Many horizontal directional drill (HDD) operators have heard a story or two about someone completing a massive bore while drilling dry or using only water. Those stories may be true, but there can be many drawbacks to boring this way. Drilling dry or using water alone can slow drilling production, put a bore at risk of failure and lead to premature tooling wear.
Drilling fluid or mud is a crucial ingredient to maximise an HDD crew's efficiency and should be used whenever possible. It helps provide lubrication and cools downhole tooling and electronics, helps maintain the integrity of the bore path and flushes drill cuttings. Here is an overview of a few of the issues you may encounter without using mud.
"In ideal ground conditions, performing short, small-diameter bores without any fluid is possible," says Tod Michael, product manager for the trenchless core products at Vermeer. "However, even in these conditions, drilling dry will typically require rotation speeds and production rates to slow. There is also a lot more friction downhole, which can cause tooling to heat up. The extra heat can potentially damage the drill head and sonde."
Over time, the lack of drilling fluid can lead to premature wear to the drilling head and drill pipe. It can also put unnecessary strain on the product being pulled back. "Just using a little bit of drilling fluid in ideal ground conditions can go a long way to help keep up production rates and help contractors maximise the life of their tooling," adds Michael.
Probably more common than drilling dry, contractors will skip using bentonite or polymer and only run water through the drill string. Michael says this is a better option than using nothing at all, but there can be risks involved with this approach. "Crews doing just a pilot bore and then pulling back small-diameter product can get by with this in loamy clay soils since those situations are a lot more forgiving," he explains. "However, using drilling fluid with the right additive can help limit the risk of the hole collapsing."
Water offers very little lubrication, which means there is more drag and friction on drill rods and the drill head. "Adding some type of additive to the water will help reduce the risk of premature tooling wear," Michael says.
Also, water lacks the viscosity to maintain hole integrity or float drill cuttings out of the hole.
Mix it up
There are numerous benefits to using drilling fluid with every bore, but to get the maximum benefit from the additives, it should be adequately mixed. "Whether contractors are buying bags of bentonite or have made the switch to liquid drilling additives in pouches, using a mixing system is crucial," says Michael. "With powders, you can see if an additive hasn't been properly mixed. However, with the newest pre-packaged liquid concentrate additives, sometimes people think they can pour it into the water tank with minimal stirring. Proper mixing and testing of your fluids should still be done for the best results."
To help with the mixing process, Vermeer offers several mix systems, appropriately sized for the directional drill a crew is running. The latest addition to the line is the Vermeer MX300 mixing system, which features a redesigned, slim rectangular profile tank and a power unit that can be paired with up to two tanks at one time to help decrease the time spent refilling fluid tanks.
How much fluid?
The estimating process should include evaluating ground conditions at the job site, the type of drilling additives you will need, and the volume of fluid required for the project.
Ground conditions dictate the drilling additives you will need, and the amount of fluid required. In sand or cobble, you will likely only need a mixture of bentonite. In reactive clay, you will probably have to use a polymer additive. Keep in mind that harder rock usually requires more fluid per bore distance.
Calculating the cost and the amount of additives and water you will require ahead of time will not only ensure you are tracking the expenses on the project but will also help determine what equipment will be needed on the job.
Once you know how much fluid is needed, the next thing to determine is how to correctly dispose of the spoils afterwards.
To begin, you must research all local regulations about disposing of drilling fluids. Today, many projects require HDD fluids to be disposed of at licensed facilities, and the costs associated with dumping can vary greatly. You will want to look into where these sites are located and estimate how much you will have to pay to use them.
But do not forget, the disposal costs are not your only expense. You also have to estimate the distance between the job site and disposal facility, as well as the fuel and labour costs involved in making the round-trip. These expenses are easy to overlook.
Additional disposal options
After adding up your fluid and disposal costs, it is time to evaluate equipment options that may provide an opportunity to reduce out-of-pocket expenditures. For projects that require large volumes of fluid, bringing in a reclaimer like the Vermeer R250C can help reduce the amount of fluid and additives used by removing solids and recycling fluids.
Solidification systems like the Vermeer MUD Hub are another option to consider for projects that have high disposal fees. Solidifying used drilling fluids can give you more disposal options. Many drilling spoils will now be able to be disposed of at a regular landfill, used for ground cover or added to composting mixes. Also, since the waste is now a solid, it can be hauled in a dumpster or dump truck, which helps keep your vacs off the road and on the job.
Finally, it is important to document your disposal process and location for your customer. Many utility companies require fluid disposal documentation, but even if your customers do not, having a paper trail can help protect your business if someone has questions in the future.
Kayla Breja is the senior product marketing specialist - Utility and Productivity Tools with Vermeer Corporation, Pella, Iowa