Fluids are the lifeblood of any drilling operation. Horizontal directional drilling is no exception. To find out more about the methods used byHDDcontractors, and some of the challenges they face with disposal and recycling, we spoke with Seth Matthesen, senior product manager for HDD with Ditch Witch. Our conversation here has been edited for clarity and space.

Q. We all hear stories of drillers who swear by water as an all-purpose drilling fluid. Is this kind of thinking going away?

A. There are many parts of the world still utilizing water with no additives and having success. But we’re seeing more and more customers understand the benefits of using drilling fluids, whether it’s to get longer life on the tooling or as kind of as an insurance policy to make sure they mitigate downhole risk. That one time out of 100 bores that you get stuck ends up costing you quite a bit of money. I wouldn’t say it’s going away, but we’re seeing customers utilize drilling fluids more and more.

Q. HDD is a slightly different type of drilling from more conventional vertical bores. Are there fluid use and management differences that someone working in, for example, water wells or geothermal might not be aware of?

A. What we do teach in our schools, when you’re drilling horizontally, your drill path or your borehole is typically not very tall. So, materials settling out, your cuttings settling out, happens much quicker in that borehole than it would in a borehole that’s, say, 100 feet deep. Your drilling fluids are really buying you time. … Even if we’re not going very deep, you still encounter many different types of soil on a single bore path. Knowing what type of fluids to use for the worst case scenario [is critical] — for instance, if I’m drilling in clay and sand, you want to mix mud primarily for the sand, because there’s much more risk in the sand than there is in clay.

Q. In your experience, what types of fluid management issues do HDD drillers typically struggle with?

A. From a fluid management standpoint, you have a couple different things. One is, what’s the proper material to use, and how much to use? The second is the disposal of the material. Once that material comes out of the hole, now we’ve got to do something with it.

Q. What is the key to maintaining steady circulation?

A. I always use the two Qs: quality of the product you’re putting in the ground, and the quantity. If you have the right mud mix, but you’re not putting enough downhole, you’re basically just wetting the material and it’s not flowable, it’s not movable. You want it to be thinner than a milkshake, so when it comes up out of the ground it can move. If the returns are too thick it will take more downhole pressure and velocity to return to the surface. What you’re looking for is to get a fluid material, a flowable material, so you can get those cuttings out of the borehole with the least amount of pressure needed. Otherwise the drilling fluid will take a different path.

Q. When it comes to fluids recycling, is there any difference between bentonite-based fluids and polymer-based fluids?

A. Any time you use a screen in your cleaning system, your screen can be blinded by either clay or polymers. There are definitely many types of long-chain polymers you cannot use in recycling. Typically, long-chain polymers are utilized in more clay materials, because it wraps itself around the clay and keeps it from packing back together. It keeps it separate. Those are typically not needed in most of the situations where you’re utilizing a recycling system. You can do some things to have a drilling fluid where you can still recycle in a clay material, but it does have effects on recyclers.

Q. Are there types of jobsites where fluid recycling and reuse are more necessary, or even required?

A. Any jobsite where you’re using more fluid. Definitely in rock, because in rock you have to have a certain amount of fluid to keep everything cool and clean, and get the material out of the bore path. In those instances, whenever you’re utilizing quite a bit of mud with not a lot of penetration rate, or a large backream. That’s where you really see the benefits of using a recycling system.

What I’ve been telling a lot of contractors — and this kind of dives into a later question — if you’re having to vac and dispose of more than one tank of mud a day, there’s a potential need for a recycling where you can see a cost benefit.

Q. Talk a little bit about your MR90 Mud Recycler system. What are a few highlights of this system?

A. We introduced it last fall. We sent out surveys and asked customers, what are some of the pains that they see on their jobsite from either a cost standpoint or just a labor intensive standpoint? It would always come back that managing and disposing of drilling fluids was always a jobsite cost that they wanted to manage better.

The smaller recycling systems really weren’t out on the market yet. Knowing that our customers were needing to utilize this method on some jobsites — and the largest market in the HDD industry is that 20,000- to 60,000-pound machine, as far as quantity and units — so there was a need.

A lot of the reason that recycling systems weren’t used in this size class in the past was, one, it was labor intensive to set it up. So it would be a half day to set up a large recycling system. And then once they utilized the recycling systems, a lot of them were made for different types of pumps. The smaller the pump the more susceptible it can be to sand content and things like that. It’s the difference between a continuous duty mud pump and a standard duty mud pump. … So there was a need to make sure we had an ultra-fine cleaning system.

What we’ve done with the MR90 is we’ve made a system that goes on a trailer. … It can be hauled full of water. A lot of the other larger recycling systems, they’re placed at the jobsite and then water has to be brought to the jobsite for it.

It is a hydraulic system, so the entire system can be hydraulically leveled. The shaker screens are hydraulically leveled fore and aft and the trailer has a hydraulic jack stand. The other thing is, we’re using six 2.5-inch hydrocyclones. So we’re keeping our sand content under a quarter percent. That’s key. When you mix mud, you’re actually taking sand that’s in every bag of bentonite — you’re taking that sand out of. So it’s cleaner than what’s in normal mixing tanks. … Now, that has to be managed. You have to pay attention to your screens and everything else like you would with any other recycling system. But it has the ability to clean it cleaner than what it was before the bentonite was introduced. At that point you just need to focus on your returns management.

Q. How does the MR90 handle spoils?

A. In the rear of the unit, there’s a spoils hopper. Material that’s taken off the screens will fall into a 50-gallon spoils hopper. That spoils hopper also has a paddle in it. So you can either offload it to a vac, [and] there’s also a hydraulic door that opens so you can put it in a skid-steer or a 55-gallon drum. You also have the ability to dry it. The mixer gives you the ability to put a material in there to dry it even more, and then you can actually just return it to the jobsite.

Q. From a cost-benefit standpoint, why should a contractor take the plunge and buy a mud recycler versus, for instance, leasing a unit?

It’s not just hauling the material away and the disposal fee at the dump site. It’s the truck at $75 to $100 an hour. It’s the labor — the person having to drive the truck. It’s the liability for that truck going up and down the road. Those are the things that customers really see. The operator could be doing something else productive on the jobsite.

From a lease standpoint, we have several of these units in rental fleets. Leasing is typically going to be a customer preference, depending on how they have their business set up. We have plenty of customers who like to lease, and we have other customers who would like conventional financing. … The advantage of leasing with a product like this is a customer may not be on a job where he needs to use a recycling system 12 months out of the year. If he’s on a certain job where he can do a short-term lease, that may be a benefit over fully amortizing out the product over a three or four year period.

Q. Who is the ideal customer for the MR90?

A. The ideal customer would be a customer that’s utilizing a 20,000- to 60,000-pound drilling unit that is having to dispose and manage fluids on the jobsite. That creates an additional cost which can be avoided or at least mitigated.

Jeremy Verdusco is editor of National Driller.