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View Full Version : OT How Do Horizontal Directional Drills Work?

john hobdeclipe
04-25-2009, 05:39 PM
The machines that are used a lot now to lay utility lines like data cables, some water lines, etc. etc. without digging trenches. They are set in place, they drill downwards for a ways, then the drilling bit can be steered back up to exit the ground at a predetermined spot. I understand that they can also be steered to some extent from one side to another.

How are they steered or controlled??? What kind of mechanism allows the operator to make the drill go in one direction or the other??

Bguns
04-25-2009, 06:09 PM
http://en.wikipedia.org/wiki/Directional_drilling

The above mentioned Mud Motor can be monitored for direction by measuring the frequency of pressure pulses in the Drilling Mud..

There are steerable units as mentioned above...

Neighbor does it on North Slope...

Guido
04-25-2009, 06:11 PM

G

camdigger
04-26-2009, 09:54 AM
Directional boring for shallow road crossings is typically distinct from directional drilling. Bored crossings hereabouts are done by shoving a rod through the soil and tracking it from surface with a sophisicated metal detector. The rod is shoved along by large hydraulic cylinders. The rods are extended by screwing additional lengths on the end. The rod is "steered" by rotating it to orient a shoe with an offset point. This stuff is done from one bell hole to another on either side of a road.

Directional drilling uses survey instruments down the hole to measure 6 vector components 3 in gravity and 3 in magnetics. This data is processed and compared to the known force vectors - gravity and magnetic north. From this point, it is a matter of math to determine where the instrument is based on how it was pointed at the last measurement station and where it is pointed now and how far it is between stations. All the steps are added up from the starting point to get an answer for the final position. Shallow drilled crossings can use metal detection tracking to verify the calcs. The basic principle outlines above is the same for drilled crossings or oilwells (North Sea).

The physical drilling asembly typically uses a type of down hole motor and some kind of bend assembly. Modern motors are typically adjustable housing motors to make them more or less aggressive as the build rate (rate of curvature) demands. It is very challenging at times due inconsistencies in the formations drilled. Some are easy to turn in and some aren't. The assembly is oriented in the desired direction and drilling starts. The drill string above the motor is held still while the motor turns the bit. The hole is drilled in a curve, the radius of which is determined by the bend in the drilling assembly and the direction of the curve is determined by the direction it is pointed in.

So far so good? Simple? Now add rocks, formation changes, and the fact that the drill string is elastic, both axially (along its length) and worse in torsion (affecting where it is pointed).. Thankfully, the instrumentation gives real time feedback as to how the assembly is pointed so corrections can be made.

Hope this helps.
Camdigger

camdigger
04-26-2009, 10:21 AM
In my previous post, I tried to explain how we know where the hole is. The drill itself is a sophisiticated machine with some basic elements.

A pump. Ususally a large high pressure piston pump. Circulation rates for drilling range from 150 gpm to 800+ gpm. Pressures are quite high in oilwell drilling ranging from 300 psi to 3000 psi depending on depth and how the assembly is made up. It takes a lot of HHP to pump 800 gpm at 3000 psi.

A hoisting assembly/derrick/mast. The derrick assembly on a horizontal bore lies at an angle to the ground. The top drive assembly rides up and down the derrick on tracks or rails. Crossing machines have pull down chains driven by hydraulic motors to force the drilling assembly against the face of the hole so the bit can cut it. the same chains provide pull force to remove the drillstring from the hole and pull the reamer back through the hole with the pipe (called the drag section for obvious reasons;) ) Oilwell rigs usually do not have pull downs as they are vertical and can rely on gravity to supply the down force, just a big block and tackle assembly inside the derrick to hold and lift the drill string. On oilwells string weights up to 200,000 # are not unusual. Larger hole needs larger tools that weigh more. Some shallow rigs are maxed out at 60,000#

