Horizontal directional drilling (HDD) is now widely used for installing underground utilities without trenching and is a method pipeline contractors vouch for more and more. It has almost become a necessity, especially in areas where surface disturbance has to be avoided due to the presence of structures or environmentally sensitive pockets. Water, gas, communication, fiber optics, and electric lines, all can be conveniently installed using HDD.
Disposing of Used Mud
HDD benefits both the contractor and the people in the vicinity of a project who would otherwise be highly inconvenienced with dug up roads and bottlenecks. However, an HDD contractor’s work does not end once the installation is complete; he has to take care of one of the most important and highly scrutinized aspects of an HDD project—dealing with the used drilling mud, or fluid.
The cost of disposing of drilling fluids is very high and accessing an approved disposal location is even more difficult and expensive. The most viable and economic option for this challenge is mud recycling. (Read also: Why Proper Disposal of Used Drilling Fluid Should Be a Crucial Trenchless Planning Step).
The Importance and Benefits of Mud Recycling
A good mix of drilling fluid is essential for the success of an HDD project. Some projects require huge quantities of drilling mud, especially when drilling large diameter, long-distance bores, and when rocky conditions are encountered. As the drilling fluid returns to the surface, it brings with it soil, sand, and rock cuttings from the bore that need to be separated before the fluid can be reused.
The used HDD drilling fluid can be recycled and reused after removing cuttings, rocks, sand, and fine particles. For one, not recycling fluids especially on a large project will make the logistics of fluid handling unmanageable and costly. According to John Miller, CEO of Mud Technology International (MTI) in Underground Construction: Recycling, even with smaller rigs, reduces the amount of water used, bentonite needed and fluid hauled off; saving time, money, and making a contribution to the protection of our planet.
In brief, mud recycling,
- Reduces the volume of water needed and saves fuel cost as multiple trucks will not be needed to bring in water.
- Reduces costs for trucks and travel time for waste disposal.
- Increases job productivity because the drill stays continuously productive.
- Improves rig uptime by eliminating the need to mix drilling mud when the rig is inactive.
- Reduces risk of inadvertent returns.
- Improves tool life.
- Lowers carbon footprint by reducing emissions.
The Mud Recycling Process
Most mud recycling units are capable of both mixing and recycling mud. The recycling process generally takes place in three steps. The fluid first passes through a shaker screen that removes large solid particles. It then goes through the de-sander cones where sand and finer particles are removed. Finally, a finer shaker screen removes any remaining solids. (Read also: Understanding the Importance of Solids Controls.)
The clean fluid can be reused after adding necessary mud material to gain the right consistency. The recycling process is repeated throughout the life of the project. This process reduces the cost of additives, water transportation, and disposal.
Mud recycling units have to be well maintained to ensure that the recycled mud is sufficiently processed to ensure it does its job as well as when the drilling mud was first used. Screens with holes or tears can lead to large particle sizes passing through the screen resulting in higher sand content levels.
The screen performance can be optimized by rinsing it continuously during the operation and washing it thoroughly at the end of shifts to prevent solids from caking. The de-sander cones can also experience wear and tear from the sand particles resulting in inadequate cone performance. High sand content can also wear out the impellers on the centrifugal pumps.
Just as operating the HDD drill rig and inserting drill rods into the ground requires a skilled operator, running a mud recycling unit also requires a skilled operator to ensure maximum efficiency. Mud recycling units can mix fluids, recycle mud, and can even be transported full allowing utility contractors to bother less with mud disposal.
This improves and increases HDD drilling efficiency, efficacy, and job site productivity. A skilled operator will know how to maintain an adequate amount of fluid and perform viscosity, sand content, and mud weight tests regularly. (Read also:Job Role: Mud Engineer).
Cost Saving by Recycling Mud
For smaller projects that utilize drill units of 30,000 pounds pullback or less, mud recycling has been given the backseat as a lesser fluid volume is required and recycling equipment has traditionally been too large for small work sites. Several manufacturers now design compact or micro mud recycling systems, enabling cost-saving for smaller projects as well.
Mud recycling can help reduce overall costs and produce less drilling fluid waste for an HDD project compared to standard disposal techniques. According to DitchWitch, the cost of additives and disposal fees for 1000 gallons of drilling fluid can range from up to $600 or more, not including water and transportation costs. When drilling fluid is recycled, it means fewer additives are needed and water consumption is also reduced.
For example, a contractor disposing 8000 gallons of used drilling mud in a week at approx. 45 cents a gallon, can cut yearly disposal and operating costs by $150,000. A project operating with a 30,000-pound pullback drill unit may pump 20,000 gallons of fluid for the duration of the project. If used, a mud recycling unit may only cause a fluid loss of about 1500 gallons throughout the project.
The investment in a mud recycling unit is easily covered by the returns in savings. Another advantage is that it helps satisfy environmental regulations and prevent expensive fines.
- Trenchless Technology.
- Trenchless Technology.