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December 2013 – What is HDD and How does it work?

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Welcome to the inaugural issue of “Inflection Points”, a newsletter published by Directed Technologies Drilling, Inc. (DTD) that will focus on the benefits and technical aspects of environmental remediation and water supply utilizing horizontal directional drilling (HDD) technology.Periodically, you will receive non-commercial information regarding the use of this innovative technology as it relates to environmental drilling, sampling and well installation. Future issues may also discuss safety, infrastructure installations and remediation topics not directly related to horizontal environmental drilling. If at any time you wish to stop accepting this valuable data, click the unsubscribe button at the bottom of this page.
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 things first; the term “horizontal well” is a misnomer, we are really talking about a technique that allows us 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 we could deliberately steer a path with curves, dips and angled wells.

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? Details on steering methods will be provided in future installments of the newsletter.

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 of your sites have impacted soil or groundwater in areas that are completely inaccessible? Think about the following types of sites; dry cleaners in retail centers, UST sites with a plume under a busy intersection, an airport (or any DOD/DOE facility) with contamination under runways and terminals, 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 contemplate surface obstructions as the only limiting factors that might favor 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 DNAPL.  Or how about having the ability to chase a 120′ 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 technologies used in conjunction with HDD wells includes:

  • Ground Water Extraction
  • NAPL Recovery
  • SVE
  • Air Sparging
  • Bio-sparging
  • Nutrient Injection
  • ISCO Treatments
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 below and you will also see terms like; entry angle, build radius, true vertical depth (TVD) and set back distance. These terms and how they relate to well design will be discussed in great detail in future newsletters.

Now sit back, review your next remediation project and imagine using a horizontal well in your design (Oh yeah, did I forget to mention we can take soil samples during the drilling process?).

The questions in your mind may be:

  • Is geology a limiting factor?
  • What type of well, blind or
  • What type of well materials can I use?
  • How deep can I drill?
  • How close can I be to the screen section (set back distance)???

Future newsletters will discuss all of the above issues.  If you can’t wait, call us at 800-239-5950.

Thank you and we look forward to sharing additional information with you.