Section 3How to Drill with the LS-100
Experience in developing countries has shown that the construction of drilled wells must be simple and efficient. This keeps projects affordable, maintains a certain momentum and enhances local enthusiasm. Section 3 describes how to set-up and drill with the LS-100 - a small mud rotary drill rig which has been successfully used in over 20 developing countries around the world with great success.
Drilling With the LS-100 Index
The LS-100 is a small, portable mud rotary drilling machine made by Lone Star Bit Company in Houston, Texas. Using this small drill rig, it is possible to rapidly complete safe, reliable water wells. As discussed by Hamann (1992), advantages of the LS-100 include: comparatively low cost, portability, and speed and depth to which the rig can go relative to manual methods (see Table 2).
A small mud rotary drill rig is only a very small part of a solution to a very large problem. Success in using the drill rig depends on many factors including favourable subsurface geologic conditions, technical aptitude and experience, community support, and a commitment to maintenance, education and communication with others regarding the successes and failures of drilling.
In addition, before deciding whether or not to use the LS-100, the following factors should be seriously considered because they have a very strong bearing on the success or failure of a drilling project:
Prior to traveling to a drilling site, there are a number of tasks which should be done. While it may be sometimes necessary to embark on a drilling project without all these tasks completed, projects will have a higher success rate and a lower level of frustration if they can be done ahead of time. Ideally, people have been trained, an Action Agency and Village Water Committee(s) established, and a Drill Team Selected (see Appendix S).
Unload all tools and equipment on dry ground near the selected drilling location. If possible, orient the drill rig so that it will be shaded during the afternoon. It is very hard to clean sand from greased threads, so keep pipes off the ground by placing them on boards (or tree branches).
Fill four 200 litre (55 gallon) drums with water and ensure that villagers are ready to keep these drums full during the drilling process. Arrange the water drums next to the area where the pits are to be dug. Add 1 cup of chlorine to each drum of water to ensure that bacteria are not injected into the groundwater during drilling - unless you are using polymer to thicken your drilling fluid (see Section 5 - Footnote #1).
Fence off an area behind which all observers must stand during the drilling process. Designate one of the local leaders to ensure that this safety rule is observed at all times. Have one of the drillers frequently explain what is happening while the well is being drilled.
Hand dig a 10 cm (4 in) diameter "well guide hole" about 15 cm (6 in) deep where the well is to be drilled.
Dig two pits (settling pit and suction pit) - see Figure 5. Keep these pits 1.5 metres away from the well guide hole so that, when the well is finished, the pump pad does not need to be built on the unstable filled-in mud pits.
Together, the 2 pits should have at least three times the volume of the hole being drilled(1) (Driscoll, 1986). It is usually good if each pit is approximately 60 cm deep, 60 cm wide and 90-120 cm long (2 ft deep, 2 ft wide and 3-4 ft long) (with the long axis parallel to the direction of flow).
Dig a 6 inch deep channel between the well guide hole and the first mud pit. Put the mud pump between the drill rig and the suction mud pit (see Figure 5).
Set-up the LS-100 and mud pump following the steps outlined below (see Figure 6):
Connect hoses as follows (see Figure):
To prevent the LS-100 engine from stalling when it is idling, adjust the choke as follows prior to initial starting:
To keep the LS-100 drive shaft from rotating when the throttle is in the idle position, check and adjust it as follows:
Secure a 10 cm (4 in) drill bit on the end of the drill pipe with a pipe wrench after cleaning and lubricating the threads of both the drill pipe and drill bit (see Section 4).
A borehole is drilled by rotating a bit at the end of drill pipe. Borehole cuttings are removed by continuous circulation of a drilling fluid as the bit penetrates the formation. The drill pipe is connected to the drill engine. Drilling fluid is pumped down through the hollow drill pipe using a centrifugal pump (mud pump) to a drill bit. The fluid flows upward in the annular space between the drill pipe and the borehole to the surface where it is channeled into a settling pit and most of the cuttings drop out. Fluid from the settling pit overflows into a second pit (suction pit). Relatively clean fluid from the second pit is then pumped back through the drill pipe and the cycle repeats.
