Key Questions to Ask When Ordering Down-The-Hole Drilling Tools

What do you look for in a drill rig? Do you choose a rig because of its capabilities to drill the majority of your business, or do you choose a rig that is capable of working outside your core scope of business? Do you look for new technology or stick with what has worked for the last 30 years? It is important to consider safety, ease of use and reliability. All three factors complement each other. Reliable equipment that is easy to use increases safety, when used within manufacturer recommended limits and operated correctly. Choosing the right rig for your business is no different from choosing the right tool for any job. You can easily install a drywall nail with a six-pound sledgehammer, but at what amount of risk? The same scenario goes for trying to break cement with a nine-ounce drywall hammer. The job can be completed, but how much time will it take?

Link to KSQ Technology

Three questions need to be answered when investing in new equipment:

1. What type of drilling job consumes 85 percent of my business time?
2. What kind of geology will be encountered more than 85 percent of the time?
3. Where does 85 percent of my business take place?

The first question to be answered is, what is 85 percent of my business? The rig required to do 85 percent of your business will be more productive than purchasing a rig that is designed for specialty projects. Sure, a big rig can drill any size hole. But at what cost? The next question is, what kind of geology will be encountered more than 85 percent of the time? Mud rotary is productive in high water table areas with consolidated and unconsolidated formations. Dense formations with low water table or fractured zones are more suited for air rotary. The downside to a smaller rig is the air compressor capabilities. A downhole hammer is invaluable in hard formation, especially when several hundred feet of hard formation will be drilled. The last question is, in what type of location does 85 percent of my business take place? Do you drill in the middle of fields, housing developments or urban areas? An ideal rig can be on and off location in less than an hour. The bigger the job, the more move in and out time is needed. However, the bigger the job, the more likely there will be a road built for access. Once all three of these questions are answered, it is time to choose the right rig for your business.

Making that Big Rig Decision

To help shed light on that decision process, I interviewed a colleague and good friend, Mike Epley. He has sold rigs in the Texas and the western United States for the past nine years. Texas is one of the most diverse states when it comes to geology, drilling conditions and types of drilling jobs.
 

Q. How do you help your customers with rig selection?

A. It depends on what the customer needs for their business. Are they replacing a rig or expanding their business? What is the scope of work that the rig is required to do?
 

Q. What type of rig seems to be most popular, air or mud?

A. Again, it depends on the required scope of work. In Texas, east of Interstate 35 and south is predominantly mud. Southwest and central Texas are “Big Air.” The rest of the state requires the use of mud and air as required.

Q. Let’s talk about the scope of work. What type of work do your customers do?

A. Many companies drill residential water wells. I am seeing a lot of diversifying to capture more work than just residential.

Q. Do they use the same rig for residential and municipal water wells?

A. No. Sure, I have customers that use their residential rigs to drill some municipal wells. But the companies that are focused on drilling large-diameter municipal wells day in and day out have 50,000-pound capacity or bigger rigs set up just for that work.

Q. How are your companies diversifying outside of water well drilling?

A. Geothermal and cathodic drilling are very popular. I have always had customers drilling these types of boreholes. A good residential drill rig can easily be set up to drill other types of boreholes.

Q. How long have you had customers drilling cathodic holes?

A. Cathodic has been around a long time. The past five years the work has increased quite a bit.

Q. Now that the oil and gas work has slowed down, did cathodic drilling slow down?

A. No. Installing cathodic protection on new and old pipelines is mandatory. I believe there are 5,000 new holes to be drilled in Texas this year.

Q. What’s the difference between cathodic and geothermal drilling?

A. The borehole size is larger but not outside what the rig is capable of. Geothermal drills 4.25- to 6.5–inch diameter holes to a depth of 400 to 500 feet. Cathodic drills an 8- to 10-inch hole to 500 feet. Once the borehole is drilled, both geothermal and cathodic require special equipment for product installation and pumping grout material down the hole.

Q. So companies drill the borehole for cathodic and install the product?

A. I have a several customers set up to do the entire job from start to finish. It is very similar to large ground source geothermal projects. In the beginning, drillers would just set the loop and grout. Now many companies want to do the whole project from start to finish.

Q. Tell me about the rig purchase process.

A. In the last couple years, a majority of drill rigs have been financed.

Q. Through local banks or big banks?

A. In the past, many of my customer’s used local banks to do the financing. Lately, large equipment financiers have been competitive — such as DLL and Wells Fargo.

Q. What advice would you give to a new water well drilling company starting up this year?

A. Work with your salesman. Make sure your expectations of the rig align with the manufacturer’s product specifications and capacity. It is important to purchase a rig that can be productive in your operating area. Take a good look at your scope of work and break down the operating costs. A good rig can’t be all things to all jobs. Choose the rig that fits best for your company.

Readers with more questions can contact Mike Epley, GEFCO Southwest territory sales manager, at .

Final Thoughts

It all comes down to using the right tool for the right application. A rig capable of drilling 1,000 feet and setting large casing could be set up to drill a 100-foot hole, but at what operating cost? Big rigs require more horsepower and consume more gallons of fuel per hour. The same could be said for a rig designed to drill 300-foot holes. Yes, it could be set up to drill to 1,000 feet, but how much time and extra equipment will be required? Choose the rig that is best for your company’s operating area. Next, choose a rig that can adapt and evolve to the work in your ever-changing drilling environment. Henry Ford said, “If I had asked my customers what they wanted, they would have said a faster horse.” His mindset pushed the automotive industry. In the drilling industry, I ask you, “Do you need a racehorse or a workhorse?” Diversifying is essential to a long successful business, but what type of work is most relevant to your area?

