OK then, let’s get started. What the heck is a horizontal (or directional) environmental well and why is it a valuable technology for remediation applications?
First thing’s first. The term “horizontal well” is a misnomer. We are really talking about a technique that allows a driller to steer a drill bit along a predetermined path. Once the hole is drilled with the steerable bit assembly, a well is installed into the borehole. The resultant well need not be horizontal, depending on the well materials (screen and casing) and geology. The well could end up with curves, dips and angles. The technology used to steer the bit is a combination of utility drilling methods (think river crossings or fiber optic cable installations) and oil field methods; we have all heard of horizontal wells in shale, right?
We know that the boom in hydrocarbon production in shale is due to the ability to drill and install horizontal wells, but how is that applicable to the environmental industry?
How many contaminated sites have impacted soil or groundwater in areas that are completely inaccessible? Think about the following types of sites: dry cleaners in strip centers, UST sites with a plume under a busy intersection, an airport with contamination under runways and terminals (or any DOD/DOE facility), an active rail yard or a residential neighborhood. All of the aforementioned sites may have access to the areas of concern that are limited by surface obstructions and they all have one thing in common; each of those types of sites have been accessed using horizontal directional drilling techniques.
Let’s not just contemplate surface obstructions as the only limiting factors encouraging the use of horizontal directional drilling. Have you ever had a plume of DNAPL resting on top of an aquitard? How about a solvent plume that was located in a long, narrow glacial outwash channel? Now think about placing the well screen immediately on top of the clay, entirely in the free phase plume. Or how about having the ability to chase a 120-feet deep outwash channel with a screen down the middle of the plume? Again these scenarios have been performed with horizontal directional drilling.
But what if I want to remove vapors from under a slab or inject ZVI into the formation? Great question. The answer is, if it can be done in a traditional vertical well it can also be performed with a directionally drilled and constructed well.
The list of remediation technolo-gies used in conjunction with HDD wells includes:
- Groundwater extraction
- Free phase contaminant removal
- Soil vapor extraction
- Air sparge
- Bio sparge
- Nutrient injection
- ISCO treatments
- Hot air/steam injection
- Radio frequency heating
One more thing to discuss: the basic nomenclature of horizontal wells. There are two types of horizontal wells: continuous and blind.
Continuous wells have a bore path that includes an entry, horizontal/screen section and an exit. This is very similar to a river crossing or utility installation. A blind well has only one entry point, as shown on the diagram.
Keep in mind that the well screen can be placed anywhere in the well.
Review the diagram and you will also see terms like entry angle, build radius, true vertical depth (TVD) and set back distance. These terms are very unfamiliar to most vertical drillers and can be confusing. This leads us to the next question. Is this a good market for water well drillers or HDD contactors? The answer to that question is complicated for several reasons.
The size of the horizontal environmental marketplace is very difficult to judge and most likely very small compared to the vertical well market. The National Ground Water Association (NGWA) included a horizontal well special interest group that tracked horizontal environmental well installations. However, that group disbanded several years ago and a reliable database on the technology is not available.
Water well contractors understand how to properly drill, construct and develop vertical wells. In order to participate in the installation of horizontal wells they would need to purchase specialty drilling equipment, as typical vertical water well rigs are not designed for shallow horizontal drilling operations. After the rig purchase, drillers and crew would require significant training in the operation of the equipment. Finally, the contractor must perform research into the consultants and owners who utilize this type of well installation, then develop a sales and marketing plan to reach potential clients. Many, if not almost all vertical drillers, choose not to enter this market due to lack of understanding the technology and the inability to accurately quantify the size of the market.
Typical utility/HDD contractors have multiple challenges to entering the horizontal environmental well market including lack of well construction expertise, lack of water well/environmental well drilling licenses and Hazwoper compliance issues. Again many HDD contractors are stymied by the unknown size of the market.
So what does all of this mean?
Shallow horizontal environmental remediation wells can be installed using technology from the petroleum drilling and utility installation industries. The methodology works for all of the commonly used remediation technologies. There are some barriers to entry for both water well drillers and HDD drilling companies to entering the market. But enterprising drillers can add horizontal to their environmental toolbox and, with the right sales and marketing plan, get into a market that their competitors might have ignored.
David S. Bardsley is business development manager for Directed Technologies Drilling. For more Bardsley columns, visit www.thedriller.com/bardsley.