Horizontal Drilling: A Valuable Tool in the Right Situation

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Horizontal Drilling: A Valuable Tool in the Right Situation

By: Evan Cox

Horizontal or directional drilling technology was originally developed by the oil industry and is also commonly used for utility installation and river crossings. Since the early 1990’s, horizontal drilling technologies have been demonstrated and deployed as an enhanced access method for the for use in the remediation of contaminated soil and groundwater.   Yet despite the success and potential benefits of this technology, it remains relatively underutilized in the environmental field.

Horizontal Wells vs. Traditional (Vertical) Wells
There are two obvious advantages of horizontal environmental wells over traditional vertical wells. The first is their ability to provide better lateral coverage of a contamination plume. In the right setting, one horizontal well may fulfill the role of multiple vertical wells. As an example, at the Williams Air Force Base (WAFB) Superfund Site, it was projected that over 80 vertical monitor wells and 16 extraction wells would be required to monitor and remediate a large jet fuel plume. As an alternative, WAFB determined that the same monitoring and remediation objectives could be achieved with just two horizontal wells.
The second obvious advantage is the ability to access areas that otherwise would be difficult if not impossible to reach using conventional technologies. For instance, beneath a building, a lake, a dam, a road, or a transportation corridor. Multiple horizontal wells can be nested within the same borehole to target different sections along the well path. For offsite contaminant plumes, access can be obtained without the need for any permanent offsite above ground infrastructure or surface completions on the neighboring property.

Challenges and disadvantages of the technology
Horizontal drilling technology is not without its problems and downsides. Firstly, installation can be more challenging than vertical wells because of the difficulty in clearing a safe bore path for the installation. While utility location is required for all subsurface drilling work, the depth and extent of the underground utilities and objects may not be accurately known. For shallow horizontal boring applications, this can result in a higher occurrence of unintended contact and damage to underground utilities. Horizontal borings are initially drilled at an angle until reaching the target depth. Consequently, the rig needs to be setback from the target point to provide the necessary distance for the borehole to reach the target depth. Although it varies depending on the entry angle, a general rule of thumb for the minimum estimated setback distance is a ratio of 5:1, meaning if the target depth is 20 feet, the approximate setback distance is 100 feet. This is a limitation for smaller properties, where the setback distance may require the rig to be placed offsite.

Although a single horizontal well may replace several vertical wells, horizontal well drilling and installation is significantly more expensive per-foot than traditional well drilling. In addition, the lead time for project implementation can be significant given the required additional planning and design of a horizontal drilling project. As a result, planning a horizontal drilling project can be a challenge when deadlines are short, and the client needs answers quickly. In the right situation and with the appropriate planning, horizontal drilling can provide a viable alternative to more traditional solutions to environmental work.

Evan Cox is a Scientist with Cox-Colvin & Associates, Inc. He holds a Bachelor of Science degree in Environmental Geology from Ohio University. He has been with the firm since he has returned to Ohio in 2017 from Michigan where he worked as an Industrial Hygienist conducting asbestos surveys, sampling, and air monitoring. Evan Cox is highly experienced in the collection and analysis of environmental data of all types and has conducted numerous drilling projects during his tenure at Cox-Colvin.