Deep hole drilling is a chance for drillers to strut their stuff and show they have what it takes. Most drillers consider a hole deep if it is deeper than 1,500 meters. At that depth, drilling is a little more complicated and extra care is required. It’s the time you step up to the plate and show your supervisor you can deal with increased load responsibilities. What you don’t want to do is mess up – the deeper the hole, the more money that has been invested in it. A mistake in a deep hole costs a lot of time and money.
With that in mind, here are 7 tips to help you drill deep holes with fewer issues.
Slow and steady wins the race
You are wiser to go slow and steady when drilling deep holes. This will reduce the stress on your equipment and reduce the number of pullouts. No one is making any money when you are pulling rods out of a 1,500 meter hole. I cannot stress enough that patience is required when drilling deep holes. You need to take the time to think things through and be 200% sure of what you are doing. Burning a bit at 100 meters is an annoyance but at 1,500 meters it’s a big problem. Mistakes compound themselves when your hole is deep.
Perform equipment inspection and maintenance
It is a good idea to closely inspect the parts of your inner tube, including the core spring, core case, joints, bearings, latch, spear head, sure lock and ball, and pins. Make sure every part is working as it should, and that everything is clean and lubricated. Use a degreaser if necessary. Remember that clean and lubricated equipment will descend quicker.
Reaching the target is key when drilling deep holes, but the deeper the hole, the greater the chance of deviation. Do everything you can to try and prevent borehole deviation (check out our blog on the subject). Prevention is easier, cheaper and quicker than dealing with a hole that is off your trajectory.
Consider higher crowns
Opting to go with 20mm or 26mm crowns, such as Vulcans, can improve your bit life and reduce the number of pullouts. It has been shown that you can reduce more than 50% of pullouts by simply 26mm instead of a 13mm crown. However, and this is a big however, you should only opt for a higher crown once you have a very good understanding of the ground in which you are drilling. Keep in mind, that even after you have finished the first hole, the second one can be different.
In deep hole drilling, you should be running a mud program even when things are going well. Use polymers and the addition of drilling fluid additives suitable for the type of ground formation you have, such as Sand Drill for sandy ground, or DD 955 for clay or shale. Use Torqueless to maintain viscosity, keep your equipment lubricated and to reduce vibration in the hole.
Pick the right rods
Make sure your drill rods are straight. Choose your rod threads carefully and make sure you use a good quality thread compound with at least 50% zinc, like Pipe Dope. Deep hole threads are the best option.
Choose the right core bit
Aside from picking a bit that is suitable to the hardness of the ground, you should consider using full-face crowns which may help improve bit life in deep holes. When choosing a core bit for deep holes, you should look for bit life rather than penetration rate.
These tips give you a good start. If you aren’t sure about some function of the equipment or rig, err on the side of caution. You are better to ask questions, or ask for advice and help than to make a mistake in a deep hole. The result can be costly. Talk to an expert if you need to, our technical team has a wealth of experience with deep hole drilling.