Core recovery, and how to improve it, is a topic that comes up often in a discussion with field technicians. This is not surprising, since it is the purpose of diamond drilling and every driller and drilling company wants to be efficient and cost effective when drilling. There are several tips that can help you improve your core recovery.
1) Choose the right core bit
Knowing how to choose the right core bit for the type of ground you will be drilling in will go a long way in helping your core recovery. Factors related to ground that you should consider include rock hardness, whether ground is competent or fractured, variability and abrasiveness. In addition, variables such as type of drill rig, level of experience, depth of drilling expected and knowledge of the area will all factor into your choice. Learn more about choosing the right core bit here.
2) Consider drilling fluid additives
If you haven’t already discovered drilling fluid additives, I suggest you take some time to learn more. When you find yourself in difficult ground, they are another product that can help with core recovery. If you find yourself drilling in sandy or gravel conditions, an additive can be used to solidify non-stable and abrasive grounds. Other additives can reduce swelling in clay or shale conditions.
A product like Torqueless is essential to keeping your core bit cool, as well as cleaning and lubricating your downhole equipment. Adding Torqueless to your drill water will help ensure that no grease or dirt sticks to your tooling and will lubricate all the metal parts, including inner tubes, latch heads, wireline, etc. And this will bring us to the next tip.
3) Perform regular maintenance
Once you have chosen your bit, remember that you should always be drilling with clean and lubricated equipment. Your inner tube should be cleaned thoroughly every time the core is removed, and you should properly rinse both the inside and the outside of the inner tube, core case and spring.
Clean tubes accept core easier and descend faster. Perform a thorough inspection of the latch head. Inspect latches and landing shoulder, inner tube cap, spearhead etc. for any wear or damage and change as needed. Make sure to use a good extreme pressure or multi -purpose grease such as Robco EP1004 to pump into the bearing assembly.
Your core lifter case and spring should be well lubricated. Once cleaned, pull the core spring out the front of the case as far as it will go, apply a thin film of grease between the spring and the core case to assure proper function of these two moving parts. This will help ensure the core enters easily without any obstruction.
4) Consider using linseed soap:
Using linseed soap is an old timers’ trick still widely used today. Linseed soap comes in a 5 gallon pail and has a gelatin consistency, like glycerin soap. To use it, grab a big handful from the bucket, about the size of a tennis ball and shove it into the throat of your clean and lubricated inner tube before you send it back down. As the inner tube makes it’s way down the rod string and comes into contact with the water column, the linseed soap will be forced up the inner tube, effectively lubricating the inside of the inner tube.
5) Check your drilling parameters
You should pay attention to your drilling parameters as they will have an impact on core recovery and performance. Try to put only enough pressure on the bit to make sure it cuts and no more. The same applies for rotation speed. Refer to the charts in this guide to learn the recommended parameters.
I hope these five tips help you improve your core recovery. We know that some tips may work better in certain situations, but now you have a few more tricks that you can try when recovery is not what you hoped for. Remember that our goal is to help you improve your drilling performance and our technical team is a great resource when you encounter problems.