A
couple of issues have been around for almost 30 years; "The
technology is too new for us to be comfortable with"
and/or "Blind (single entry) wells are too
risky/expensive/need a giant rig or a giant site like an Air Force
Base". More on those comments later.

The two comments we heard more than any others were – "I
would love to use a horizontal well for sparging applications but all
the air comes out the front of the well,"
and/or "It’s impossible to design a horizontal substrate
injection well so the injectate makes it to the end of the well".

These two comments are very frustrating to all horizontal well
installers. Quite frankly it all boils down to math; fluid dynamics
to be precise. We have a volume of fluid to move, friction loss, and
head pressure differentials. But rather than get into the weeds with
the math and prove that it works, let’s go back to the Battelle show.

Two
of DTD’s scientists (chemical biology major and a PG) were having
dinner with one of our consultant clients and this topic came up. A
much respected member of the consulting team, he has PE, PG, PHG and
CHG behind his name, made the following comment – "This
is easy to explain and design, it’s a classic Ag Engineering
irrigation problem".  The entire table
got quiet and I looked at the client and said "What
the heck does Ag Engineering have to do with a horizontal
injection/sparge well?" His simple comment was "center
pivot irrigation".

He went on to explain that driving water from a central
point, along a pipe and through multiple, evenly spaced sprinkler
heads is exactly the same as what a horizontal well does. Both have
fluid (water/water based remediation fluid/air) flow along a pipe,
and multiple places (individual sprinkler heads/slots) for the fluid
to leave the pipe. Obviously, a well is buried in the ground and we
have head pressure and formation issues – but the math is essentially
the same!

What
a brilliant description, now instead of talking about math we can use
this as a real-world comparison. Is a center point irrigation system
exactly like a well? – no, but the idea is the same. Just as a quick
note, this type of irrigation system was invented in the early
1940’s; some systems have pipe lengths of over 1,600′. In addition to
the math and this agricultural analog, there are multiple examples of
horizontal sparge/injection wells, many exceeding hundreds of feet in
length, operating successfully in the US (check out the Battelle
final program for both posters and platform presentations on the
subject).

Let’s get back to the math for a second. Is designing a horizontal
sparge/injection well difficult? It could be, but remember it’s fluid
dynamics, not black magic. Most environmental consultants have staff
capable of working out the details.

OK, now that we’ve discussed horizontal sparge wells let’s tackle a
couple of other misconceptions:

1. The
   technology is new and experimental – the first documented use of
   horizontal directional drilling (HDD) being used for
   environmental remediation is in May of 1987 at a UST site in
   Ponca City, OK¹ . The same report (dated April of 1996) that
   identifies the first well, documents 231 other wells not
   completed by DTD. We have completed over 850 horizontal
   environmental wells. Drilex/Longbore installed 76 and one other
   horizontal environmental drilling company claims over 1,000
   completions on their web site. That rough total is over 2,000
   wells – hardly a new or experimental technology. One thing to
   note – the last "official" horizontal well catalog we
   can locate is twenty-two years old.  
2. Blind
   wells are difficult – they were at first, but things have
   changed, technology and tooling are better, and drillers are
   more experienced. Without going into minutia; in 2017 DTD
   completed twenty-eight blind well installations ranging in
   length from 76′ to over 950′. Moreover, most of the blind wells
   were less 300′ in length, completed under buildings using small
   or mid-sized rigs.

We
hope this has helped explain some of the misconceptions regarding
horizontal environmental wells. They aren’t experimental and are not
impossible to design. If you still have concerns, contact your local
horizontal environmental driller for more details.

1. Horizontal Environmental Wells in the United States:
A Catalog. Published by the Colorado Center for Environmental
Management. April 1996.