November 1, 2008Drilling fluids have been described as a project’s lifeblood, comparing them to the blood that circulates through a human body. Ask the drilling fluid specialists and they’ll tell you how critical drilling fluids are to having a successful HDD project, with their proper usage resulting in cost-effectiveness and efficiency.
But while most HDD contractors agree with that assessment, many don’t always engage in or regularly practice the most basic elements of a proper drilling fluid program. They don’t have time, they forget or fill-in-the-blank as to why they choose to skip over a few easy steps to get the right fluid mix. It happens everyday and it drives drilling fluid specialists crazy, as these same contractors will dial them up to find out why they’re having a problem with their fluids.
Trenchless Technology checked in with a couple of top drilling fluid manufacturers on what shortcuts, mistakes or things that are overlooked by today’s contractors when preparing and using drilling fluids on the job. They describe the items most commonly ignored as “pretty basic” stuff that take only a few minutes to do but in the end can save a contractor from a big ol’ headache — in terms of time and money.
Rick Zavitz, a technical sales engineer with Wyo-Ben Inc., Billings, Mont., has worked in the HDD industry — specifically the drilling fluids segment — for 15 years. When asked to put together a litany of contractor sins when it comes to drilling fluid use and preparation, he practically had a list ready to go. The same goes for Randy Peterson, a senior HDD account manager for M-I SWACO, Houston. Peterson has been involved in the HDD industry for more than 20 years.
Their lists touched on several key areas: measuring viscosity, knowing the water source and fluid in the hole.
“I’ve seen a lot of mistakes over the years by contractors but I’ve also seen a lot of growth in their knowledge,” Zavitz says. “When the HDD market had that big boom [in the late 1990s] with the fiber market, that was a huge teaching cycle for us. Those who made it began to understand the need for all the things we were teaching them. And now we’re having more people come into the market and that’s a whole new audience that we need to work with. And they have a pretty steep learning curve.”
One facet of mud that contractors either ignore or just don’t realize is that not all water is the same when they are mixing their mud. The fact is all water sources are not created equal and that variability routinely affects how well the drilling fluid will work for the contractor.
“Drilling mud is 96 percent water and [water] has a significant impact on your fluid. So whether you are getting it from a hydrant, a pond or a lake, all water is different,” Zavitz says. “You need to understand your water.”
By understanding your water, he is referring to its makeup. Peterson explains that contractors must test the water for its pH levels to make sure it is high enough to produce an effective drilling fluid mix. “The most common thing overlooked by a contractor is the makeup of the water,” he says. “They think all water is the same and nobody tests it. And with anybody’s fluids, it can make as much as a 50 percent difference in how well it works and how you use it.”
Testing the water is a pretty simple step and is just like testing the water in your swimming pool, typically with pH strips. By finding out the pH level of the water, contractors can determine how much soda ash to add to raise that pH to the desired level and then the proper amount of bentonite, which will yield a better product. So instead of mixing three bags of bentonite, you may only need two.
As to why some contractors don’t test the water source, reasons vary. “I assume that one reason contractors don’t test the water is that they weren’t trained to do it,” Peterson says. “Another reason is that they just forget.”
Peterson equates not testing the water source to how often people check the air in their car’s tires. “Tires will last 20 to 30 percent longer and you get 10 to 15 percent better mileage just by having your air pressure where it’s supposed to be. Yet nobody does it [regularly],” he says. “It’s the same with the makeup water.”
Maintaining the proper viscosity allows the drilling fluid to effectively suspend solids and support the borehole. Before starting a bore, the contractor should always check the marsh funnel calibration. By checking the mud’s viscosity, the contractor can adjust the viscosity by adding bentonite to address the drilling day’s soil conditions. Sounds simple enough, except that many contractors don’t always use a proper marsh cup and funnel.
The marsh funnel is a field device for indicating viscosity of the drilling fluid that literally takes a few minutes of the contractor’s time and effort. Also needed is a graduated container (measuring cup) to receive the fluid as it flows out of the funnel, a means to measure elapsed time (a stopwatch) and a thermometer for measuring the temperature of the sample.
Zavitz says some HDD contractors, mostly newer, inexperienced ones, tend to use the marsh funnel for things other than testing the viscosity. Often they cut off [the end] of the funnel and use it for other things, such as hydraulic fluid, or they will use the cup for polymer additions. Or more often, they just don’t properly clean the funnel after using it, causing its small oriphus to get even smaller, affecting the viscosity results.
“So when they test their mud and they look at it, they think maybe it’s a lot thicker than it really is,” Zavitz says. “So after you use it, throw it in a bucket of clean water.”
Zavitz further notes that it’s not just the newer guys making missteps with the funnel. There are HDD contractors who have been in the industry and still make the mistake of not using the cup and funnel at all, trusting that their years of experience in the field will tell their eyes what they are seeing. “They think they can just look at the mud and know what its viscosity is. It doesn’t work that way,” Zavitz says.
He adds that the purpose of the cup and funnel is to help contractors prepare their drilling fluids for the soil conditions they are drilling in that particular day and that’s why it should be used every time. “And that’s a mistake that we see made, especially with new contractors: They’ll use the same fluid mix day in and day out,” Zavitz says. “They gain confidence because it’s worked for them but they either change a water source or change the drilling conditions, meaning they go from clays to sands or cobbles. And that dramatically changes the way they need to drill.”
Filling that Hole
Peterson says another mistake many contractors make is that they don’t use enough drilling fluid to fill their hole. “Honestly, this is probably the one thing that affects their efficiency the most. Very few people fill the hole,” he says.
Using a 10-in. hole as an example, Peterson says the way you figure out the volume for that hole is to take 10 times itself and then divide it by 24.52, giving you how many gallons per foot of soil you have and how much fluid you need. Peterson says you’ll never need less than that amount. “In most cases, you need considerably more, up to five times more. But never less than that,” he says.
“And nobody, I repeat nobody, makes a big deal to fill that hole,” he notes. “Even experienced contractors will turn the pump on until they see the flow and when they see flow, they think they have enough.”
Zavitz concurs that not using enough fluid is a common mistake or concerted effort to have less fluid to clean up and dispose of afterward. “Pumping enough fluid is a problem. Usually they pump way too little,” he says. “But they need to find a balance so they still pump enough mud to be able to remove enough cuttings from the hole and prevent any problems with the hole itself.”
Mud schools are a great way for contractors to learn the basics of drilling fluids and the science behind why they are asked to handle the fluid process in a certain way. Drilling fluid manufacturers typically have formal mud schools each year to educate contractors, as well as informal ones with individual contractors to train. Contractors need to take advantage of them, Zavitz and Peterson say.
“They should talk to the person who is supplying their mud. They need to ask questions and educate themselves,” Zavitz says. “If they have the right information, they can make an informed decision.”
Sharon M. Bueno is managing editor of Trenchless Technology.