Understanding Drilling Fluids Solids Control with Horizontal Directional Drilling Rigs

By Denise Sullivan
Published: May 9, 2019 | Last updated: July 5, 2023
Key Takeaways

Through the use of proper solid management devices, workers can lengthen the life of horizontal directional drilling fluid.

Controlling solids in the horizontal directional drilling is an integral part of equipment maintenance. Project managers knew that disposal of the drilling fluid is both hazardous to the environment and costly when disposed of properly.

However, using useful solid control equipment, the drilling fluid life can be doubled if not tripled, saving the environment and cutting costs.

Environmental Issues Associated with Solids Management

Drilling fluid disposal is a hot button topic with many environmentalists. The mud, as is known, is hazardous to the environment. Lubricants containing oil and grease have heavy metals and organics. Water and oil-based muds have heavy metals, inorganic salts, hydrocarbons, and biocides. (Read Mixing the Mud: The Science of Drilling Fluid in HDD.)

If workers mishandle these fluids, they can have an adverse effect to the surrounding environment. Not only do they have the potential to contaminate water supplies and surrounding soil they can also damage vegetation and cause illness and injury to wildlife and the human population of the area.

Stringent environmental regulations make it difficult to dispose of used mud. While onshore drilling operations have a much more extensive array of waste management options, offshore drilling face greater limitations, their sites have limited space for such a process, and they must haul used fluid to an onshore reclamation facility for proper processing.

By using solids control equipment to filter out bigger cuttings from the mud before it reenters the pit, the chances for environmental impact diminish.

Understanding Particle Size in Horizontal Directional Drilling

As the horizontal drilling bit bores into the ground, it uses a drilling fluid mixture to keep the bit and rod lubricated and cooled. (Read A Complete Guide to the Usage and History of Drill Bits and Tooling.)

While there are some solid particles naturally occurring in the mud, the blowback from the drill head is the most problematic contaminants in the mixture. If not properly removed, the waste can reduce the effectivity of the lubricant causing the bit and rod to overheat or fail. Heavily soiled mud must be replaced causing added expense and disposal issues.

Solids naturally found in the mud has a relative size of less than a micron. The debris from drilling will vary based on drill speed, amount of push/pull force on the bit, and the type of dirt being cut. However, most cuttings are around 440 microns or larger. Sand particles run between 74 and 440 microns. Silt has a particle size of 2 to 74 microns. Clay particles range from 0.5 to 2 microns, and colloids have a diameter of 0.5 microns or less.

Effective Control of Solids During Directional Drilling

To effectively control solids during drilling, workers need solid extracting equipment working alongside the horizontal directional drill. For the best solids control, companies need to employ multiple pieces of solid removing equipment to work together to eliminate as many solids as possible.

Shale Shakers with Screens

The first line of defense for any horizontal directional drill is the shale shaker with appropriate screens. As the name implies, this piece of equipment works by passing the mud over the top of the vibrating screen. The liquid mud and particles smaller than the mesh pass through the filter and back into the system. Solid pieces too large for the mesh are trapped on top of the shaker screen, separated for disposal.

Shale shaker screens are multilayered woven wire screen cloths. They come in a variety of screen opening sizes for various projects. It is important to remember it is the screen opening size, not the mesh count which dictates the size of the particles separated from the mud. Workers should consult the American Petroleum Institute’s API 13C RP designations to choose the right mesh.

Centrifugal Pumps

An excellent way to control solids is using a centrifugal pump. This pump has a dual purpose of mixing the mud pumped into the borehole and feeding the volume and pressure to hydrocyclones for operation.


Hydrocyclones are simple devices that help to speed up the settling process of solids suspended in the drilling fluid. These machines have no moving parts and work with centrifugal pumps to achieve the centrifugal force necessary to separate the heavier solids from the liquid components.

With the addition of a centrifugal pump, the feed pressure within the hydrocyclone transforms into a centrifuge within the cone of the equipment. The velocity of the centrifuge causes finer, lighter solids to separate with the liquid and discharge upward through the liquid outlet. More significant, heavier solids release downward through the solid outlet.

Controlling solids in the drilling fluid mixture helps to keep the horizontal directional drill running smoothly and lengthens the life of the fluid. It reduces the environmental impact while saving excessive disposal costs during the project.

It is essential to use a solids control system composed of multiple pieces of separating equipment. The removal set up should be able to handle anywhere from 100%-125% of all drilling fluid to be most effective during the process.

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Written by Denise Sullivan | Technical Writer @ Trenchlesspedia

Denise Sullivan

Denise Sullivan is an accomplished freelance writer from Louisiana, with a Associate's Degree in Journalism from Eastern Oklahoma State College. She also graduated from East Central University with a Bachelor's in Biology. Denise began her writing career writing operations and maintenance manuals and software utility manuals for flight simulators. Since, she has expanded her writing to a broad spectrum of topics.

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