The purpose of this article is to compare some of the more common drilling methods forsmall water wells in developing countries. In field terms, these types of water suppliesare often referred to as “rural,” meaning that they are smaller in scale than municipalwells which may provide piped service to buildings, through supply infrastructure (e.g.an electric pumping system and buried distribution pipework). Conversely, rural wellsare typically equipped with a manual pump. They may be dedicated to a smallcommunity or facility (e.g. a church, mosque, or orphanage). These smaller watersupplies are important because they represent a large component of the water used bypeople in developing countries.

Smaller water supplies typically have scaled-back drilling requirements relative to largecommunity or municipal wells because the latter require higher yields. For example, theboreholes for the small supplies may be shallower and smaller in diameter.Consequently, it is often feasible to drill small water supply wells using more compact,less expensive drilling rigs.

At World Thirst Solutions (WTS), we specialize in smaller, more compact types of rigs thatcan be used for drilling rural wells. Drilling rigs in this category are smaller than full-sizedtruck-mounted equipment. They may be trailer-mounted and capable of being towed tosite by a small truck. Some may even be capable of being dismantled and transported ina small truck or boat. Some of the primary smaller rig types and their relative advantagesare described below.

A Review of Small-Scale Drilling Methods

July 28, 2020By: Dr. Mark Kingand Luke Pinneo

In this drilling method, the cutting action is derived from motorized rotation of thecutting head (the bit). Cuttings are removed from around the bit by direct circulation ofdrilling mud down the inside of the drill stem and back up to the ground surfacethrough the space between the drill stem and the borehole wall. At the ground surface,the cuttings settle out in a series of two or more excavated pits (sumps). The mud ispumped back down the drill stem from the last sump in the series.

DIRECT CIRCULATION ROTARY, MOTOR-DRIVEN

July 28, 2020By: Dr. Mark Kingand Luke Pinneo

Trailer-mounted versions of the gear described above often have the capability to befitted with what is known as a down-the-hole (DTH) hammer. With this additional tool inplace, a small rotary rig can penetrate very hard geological formations. The DTH hammeris driven by a large compressor, and it may be initiated at the depth at which standardrotary drilling becomes impractical due to formation hardness.

The borehole diameter provided by a DTH hammer is generally smaller than thestandard rotary gear. Consequently, the design of the well and the pump installationmay need to be modified, relative to a borehole that is drilled with rotary from top tobottom.

DIRECT CIRCULATION ROTARY, MOTOR-DRIVEN +DOWNHOLE HAMMER

In addition to removing the drill cuttings, the use of drilling mud helps to stabilize theborehole walls and minimize the chance of collapse during drilling. However, theborehole must be thoroughly developed after drilling to ensure that mud does not coatthe borehole walls and interfere with water entry. This method can be effective for arange of sediments and bedrock types, although the lighter rigs in this class may bechallenged by moderately hard to very hard bedrock.

WTS represents a wide range of small to medium-sized, motor-driven, direct rotary rigs,from several suppliers (to learn more specifics about these rigs please contact us). Therigs at the small end of this range are disassembled and moved from site to site in theback of a light truck. The cost for these is around $10,000USD. The larger rigs—but still inthe portable class—are trailer-mounted. Depth and penetration capabilities aregoverned by the amount of torque they can apply to the drill head, and by thedownward and upward force that they can exert on the drill stem. These larger rigs cancost as much as $160,000USD.

Of course, there is also a whole range of larger and more powerful, truck- or track-mounted rotary rigs. These may not be the type of equipment that is of interest totypical WTS customers.

The additional cost for outfitting a rotary rig with DTH hammer capability may be around$50,000USD, with much of that cost associated with the purchase of a large compressor.In most cases, the compressor itself may be trailer-mounted, in addition to the trailercontaining the drill rig. Consequently, there are additional logistic and transportationconsiderations associated with adding DTH hammer capability.

This is one of the oldest drilling methods, based on a very simple operating concept. Incable tool drilling, a heavy drill string is repeatedly lifted and dropped to the bottom ofthe borehole. The geologic formation is gradually chipped away by a chisel bit on thebottom of the string. During the drilling process, the drill string is occasionally removedfrom the borehole, and a bailer is lowered to remove the drill cuttings and slurry fromthe bottom of the hole.

