How Do You Steer a Drill Below The Earth? — Transcript

Full transcript

1. 0:00In December 2019, the City of Fort Lauderdale,  Florida experienced a series of catastrophic
2. 0:05ruptures in a critical wastewater transmission  line, releasing raw sewage into local waterways
3. 0:11and neighborhoods. Recognizing the need for  improvements to their aging infrastructure,
4. 0:15the City embarked on a plan to install  a new pipeline to carry sewage from the
5. 0:19Coral Ridge Country Club pumping station  across 7 miles (or 12 kilometers) to the
6. 0:24Lohmeyer Wastewater Treatment Plant.  But just drawing a line on the map
7. 0:28hides the enormous complexity of a project  like this. Installing an underground pipeline
8. 0:33through the heart of a major urban area while  crossing three rivers is not a simple task.
9. 0:38Underground utilities are usually installed by  a technique known as trenching. In other words,
10. 0:42we excavate a trench down from the surface, place  the line, backfill the soil, and repair whatever
11. 0:48damage to the streets and sidewalks remains. That  type of construction is profoundly disruptive,
12. 0:54requiring road closures, detours, and pavement  repairs that never quite seem as nice as the
13. 0:59original. Trenches are also dangerous for the  workers inside, so they have to be supported
14. 1:04to prevent collapse. Beyond the human risk,  in sensitive environmental areas like rivers
15. 1:09and streams, trenching is not only technically  challenging but practically unachievable because
16. 1:14of the permits required. In fact, trenching  in urban areas to install pipelines these days
17. 1:19is for the birds. When the commotion of  construction must be minimized, there are
18. 1:24many trenchless technologies for installing pipes  below the ground. One of those methods helped Fort
19. 1:29Lauderdale get a 7-mile-long sewer built in less  than a year and half, and is used across the world
20. 1:35to get utility lines across busy roadways and  sensitive watercourses. I’m Grady and this is
21. 1:41Practical Engineering. On today’s episode, we’re  talking about horizontal directional drilling.
22. 1:54This video is sponsored by Curiosity  Stream and Nebula. More on them later.
23. 2:05If you’ve ever seen one of these machines on  the side of the road, you’ve seen a trenchless
24. 2:09technology in action. Although there are quite  a few ways to install subsurface pipelines,
25. 2:14telecommunication cables, power lines, and sewers  without excavating a trench, only one launches
26. 2:20lines from the surface. That means you’re much  more likely to catch a glimpse. Like laparoscopic
27. 2:25surgery for the earth, horizontal directional  drilling (or HDD) doesn’t require digging open
28. 2:31a large area like a shaft or a bore pit to get  started. Instead, the drill can plunge directly
29. 2:37into the earth’s surface. From there, horizontal  directional drilling is pretty straightforward,
30. 2:42but it’s not necessarily straight. In fact, HDD  necessarily uses a curved alignment to enter
31. 2:48the earth, travel below a roadway or river,  and exit at the surface on the other side.
32. 2:54Let me show you how it works and at the end, we’ll  talk about a few of the things that can go wrong.
33. 2:59The first step in an HDD installation is  to drill a pilot hole, a small diameter
34. 3:03borehole that will guide the rest of the  project. A drill rig at the surface has
35. 3:07all the tools and controls that are needed.  These rigs can be tiny machines used to get
36. 3:12a small fiber-optic line under a roadway or  colossal contraptions capable of drilling
37. 3:17large-diameter boreholes for thousands  of feet at a time. As such, many of the
38. 3:22details of HDD vary across projects, but the  basic steps and equipment are all the same.
39. 3:28As the drill bit advances through the earth,  the rig adds more and more segments of pipe
40. 3:32to lengthen the drill string. Through this pipe,  drilling fluid is pumped to the end of the string.
41. 3:37Drilling fluid, also known as mud or slurry,  serves several purposes in an HDD project. First,
42. 3:43it helps keep the drill bit lubricated and  cool, reducing wear and tear on equipment
43. 3:47and minimizing the chances of a tool breaking  and getting stuck in the hole. Next, drilling
44. 3:52fluid helps carry away the excavated soil or rock,  called the cuttings, and clear them from the hole.
45. 3:57Finally, drilling fluid stabilizes and seals  the borehole, reducing the chance of a collapse.
46. 4:02I have here an acrylic box partly full  of sand, a setup you’re probably quite
47. 4:07familiar with if you follow my channel. Turns  out a box of sand can show a lot of different
48. 4:10phenomena in construction and civil engineering.  Compared to soils that hold together like clay,
49. 4:15sand is the worst case scenario when it comes  trying to keep a borehole from collapsing.
