Using DTH (down the hole hammer) drilling method

Published on by

We are in the business of water wells drilling in Romania, Europe. In Romania the soil varies from non-cohesive to cohesive and hard rocks. How feasible it is to use DTH (down the hole hammer) technique in this situation for drilling?

We want to learn more about the drilling with DTH and its benifits at our site perticularly for water wells.

Can you give some information about the feasibility of DTH in different soil conditions, types of bit required and recomendation for casing types while using this technique.

Help would be much appreciated.

Best regards,

Madalin Neagu

SC FORMIN SA

www.formin.ro



Taxonomy

7 Answers

  1. DTH is only usable on hard rocks that may include metamorphic, most Triassic and pre-Triassic rocks and basement rock.  It is completely unsuitable for soft poorly indurated rock such as marl, evaporites, soft chalk and Tertiary to recent sediment.  An Ingersol Rand TH 20 can drill a 500 foot bore hole in hard siliceous Permian limestone can be drill in two days with a total crew of 2.  However, I have seen the TH20 operated by the Regie Sondage in Tunisia take 9 months on the same boreholes.  Tell me what you are drilling and I will tell you if it is appropriate.  I have direct experience with DTH in many places in Africa and around the United States.  Otherwise use mud rotary or reverse rotary methods.  Best you buy a copy of "Groundwater and Wells" by Driscoll, 1986.  Available from Abebooks.com for abot $88. 

  3. When you need to drill high quality holes with diameters between 100-254 mm, DTH (Down The Hole) drilling is by far the best and most effective method. You may read details here : http://www.driconeq.com/en/dth-drilling

  4. The fast hammer action breaks hard rock into small flakes and dust and is blown clear by the air exhaust from the DTH hammer. The DTH hammer is one of the fastest ways to drill hard rock. But if the soil is loose you can use it effectively.

  5. Hi Madalin,

    Rotary Percussion or DTH drilling is the fastest and most efficient method for drilling in hard rocks. It is not good for non-cehesive or cohesive soils or unconsolidated overburden deposits, but if you are just casing through these (up to 30m deep) to get into deeper drilling in the bedrock formations that is fine.

    In my experience as a consulting geologist and professional water diviner, I find drilling with air-flush DTH method is great for fast drilling and excellent borehole logging information (recording the geology and water flow profile of the boreholes). I have done over 2,500 boreholes this way and satisfied 97% of my clients with all the water they required.

    In hard fractured igneous and metamorphic rocks and fractured sedimentary aquifers my survey methods are second to none in locating exactly where to drill for best fracture intersections to get optimum borehole productivity (high yield at least depth). With DTH drilling you can drill to hundreds of metres but sometimes get no water. This is expensive for you and the clients and sometimes the clients refuse to pay. I am the troubleshoot expert in such cases and will usually find plenty of water where other boreholes have failed.

    Casing systems are many, and sizes vary from under 100mm to over 1,000mm depending on the type and purpose of borehole to be drilled. For water wells always size the casing and borehole diameter to accommodate the pump and borehole lining installations required. If a client requires only a small water supply boreholes of 4-inch to 6-inch (100mm to 150mm) diameter can accommodate 3.5-inch to 5-inch borehole linings / well-screen and 3-inch pumps for yields up to 4,000 litres per hour or 4-inch pumps for yields up to 16,000 litres per hour. This covers most private water supplies.

    For some bigger farm irrigation wells and industrial or municipal water supplies in excess of 16,000 l/hr you need to drill 7-inch to 12-inch diameter wells to accommodate 6-inch or 8-inch pumps with suitable borehole linings. Sometimes it is best to drill an exploratory hole first at small diameter to test presence of water in good quantity without excessive cost then, if you find it, to drill out the hole to larger diameter.

    In general doubling the diameter will double the yield (yield is proportional to internal surface area of borehole (pi x diameter x depth).

    If you want to just have one system for all water wells, I find that for most boreholes typically in the 30m to 120m depth range, I prefer the 8-inch (200mm) diameter, which allows plenty of yield capacity and diameter enough to install any size of lining tube up to 6.5-inch with gravel filter pack if necessary, and 4-inch or 6-inch pumps for yields up to 75,000 litres per hour.

    If you are buying drilling rigs you need to match the drilling rig capability to the size and depth of holes you plan to drill, and also need to match compressor capacity (pressure and volume) to the planned borehole depth and diameter.

    I hope this advice is helpful. - DB.



    2 Comments

    1. You might want to buy  "Groundwater Resource Evaluation" by William C. Walton. About $6.00 from AbeBooks.com . A 5 inch radius well given an example in Walton on page 319 will have a specific capacity of about 8.2 gpm/ft.  A 10 inch radius well will have a specific capacity of about 8.8 gpm/ft.  This not double.  Also you should get familiar with lineament analysis.  There are many references on a google search.  Lineaments are very narrow and are best used with old aerial photography.  Pixel dimensions of digital photographs can obscure the lineaments.  I wont take the time to explain how this works.  The method was developed by Richard Parizek and Larry Lattman at Penn State back in the 60s.  Larry was one of my Professors. If you have any questions contact me at wturner@waterbank.com  I have worked throughtout Africa, South America.  the Middle East and North  America.

