During the horizontal directional drilling boom in the 1990s, most of the drilling fluid that existed was meant for vertical applications. As such, drillers and contractors didn't see the need for anything besides water. Some of the old-schoolers among us might still be apprehensive to use modern HDD drilling fluid, thinking of it as overly complex — and expensive. However, most tend to come around after seeing the kind of results it can bring to the jobsite. Whether you're a skeptic, a recent convert or a true believer, you may still have some questions about HDD drilling fluids, so we're here to offer a little guidance in this high-level overview.

What Is Drilling Fluid?

Drilling fluid, also commonly called "mud" or "slurry," is a mixture of water and additives that is used to make the horizontal directional drilling process easier. The most common additives, which usually only account for around 3% of the mixture, are bentonite and polymer — sometimes a combination of the two, depending on the ground conditions. Bentonite is a type of clay that can be ground, refined and mixed with water to make a mud-like fluid used in the drilling process, hence the term "mud." Proper HDD drilling fluid must be mixed correctly for the type of soil a bore will encounter.

How Does It Work?

A mud system delivers drilling fluid to the drill itself. For smaller rigs, the system may be attached, while larger drills often require standalone pumps. During operation, drilling fluid ensures downhole stability, cools and lubricates tooling and extracts cuttings and other particles from the borehole.

Why Do You Need Drilling Fluid for HDD?

To be frank, whether or not to use drilling fluid shouldn't even be a question at this point — it is an essential part of the jobsite. However, a lot of contractors still grapple with it due to the added costs and perceived annoyances. Some may even try to get by using only water, but simple water will not:

  • Stabilize and seal the borehole
  • Suspend cuttings and clear them out of the hole
  • Protect the drill pipe
  • Cool and lubricate all the downhole tooling

Drilling fluid does all of this, provided it's mixed correctly. Without it, you risk having cuttings and other materials that the bit removed blocking the bore path, which could stall the entire operation. Additionally, anytime you drill into the ground, it creates a ton of excess heat. That heat can damage any pipe you're installing, as well as your tooling. If the heat harms any electronic components, your locating system may not function properly. What does all of this add up to? Higher costs, whether from downtime or replacement parts.

Using mud reduces the torque required for drilling while stabilizing the borehole and cooling the tooling. With the right gel strength, drilling fluid will keep the path clear and speed up your job. Another factor to consider: water alone can have a negative reaction with certain ground conditions. In particular, water makes clay and sand well up, which can lead to a sticky situation for your tooling. The right additives in your drilling fluid will keep that from happening and make your operation run much smoother.

How to Mix the Best HDD Drilling Fluids

As we mentioned, bentonite and polymer are the most common additives to use in drilling fluid, with xanthan gum sometimes being used for added gel strength to aid in suspension. The most important factor to consider is the ground condition for your job, whether the soil is cohesive (structured) or non-cohesive (loose).

A bentonite base is generally the best choice, but cohesive soils like clay and shale may require polymer additives (such as PHPA) to prevent swelling. After all, bentonite is clay, so adding more of it to clayey soil isn't going to help matters much. We all know that backreaming in clay can be difficult, but quality HDD drilling fluids can make the process a bit easier. On the other hand, adding more bentonite to the mix is good for non-cohesive soils like sand and gravel, providing added stability.

The other factor to consider is the water you'll be using for your drilling fluid, particularly its pH level and calcium content. If your water's calcium content is over 100 parts per million, it's probably "hard water," which could prevent your additives from doing their job. Likewise, your pH level should be around 9 on the pH scale for effective drilling fluid, but you can use soda ash to alter it if necessary. Also, the ground conditions may require further changes related to:

  • Viscosity
  • Density
  • Gel strength (for suspension)

Unfortunately, while there may be some guidelines for getting the right mix, a lot of it comes down to trial and error.

General Drilling Fluid Guidelines

First of all, the biggest thing to stress is that there is no catch-all drilling fluid that is perfect for every job. And, there isn't one right answer to every problem you'll run into. Drillers and contractors who don't have a lot of experience with HDD drilling fluids will have to work out a lot of the kinks over time — or, better yet, rely on someone who is already an expert. That's why a lot of people recommend having a dedicated expert on-site at all times, sometimes called a "Mud Man." While it would require adding another person to the crew, you'll be able to avoid a lot of the pitfalls that happen with drilling fluid.

Some other factors to keep in mind:

  • Use plenty of drilling fluid.
  • Keep an eye on the mud to ensure that it's doing its job and circulating through the borehole — if not, don't overuse it.
  • You may need to have a small pit for catching any extra drilling fluid.
  • HDD drilling fluids are not hazardous by nature, but they may mix with pollutants in the ground during operation — always be aware of any laws and requirements regarding proper disposal.

Common Mistakes for Drillers and Contractors

There are a lot of potential problems your team can run into when it comes to drilling fluid. The biggest mistakes that contractors make are usually the result of attempted cost-cutting. Notably, never underestimate how much drilling fluid you need, or the amount of additives you need for the formula. Get an expert opinion on the ground conditions and the amount of drilling fluid necessary to work under those conditions. Also, keep in mind that conditions can change even after drilling begins — yet another reason a dedicated Mud Man is a good idea. However, having an expert train your crew can help them prepare for this situation, too. Making a bad call about your drilling fluid before the job starts can lead to damage — and inflated expenses — later on. Let's face it: cutting corners is never a good idea for HDD.

Are There Any Good Methods for Lowering Costs on Drilling Fluid?

Some contractors have taken to recycling their drilling fluid to lower costs. This is a legitimate way to save on resources and improve your return on investment. However, you'll need a proper recycling system to do this, and it works best when the fluid has been used in sand or gravel. To do it right, you'll need to do some research and, as always, consult with a drilling fluid expert.

The Right Drilling Fluid Goes Best with The Right Tooling

Determining your drilling fluid needs is as important as having the proper tooling for the job. Luckily, you can find everything you need at Melfred Borzall. We have a directional blade and bit selection that covers every ground condition, along with plenty of other options to help your crew do their best work. If you have some questions about HDD drilling fluids, contact us today — we'll point you in the right direction.