Casing Advancement Systems for DTH Hammers

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Underreamers are generally used in softer formations containing sands and gravels but can also work in harder formations.

By Mike Price

Water well contractors have several options when deciding the best underreamer style for their drilling formations and down-the-hole (DTH) casing advancement system needs.

Unlike ring bit systems, which were spotlighted in the September issue of Water Well Journal, where the drilling gauge is on the ring bit assembly, underreamers will typically have some type of retractable bit wing or bit head that will extend to start the drilling process.

Underreamers are generally used in softer formations containing sands and gravels. They can also be used in harder formations, but the leading edge of the wings/heads will wear out faster and can cause increased rotational torque. They are engaged when turned to the right.

Contractors who use underreamers commonly say to:

• Keep the device inside the casing and don&#;t over-rotate
• Rotate slower and let the hammer do the work
• Have the pipe float down the hole with little (if any) driving.

&#;Underreamer systems have moving parts like wings, heads, or lugs. These parts are held in by various means depending on their manufacturer and should be inspected after every hole for damage and wear,&#; said Justin Lewis, product manager of casing advancement and DTH at Mitsubishi Materials USA in Mooresville, North Carolina, in the August WWJ Q&A.

&#;The foot valve should be inspected after every hole and the buttons should be checked and sharpened when they start to wear. Drive shoulders on shoed systems should be checked to ensure adequate surface area to prevent from binding in the drive shoe.

&#;The drive shoulder surfaces can be built up and machined to be like new, greatly prolonging the life of the tool. Whichever type of retaining pin system is used on the device should also be inspected for damage and wear.&#;

Lewis, who presented the workshop &#;Casing Advancement 101&#; at Groundwater Week , also shared in the August WWJ Q&A that most casing systems need to run at a lower pressure than standard DTH bits, around 150 to 200 pounds per square inch [PSI] depending on formation and an uphole velocity of to FPM [feet per minute] in order to flush cuttings.

&#;With higher pressures you run the risk of breaking the welds at the drive shoe or ring bit assembly as well as damaging the device itself. When using a casing system, it is also recommended to flush the hole regularly in order to keep the inside of the casing from building up cuttings,&#; Lewis said. &#;Rotation speeds vary from 10 RPM to 80 RPM depending on device size and formation.

&#;Weight on bit also varies depending on device size and formation, but I do recommend running a heavy stabilizer on top of the hammer anytime a hammer is used, not just when using a casing system.&#;

Underreaming in Alaska

Johnny Kay, president of Hefty Drilling Inc. in Anchorage, Alaska, has used casing advancement systems for 30 years on most wells since the formations he works in are primarily glacier till, gravel, and bedrock.

Kay uses the NUMA Super Jaws ND (no drive shoulder) Overburden Bit model (see image) which allows him to use a conventional drive shoe that works well with his drilling method. He runs a casing hammer in glacier till and boulders, which also works for setting casing into bedrock. The casing hammer works as a diverter and the weight of the casing hammer usually allows for the casing to follow it.

&#;Occasionally I have to fire the casing hammer to advance the casing due to boulders or just wall friction,&#; he says. &#;I use a normal cable tool-type drive shoe that has an inside diameter of 6 inches. That way when bedrock is encountered, I can drill a 6-inch hole, and it also allows for more clearance if a 4½-inch liner needs to be set due to an unstable rock hole.

&#;For our full-size rigs, we primarily use the casing hammer for our unconsolidated material. I do have a new Nordic Drill lower drive conversion to install on one of my rigs when I find the time. As for the DTH hammer, we use it for the Super Jaws, the ring bit systems, and normal bedrock drilling. I can&#;t say which one is better [underreamer or ring bit], but I do use both with pretty good success.&#;

Kay, who was scheduled to be part of a driller panel discussion on the benefits of underreaming at the Wisconsin Water Well Association Annual Conference in January, shares some other key points:

• Patience is key.

&#;It&#;s not a race to get that pipe in the ground,&#; he says. &#;Although we are always trying to get done to get to the next job, but if you get into trouble, it&#;s going to take longer.&#;

• A proper cuttings diverter is important when running the drive shoe systems.
• Kay uses the NUMA Super Jaws ND (no drive shoulder) model with a regular cable tool-type drive shoe. Since he uses a good-sized casing hammer, the weight of it pushes the casing down. When it doesn&#;t fall right in, it takes just a little hit, and then it goes.

&#;The best thing is it provides a really straight hole and enables us to go right through boulders and it drills fast,&#; he shares. &#;When I mount my Nordic lower drive, I will be experimenting to see if it helps with drill speed also.&#;

• Welding is also key. While the manufacturer has requirements to follow, Kay takes extra steps. After they weld a casing advancing type of shoe to the casing, they wrap it with insulation to slow cool the weld (see photos).

&#;It&#;s what we do when we do a structural weld on a drill rod or something along those lines,&#; he says.

• Kay appreciates that with Super Jaws ND he doesn&#;t have to turn to the left to retract to get back into the casing.

