We recently had the very first webinar in our drilling series - Drilling 101. In this webinar we discussed drilling basics- the various drilling methods, technologies, and their applications. But before diving into each technology, we laid the fundamental foundation of environmental and geotechnical drilling: choosing the appropriate drilling technology for the task at hand.
There is a vast array of drilling technologies available for a variety of different job sites and applications. So, how do we choose the right drilling method for a particular job site?
There are three fundamentals that almost all drilling methods share. If you’re able to answer these three fundamental questions about the particular drilling technology then you clearly understand it and are able to determine whether or not it’s suitable for a particular job site. The three questions are:
How do you physically cut through the soil? If you’re digging in your backyard, the method of penetration is putting weight on the spade of the shovel to cut into the dirt. Of course, with environmental and geotechnical drilling, the method of penetration is typically much more sophisticated than a shovel.
Sticking with our shovel example, the dirt in that hole is removed a shovel-full at a time and set aside. Each drilling method has a specific way of removing cuttings from the boring, and that’s one of the main aspects that differentiates one drilling method from another in terms of applicability.
In our backyard hole, you’re relying on the natural confidence of the formation to keep that hole open. If you’re drilling a 300 feet deep hole that's 8 inches wide, you’re likely going to need another method of keeping that hole open. Methods of stabilization vary by drilling technology.
These are the three fundamental characteristics of almost all drilling methods, and these questions are the primary means of determining a particular drilling method for a given site.
An important note to make, and perhaps the #1 takeaway of our Drilling 101 webinar is the fact that the drilling method is independent of the rig or platform. By that we mean that different rigs are capable of different methods, and conversely different methods can be deployed on multiple platforms.
As drillers we do this often; we refer to a rig by its particular method, but that’s not technically right. For the purpose properly understanding the various drilling methods and technologies, it’s important to distinguish between method and rig or platform.
Let’s see how a method like Direct Push lines up with our three fundamental questions.
Directly pushing casing into the ground. A flush threaded casing is pushed with a static weight or a percussion hammer down into the soil.
Direct Push is distinct from other drilling methods in that cuttings are not brought to the surface. They are still displaced as the casing is pushed downward, the cuttings are pushed outward into the walls of the boring. This is one of the drawbacks to Direct Push, because if that soil can’t be displaced you get a refusal.
The hole is stabilized by the flush threaded casing that’s pushed into the borehole.
Direct Push is very economical and versatile in shallow, unconsolidated geology. You can attach a variety of different tools to the end of the lead rod in the drill string for a number of different applications. The limitation, of course, is that it’s very susceptible to early refusal. i.e. when the cuttings cannot be displaced the drill will simply not move and the deeper you drill, the greater the friction on the outside of the drill becomes.
The benefits and limitations of the Direct Push Method are obviously important things to consider when determining if it’s a suitable method for the particular task. You’re only able to understand those benefits and limitations if you first understand the three primary factors of penetration, removing cuttings, and stabilizing the boring. The Direct Push method is highly versatile and capable of completing a number of objectives, but for other applications and job sites you’ll need to rely on different drilling methods and technologies. Drilling Expert Jacob Gallagher breaks down a dozen of the various technologies and their applications - far too many to cover in this post - in the webinar. If you’re interested in these applications and methods, feel free to check out the recorded webinar.