Cable tool rigs are less expensive and simpler to operate than a comparable sized rotaryrig. The drilling process is also less labor-intensive and much of the operation can behandled by a single person. Another advantage of this method is that it can usually bedone without drilling mud, and it may enhance the yield of the completed well. It does  

July 28, 2020By: Dr. Mark Kingand Luke Pinneo

CABLE TOOL DRILLING

Lifewater Drilling Technology 360

The operating principle of this method is identical to that described above for the motor-driven version. In short, the borehole is advanced by the rotation of the bit and drillcuttings are removed by drilling mud pumped down the drill stem. The outstandingdifference is that drill stem rotation is provided by the manual efforts of a number ofworkers.

As might be expected, the potential drilling depth of manual rotary is less than largermotor-driven rigs. The geological formations that can be drilled with manual rotary alsotend to be limited, for practical purposes, to materials no harder than moderately hardbedrock. However, for applications with suitable hydrogeology, the cost and logisticaladvantages of such a drill can be impressive. Suitable conditions would include soft tomoderately hard geological formations where the potential water supply layers arerelatively shallow.

WTS represents a manual-driven rotary drill known as The Village Drill (pictured on thefollowing page). The cost of this unit may only be 10 – 20% of the cost of a trailer-mounted motor-driven drill, which makes it an attractive option for applications withappropriate ground conditions. The Village Drill comes with enhanced drilling gear thatcan be implemented on-the-fly, if harder materials are encountered. Theseenhancements will typically require a corresponding increase in manual effort.

July 28, 2020By: Dr. Mark Kingand Luke Pinneo

DIRECT CIRCULATION ROTARY, MANUAL-DRIVEN

this by the turbulent effect of repeatedly raising and lowering the drill string, and also bythe percussive, fracturing effect at the bottom of the hole. Cable tool drilling is generallyslower than rotary drilling, and for that reason it has become less popular in NorthAmerica. However, for applications where drilling time is not a critical factor, the cabletool method may be a strong choice.

Full-size, truck-mounted cable tool rigs are available from several manufacturers.However, supplier options are much more limited for smaller trailer-mounted rigs thatcan be towed by a small truck. WTS represents a small cable tool rig manufactured byLifewater Drilling Technology (pictured on the previous page). This equipment is capableof reaching depths of as much as 400 ft. (~120 m). The simplicity and relatively low cost ofthis unit can make it an attractive option for rural water supply wells in some settings.

July 28, 2020By: Dr. Mark Kingand Luke Pinneo

This group of drilling techniques is nicely described in a set of manuals prepared byPractica (Understanding Groundwater and Wells, 2010) and also in a document preparedby the Rural Water Supply Network (RWSN, Manual Drilling Compendium, 2015). Theoperating principles of the methods are diverse, and include: augering, percussion,sludging, and jetting. However, they have in common that they require minimalequipment and materials that can be acquired or assembled almost anywhere.Alternatively, several of the methods are available as pre-assembled kits. For the mostpart, these techniques are suitable for relatively shallow applications, where they may beused primarily to penetrate unconsolidated materials (e.g. silt, sand, gravel, and clay),though soft rock may be feasible for the percussion method. Nevertheless, there aremany locations in the developing world where they have been successfully used. Thedocuments referred to above provide excellent guidance on applying and assemblingthe necessary materials for these methods.

MANUAL DRILLING METHODS

The Village Drill

Prevailing groundwater and geology conditions in the region where the drill willbe operated, The usage and water supply requirements of the target well(s) to be installed, The logistics, supplies, and equipment maintenance capacity in the project area,Project budget parameters (capital and operating), andAny applicable local and national drilling and water supply regulations.

1.

2.3.4.5.

In evaluating all the drilling options described above, it is critical to understand andconsider the primary project constraints, namely:

At World Thirst Solutions, it’s our pleasure to aid in the process of determining whichsolution best fits your organizational needs. Please feel free to email us with questions, orto learn more about our process and how we might help.

July 28, 2020By: Dr. Mark Kingand Luke Pinneo

CONTACT MARK KINGPhD, PGeo (Canada), Hydrogeologist

CONTACT LUKE PINNEODirector and Founder of World Thirst Solutions