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Comparing HDD Steering Methods

"The hardest thing to explain is the glaringly evident which everybody has decided not to see."

― Ayn Rand, The Fountainhead

As the industry's growth stabilizes, safety has become HDD's leading issue. The front line of drilling safely has to be avoiding strikes. This requires three elements; know the precise location of existing lines, know the precise location of the advancing drill bit and, know & record the precise location of the newly installed line. All three relate to steering accuracy, yet far too many HDD engineers/planners do not know which steering method is the most accurate or why. HDD articles, committees, panels and round tables are seldom more than an organized sales pitch for one product or another. There are no HDD fact filters; wrong and bad information are spread as efficiently, and as freely, as good information.

The laws of physics have not changed. When it comes to steering accuracy, the facts are the same as they were thirty years ago. DC tracking, known by many as Tru-Track is the most accurate method available. The physics of DC tracking dictate that it is the most accurate. There majority of HDD veterans know this, but the industry's unbridled growth has blurred the facts. Claims of "new technology" easily mislead the less informed. New isn't automatically better and often isn't even new.

Accurate steering begins with project planning. Shortcuts hinder accuracy. Select the most accurate steering method and design the drill for success. Many of today's projects start with a list of things the HDD contractor isn't allowed to do, many nothing more than arbitrary restrictions having nothing to do with anything other than establishing authority. Often, in the name of safety or the environment, these restrictions negatively affect the potential steering accuracy. How counterproductive is that? That is the point. A well planned, properly laid out HDD project takes a little extra effort, but if safety and accuracy are really the issue, this should be demanded by the authorizing parties, not limited. Yet, all too often, contractors are required to use less accurate steering methods.

Why is the steering method important? Safety & Liability.

When it comes to HDD nothing is more important than knowing the precise location of the installed line. An accurate location is the lifelong responsibility of the owner. Future questions, and liabilities, will funnel directly to the owner. A line, installed via HDD, is often in an area where future construction will take place. Installed lines, of any type, simply have to be where they are supposed to be. It is critical to document and then communicate the drilled line's precise location. If someone hits your line with a piling, excavation or even another drill, tomorrow or a decade from now, the liability remains. In court, the winner may well be decided based on how the steering method was chosen and who has the most accurate records. If a less accurate steering method is specified, will that engineer accept the responsibility of the lies location for you? How hard will it be to find your HDD consultant at that time? Select the most accurate steering system. If not, your cloud of uncertainty never fades.

Steering was the catalyst for HDD's tremendous growth. Originally called River Crossing, HDD originated with Martin Cherrington about four decades ago. Growth, although based on the positive economics of HDD and enhanced by its environmental advantages, was very limited. The holdup was steering; in those early years there was no reliable method to verify the drill bits location or direction. With the placement of a magnetic steering tool, developed by the oil & gas industry, behind the drill bit, capabilities improved. The technique became known as wire-line steering, because a wire, inside the drill pipe, connected the down-hole steering tool to the surface computer.

Steering technicians/navigators became very adept at reading magnetics. Often, drills exited at or very near the proposed exit point. The problem was that many did not. The steering tool was basically a compass. Data is affected by magnetic interference and magnetic anomalies exist, both man-made and natural. A one half degree (.5) fluctuation in azimuth could result in a 15 foot error on a just a 1,800 foot crossing. The purchase of a pipeline right-of-way often waited, and then depended on, the drill bit's location at exit. The majority of the HDD work was still limited to un-congested areas.

A single event changed the pipeline and utility construction industry forever; the advent of Tru-Track. This patented surface tracking method allowed the contractor to know the precise location of the drill bit at any time. By temporarily placing a thin wire, in a somewhat rectangle shape, along the planned drill path and inducing a momentary DC current (readily available through the DC welder already on most every rig site), which created a known magnetic field, the operator could take a stand alone survey (DC tracking's most important attribute) and verify the magnetic steering tool's precise location at any time.

