Bits ‘n Pieces – The Driller’s Blog

Preventing Core Washout

Posted by Rod McCoremick on Sep 25, 2017 10:30:00 AM

It’s all about the core. When a drilling project is started, the purpose is to drill and get a decent core sample. You may have to deal with a few challenges but once you’ve dealt with them the last thing you want is to lose the core because of wash out. Your core being washed out is most likely to happen when your ground is not competent, fractured, sandy or full of cobbles. Luckily, there are a few tips that can help you hold onto the whole core sample.


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Choose the right configuration

It goes without saying (or should) that you need to choose a core bit that is suited to the ground you will be drilling in. But beyond the hardness of matrix, you need to consider the configuration meaning variables like discharge options and waterways. Lateral discharge and deep lateral discharge are both good options to prevent washout. Both designs allow more water to pass, providing better flushing capability. In fragile formations, face discharge bits will deliver more water directly to the face of the bit and will minimize the risk of washing away the fragile formation. To learn more about choosing core bit configuration options, check out our guide here.

 

Make tube adjustments

Remember that the pressure of the water you are using in the hole can be very high. To avoid core washout, find the happy medium between enough water to keep the bit cool and flush cuttings but not so much that the water will wash out a fragile formation. Make tube adjustments so that you leave minimum space between the core lifter and the bevel of the bit.

 

Consider Q3 barrels

For really tough formations, the Q3 barrel is a good option that you should consider. This is a triple tube system with 2 split tubes inside the regular tube. These split tubes help protect fragile formations, and can be pumped out of the inner tube by mechanical means providing a better sample, and saving time and frustration for the helper.

 

Use drilling fluid additives

Luckily, there are drilling fluid additives that are specially formulated for sandy ground or ground with cobbles. Problems recovering intact samples are common due to the granular nature of the ground. Often the sample will have a crumbly consistency which can break or fall apart during recovery. A product such as Sand Drill is a type of polymer used to solidify non-stable grounds such as sand or gravel. Its gel like consistency can hold together a crumbly core so that it can be retrieved intact.

 


 

These tips are not that hard to implement if you are familiar with the equipment or products suggested. As always, should you require extra information or advice, our technical team is ready to help. Our goal is to make your life easier.



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Topics: Tips on common drilling issues, Basic drilling information



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