Reclaiming Progress

Trenchless technology, which has advanced our infrastructure and brought services such as gas, water and telecommunications to our homes, has come a long way since the early 20th century when underground drilling emerged. When horizontal directional drilling (HDD) gained momentum in the 1990s, productivity increased greatly; however, contractors quickly learned that disposal of used drilling fluid was problematic.

To address the issue, forward-thinking pipeline contractors began developing customized solutions that would separate solids from drilling fluid, and recirculate cleaned fluids back into the drill. By the turn of the millennium, the fiber industry was booming and equipment manufacturers were developing standalone reclaimer systems.

“A reclaimer is standard on all large drill sites and we are seeing significant growth of their use with smaller drills,” says Jon Heinen, pipeline business manager for Vermeer. “The reason for this increase is regulatory and financial considerations for the contractor.”

Vermeer began manufacturing reclaimers in 2010, recognizing their advantages on large pipeline projects. Heinen sees growth in their acceptance, and the image of reclaimers moving away from nice to have to necessity.

“Typically, the reclaimer was set in the corner of the job with one crewmember operating it, but now it’s recognized as an integral part of the HDD installation,” he says.

Also referred to as “mud,” drilling fluid is a critical component of the drilling operation. According to Heinen, there is no universal recipe for drilling fluid. Because different soils react differently, proper drilling fluid mix is more of an art than a science. It takes meticulous calculation and planning to determine the amount of drilling fluid necessary for a drilling project.

“Many bores that fail can be attributed to poor quality fluid mix, but bores also fail for not properly following standard procedures and accepted formulas for fluid-to-soil ratio,” says Heinen.

Reclaimers Becoming Standard Equipment

A reclaimer differs from a mixing system, which only supplies water mixed with drilling fluid additives downhole to aid the drilling process and maintain the integrity of the opened hole. A reclaimer has an on-board mixing system, but the main purpose of the unit is to recycle the used drilling fluid in order to reuse fluid. The reclaimer is a system of hydro-cyclones, shakers and screens — collectively referred to as solids control equipment — that separates solids out of the fluid and recirculates reusable fluid, consisting of bentonite, water and other additives, back into the active fluid system.

“Recycling not only eliminates the need to constantly dump drilling fluid after only one trip in the bore path, it also reduces the amount of make-up water, bentonite and additives outside the volume needed,” says John Cope, pipeline applications engineer for Vermeer. “It lessens the need for extraneous amounts of drilling fluid on hand, concerns over how much fluid is needed and how far out the vacuum needs to reach.”

Used drilling fluid is pumped into the reclaimer from the return pit. The first stage of the reclamation process is the scalping pass, which is achieved by the primary shakers. Scalping shakers receive 100 percent of the flow that is pumped into the system from the return pit. According to Cope, the screen selection for this first stage is critical and has the widest variation of screen mesh size.

“The screen mesh that is needed has several determining factors: flow, classification of solids, solids loading, fluid properties and achievable cake dryness. Scalpers are not meant to remove all the solids from the drilling fluids, just enough of the larger solids so the downstream equipment can work to their utmost efficiency,” he says.

Large reclaimers (400 gpm and larger cleaning capacity) have three tanks and stages of the process: scalping, desanding and desilting. Fluid is transferred to the different stages by centrifuge pumps. Smaller reclaimers (350 gpm cleaning capacity and below) may have only a two-tank system, skipping the desanding stage and transferring the fluid directly into the desilting stage.

The second and third stages — desanding and desilting — are accomplished by feeding the scalped fluid into polyurethane hydro-cyclones (cones) at a predetermined pressure. Once the fluid enters the cones, the fluid starts spinning on the inside wall. As this fluid spins, heavier solids move toward the outside wall and the lighter solids and fluid occupy the middle. The heavier solids feed to the bottom of the cone where they are then deposited on a shaker for further drying and for the extraction of free liquid where possible. Solids are finally conveyed toward the end shakers and sent to a pit or roll-off box for disposal.

The process rates for the cones should be double that of the incoming fluid. This process not only allows the cones to have another chance at extracting any stubborn solids, it dilutes the solids’ loading ratio so the hydrocyclones can work more efficiently. It is only at this point that the drilling fluid is ready to be received back into the drilling process. A pump will send the cleaned fluid to a high pressure pump for another trip down the bore path to extract cuttings and carry them to the surface.

Contractor’s Choice

According to Cope, utilizing a reclaimer is mostly contractor-driven based on the cost to the contractor for fluid disposal; however, he says the industry is seeing more project owners including reclaimers in HDD specifications.

“Ultimately, it’s the project owner’s responsibility for everything that happens to that jobsite, including fluid disposal,” Cope says. “That is where the reclaimer comes into play; because they are getting the spoils down to certain cake dryness that can be more readily disposed of, and any fluids left over at the end of the job.”
Defining the typical HDD project where a reclaimer is necessary is trickier. Cope says there are no set factors that point to the use of a reclaimer, but a contractor needs to take into consideration the cost of fluid disposal, hole diameter, bore length, ground conditions and water source.

Cost of disposal factors include transportation of used fluid. Dumping fees are expensive as well, and many times the contractor needs to mix special additives before disposal.

“General rule of thumb, anywhere from 7,500 to 10,000 gallons of fluid per day is a strong indicator that a reclaimer should be considered and may benefit the contractor,” Cope says.

Cope highly recommends a dedicated person to operate, monitor and maintain the reclaimer, especially for larger bore projects.

“When no one monitors the reclaimer, there is a higher chance of pump contamination due to high sand content and variation in mud properties,” he says. “Also, the drill operator won’t know what their solids loading coming back to the drill is, and if they are running at the most efficient penetration rate.”

With drilling fluid recycling more embraced by project owners and contractors alike, the use of reclaimers is expanding. Heinen says they are seeing contractors using multiple units on the same project — one on the drill side and another on the exit side. As technology helps make reclaimers more efficient and contractors continue to see the benefits of fluid recycling, reclaimers will be viewed as an essential part of your jobsite success.

Dawn Buzynski is senior public relations supervisor at Two Rivers Marketing, Des Moines, Iowa.