In diamond drilling, vibration in the bore hole is sometimes unavoidable since rotating tools and equipment are being used, but drillers want to keep vibration to a minimum. In-hole vibration can cause premature damage to the bit, the core barrel, the drill rod and other machine components. Excessive vibration can have a detrimental effect on core recovery. All of these will increase your operational costs. A variety of things can cause excessive vibration in your bore hole.
Causes and fixes
Fractured ground: Fractured ground, or ground with faults or fissures can lead to your hole changing size and allowing more room for your rods to move. The bore hole annulus should not be so large as to allow your drill rods to bang around as this will cause vibration. DD X-Pand is a good example of a product that fills in fissures, cracks and holes easily and efficiently. (Read this blog post to learn more about the top four drilling additives.)
Clay conditions: When drilling in clay ground, the clay can swell and cling to the rod string and reduce its ability to move. This will then increase the torque which leads to an increase in vibration. In the case of clay, DD-955 is a product that is absorbed directly into the clay and shale and reduces in-hole swelling and instability.
Poor drill string lubrication: When a drill rod is not lubricated properly, friction and torque increase vibration. The use of a drill rod lubricant will reduce the friction and the torque during operations. A product such as Torqueless will lubricate well in addition to reducing torque.
Poor water circulation or dry hole conditions: The flow of water in the bore hole has a cushioning effect on the drill rods. If you encounter a fault at some point in your hole, the water may not flow back up to the surface. This means that parts of the drill string may not experience this cushioning effect and vibration may be increased at that point. The use of a polymer that can expand in volume, such as DD X-Pand can be an indispensable tool. Read this blogto learn more about how to control water loss in a bore hole.
Incorrect Weight on Bit (WOB): Bit pressure is the force applied on the rod by the drill rig. Pressure that is too high will increase vibration and cause premature wear of the rods and core barrel. Make sure to check drilling parameters so you can aim for the ideal combination of rotation speed and bit pressure.
Excessive rotation speed: The higher the speed of rotation, the faster the rods are rotating and the higher the friction and torque that cause bore hole vibration. The correct RPM will depend on factors such as penetration speed, bit diameter and depth of hole. Be sure to check drilling parameters so that drilling performance is optimized.
Download our guide to learn more about drilling parameters here
Worn out drill rods: Worn out drill rods are thinner and as a result, they have more “give” to them. This increase in flexibility can cause increased vibration, especially if the hole is very deep and rod string is very long.
Bent drill rods: Drill rods that are bent will also cause excessive vibration. The point at which the rod is bent will hit and bang against the bore hole walls and this will worsen with longer rods.
Download our guide to learn more about the proper handling and maintenance of drill rods here
Drilling over dropped core: Once dropped, it’s very difficult to recover lost core and drilling over it will increase the vibration in your bore hole. Make sure to avoid this situation by replacing your core lifter springs regularly as needed and by ensuring your inner diameters are within the correct tolerances.
CONCLUSION:
When vibration is too high, it is important to slow down drilling operations until excessive vibration can be alleviated. Like so many other situations, proper handling and maintenance of your drilling equipment can help prevent problems such as vibration. Remember that technical support for any drilling issues is always available. We also have an excellent selection of how-to guides that can provide advice and tips on many subjects.