50. 4:20If I pull away this support, the simulated  borehole face caves in no time. If I add
51. 4:25groundwater to the mix, the problem is even  worse. Pulling away the support, the wall
52. 4:30of my borehole doesn’t stand a chance. Let me  show you how drilling fluid solves this problem.
53. 4:35I’m mixing up a handcrafted artisanal batch of  drilling mud, a slurry of water and bentonite
54. 4:40powder. This is a type of clay created by  volcanic ash that swells and stays suspended
55. 4:45when mixed with water. It’s pretty gloopy stuff,  so it gets used in cosmetics and even winemaking,
56. 4:51but it’s also the most common constituent in  drilling fluids. If I add the slurry to one
57. 4:55side of the demo, you can see how the denser  fluid displaces the groundwater. It’s not the
58. 5:00most appetizing thing I’ve ever put on camera, but  watch what happens when I remove the rigid wall.
59. 5:05The drilling fluid is able to support the face  of the sand, preventing it from collapsing. In
60. 5:10addition to supporting the sand, the drilling  fluid seals the surface of the borehole to reduce
61. 5:14migration of water into or out of the interface.  In most HDD operations, the drilling fluid flows
62. 5:20in through the drill string and back out of the  borehole, carrying the cuttings along toward the
63. 5:25entry location where it is stored in a tank or  containment pit for later disposal or reuse.
64. 5:32So far HDD follows essentially the same steps as  any other drilling into the earth, but that first
65. 5:37‘D’ is important. Horizontal directional  drilling means we have to steer the bit.
66. 5:42The drill string has to enter the subsurface from  above, travel far enough below a river or road
67. 5:47to avoid impacts, evade other subsurface  utilities or obstacles below the ground,
68. 5:52and exit the subsurface on the other side  in the correct location. I don’t know if
69. 5:57you’ve ever tried to drill something, but  so far when I do it, I’ve never been able
70. 6:01to curve the bit around objects. So how is it  possible in horizontal directional drilling?
71. 6:06There are really two parts to steering a drill  string. Before you can correct the course,
72. 6:11you need to know where you are in the first  place, and there are a few ways to do it.
73. 6:15One option is a walkover locating device that  can read the position and depth of a drill bit
74. 6:20from the surface. A transmitter behind the bit  in the drill string sends a radio signal that
75. 6:25can be picked up by a handheld receiver. Other  options include wire-line or gyro systems that use
76. 6:31magnetic fields or gyroscopes to keep track  of the bit's location as it travels below
77. 6:36the surface. Once you know where the bit is,  you can steer it to where you want it to go.
78. 6:42I’ve made up a batch of agar, which is a  translucent gel made from the cell walls of
79. 6:46algae. I tried this first in the same acrylic box,  but the piping hot jelly busted a seam and came
80. 6:52pouring out into my bathtub, creating a huge mess.  So, you’ll have to excuse the smaller glassware
81. 6:57demo. My simulated drill string is just a length  of wire. There are two things to keep in mind
82. 7:02about directional drilling: (1) Although they seem  quite rigid, drill pipes are somewhat flexible
83. 7:07at length. If I take a short length of this wire  and try to bend it, it’s pretty difficult, but a
84. 7:12longer segment deflects with no problem. And, (2)  you don’t have to continuously rotate the drill
85. 7:17string in order to advance the borehole. You can  just push on it, forcing the bit through the soil.
86. 7:23My wire pushes through the agar without much  force at all, and a drill string can be advanced
87. 7:27through the soil in a similar way, especially  when lubricated with water or drilling fluid.
88. 7:32The real trick for steering a drill string is  the asymmetric bit. Watch what happens when I
89. 7:36put a bend on the end of my wire and advance  it through the agar. It takes a curved path,
90. 7:42following the direction of the bend. If I rotate  the wire and continue advancing, I can change the
91. 7:47direction of the curve. The model drill string is  biased in one direction because of the asymmetry,
92. 7:52and I can take advantage of that bias to  steer the bit. I can steer the string left,
93. 7:57then rotate and advance again to steer the bit  to the right. I’m a little bit clumsy at this,
94. 8:02but with enough control and practice, I could  steer this wire to any location within the agar,
95. 8:07avoid obstacles, and even have it  exit at the surface wherever I wanted.