On the top drive there has to be some kind of swivel to put the fluid from the pump down the hollow drill string. The swivels are usually top entry as these only require one high pressure seal. If the seal fails in service, everybody takes a shower.:rolleyes: Side entry swivels are sometimes used, but they have dual weak points in the seal areas. Drilling fluids have a lot of grit from fines being recycled. Erosion is a huge problem if a small leak happens. Fluid up to 10% solids at 1000 + psi and 300+ gpm makes a very effective sand blaster (thats how water jetting is done). However the drill string is turned, there has to be provision to prevent the string from turning, so most swivels have a rotational brake to hold the string pointed in a particular direction. Older tecnology uses kelly drive bars on the oilwell rigs. A kelly bar is square or hex on the outside and has a bore down the middle. The bar runs through a bushing that has rollers to engage the corners of the kelly bar. The kelly bushing fits into a recess in the rotary table which is driven by a huge crown and pinion gear ( standard opening inside the table is 17 1/2" or 26"). The table is driven off the floor drive motor(s) and can be locked by jamming a lock pin into the teeth of a lock ring mounted on the crown gear. The kelly bar is usually at least 10' longer than the drill string elements so that it can turn the whole length as it slides through the kelly bushing.

Cam

Paul Alciatore
04-26-2009, 03:55 PM
Camdigger,

I don't think he was asking about oil wells where a "turn" can be very gradual. He was asking about lines under the street where a 90 degree turn would be accomplished in a few feet or less.

I am not in the industry, but as I understand oil well directional drilling, it uses VERY gentle curves over hundreds of feet to allow the drill stem to follow the curve. Those things are not that flexable. This is not obvious from the popular (ignorant and misleading) diagrams in magazines and museums that often show tight right angle turns. Grrrrrrrrr! If they are trying to teach something, why can't they get it right?

Drilling for a utility line under a street would be quite different. You wouldn't want to drill hundreds or thousands of feet in a gentle curve only to pop up 25 or 50 feet away. And it would be very desirable to know the exact depth of the horizontal bore to avoid hitting other utilities; so a tight, precise right angle turn would be needed. I believe this is what he is asking about.

I have personally run a line under a sidewalk for about 4 feet. Dug a horizontal trench long enough for the pipe to lay in and then used a water hose (my drill head) run through the pipe to flush out the soil in front of it as I inched it along. Rocks were a problem, but it worked without breaking up the sidewalk. Not high tech, but effective. The real problem going under a street would be adding additional sections of pipe as you progress. You will need a pit wide enough to assemble them below ground. Or perhaps flexible tubing?

As I said, I am not in the business and would also like to know how it is done now.

Ian B
04-26-2009, 04:06 PM
Paul,

You're right about the average drawing of an oil/gas well being misleading. To have it to scale, you need to be thinking along the lines of a human hair stretched half way from floor to ceiling. We tend to draw wells as short, fat things so that we can see the details of the various size casings & tubing(s).

Ian

camdigger
04-27-2009, 08:22 PM
Camdigger,

He was asking about lines under the street where a 90 degree turn would be accomplished in a few feet or less.

Bolderdash. Drilled crossings follow the same nominal build rate parameters as oilwells do now +/- 45 */100 feet is absolute max, that's one reason why crossing machines start at 60* + from vertical or 30* from horizontal. The pipe dragged through the crossing is as stiff as production tools.

I am not in the industry, but as I understand oil well directional drilling, it uses VERY gentle curves over hundreds of feet to allow the drill stem to follow the curve. Those things are not that flexable. This is not obvious from the popular (ignorant and misleading) diagrams in magazines and museums that often show tight right angle turns. Grrrrrrrrr! If they are trying to teach something, why can't they get it right? Why can't machinists acknowledge that CNC isn't plug and play - there's a learning curve associated with it????
15* / 100 feet isn't gentle when you're pushing a 4" pipe. Radii of curvature on directional work has gotten very aggressive. The drilling assemblies are specifically designed to be flexible. In my experience, short radius drilling uses higher build rates and shorter radii than crossings. 50 m radii are at the edge of what is possible.

