Deciding between various drilling methods and tooling can be fairly straightforward if the same ground conditions can be expected on every drill site. However, in many areas conditions change from drill site to drill site. Even a single borehole may involve a diversity of material, including overburden, unconsolidated and consolidated material, aquifers, etc.
When this is the case, selecting a drilling method sometimes involves a compromise. For example, if 80 percent of a 200-foot borehole consists of unconsolidated formations such as clay and sand and only 20 percent is consolidated rock, mud drilling, while slow through the rock, would be efficient through 80 percent of the borehole and therefore the most likely method of choice. Conversely, if 20 percent is unconsolidated overburden and 80 percent rock, augers can be used to drill efficiently through the overburden, casing being inserted if necessary. The augers can be quickly removed and a DTH hammer will efficiently complete the remainder of the borehole. It should be noted that the above scenario has been simplified for example purposes. There are many other variables to consider when choosing the most efficient drilling methods for your particular borehole and application.
Compromising, however, is not an efficient option if near equal percentages of consolidated and unconsolidated materials will be encountered. The good news is that you don’t have to compromise. Again, thanks to advances in drilling technology, many rotation heads offer a versatile balance of torque, rpm and down force to match your drilling method — mud drilling requiring higher rotation speed and down force compared with DTH hammer drilling, and auger drilling requiring much more torque. Also, universal drill rods are available allowing both mud and air to be used without changing rods, which also reduces costs. These do, however, have their limitations.
While some rigs are equipped with both mud pumps and air compressors on-board, portable units can also be purchased or rented and easily coupled to the drill rig, providing the necessary air or water flow and pressure. To some, that may sound like a lot of support equipment and tooling to have on hand, but when you consider the efficiency and versatility afforded, it makes a lot of sense.
Drillers are constantly analyzing and adapting their work methods to contend with the ever changing and sometimes unexpected conditions in the field. Meanwhile, manufacturers are relentless in their quest to make equipment safer, more user friendly and more efficient. It is no wonder why operator feedback is so essential in improving equipment design and functionality. Their combined efforts have resulted in an industry and technology that continues to advance.