|
|
Confessions of a Recovering Vertical Driller or How I Learned to Stop
Worrying and Drill Crooked on Purpose
A little over a year ago I gave up a 13-year career in the vertical
drilling industry and ventured out into the world of horizontal directional drilling (HDD).
Now as far as big career moves go, I’ll admit that this one was relatively tame; I mean it’s still the drilling industry after all. And because DTD focuses on horizontal well installations (as opposed to trenchless utility applications) there’s really quite a lot of overlap with what I was doing before. For the most part I’m working with the same clients on similar types of projects.
At the same time though, it is extremely different. From a technical standpoint, putting in a horizontal well is more complicated than putting in a vertical well. Sure, the physics are different; that’s obvious. But there are site logistics and other considerations that aren’t as immediately apparent.
|
|
|
|
|
|
|
When I first started at DTD I had a crash course in environmental HDD applications. For about six months I worked as a helper on our rigs in the field. I was able to spend time mixing mud, fusing HDPE pipe, locating the bit and doing all the other miscellaneous tasks a helper has to do.
Going back to the field, albeit temporarily, wasn’t exactly the most fun I’ve ever had, but it helped me understand some the nuances between vertical and horizontal well drilling and construction.
I’ve learned a lot over the last year, and I thought now was a good time to sit down and chronicle what I see as some of the most crucial differences between HDD and traditional vertical well installation methods.
I believe that a good understanding of these nuances is
crucial for anyone considering the technology for their projects.
|
|
|
|
Lesson #1: Directional Control – The Bit is
Bent
For years I knew conceptually that directional drilling was a thing; like it’s possible to steer a drill bit. But I have to admit that it never really occurred to me how exactly the process worked. The answer is astonishingly simple: the bit is bent ever so slightly.
In vertical drilling we’d try to drill as straight as possible, which was hard because steel drill pipe bends if you apply downforce to it. This will kick the bit off its intended path and then your hole will end up deviating.
Of course, in HDD we’re counting on that deviation occurring, but we need to be able to control which way the bit kicks off, which is why a bent bit is perfect. As long as we know the orientation of the bend (we do thanks to locating electronics in the bit housing), we can control the deviation to go the way it needs to in order to remain true to the intended bore path.
It still kind of blows my mind.
|
|
Lesson #4: You Don’t Need a Filter Pack
This is a consequence of slightly more specific lesson…let’s call it 4A: Centralizers will not survive installation in a horizontal bore. Most, if not all the time they break or fold while the well screen and casing are being pushed or pulled into a long horizontal bore. This can cause well material failure or result in the screen and casing becoming stuck in the borehole.
So a horizontal well will always have one side of the screen sitting on the bottom of the borehole, which means it’s impossible to pump a sand pack into the annular space in a way that fully envelopes the screen. So, we install “naturally packed” wells, meaning the formation collapses around the screen and a zone of graded formation materials is created during development.
Initially I found it hard to wrap my head around the idea of not installing a filter pack. But it’s important to realize that vertical wells tend to have a lot less screen area in their target zones because of the horizontal orientation of the geology. As a result, vertical
wells tend to see much higher entrance velocities than horizontal wells, which makes the filter pack more
crucial in fine grained formations.
|
|
|
Lesson #2: Steel Bends More Than You’d Think – But There IS a Limit
Using the bent bit, we can control the deviation of the borehole…to an extent. The drill pipe has to follow that bit, so there are limitations to how sharp of a bend radius we can follow. Basically, our steering is restricted to gentle arcing curves rather than sharp angles.
This means that it takes a significant amount of footage to affect a change in direction. It seems like environmental remediation sites always have some obstacle or limitation making it challenging to “fit the curve” to the situation at hand.
Thinking three dimensionally and simplifying the bore path as much as possible given the
site’s constraints and project objectives is hard to do, but it’s really important.
|
|
Lesson #3: Bore Path Logistics – It’s Complicated
One of the first things that jumped out at me on my first HDD project was how many times the project manager and the driller walked up and down the bore paths before we ever broke ground. There’s so many little things to think about.
Where are the utilities relative to the bore path? You’re potentially in the “zone of utilities” for a long time compared to a vertical bore. And altering the bore path even just a little bit changes EVERYTHING. The footage of the well is different, the bend radius is different, your target angles are different. It’s a big deal.
What is the surface elevation profile along the bore path? We are wired to think of the concept of depth relative to depth below ground surface (BGS). But the ground surface isn’t necessarily level along the bore path now is it? So that means our bore path will reference a target elevation as opposed to a target depth BGS. It doesn’t seem like that big of a deal until your exit point is situated underneath a big hill…
How is access to the bore path along the surface? One of HDD’s great benefits is that it allows for the installation of well screen in an area that may otherwise be inaccessible to a vertical drilling operation. But we need to locate the bit somehow as we steer along the prescribed path. The simpler (read: less expensive) locating technologies still require a basic level of access at the surface to get the readings we need.
|
|
Lesson #5: Everything Is Sideways
Okay, so maybe this is fairly obvious, but it constantly keeps coming up. The borehole’s orientation is perpendicular to the overburden pressure, so your battle against borehole collapse is that much more involved.
Running tooling with tight tolerances into a well is REALLY risky because it’s way more likely to get stuck in a horizontal orientation. Also, whatever you’re running in and out, you will have to push it or pull it since you’re fighting gravity. Packers, swabs, pumps, cameras…these are such handy tools, but it can be really challenging to deploy them.
It takes a LONG TIME to trip pipe in and out of the hole (you can’t just run a winch line and hang the pipe in the fingerboard…)
You can’t just lower your well materials into the hole. You need to use the force of the rig to push or pull them into place. And you need to do it quickly because hole collapse is such a more imminent threat. (Oh and the stresses that the well materials are subjected to
are TOTALLY different.)
The cool thing is that while the orientation does make everything more complicated, it opens up a whole world of possibilities in terms of what can be achieved. Consider that just one horizontal well can have hundreds of feet of screen in contact with a contaminant plume.
|
|
|
|
|
|
|
|
So just like the old adage “it’s the same but different”; horizontal drilling and well installation is similar to what I did for thirteen years – but very, very different.
Jacob Gallagher is the Business Development Manager for Ellingson DTD (DTD). He resides in Denver, CO and focuses on projects in the Western United States. Jacob can be contacted at 510-334-6455 or via email
at [email protected].
|
|
|
|
|
|
|
|
|
|
|
|
|
|