96. 8:12This is exactly how many horizontal directional  drills work. The controls on the rig show the
97. 8:17operator which way the bit is facing. The  drill string can be rotated to any angle
98. 8:21(called clocking), then advanced to change the  direction of the borehole. Sometimes a jet nozzle
99. 8:27at the tip of the bit sprays drilling fluid  to help with drilling progress. If the nozzle
100. 8:31is offset from the center, it can help create a  steering bias like the asymmetric bit. Just like
101. 8:36the Hulk’s secret is that he’s always angry, a  directional drill string’s secret is that it’s
102. 8:41always curving. The rig operator’s only steering  control is the direction the drill string curves.
103. 8:47And hey, if that sounds like something you’d like  to try for yourself, my friend Dan Shiffman over
104. 8:51at the Coding Train YouTube channel built a  2D horizontal directional drilling simulator.
105. 9:01This is an open-source project, so  you can contribute features yourself,
106. 9:05but it’s also really fun if you  just want to play a few rounds.
107. 9:09If you’re into coding or you're wanting to get  started, there is no better way than working
108. 9:13through all the incredible and artistic examples  Dan comes up with for his coding challenges.
109. 9:18Go check him out his video on HDD after  this one, and tell him I sent you.
110. 9:22Once the drill string is headed in the right  direction, it can just be continuously rotated
111. 9:27to keep the bit moving in a relatively  straight line. The pilot hole for an HDD
112. 9:31project is just an exercise in checking the  location and adjusting the clock position
113. 9:36of the drill string over and over until  the drill string exits on the other side,
114. 9:41hopefully in exactly the location you  intended. But, not all soil conditions
115. 9:45allow for a drill string to simply  be pushed through the subsurface.
116. 9:49Rocky conditions, in particular, make  steering a drill rig challenging. An
117. 9:53alternative to simply ramming the bit through  the soil is to use a downhole hydraulic motor.
118. 9:58Also known as mud motors, these devices convert  the hydraulic energy from the drilling fluid
119. 10:03being pumped through the string to rotate a  drill bit that chews through soil and rock.
120. 10:08This allows for faster, more efficient drilling  without having to rotate the whole drill string.
121. 10:13The housing of the mud motor is  bent to provide steering bias,
122. 10:16and the drill string can be clocked to  change the direction of the borehole.
123. 10:20Once the pilot hole exits on the other side, it  has to be enlarged to accommodate the pipe or
124. 10:26duct. That process is called reaming. A reamer is  attached to the drill string from the exit hole
125. 10:31and pulled through the pilot toward the drill  rig to widen the hole. Depending on the size of
126. 10:36the pipe to be installed, contractors may ream  a hole in multiple steps. The final reaming is
127. 10:41combined with the installation of the pipeline.  This step is called the pull back. The pipe
128. 10:46to be installed in the borehole is lined up on  rollers behind the exit pit. The end of the pipe
129. 10:50is attached to the remaining assembly, and the  whole mess is pulled with tremendous force through
130. 10:56the borehole toward the rig. Finally, it can be  connected at both ends and placed into service.
131. 11:06That’s how things work when everything goes  right, but there are plenty of things that can
132. 11:10go wrong with horizontal directional drilling too.  Parts of the drill string can break and get stuck
133. 11:16in the pilot hole. Drilling can inadvertently  impact other subsurface utilities or underground
134. 11:21structures. The pipeline can get stuck or damaged  on pullback. Or, the borehole can collapse.
135. 11:28The controversial Mariner East II pipeline in  Pennsylvania experienced a litany of environmental
136. 11:33problems during its construction between 2017  and 2022. Most of those problems happened on
137. 11:39HDD segments of the line and involved  inadvertent returns of drilling fluid.
138. 11:43That’s the technical term for the situation when  drilling fluid exits a borehole at the surface
139. 11:48instead of circulating back to the entrance  pit. The inadvertent returns in the Mariner
140. 11:52East II line created water quality issues in  nearby wells, led to sinkholes in some areas,
141. 11:58and spilled drilling fluid into sensitive  environmental areas. The pipeline owner was
142. 12:02fined more than $20 million over the course of  construction due to violations of their permits,
143. 12:07and they are still mired in legal battles and  extreme public opposition to the project to date.
144. 12:13In the case of Mariner East II, most of  the drilling fluid spills were partially
145. 12:17related to the difficult geology in Pennsylvania.  Clearly HDD isn’t appropriate for every project.
146. 12:23But in most cases, trenchless technologies  are the environmentally-superior way to
147. 12:28install subsurface utilities because they  minimize disruptions on the surface to the
148. 12:33people in urban areas and sensitive  habitat around rivers and wetlands.
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