The environmental and financial impacts of drilling fluid on HDD jobsites continue to be a priority for HDD contractors. The visibility of jobsites due to social media increases exposure to “visual prosecution” by the general public, who are often uniformed about the nature and purpose of HDD drilling fluid. In addition, the length and diameter of some bores on HDD jobsites require several thousand gallons of drilling fluid to complete a bore successfully. Therefore, contractors are faced with the daunting and many times expensive task of containing and disposing of used drilling fluid.
The costs associated with containing and disposing of used drilling mud can be significant and are based on many factors. These costs may include containment equipment (vacuum excavators), transport equipment to send the used drilling fluid to an approved disposal site (truck/vacuum excavator/CDL driver/fuel, mileage), and disposal charges. And the hassle does not end with disposal costs.
HDD contractors may have to mix additional drilling fluid, resulting in further costs and downtime. These factors and associated costs are driving contractors to explore cleaning drilling fluid on site using a portable cleaning system, in order to reuse the drilling fluid or minimize disposal and containment costs.
There are certain components and processes needed to clean drilling fluid to ensure the fluid being reused in the drilling process does not harm the drilling system or its components, nor inhibit the performance of the drilling process. It is commonly recognized that when reusing drilling fluid, solids can do serious and costly damage to everything the fluid passes through as it performs its function in the drilling process.
For this reason, it is imperative to remove these solids from the drilling fluid before it is returned through the system. “HDD drilling fluid has multiple functions, including cooling downhole electronics, lubricating downhole tooling, and stabilizing and sealing the bore hole to prevent fluid loss into the formation. But, a less recognized property is that drilling fluid acts as a conveyor belt to move the solids from the drilling head through the bore hole to the surface,” says Richard Levings, director of product management for American Augers.
In many cases, this transmission creates a very high concentration of solids in the returned drilling fluids that must be removed in order for the fluid to be reused. In one recent example of a company looking to minimize haul off costs and prevent damage to their drilling processes, a solution was found in an American Augers M-200D that utilizes a Derrick FLC 503 Shaker.
An Oklahoma contractor was performing a 1,340 ft river crossing bore installing 16-in. steel pipe. The process of opening the hole was producing solids as high as 30 to 40 percent and sand contents as high as 11 percent. Mud weights in the pit were experienced above 13 lbs per gallon. The goal of any cleaning system is to remove as many drilled solids from the drilling fluid as quickly and efficiently as possible, all the while drying solids to decrease their weight and minimize disposal costs. The cleaned fluid should have the least amount of drilled solids possible (normally mud weights below 9 lbs per gallon) and the sand content should remain less than .5 percent to be pumped back down hole. Maintaining proper fluid properties and removing solids from the fluid mixture have proven to help facilitate a more efficient and cost-effective drilling operation.
In order for the contractor to minimize the amount of fluid required for the job and avoid high disposal costs, he employed a portable drilling fluid cleaning system. An American Augers M-200D fitted with a single FLC 503 3-Panel shaker from Derrick with five 4-in. cones over the second screen panel to handle high capacity solids laden drilling fluid from a backreamed hole was used in this operation. Equipped with Derrick’s patented Pyramid screen technology, the FLC 503 acted as both a scalping shaker and mud cleaner. The drilling fluid was pumped from the pit onto the shaker and the first screen panel, providing the primary separation. The fluid and undersized solids flowed through the screen to the first tank compartment below the shaker.
The M200D tank agitation worked to ensure no solids settled in the tank. From this tank, the fluid was pumped to the cones which were intentionally positioned over the second screen panel. Finer screens were run on the second and third screen panels to dewater the cone underflow, essentially acting as a mud cleaner. Proper cone pump size ensured coned pressures were consistent so smaller solids could be separated from the fluid in the cones. Cleaned fluid flowed out the top of the cones and into the second tank compartment. The fluid was then pumped back through the HDD unit for use down hole. While back reaming from a 12- to 18-in. hole for 1,340 ft over two days, the M-200D processed 100 percent of the fluid from the hole. The percentages of solids and sand content were monitored during the entire process. Over the course the 1,340-ft backream, 213 tons of solids were produced by the M-200D.
During the operation, unprocessed slurry in the exit side pit averaged as high as 11 percent sand content. Due to Derrick’s patented Pyramid screen technology and leading-edge shaker design coupled with proper pump and cone design of the M200D, the clean mud’s sand content was maintained at .5 percent or less throughout the duration of the job. Fluid was only added for hole volume and no known losses occurred during the operation. The job demonstrated the ability of a compact, single-deck fluid recycling system with high performance shaker and innovative screen technology to provide value added savings by way of reducing the dilution needed and the quantity of abrasive sand size particles. Findings showed the M-200D with its’ next level design and components to be as effective as larger conventional mud systems with double deck shakers and/or multiple shaker systems.