Jim Watland has been working in the horizontal directional drilling (HDD) industry for 26 years. But he acknowledges that it wasn’t until several years ago that he realized the importance of drilling fluids.
After “learning the hard way,” as he puts it, drilling mostly with water and occasionally a bit of polymer mixed in, he’s adopted modern drilling fluid practices.
The results are night and day for the 15 HDD crews he oversees as operations manager for Dakota Utility Contractors, a Texas-based company that does utility and pipeline installations in multiple states.
“Compared to 10 years ago, I can take the same size horizontal directional drill and bore an additional 500 ft or an additional 10 in. in diameter because we’ve learned how to utilize the drilling fluid products that are available to us,” he says.
Watland’s experience is not uncommon. Drilling fluids, commonly referred to as “mud,” are underappreciated by some people and can be viewed as complicated.
This probably shouldn’t be a huge surprise. Although HDD has been around for a few decades, it didn’t really
take off as an underground construction technique until around 1990. The drilling fluids being used in HDD applications at that time were designed for vertical drilling. The early 1990s saw the introduction of drilling fluids developed for HDD, but it took some time for them to catch on.
“We underwent a tremendous learning curve during the 1990s,” says drilling fluids expert Frank Canon. “Most contractors were using only water, for example. Through road shows, schools and seminars, contractors started using bentonite and then polymer additives.”
Canon is considered something of a drilling fluid guru after a 40-year career at Baroid Industrial Drilling Products and by building a strong relationship with Vermeer. After retiring in 2015, he formed a consulting company, Frank Canon LLC, and remains active in the HDD industry.
Mud Vital to Successful Boring
Drilling fluids serve multiple purposes during a bore that water alone cannot accomplish, but Canon names three as being most critical:
- Create borehole stability.
- Suspend cuttings, or spoils.
- Carry the cuttings out of the hole.
Watland agrees those are important and says what it translates to for contractors is the protection of drill rods and other downhole tooling. He gives an example: In Texas, his crews bore through clay a lot. Clay reacts to water by swelling, which can cause tooling to get stuck. Additives help prevent that. It’s a similar situation in sand.
“In layman’s terms, we don’t want to get our rods hung up, and we want to get the product pulled back in without it getting hung up,” he says. “So that’s the reason why you have to get those cuttings out.”
Even though it is called mud and it’s the additives in it that get a lot of attention, drilling fluid is primarily water. Canon says drilling fluid usually is no more than 3 or 4 percent additives, typically bentonite, polymer or a combination of the two.
He stresses the importance of testing the calcium content and pH level of the makeup water. Bentonite and polymers are most effective when the pH is between 8.5 and 9.5 on the pH scale. Soda ash can be used to adjust the pH. Calcium affects the hardness of water, and water that is too hard can reduce the effectiveness of additives. Canon says calcium content below 100 parts per million is preferred.
The pH level and hardness are two primary properties of drilling fluid. Others that contractors should be aware of are: viscosity (fluid thickness), density (fluid weight and the solids content), filtration loss and fluid cake (which help create borehole stability), and gel strength (suspension characteristics).
Know Your Mud Needs Before Bidding
Drilling fluid selection and management is critical to the success of a bore, and the process should start even before bidding on a job.
Where will the crew get water? How much drilling fluid will it take to do the job? What are the ground conditions? What are the requirements for mud disposal? How far away is the nearest disposal site? These are just some of the questions a contractor needs to answer before submitting a bid.
The consequences of getting them wrong can be significant. Jon Heinen, commercial business manager for pipeline at Vermeer, says drilling fluids can account for half of an HDD contractor’s expenses on some jobs, and he’s aware of projects where the contractor walked away because mud disposal proved to be too cumbersome.
“Because of the requirements, the job just didn’t make economic sense for their business,” he says. “The dumping station was two hours away. They had to double up on vacuum excavators, and if the vacs are gone, the crew had to wait until the vacs returned to the jobsite.”
Watland says mud disposal is becoming “more painful for all of us HDD contractors to deal with.” It used to be that mud could be spread on a right of way or otherwise disposed of in more convenient ways. Now that’s almost unheard of, and instead contractors have to haul mud to landfills — often specially classified facilities for hazardous waste that are less common. And project owners and the government require manifests, receipts and other documentation to prove drilling fluid was discarded as required.
“It’s my job as operations manager — and I have four managers underneath me who also help — to figure out where we’re going to get water, what we’re going to do with our mud, how we’re going to dispose of it and answers to other questions,” Watland says.
Know the Soil
When it comes to selecting drilling fluid for a project, Canon and Watland agree that the top consideration should be ground conditions.
Canon classifies soil into two groups: cohesive and non-cohesive. Cohesive soils have a structure, with clay and shale being examples. Non-cohesive soils are looser and include sand and gravel.
In both, Canon typically recommends a bentonite base about 90 percent of the time. In cohesive soils, he’ll also look at products that contain polymers referred to as PHPA that inhibit the swelling of clays and shales.
In non-cohesive soils like sand, bentonite is the key additive because it helps form the filter cake that stabilizes the borehole. Another additive, called xanthan gum, can be included to help with suspension.
“By doing that we can come up with a fluid that will give us the borehole stability that we need and the suspension that we need, and a lower viscosity, that will be easier to work with than just using bentonite,” Canon says.
These are just general rules of thumb. What’s important to understand is that there’s no single solution, so contractors need to either rely on their experience or consult an expert — or do both.
“Different ground conditions require different sets of drilling fluid properties,” Canon says. “For this reason, there is not a universal fluid.”
The significance of ground conditions means geotechnical investigations are important. But as HDD contractors know, surprises sometimes occur downhole. Canon recommends treating the pilot bore like a geotechnical investigation of its own. And even once a crew starts drilling, they need to be aware that conditions can change.
Watland says all of his HDD crew members have some level of training on mud management, and the best drill operators can tell when the soil has changed and know that the drilling fluid properties may need to be adjusted. He recalls a job in Houston where the ground switched from clay to sand without warning.
“If the driller hadn’t realized that there had been a change and stopped right then, it could have been somewhat disastrous because they were drilling with a mud motor and they probably would have lost the bottom hole assembly,” he says.
When it comes to estimating the amount of drilling fluid to be used on a project, there are calculations that can help contractors. Some are available in apps for smartphones and tablets. Watland uses an app when submitting bids. But he also leans heavily on his experience.
“Because of my experience, I can pretty much tell about how much water I’m going to need to complete a bore, based on the length and the product we’ll pull back and other factors,” he says.
Canon says the most common mistake he sees when it comes to drilling fluid can be summed up in one word: enough.
“That would be not using enough additive and not pumping enough fluid downhole,” he says.
There’s a temptation sometimes to skimp on additives and the overall drilling fluid to control costs, but as Canon and Watland have made clear, the appropriate use of drilling fluid can be critical to a successful bore.