&#;With no shoulder, it allows me to drill out beyond the drill shoe,&#; he explains. &#;It works out well. That way when we encounter a boulder, we can drill through it and see if it&#;s actually a boulder or possibly bedrock. Since I tap on the casing with the casing hammer, I don&#;t want to chance folding the end of the casing without a drive shoe.&#;

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Benefits of Super Jaws Overburden Bits

NUMA&#;s Super Jaws Overburden Bits are used for simultaneously drilling and casing 5½-inch to 48-inch holes in hard rock and unconsolidated ground conditions of overburden, boulders, or bedrock.

Made in the company&#;s facility for more than 20 years in Thompson, Connecticut, Super Jaws utilizes wings that extend out to drill a full diameter hole while in the drilling position. Upon completion of drilling, the wings retract back under the guide body for extraction of all tooling to the surface while leaving the casing in place. There is no reverse rotation required, nor any rings left in the hole.

&#;This saves drillers time and money in various applications,&#; says Virginia Barron, NUMA&#;s western United States regional manager in Brownwood, Texas. &#;We offer many of the standard shank sizes that are currently out in the market as well as our own shanks in the larger diameter sizes.

&#;NUMA&#;s ND models are also used in conjunction with DR [dual rotary] rigs and casing hammers. Utilizing the Super Jaws ND bit to drill through the formation when running a DR rig can save your carbide drive shoe, which is beneficial for many of the deeper hole applications. Using Super Jaws to drill the formation can also assist with projects that require telescoping.

&#;Super Jaws will allow you to drill faster and oftentimes helps eliminate the need for several casing sizes. This is huge when you are talking about drilling larger diameter municipal wells. This model is not locked into any drive shoe and can drill out past your casing when needed or be removed easily without needing to remove the casing.&#;

There are certain areas of the country where casing hammers are much more prevalent, like the Northwest, so they use the ND model, but Barron says many dual rotary rig owners are beginning to take advantage of the ND bit as well. However, she says overall the drive shoe model for the water well market is slightly more common (see image showing both models).

&#;With the ND model, the driller will use a drive shoe but not ours,&#; she explains. &#;Ours are made specially to meet up with the bit body shoulder on only the standard model.

&#;When running the ND model, they will typically use a casing shoe with carbide in it or at least hardened and they are usually larger than the OD [outside diameter] of the casing but flush with the ID [inside diameter] so there is no interference with the bits that go inside the casing.&#;

Barron, who has been with NUMA for more than 20 years, shares that many of her customers operate Super Jaws on one side of the mountain and switch to a ring bit or similar system for the other side due to different formations.

&#;I do hear often that guys who are new to underreamers say the Super Jaws Bit seems a bit easier to operate as they do not have to lock and unlock in and out of a drive shoe or ring bit,&#; she says. &#;They also appreciate the cost of our drive shoes, knowing they will be leaving that down the hole with the casing.&#;

The Super Jaws wings will want to go out into the drill position when they are against the formation. If a contractor pulls up the DTH hammer for the night and formation fills inside the casing, Barron says they can kick on a little air and do a very slow feather-like rotation down until they have cleared out the ID casing.

&#;They can easily hear if their wings are still inside the casing,&#; she says. &#;If so, they pull up just a bit and repeat the process slowly advancing until they feel the bit shoulder hit the drive shoe.&#;

Maintaining Super Jaws Overburden Bits

Barron says the best way to maintain the Super Jaws Overburden Bit is to:

• Check for pocket play, which is where the wings will have side to side movement over time due to the rotational forces applied to the pockets while rotating and drilling.

&#;Once this becomes excessive it&#;s time to change your wings out,&#; she says. &#;You should also check your carbides on the wings and change or sharpen them based on the wear or condition of them.&#;When changing the wings, it&#;s an easy process of grinding the tip off the pins behind each wing. These pins are threaded and once you pull these out you can slide your old wing out and the new wings in and press fit the new pin in.

&#;The bits for 6-inch casing do not have pins that are pre-threaded, but there is a pre-drilled hole through the pin that allows for drilling and tapping of the hole to be able to remove the pins. We have made this very easy so that it can be done even on the jobsite if needed. We also have wear protection on the drive side of each wing.&#;

• In addition to bit face maintenance, Barron says it&#;s always crucial to check the spline wear on Super Jaws or conventional bits. If this wear is excessive with rollover or at an angle, she says it can lead to shanking of the bit.

&#;Too much side wear on the splines can be transferred to the internal chuck splines also,&#; she says. &#;If so, the chuck should be replaced as this can damage any new bit you put into the hammer.

&#;This is just typical maintenance on any hammers and bits regardless of manufacturer or style of bit. As long as you&#;re checking to see how the carbides are holding up and changing the wings when needed, this is all you need to do to maintain your Super Jaws Bits.

&#;We have some videos on our YouTube channel for drillers to get a better visual of how the wings work and how to change them out.&#;

Mike Price is the senior editor of Water Well Journal. In addition to his WWJ responsibilities, Price contributes to the Association&#;s scientific publications. He can be reached at , or at (800) 551-, ext. .

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