Talking mud, from mixing to disposal

Mud, or drilling fluid, can have an impact on your company. From selecting the right additives to choosing the right volume of fluid to pump to determining the most efficient way to dispose of the used slurry, managing mud is a skill that horizontal directional drilling (HDD) crews need to understand.

Mud is key to making an HDD crew work more efficiently. It provides coolant for downhole electronics (sonde), suspends and displaces cuttings, reduces wear on tooling and aids with stability by reinforcing and maintaining the walls of the borehole. However, to do all of that, contractors and their crews need to understand the art and science behind using mud. 

Start with the right additives

Bentonite is the staple drill additive for almost every HDD crew. While many bores can be completed with just bentonite alone, there are certain soil conditions where other drilling fluid additives can be helpful. 

• Working in nonreactive clay? Start with bentonite for primary filtration control. Users may also need to add soap or detergent to keep downhole tooling clean. 

• Working in reactive clay? Bentonite should be used for primary filtration control with a PAC polymer for secondary control. If there are concerns about the clay swelling, a PHPA polymer can also be used. Drillers may also want to use a soap/detergent to prevent clay from sticking to your tooling. 

• Working in sand? Again, bentonite is an excellent primary filtration control agent, but a PAC polymer and/or a larger-molecular-weight polymer can also help with suspension.

• Working in rock or fractured rock? Bentonite may be all that's needed, but if cuttings aren't making their way out of the drill hole, the crew may want to use a larger-molecular-weight polymer to aid with suspension. A secondary filtration control additive like a PAC polymer may also help.

Bagged versus premix additives

In recent years, liquid premixed drilling additives have found their way into the HDD industry. Drilling additive manufacturers have made mixing mud more convenient with premixed drilling additives for a wide range of soil conditions. These new liquid additives are giving HDD crews even more options to consider. 

Fluid needs

In addition to making sure the right additives are being used, and that they are being thoroughly mixed to the appropriate viscosity, drillers need to make sure they are pumping the optimum amount of fluid through the drill string to maintain hole integrity and flush cuttings. 

Soil conditions, hole diameter and distance are all factors in how much fluid the driller should be pumping. 

The critical thing to remember is ensuring the drill operator is seeing returns that are in line with what's being pumped into the hole. If the crew isn't seeing the level of returns it should be, it could be the result of cuttings not being flushed from the hole, which can lead to inadvertent returns or cause downhole tooling to become stuck.

On the subject of inadvertent returns or frac-outs, it's essential for HDD crews to understand their causes. A common misconception in the industry is that inadvertent returns are caused by using too much mud, but that is not always the case.

When crews try to use less mud, cuttings don't get flushed from the hole, which causes the material to build up around the drill string. As this pressure builds, the liquid material forces its way out through the path of least resistance, and that way is usually up to the surface. 

Inadvertent returns can also be the result of dry soil conditions at shallow bore depths or the result of using the wrong kind of drilling fluid additives.

Slurry disposal and management

With the rising costs of water, additives and disposal fees, contractors need to determine the most cost-effective methods of handling used drill slurry. 

For utility crews performing small diameter bores, using a vac system to suction the drilling slurry and then hauling it off to an approved disposal site is standard practice. However, depending on where crews are working in proximity to the closest disposal station, it can be a significant out-of-pocket expense and affect production rates. Vacs stuck in traffic or having to travel long distances can bog down drilling operations. Also, if there are several crews working in the same area, travel times and disposal costs can multiply quickly. 

If crews find themselves in this type of situation, contractors may want to visit with their equipment dealer about the possibility of solidifying used drill slurry. By solidifying the slurry, it can then be stacked into a roll-off dumpster or the back of a truck, a method that can offer more dump site options, including a regular landfill. Vermeer has developed the MUD Hub solidification system to aid with this process. 

If a drilling operator is using large volumes of fluids and additives on longer bores or in challenging ground conditions, it may be time for a reclaimer – they aren't just for use with maxi rigs. Using a reclaimer like the Vermeer R250C modular mud reclaimer can help reduce water and additive usage, and afterward the reclaimed material can be disposed of using one of the ways outlined above. 

As you can see, from mixing to disposal, there are many factors involved with drilling fluid. If contractors are in need of advice, they may benefit from a discussion with Vermeer dealers to help understand the latest in mud management.