This capability proved to be the catalyst on which the HDD industry was waiting. The HDD boom began. Contractors could now drill in congested areas where HDD was more critically needed. The DC tracking accuracy is so precise that pipelines can be safely installed via HDD on the same right-of-way of existing lines. HDD contractors can know the location and heading of the drill bit, survey after survey, from entry to exit and have full knowledge of the exact exit location prior to the bits appearance. In addition, the length of HDD limits were extended as the DC tracking was so accurate that rigs placed on either side could drill towards each other and tap bit to bit.

Magnetic vs Gyro

Today, there are two methods of HDD wire-line steering; magnetic and gyro (Walk-over is a third method of HDD steering that sometimes uses wire-line type communications but it is not usually viable in larger diameter or deeper projects therefore not discussed in this context). Many in HDD assume the gyro is the newest steering product, therefore most accurate. After all, isn't it the tool of choice in the oil and gas drilling business? First of all, the gyro isn't new and, in most cases, the oilfield's tool of choice is the magnetic steering tool. The fact is that oil & gas sidetracks take place through steel cased holes. While in casing, they will often use a gyro but, more often than not, once out of the casing they can trip and switch to a magnetic steering tool.

For HDD, the accuracy factor is even greater. A magnetic steering tool, used in our application, can utilize the surface tracking system to verify the tools precise underground position and the gyro can't. For construction, accuracy is the number one goal and precisely plotting each survey is the difference between the systems. For the protection of the owner, the distinction couldn't be any more important. If you simply compare the DC surface tracking with a gyro, method against method, accuracy against accuracy, the magnetic steering tool wins hands down. Do not misunderstand, there are projects where a gyro makes sense but not as a tool to improve accuracy.

I listened to a gyro salesman tell a group of HDD contractors that the big advantage to a gyro was that you didn't have to set a coil on the surface. That statement is very misleading. A gyro's position cannot be verified, so, you can't use a coil, and that is a big HDD disadvantage. The truth is that you cannot verify a gyro's location. Even if you use a magnetic steering tool with DC tracking in conjunction with a gyro, the accuracy comes from the magnetic steering tool and the DC tracking, not from the gyro.

A magnetic steering tool is an accurate instrument that, in many cases, can be successfully steered without a surface coil. But, a coil makes the tool so accurate that drilling without it has come to be known as drilling blind which has been frowned upon for a couple decades. For safety, standard HDD practices dictate setting a coil when possible and not take short cuts. The gyro cannot be tracked; therefore, using the same definition, the gyro is always drilling blind. When using a gyro, the contractor is often asked to trip out of the hole and install a battery powered walk-over beacon between the gyro and the bit. As the bit approaches the exit an above ground sensor is used to try and locate the drill bit to confirm its location. The actual comparison, at this point is a walk-over location method, which isn't acceptable with most major pipeline projects, with the DC tracking where the bits precise location is documented.

Just how accurate is the DC tracking method? If asked, navigators could place a dime on the ground at the point the bit will exit. Knocking over the exit stake is so routine that it is rarely mentioned in the daily reports. If a gyro knocked over the stake it would likely be a magazine cover article. The surface tracking of magnetic steering tools is so precise that HDD contractors are often required to pull back, at points, along the drill path and redirect a drill that is less than a single degree off, sometimes that's no more than the equivalent of that same dime lying flat under one end of a magnetic steering tool. Obviously a gyro is never held to this standard and can't be because they don't know the exact location of the steering tool. This type of directional oversight supports the HDD industry's acceptance and recognition of the magnetic steering tools superior accuracy.

Driller's bias affects steering calculations 100% of the time. This is hard to explain but is basically the patterns and methods drillers utilize to move/correct the bit in a desired direction. Styles differ, formations differ, BHA's differ and all have a cumulative effect on the bit's calculated position. Gyros also have drift. By taking DC tracking shots, the magnetic steering tool eliminates the driller's bias problem at each survey. A gyro's drift and drillers bias worsens with distance and time.

