posted by the Epiroc Exploration & OreBody Solutions team
February 26, 2020
Like many other industries, diamond drilling has its own language. I’ve done a few blogs about the acronyms and the terminology that newcomers to the industry should know. There are always a few expressions that don’t get onto a list and “pushing a block” is one of them.
While most experienced drillers will know what pushing a block is, not all will and new drillers may not be familiar with the expression at all. So, what does it refer to and why should you avoid doing it?
To understand pushing a block, you need to understand what a core block is. Let’s imagine that you are drilling in unconsolidated or broken ground. As the core bit and outer tube advance in the hole, the broken and wedge like pieces of core can become jammed as the core enters the inner tube. The driller should notice a spike in his water pressure due to the expansion of the shut off valves on the head assembly. This signal should never be ignored.
When this happens and you continue advancing, it is known as “pushing a block” and pushing a block is something you don’t want to do. Let me repeat - do not ignore the signs of a core block! Rising water pressure is a sign that the core is blocked and if you continue to try to advance, the shut-off valves will become compressed due to the feed force being exerted. This compression will cause them to expand in diameter until they spread out and touch the walls of the drill rod. This will keep the drill water from flowing freely. Of course, the exception to this is if you are drilling in a dry hole. Dry hole drilling is common in certain areas, such as Nevada. We’ll discuss that topic in another blog.
When the drilling fluid cannot keep the bit flushed, as will happen due to the shut-off valves compressing, you run the risk of burning the core bit. The drilling fluids will not be cooling the bit and the cuttings will not be flushed away from the face of the bit. If you don’t burn the bit outright, you may still reduce the bit life. As the shut-off valves are crushed by the upward force of the inner tube, enough heat is created to burn them off and damage the bearings and other parts in the head assembly.
So what should you do? When you encounter a core block, pull back on the feed a bit, and allow some time for the water pressure to return to normal. If it does drop, you can try advancing again. If you cannot get any advancement without rising water pressure then you must pull the tube, remove the core and try again.
A lot of successful diamond drilling comes from learning how to read your instruments and the “feel” of the equipment. Patience goes a long way and the ability to finesse a problem rather than jamming through is an asset. Our goal is improve drilling performance one drill site at a time. If you need advice on any drilling problems, you should know that our technical support team has a depth of knowledge and experience that can help guide you.
