A Primer on Casing Shoes and Crown Shoes in Diamond Drilling
posted by the Epiroc Exploration & OreBody Solutions team
March 20, 2018
Casing is a tube or pipe made of lower grade steel and is used to stabilize the upper section of a bore hole to prevent it from caving in and to prevent loss of drilling fluids.
A casing shoe is found on the leading edge (the bottom) of a casing string to help advance it through the overburden layer and into the bedrock. Basically, its purpose is to make a hole for the casing which goes from the surface through the overburden to the bedrock. Because it is used to drill through overburden, the materials used in its composition are simpler and less expensive.
Casing shoes are often considered “disposable” because sometimes, once the driller reaches the bedrock with the casing, everything can be left there. This is a decision left up to the geologist or the mining company. As a result, a driller will want to choose an inexpensive casing shoe. On the other hand in really tough overburden, choosing a shoe with a high performance matrix is important in order to achieve a good penetration rate through boulders. You want to make sure it doesn’t wear out before it reaches the bedrock.
There are a few types of casing shoes, each for different conditions, and like most drilling equipment, choosing the right one is important.
Standard shoes:
Standard casing shoes are ideal for overburden with sand or gravel. Their matrix is made for drilling in easy to average ground and they come with 5 mm of diamonds impregnation and 6 waterways. Standard casing shoes are the most economical choice. You should consider a standard when the bedrock is not far from the surface.
Super shoes:
When you have overburden that is moderately difficult, a super casing shoe would be a good choice. The super shoe is made of a matrix that is more suitable for rocky overburden and it is taller, featuring 6 mm of diamond impregnation and 8 waterways. A super shoe is a good choice when the bedrock is deeper.
High performance shoes:
When the situation requires better performance, choose a high-performance casing shoe that provides a matrix more suitable for very difficult ground or overburden with a lot of rocks. As you can see in the diagram above, you can choose the matrix from different types according to the hardness of the ground. For example, in Western Canada, where the ground has a lot of sand, gravel and boulders, the 823 matrix is a good choice. You can get a high-performance casing shoe in 5mm or 6mm diamond impregnation.
Gator RT64 or Crown shoes:
You should consider a crown shoe for projects when you need really the highest performance in extremely difficult conditions. With a crown shoe you get 8 mm of diamond impregnation in the crown, along with a different shape of crown that is more similar to a core bit. Plus, you get to choose from the same matrices that are better suited to harder ground. Because of this extra height and thickness and its optimal cutting properties, it is ideal for deeper depths and going through overburden with large boulders.
What you need to keep in mind is that manufacturers offer a complete line of casing shoes. We design custom shoes for special applications as well, HQ to PQ diameters for example. You can contact our technical field support team for advice on choosing the best product for the lowest cost per meter.