Drilling for a utility line under a street would be quite different. You wouldn't want to drill hundreds or thousands of feet in a gentle curve only to pop up 25 or 50 feet away. And it would be very desirable to know the exact depth of the horizontal bore to avoid hitting other utilities; so a tight, precise right angle turn would be needed. I believe this is what he is asking about. A right angle is not what is needed. a modest curve is all that is required to pop out across the street when you start at 30* from horizontal

I have personally run a line under a sidewalk for about 4 feet. Dug a horizontal trench long enough for the pipe to lay in and then used a water hose (my drill head) run through the pipe to flush out the soil in front of it as I inched it along. Rocks were a problem, but it worked without breaking up the sidewalk. Not high tech, but effective. The real problem going under a street would be adding additional sections of pipe as you progress. You will need a pit wide enough to assemble them below ground. Or perhaps flexible tubing? Flexible tubing drilling is at the cutting edge and big \$. The trick with starting from a hole is to use short drill rods - often only 5' long for push rigs and 10' or 20' for drill units. Oilwell pipe is usually 33' or 45'

As I said, I am not in the business and would also like to know how it is done now. I am in the business and this is how we do it

For a drill unit, google "the crossing company". I don't know offhand who the big players are in push units, they tend to be run by Mom and Pops... Baker, Halliburton, Schlumberger, and Weatherford are the big international players.

john hobdeclipe
04-27-2009, 11:28 PM
OK, so the machines that the local utilities contractors use are rammed, or pushed, through the soil. And the deep hole rigs for oil and gas drilling are rotary, at least at the very tip. I did eventually find a diagram on one website that showed the inner workings of a steerable drill head...very interesting.

Camdigger, thanks for the short essay. I always enjoy learning about stuff like this.

My interest in these steerable drilling rigs is that I would like to work out a way to drill a curved hole (in a controlled manner) of, say, 1/2" diameter, in a home shop setting. And my first thought was to learn how the large equipment works, then scale it down. It looks like it will be quite a challenge. I'm not sure if I can literally scale down an oilfield design and make it work. A lot of stuff has to happen in a small space, and still allow a channel to evacuate swarf. This will be fun, whether I ever actually make it or not.

Thanks.

Ian B
04-28-2009, 04:02 AM
John,

As Camdigger says, directional drilling is generally done nowadays using downhole hydraulic motors. However, before those new-fangled things came along, a lot was done using a thing called a whipstock. This may be more applicable to your 1/2" hole, as I haven't seen that many 1/2" OD hydraulic motors on Ebay recently.

Imagine a solid round rod that's had a hole drilled through it, end to end, of the same diameter as the rod, but slightly off axis. You get a long tapered piece that's sharp at the top and full diameter at the bottom. Sort of a wedge that fits in a round hole, and has a concave face.

Drill a hole twice as deep as the (hardened) whipstock is long. Drop the whipstock in, concave face pointing in the direction you want the drill to go. Drill past the whipstock, and the drill should get pushed off to one side, along the whipstock. Drop a second whipstock in, drill further etc. You could even drill a corkscrew hole this way.

Might work, let me know if it does...

Ian

Paul Alciatore
04-28-2009, 04:46 AM
clamdigger,

Sorry, didn't mean to offend. I don't think we are so far apart. I was just going from the original question which suggested "down" as in vertical. Perhaps I misunderstood. I think I was saying much the same as you are now saying. I will admit that I find 45 degrees in 100 feet to be a bit wild. If they can do that, I am impressed. But, it is still a somewhat gentle curve, not a right angle in under a dozen feet. And you also seem to say that is a lot.

I can see where starting at 30 degrees to horizontal would make things a lot easier.

Anyway, I bow to your knowledge and I appreciate your explaining it a bit better. Thanks.

I would still love to see a better explanation of these below ground motors that do some of the steering. What exactly do they do down there?

Paul A.