DC tracking vs AC tracking

Tracking makes the difference but not all tracking methods are equal. There are two distinctive methods of surface tracking. The most accurate is a DC method. This requires a wire, geometrically looped, in a rectangle shape, usually starting and ending at the power source. Early instruction suggested the coil be placed evenly above and twice as wide as the projected drill path was deep. With experience and better tools, operators have learned they can place the coil in a variety of manners, sometimes completely off to one side and maintain precise accuracy. The DC method basically triangulates the tools position in relation to the magnetic field from each side of the looped wire. The AC method uses only one side of the wire, allowing for greater error. The current AC method also charges a fee for each foot drilled, even if the footage wasn't tracked, plus double footage fees for intersects.

The inventors of Tru-Track experimented with both AC and DC currents, patenting the DC method because the DC was more accurate and nearly every HDD rig had a DC welder. Years later, the AC method resurfaced, first in Europe, as a consequence of a non-compete, and was marketed as a new tracking method. The industry was expanding very quickly domestically and to many, who just didn't know one method from another, the tag "new" meant better. Comparing the accuracy between DC and AC is a lengthy paper in itself but few will argue the superior accuracy of the DC method.

Size and Durability

There are major differences in types and brands of instruments utilized in the various magnetic steering tools. Some are better than other but, as in most cases, you get what you pay for. The magnetic steering tools are generally very durable, about 3' in length and 1 ¾" OD. They can be used in all but the smallest of HDD applications. They are in the 35 lb. weight range and can be flown or shipped with relative ease. The gyro is housed in a large, steel sub, approximately 8.5' in length and weighs up to 1,200 lbs. Gyro's, by comparison, are fragile instruments, sensitive to shock/vibration and it often takes multiple tools to complete a rock job.

Set Up

I understand the gyro people will not survey an HDD job and require the contractor to provide entry and exit coordinates. This will require the contractor to hire a surveyor or obtain the coordinates from some other source. Any errors are not the problem of the gyro operator. Most magnetic steering tool service companies use the onsite navigator to survey and set up a job. This does take more time than asking the contractor for coordinates but is usually done while the crew is setting up the rig.

The Operator

"About 8 hours and ten years", the answer when a rookie inspector asked the veteran superintendent how long it would take a navigator to set up steering for an HDD project. The importance of well trained, experienced steering technicians/navigators cannot be over stated. Training never ends and annual proficiency verification is critical. There is no short cut to experience.

Due Diligence is not only selecting the most accurate steering method but to consider the entire package; the training, and experience of the systems operator, not to mention ongoing technical support from the steering company's office. Another consideration is the job completion package. Do the post-bore records and data provide industry recognized proof of where your product line is located? It should, after all, that is all you have.

Not all steering hands work for the company you are hiring. Some steering companies employ independent contractors or share navigators with other companies having little influence towards their training or knowledge of their experience.


The HDD industry's focus on safety, while displaying a lack of attentiveness to the accuracy of various steering methods, is a conflict. The good news is that this is a result of great growth and wonderful opportunity. While the HDD boom started as a result of precise steering capabilities the trend has been toward an acceptance of less accurate methods, if they are claimed as "new technology". Comparing one type of tool to another isn't practical if you fail to compare the accuracy of the entire method. The less experienced tend to hide behind "new technology" because they don't have the background to discuss proven methods and techniques. When planning an HDD project, safety should be factored in all decisions.

The goal should be safety, therefore accuracy. The industry's growth is stabilizing and the HDD IQ level is catching up. Proven practices and procedures continue to be the foundation for success. Take the time to do it right applies to every other type of construction, yet steering short cuts are still accepted and sometimes specified, by HDD experts daily. New methods and products will be marketed but contractors who exercise proven techniques and maintain a healthy level of skepticism will continue to outperform the others. Steering accuracy will always be the key to HDD's success.

Note: A rough draft of this article was sent to numerous veteran HDD experts including experienced navigators, current and former. Based on their replies, edits were made and some points were clarified. None disagreed with the papers theme. To highlight the fact that HDD steering is as much a political issue as a study of facts, some asked that their names not be mentioned. I honor those requests, knowing each will speak out, as needed, to improve the HDD industry. I thank everyone for their help and the sharing of their HDD experiences.



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