For more information, please visit Down-The-Hole Drilling Tools.

Down the hole (DTH) drilling rig is the equipment that the impactor dives into the hole and directly impacts the drill bit, while the rotary machine drives the drilling hole to rotate and drill to the ore rock. In addition to drilling main blast holes in open-pit mines, down-the-hole (DTH) drilling rigs are also used to drill pre-split holes, anchor holes, slope treatment holes and groundwater drain holes, as well as vent holes, filling holes, pipe cable hole, etc. Down the hole (DTH) drilling rig is mainly composed of impactor, drill bit, lifting mechanism, pressure device, walking mechanism, slag discharging system, drilling rig and drill pipe. When choosing a down-the-hole (DTH) drilling rig，you need to consider various factors. This article will guide you on how to choose the right down-the-hole (DTH) drill from three important parts: drill bit, drill pipe, and impactor.

Down the Hole (DTH) Drilling Equipment Structure

In order to achieve higher drilling speed and lower perforation cost, it is necessary to select a suitable down-the-hole drill bit to drill in a specific rock.

(1) When drilling in hard rock, due to its large rock drilling power, each column tooth and bit body bears a larger load, so the bit body and column tooth are required to have greater strength. When choosing the drill bit, the number of chipway should not be too many, generally choose the double-airfoil drill bit. The size of chipway should not be too large, so as not to reduce the strength of bit body. At the same time, the alloy tooth of the drill bit is recommended to choose the ball tooth, and the height of the ball tooth exposure should not be too large.

(2) When drilling in the soft rock with good drillability, the drilling speed is fast and the relative slag discharge quantity is large, which requires the drill bit to have a strong slag discharge capacity. It is recommended to choose the tri-airfoil or quad-airfoil drill bit. Slagging chute can be appropriately larger and deeper. Alloy teeth can choose spring teeth or chipped teeth, and tooth height can be relatively higher.

(3) When drilling in crushed zones with relatively developed joints, in order to reduce the deflection, it is recommended to use the middle concave or middle protruding drill bit with better steering.

(4) When drilling in the rock with better toughness, it is recommended to use the wedge-shaped tooth bit.

The shape of the drill pipe will affect the drilling efficiency. According to the hydrodynamic theory, only when the air velocity in the annular channel formed by the drill pipe and the hole wall is greater than the suspension velocity of the slag, the slag can be smoothly discharged out of the hole. The airflow velocity in the channel is mainly determined by the channel cross-sectional area, the channel length and the impactor discharge volume.

• The smaller the channel cross-sectional area, the higher the flow velocity.

• The longer the channel length, the lower the flow velocity.

It can be seen that the larger the drill pipe diameter, the higher the air velocity, and the better the slag discharge effect. Generally the diameter of the channel is between 10-25mm. Lower limit for deep holes and upper limit for high pressure.

The choice of drill pipe should not only consider the slag discharge effect, but also its bending resistance, torsion strength and weight, which are mainly determined by the wall thickness of the drill pipe. Under the premise of ensuring strength and rigidity, the selected drill pipe wall should be as thin as possible to reduce its weight, and the wall thickness is generally 4-7mm.

Geometric parameters of drilling hole, working pressure and rock consolidating coefficient are the original parameters for the design of drill impactor. Thus the appropriate size of the drill impactor can be determined and the ideal impact energy and impact frequency can be obtained. The drill impactor can only play a better rock drilling effect in the specific working pressure, specific process parameters and specific lithology.

(1) Working Pressure

The higher the working pressure of the down-the-hole drilling impactor, the faster the rock drilling speed. Since the drill impactor is designed according to a specific pressure, it performs best only within a given design pressure range. If the impactor is not used within the designed pressure range, not only will it not be able to exert its due efficiency, but it will cause the impactor to fail to work or prematurely damage. Therefore, the corresponding drill impactor must be selected according to the pressure grade.

(2) Impact Energy

The impact energy of the down-the-hole drilling impactor must ensure the specific energy of the drill bit, so as to effectively break the rock, and at the same time obtain a more economical specific energy and a higher drilling speed. If the impact energy is too large, it will not only cause energy waste, but also shorten the life of the drill bit. If the impact energy is too small, the rock cannot be broken effectively and the drilling speed will be reduced. Different rocks require different specific energies for chipping, so drill impactors with different impact energy need to be selected.

(3) Impact Frequency

Generally, when the impact energy is constant, the higher the impact frequency, the greater the impact power. However, the outer diameter of the impactor is constrained by the diameter of the borehole. The higher the impact frequency, the smaller its impact energy. Therefore, the increase of impact frequency is limited by the specific work of rock chipping.

The above describes how to choose the right down-the-hole drill equipment from the perspective of the drill bit, drill pipe and impactor. In addition, the specific conditions of the mine, mining technology, blasting parameters, equipment prices and other factors must be considered comprehensively. Or you can directly consult a professional mining equipment manufacturer to choose a down-the-hole drilling rig that is really suitable for your mine.

If you are looking for more details, kindly visit PDC Drill Bit.