Bolderdash. Drilled crossings follow the same nominal build rate parameters as oilwells do now +/- 45 */100 feet is absolute max, that's one reason why crossing machines start at 60* + from vertical or 30* from horizontal. The pipe dragged through the crossing is as stiff as production tools.

Why can't machinists acknowledge that CNC isn't plug and play - there's a learning curve associated with it????
15* / 100 feet isn't gentle when you're pushing a 4" pipe. Radii of curvature on directional work has gotten very aggressive. The drilling assemblies are specifically designed to be flexible. In my experience, short radius drilling uses higher build rates and shorter radii than crossings. 50 m radii are at the edge of what is possible.

A right angle is not what is needed. a modest curve is all that is required to pop out across the street when you start at 30* from horizontal

Flexible tubing drilling is at the cutting edge and big \$. The trick with starting from a hole is to use short drill rods - often only 5' long for push rigs and 10' or 20' for drill units. Oilwell pipe is usually 33' or 45'

I am in the business and this is how we do it

For a drill unit, google "the crossing company". I don't know offhand who the big players are in push units, they tend to be run by Mom and Pops... Baker, Halliburton, Schlumberger, and Weatherford are the big international players.

camdigger
04-28-2009, 11:22 AM
Typically the down hole motors are progressive cavity motors. The original downhole motors were turbines, but they spun the bit too fast, and had durability issues. Modern PCM have run lives to several hundred hours without a failure. The old turbines with unsealed bearings rarely made 100 hours.

As simply as possible, the motors are made up of 3 sections

1.) The power section where the torque energy is produced out of the kinetic energy of the drilling fluid. They run a multi lobe helical rotor inside a lobed stator. The stator is molded out of a hard rubber and has one more lobe than the stator (just like a certain square hole drill design). The rotor is polished chrome steel and is an interference fit in the rotor. The most common power section is from Moyno. http://www.moyno.com/500pumps.html The rotor stator combos are made by the same plants and look the same as the pumps.

2.) The bend section. The bend section on an adjustable housing looks like a furnace duct elbow with a lock mechanism which is manufacturer specific and closely held patent protected. As the two segments of the furnace elbow are rotated the bend angle of the motor housing changes. After the motor angle is set, the assembly is locked. The power is transmitted through this section via a drive shaft and universal joints to section 3.

3.) The bearing pack. Motors must withstand bit loads on the order of 3000 - 5000 #/inch of diameter so the bearings have to be hefty. Older designs were unsealed, but the newer ones are sealed. On the lower end of the bearing pack is the bit box where the bit is screwed on. The bit is the only external piece of the motor that turns.

In service, the directional driller needs to know where the motor is pointed. On the outside of the bend section lined up with the inside of the curve of the motor housing, is a scribe mark that indicates the inside of the curve. The position of this mark is transferred by the tool hand up to his instrumentation above and the offset between the scribe and the tool's zero noted. The instrumentation supplies that info and allows orientation corrections to be made at surface.

A few more posts like this and you can apply for a job in the directional drilling field.:D

P.S. I ain't offended. You'd have to work pretty hard at it. I rubbed shoulders with roughnecks for 20 years, lots of whom were drummed out of other industries because of their marked lack of people skills and creative profanity... I've heard whole conversations using the F word and about 4 others

digger_doug
04-28-2009, 11:43 AM
Camdigger gave us all a good introduction to a world
most of us never see (including me) Thank you.

My relate to this:
A fiber optic crew was running along the roads right-of-way
(just have to pay off the govenor, not get any landowners permision....)
It was the smallest unit, on little crawler's, I believe it was a ditch witch brand.

I inquired how, at the end of 500' (the machine's limit) they
would not be in my neighbors basement...

He said "see my brother there with the metal detector,
the drill goes to it. We can put it in a 1' square box at 500'."

On a lighter note, the contractor miscalculated the time greatly.

This crew was from alabama, and planned finishing and running back
down south before winter....

They were still here in February, they do NOT like snow.