When it comes to drilling solid rock life doesn’t get any better for United Drilling! However, when you are drilling through boulders or any other unconsolidated ground formation United Drilling needs to utilize a special drilling system: SymmetrixTM. Prior to this innovative design, the only way to drill through unconsolidated formations was to reduce the size of the hole. As an example let’s imagine a hole was started with a 20” casing and rock was encountered at 12’. The 20” casing would stop where rock was encountered and the 19” rock bit would continue to drill an open rock hole. If the ground formations deeper in the hole change from solid rock back into an unstable ground formation (clay, sand, gravel, etc.) casing would be required to keep the remainder of the hole intact. The only way to extend casing through this layer of material is to install a smaller diameter than the first. In this scenario, we would put an 18” sleeve of casing inside the 20” casing and drive the casing for the remainder of the required hole depth or until another layer of rock is encountered. You can imagine in certain areas some holes would require 2 or 3 reductions; creating substantial casing costs as well as time on the site.
Some of you might be wondering why the original drill casing is not driven through the initial rock and continued on into the next layer. It is important to know that once rock is encountered the hole diameter slightly reduces; the rock bit must be smaller than the drill casing to allow it to fit through the inside of the casing. Needless to say, if you go ‘in and out’ of rock the initial casing can only go as far as the first layer of rock. You would never want to drill a hole ‘open’ through any unstable ground formations because you would be taking a chance that the uncased hole could collapse – trapping your drill bit in the ground.
To remedy the problems associated with drilling through unconsolidated ground formations a new drilling system was created. Previously known in our industry as Concentrix, the updated Symmetrix system allows for the simultaneous casing and drilling of a hole. The system consists of three main components: pilot bit, ring bit (reamer), and casing shoe. The pilot bit and ring bit are locked together to drill a hole that is larger than the casing; this setup allows the casing to be pulled into the hole behind the bit. After completing the hole the pilot bit is unlocked from the ring bit and the ring bit is then left at the bottom of the hole. Symmetrix is used only when necessary as the cost of the ring bit is approximately $5,500. You are probably thinking that the cost of the ring exceeds the pricing on some holes; however, when you factor in the costs of labor, steel casing, and the expenses to run the rig, it is definitely more cost-effective to drill with this system and finish the project as quickly as possible.