Using water from the 208 litre (55 gallon) drums, fill the mud pits to the very top. Make sure that one person is responsible for keeping the pits full of water during the entire drilling process. This must be done to ensure that the cuttings will settle-out.
Fill the fuel tank of the drill engine and start it. With engine running in idle, raise the drill head to a sufficient height to allow the installation of a drill pipe section with the drill bit. Turn pipe by hand to thread it onto the swivel thread until it is all the way on.
Lower the drill bit into the prepared hand dug guide hole. Allow the drill pipe to rotate above the bottom of the guide hole.
Fill the fuel tank of the mud pump and start it using the following process:
Increase the engine RPM until the clutch engages and the pipe starts turning. Turn the 3 way Valve so that the water will circulate from the Mud Pump through the bottom by-pass hose back to the pit. Add water as required to top-up the pits.
Then turn the valve so that water flows into the drill swivel. Make sure no water is leaking from the swivel seals. If it is, re-direct the water through the by-pass hole or stop the mud pump. Loosen set screws and tighten gland nuts quite snug and until leaking stops. Re-tighten set screws. It may be necessary to repeat this process during the drilling operation. Pump grease into the top & bottom gland nuts before tightening.
When the water begins pumping through the drill pipe, it will make a lot of splashing so make sure the drill operator is ready to lower the drill pipe into the hole fairly rapidly. After the drill has penetrated 30 cm (1 ft) or so, there will be a smooth flow of water.
Maintain a slight back pressure on the winch handle; at an easy drilling speed, the winch handle should make a full circle every 20 seconds or so. Do not exceed this speed or the water will not be able to circulate the cuttings out of the hole fast enough (causing the bit to seize) and/or the borehole walls will not be coated with enough fines to resist caving ! In harder formations it should make a full circle every 40 seconds. In very hard rock, a drilling rate of 30-150 cm/hr (1 - 5 ft/hr) is to be expected.
In hard rock, insufficient pressure on the drill pipes may result in an extremely low drilling speed. Caution should be used to avoid excessive pull-down pressure (weight) exerted on the drill string because this may result in crooked holes, bent drill rods and jammed drill bits (see Appendix G-3). Rotation speed should be slowed as the pull-down pressure increases.
Watch that the water is circulating continuously when the drill is rotating.
As soon as the drill has penetrated 60 cm (2 ft) or so, take sample cuttings from the first small pit and place them on the appropriate record location.
Continue the drilling process until all 1.5 m (5 ft) of the drill pipe has penetrated the hole.
Leave the drill string turning at the bottom of the hole and continue circulating drill mud until all cuttings are removed from the borehole (even if it takes 5 minutes or longer). This cleaning process is increasingly important as the hole is deepened: if not fully done in the manner described, cuttings may settle to the bottom of the borehole and make it impossible to add another length of drill pipe, cause the hole to cave-in or plug-up (see Appendix G-2) or the drill bit to jamb (see Appendix G-3). Note that the deeper you drill, the longer it takes the cuttings to be removed from the hole.
Switch the 3-way valve so that the drilling fluid circulates back into the mud pits rather than down the drill pipe. Clamp off the drill pipe and unscrew the drill head.
Raise the drill head to the full mast height (be careful not to allow the cable buckle to enter the top hole in the drill mast head and get jammed). If the drill engine is stopped, start it when it is at an easy operating level as the drill head is being raised. Work rapidly to prevent problems caused by cuttings settling in the borehole.
Lubricate the threads of the next drill pipe and screw it into the one clamped at the well head. Screw the other end onto the output shaft. Tighten the joints with wrenches.
Switch the 3-way valve so that the drilling fluid starts to circulate back down the drill pipe. Do not lower the drill head until there is clear evidence that the mud is circulating through the pits again.