  6. Dear Madalin

    A “Down-the-Hole” Hammer is probably the most important component on the drill rig and the DTH system holds many advantages over other alternatives, for instance:  Rotary Drilling is fine for large diameter holes in softer more friable rock but less effective in hard rock or where small diameter holes are needed. Top Hammer (Drifter) drilling systems can produce satisfactory results for short hole drilling in hard homogenous rock conditions but would likely experience difficulty in deep holes and in soft ground with large diameters. The DTH system is by far the most versatile and can be used very successfully in a wide range of ground conditions from soft, through medium to very hard.

    When you need to drill high quality holes with diameters between 100-254 mm, DTH (Down the Hole) drilling is by far the best and most effective method. DTH drilling can be performed in most types of rock, hard or soft. It's a commonly used method in the mining industry (blast hole drilling), water well drilling, construction, and in the oil and gas industry.

    In DTH drilling, the drill string rotates while the drilling hammer continuously strikes down into the rock. Inside the hammer, a piston powered by compressed air gives the drill bit its striking power. This combined with the rotational movement means the rock is crushed in a very efficient manner.

    The mechanical difference between the two types of drills is where the hammer is situated in the machine. The hammers applying repeated percussive pressure to the drill bits of DTH drills are situated in  direct contact  with the bit, and are thus actually ‘down-the-hole’. Top hammer drills, however, apply that pressure at the top of the drill string, outside of the hole.

    Drilled wells are typically created using either top-head rotary style, table rotary, or cable tool drilling machines, all of which use drilling stems that are turned to create a cutting action in the formation, hence the term  drilling .

    Drilled wells can be excavated by simple hand drilling methods (augering, sludging, jetting, driving, hand percussion) or machine drilling (rotary, percussion, down the hole hammer). Deep rock rotary drilling method is most common. Rotary can be used in 90% of formation types

    Drilled wells can get water from a much deeper level than dug wells can—often up to several hundred metres.

    Drilled wells with electric pumps are used throughout the world, typically in rural or sparsely populated areas,. Most shallow well drilling machines are mounted on large trucks, trailers, or tracked vehicle carriages. Water wells typically range from 3 to 18 metres  deep, but in some areas can go deeper than 900 metres.

    Rotary drilling machines use a segmented steel drilling string, typically made up of 6 metres  sections of galvanized steel tubing that are threaded together, with a bit or other drilling device at the bottom end. Some rotary drilling machines are designed to install (by driving or drilling) a steel casing into the well in conjunction with the drilling of the actual bore hole. Air and/or water are used as a circulation fluid to displace cuttings and cool bits during the drilling. Another form of rotary style drilling, termed  mud rotary , makes use of a specially made mud, or drilling fluid, which is constantly being altered during the drill so that it can consistently create enough hydraulic pressure to hold the side walls of the bore hole open, regardless of the presence of a casing in the well. Typically, boreholes drilled into solid rock are not cased until after the drilling process is completed, regardless of the machinery used. Following steps may be taken-

    1. Planning a Well.
    2. Consider the costs and benefits of drilling a well against piping or shipping water in.
    3. Know the specific location of the property where the well is to be drilled.
    4. Find out what previous wells have been drilled on the property.
    5. Consult geologic and topographic maps.
    6. Ask people who live near the property.
    7. Get assistance from a consultant.
    8. Get whatever well-drilling permits you need.
    9. Drill the well away from any potential contaminants.
    10. Choose the appropriate construction method.

    Wells are dug when there is sufficient water near the surface and no intervening dense rock. After a hole is made with shovels or power equipment, a casing is lowered into the aquifer, and the well is then sealed against contamination. As they are shallower than driven or drilled wells, they are more likely to go dry when drought lowers the water table.

    1. Augers can be either rotating buckets or continuous stems and can be turned either by hand or with power equipment.
    2. Rotary drills exude water based drilling fluid or compressed air from holes in a rotating bit to make drilling easier and pump out the drill cuttings.
    3. Percussion cables work like pile drivers, with bit or tool moving up and down on a cable to pulverize the ground being drilled into
    4. High-pressure water jets use the same equipment as rotary drills, without the bit, as the water both cuts the hole and lifts out drilled material. p and down on a cable to pulverize the ground being drilled into.
    5. Once the well is drilled, casing is inserted to prevent the water from wearing away and being contaminated by the sides of the well.

     

    Good Luck!

    Prem Baboo

     

     

    1 Comment

  7. Dear Madalin Neagu,

    In response to your questions about the use of DTH (down the hole hammer) while drilling; DTH does not start to work in non-cohesive and cohesive formation but starts working as soon as you enter the hard rock.

    Since you are going to drill through non-cohesive to cohesive to hard rock; I believe you are going to go deeper. So, to execute this drilling successfully, you will need a drilling bits size of possibly 4.250 and 4.125 for 5 inches casing and 4.500, 4.625, 4.750 and 4.758 for 5.5 inches casing and 4.875, 5.125 and 5.375 for 6 inches casing.

    Cheers