What Is Rotary Drilling And How Does It Work?

by | Jul 17, 2020

One of the many geotechnical drilling services we offer here at Borehole Solutions is rotary drilling. This commonly used method of drilling suits many different types of project, both small and large. The team here at Borehole wanted to look at the process in more detail – which, it’s worth noting, this method dates back as far as 3,000 years ago! – and examine where and when it’s used, and some of the different types of rotary. Because as you’ll see, it isn’t a one-size-fits-all kind of drilling!

 

The Process

Rotary drilling rigs utilise high levels of torque and rotation, with a drill bit at the end of the drill pipe rapidly rotating (between 50 and 120rpm) and boring through the rock formation. The drill bit tends to come in two primary forms: firstly, roller-cone bits, and secondly, fixed cutter bits. Both drill bits see similarly high levels of use within the drilling industry. Fixed cutter bits are also commonly referred to as PDC bits (polycrystalline diamond compact bits – though there are other common types of fixed cutter bits, PDC are amongst the most prevalent).

The high frequency and speed of rotations make this form of drilling an effective means of carving through both hard and soft rock formations, alike. This form of drilling uses either air or drilling fluids to clear out the borehole, cool the drill bit and generally reduce friction on the bit, so that it can continue to run optimally.

 

What Rock Formations Does Rotary Drilling Suit?

This form of drilling can be used in a broad range of geological formations, deeper boreholes suit rotary drilling using air, whilst ‘mud’ rotary lends itself to unconsolidated, less stable formations (these include sand and gravel formations); mud rotary is where an additive is added to the drilling fluid which subsequently coats the borehole’s sides to help keep it supported. This drilling method can drill down to depths of thousands of metres, and is often used in a mining or quarrying setting, however it is just as useful in more conventional geotechnical settings, as well. Rotary drilling, for instance, can be configured so as to provide a high quality of core recovery for analysis.

 

Benefits And Limitations

 

Benefits

As with any type of drilling, rotary drilling has its positives and its drawbacks. Some of its benefits include:

  • Rotary drilling is fast. In fact, it’s several times quicker than other conventional drilling methods. At the same time, it manages to deliver high-integrity results as it does so.
  • Rig flexibility. These rigs are a geotechnical company’s dream; their ease of setup (and subsequent dismount) make them easy to transport and use all over the country, wherever they’re needed.
  • It’s incredibly dependable. This is a tried and tested means of drilling, that has been refined over time. Drilling companies such as Borehole Solutions have now got it down to a fine tee!

Limitations

By the same token, however, rotary isn’t perfect. Or rather, no one form of rotary drilling is perfect. As we’ve established, there are several kinds of rotary drilling like air and mud; there are also other options, such as dual rotary and reverse circulation. In other words, whilst one form of rotary may not be right for one situation, it’s more than likely that a different form of rotary drilling could complete the job to a high standard. For example, if cross-contamination is an issue from drilling fluids or mud, then air rotary solves that issue. Likewise, if you’re worried about the borehole’s integrity, then mud rotary is the solution. In this way, then, we see that rotary drilling is an immensely versatile drilling methodology.

This form of drilling is undoubtedly one of the most effective forms of drilling out there. So, if you’d like to find out more about our various drilling services, then get in touch! Contact Borehole Solutions today on 01733 200 501. Whatever the size of the job at hand, the team at Borehole will have you covered.