and Footage: The presence of the shock absorber raises the penetration rates and the depth that can be drilled. The retrievable drill bit requires less energy to operate and wears out at a slower rate. So the drill bit can work for a longer period with less failures.

3. Cost Savings: The cost per meter of the drilling operation is lower with wireless coring technology than conventional methods. The reliability of wireline drilling is higher and thus the cost of maintenance is lower. Also, the cost of energy used to drill each meter is less than the cost of conventional drilling. For instance, the fixing device for the retrievable core barrel uses a different working principle whereby the junction between the fixer and the rollers are connected through frictional forces. Thus, the cost of energy needed to release and connect the core barrel is drastically reduced.

4. Increased Safety: Rig crews can enjoy a safer drilling operation since the need to trip the drill pipe will be drastically reduced by wireline retrieval. In fact, since tripping to retrieve the drillstring has been eliminated by wireline coring technology, fewer accidents will occur on rigs that use this drilling method.

Conclusion
The wireline coring system is easy to adapt to many conventional drilling rigs. It is designed to work with most conventional drillstrings that are used in non-stop core-recovery and slim hole drilling. This makes it easy to move from other drilling methods to a more efficient and cost effective system.

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