Once drilling, it is important to:
Special measures must be taken if you drill into:
After the 10 cm (4 in) "pilot" borehole is completed to the desired depth, allow the drilling fluid to circulate for 10 minutes to remove as much cuttings as possible from the well.
After 10 minutes, raise the drill head until the slip clamp on the drill table can be engaged at the coupling of the next length of drill pipe. Turn-off the mud pump.
Remove the upper length of drill pipe and lower the drill head to engage the socket in the next length of drill pipe.
Continue to carefully remove the drill pipe from the well. BE SURE THE SLIP CLAMP IS FULLY ENGAGED EACH TIME AND THAT EVERYTHING IS SECURED because it is very easy to drop drill pipe and tools into the borehole! If this happens to you... pray.... and read Appendix G-5!
Be sure to keep the mud pits and borehole full of water during this process.
When all the drill pipe is removed, the crew must now decide if subsurface conditions warrant completing a well. Careful action should be taken if the aquifer is marginal (see Appendix G-9);
If it appears that the borehole has only penetrated a marginal aquifer see section on "When to Stop Drilling" (Section 6), set a 5 cm (2 in) PVC casing with 3 mm (1/8 in) slots in the aquifer area. Then rapidly bail-out the casing, pump it using Waterra tubing or blow-out water using an air compressor (see Section 10.3). If the casing can be easily pumped dry, it may be worthwhile to abandon the well and drill elsewhere.
If there is a good flow from the aquifer, add a 6 inch reamer bit behind the 4 inch bit (see Section 4). Then re-drill the hole to widen it to the required 6 inches. While this is being done, the screen interval, length of casing, volume of gravel pack, grout etc can be planned, materials cut to size etc. This is very helpful to do since time is always of the essence when the drill pipe and bit are pulled from the completed borehole and the screen and casing installed.
If there is much sticky clay, the water-bearing portion of the 10 cm (4 in) hole may be filled with clean sand prior to reaming. This keeps clay from dropping into the borehole and smearing onto the borehole walls (causing severe well development problems).
Replace the drilling fluid with clean water or drilling mud prior to drilling into the aquifer (see "Section 5"). If not done, the well may never reach its full yield!
If in doubt, keep drilling until you are sure that you have found enough water. For tips on "How to Decide When to Stop Drilling", see Section 6.
After you have decided to stop drilling, allow the drilling fluid to circulate for 10 minutes to remove as much cuttings as possible from the well. Then circulate the "mud" out of the borehole by replacing it with fresh (clean) water.
When removing the drill pipe from the well, keep the bit rotating and water circulating. This leaves a nice smooth borehole wall behind the bit as it is coming out of the hole(2).
The casing, gravel pack, annular seal, cement pad and hand pump can then be installed.
There are many problems that you will encounter when drilling wells. Learn from the problems and try not to repeat them too often!
In addition, the following problems have also been encountered:
1 Ideally, for a 30 m (100 ft) deep borehole drilled with the LS-100, the settling pit should be 60 cm (2 ft) deep, 75 cm (2.5 ft) wide and 2 m (6 ft) long; the suction pit should be 60 cm (2 ft) deep, 75 cm (2.5 ft) wide and 1 m (3 ft) long. However, while these pits provide optimum settling capability, they require large quantities of water to be brought to the site.
2 If this is not done, the fins of the blade bit may disturb the borehole wall and cause silt/clay cuttings to "ball-up" or bridge within the borehole. In addition, drilling fluid may cause silts and clays (especially above the water table) to swell and bulge into the borehole. Getting the screen past these blockages can be very difficult and it is almost impossible to avoid severely plugging the screen.
Hamann, M. (1992) "Utilization of Small Mud Rotary Drilling Rigs for Development of Safe, Village-Level Groundwater Resources", Paper presented at the 5th African Water Technology Conference, Nairobi, Kenya, February, 1992.