Choosing the Right Drilling Rig - Buying Guides DirectIndustry

You could need a drilling rig for a multitude of applications, for example to drill a well to access a natural resource (water, oil, geothermal energy, etc.), to build foundations, to make blasting holes in a mine, to take samples from the ground, etc.

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It is necessary to determine what the drilling rig will be used for, as well as what kind of terrain it will mainly be operating on. Depending on the terrain, you can choose between different types of drilling rigs: rotary drilling rigs, percussion drilling rigs, down-the-hole drilling rigs, top hammer drilling rigs (with high hammer), etc.

In order to make the best choice, it is important to determine whether the drilling rig will be used for your core business or for occasional operations, and in particular whether you want to take advantage of the latest innovations or whether a machine that has proven its worth over several decades might be suitable for you.

Safety, reliability and ease of use are also important elements to consider and are directly linked to each other. A machine that’s reliable and easy to operate, when used according to the manufacturer’s recommendations, increases user safety.

It is also important to define the type of mobility you will need. There are autonomous crawler drilling rigs and truck-mounted or trailer-mounted drilling rigs that need to be powered by a generator or the truck that carries them.

Once you have determined the type of machine you need, you can calculate the size required according to the diameter and depth of the borehole.

Drilling type Soil type Comments Rotary drilling Soft rock Significant depths up to 5,000 meters
Possibility of inclined or horizontal drilling Down-the-hole drilling Hard and cracked rock (limestone, granite, etc.) Depth up to 4,000 meters Top hammer drilling Consolidated land Small diameter (150 mm maximum), shallow depth
Able to do inclined drilling Auger drilling Clay, clayey sand, gravel Depth of a few dozen meters Core drilling All soil types Drilling for soil analysis
Able to do inclined drilling Percussion drilling Hard rock: sandstone, limestone, shale Depth up to 100 meters Pipe Jacking Clay, clayey sand, gravel Installation of horizontal or vertical pipes

Rotary drilling: This type of drilling digs a hole by grinding the rock with a tool under the effect of weight and rotation. It is mainly used in oil production. The cuttings are brought to the surface under the pressure of a drilling fluid that is injected into the drill string. Drilling fluid also helps consolidate the walls of the borehole, so it is not necessary to case it as the operation progresses.

Down-the-hole drilling (rotary percussion drilling or rotary hammer drilling): this type of drilling uses drilling rigs that drill with a rotary cutter (drill head) and hammer the bottom of the hole with a pneumatic hammer. The excavated material rises to the surface under the pressure of the compressed air used for the hammer. These drilling rigs are powerful and have high drilling rates, especially in rock. For artesian wells (wells where water naturally rises to the surface under groundwater pressure) or geothermal drilling, an air injection at the end of the drill pipe pushes the water up the borehole, allowing the operator to immediately determine the water flow encountered. This type of drilling is used for hard and cracked ground up to 4,000 meters deep. When the drilling bit is eccentric, the drilling can be done with a casing advancement system (installation of tubes by gravity) which reinforces the hole as the drilling progresses.

Top hammer drilling: this type of drilling uses drilling rigs that also operate on a percussion system, but one that remains outside the borehole. They are mainly used for small diameter drilling, for example for mineral exploration or the installation of tie rods in rock. This system is used for shallow boreholes, as there can be significant deviation due to the structure of the ground drilled through. These drilling rigs can operate in any direction however.

Auger boring: This is a type of rotary drilling using a worm screw (the auger). This type of drilling is mainly used for unconsolidated clay or sand terrain. The excavated material is directly brought to the surface by the worm screw. For deep drilling, it may be necessary to regularly raise the auger to empty it of its excavated material.

Core drilling: Core drilling is similar to rotary drilling, but it uses a crown to extract a sample, called a core, inside the tool.

Percussion drilling: consists in breaking the rock by dropping a tool, the drill bit, by gravity. This type of drilling can only be used vertically. To prevent the borehole from collapsing, it is necessary to case it as it is drilled. The cuttings are reassembled as soon as they interfere with drilling by replacing the drill bit with a flap valve bailer. The flap valve bailer is a type of tube equipped with a tilting flap in the lower part. This tilting flap allows the tube to be filled with excavated material which is then transported to the surface.

Pipe jacking: is mainly used to install horizontal pipes. The tube is pushed progressively by percussion, the excavated material being removed at the end of the drilling operation either by water injection or with an auger. This technique is used in particular to avoid transmitting vibrations to the surrounding buildings or to avoid digging a trench.

For water well drilling rigs, the general requirements are simple configuration, low energy consumption, easy operation, mobility, versatility and small size. In practice, the choice of drilling rig must be based on the stratigraphy, hole size, and depth as well as the drilling method.

1. Drilling efficiency

Drilling efficiency depends on the formation, the skill/experience of the operator, the type of drilling machine and the drilling method.

For rocky conditions, the most efficient method is to use a downhole drilling rig in conjunction with an air compressor.

For soil, clay and sand conditions, the best method is to use a drilling rig with a mud pump.

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For cobbles, a reverse circulation system is the most suitable method of drilling. Simply add a set of reverse circulation drilling tools to the existing rig.

Truck Water Well Drilling Rig     

2. Price

The price of the machine is a key factor in one's choice of the right drilling rig and is a one-off investment. The price of the machine increases with the diameter and depth of the hole.

From the Drilling method point of view, a DTH drilling rig is more expensive than a coring drilling rig, and the price of a hydraulic drilling rig is higher than a vertical shaft drilling rig, which is a more mechanical drilling machine

From mobility point of view, truck-mounted drills cost more than crawler-mounted drills.

3. Operating costs

Operating costs significantly affect the profit one can make in the drilling business. Net profit is the amount of money a driller receives from well users for water well drilling minus operating costs.

Operating costs include personnel salaries, casing, mud and fuel costs, and rig maintenance costs.

In terms of rig type, Down The Hole (DTH) rigs have higher operating costs than rotary rigs that work with mud pumps. This is because submersible drilling rigs require air compressors and consume very high amounts of fuel. Vertical drilling rigs (mechanically driven) are more economical than hydraulic rigs.

Water Well Drilling Rig     

4 . Drilling methods

• In terms of the working principle of the drilling rig, there are 3 main drilling methods.

The Down The Hole drilling method needs to be used in conjunction with an air compressor. This is a good method for rock conditions.

Mud pump rotary drilling is a more economical way of drilling and is ideal for soil, sand, and clay formations and, for rock, has a lower drilling speed than submersible drilling.

With auger drilling, no air compressor or mud pump is required for the drilling process. However, it can only drill soils, clays and sands.

• In terms of the drilling process, we have 2 drilling methods.

Direct circulation drilling, where the drilling fluid (air or mud) is passed through the drill pipe and the drill cuttings are removed through the space between the outside of the drill pipe and the hole wall.

Reverse circulation drilling, which requires a double-walled drill pipe. The drilling fluid passes through the space between the inner wall of the outer pipe and the outer wall of the inner pipe. It is the most effective drilling method for cobbles and sandy, soil geological structures.

5. Availability of spare parts

One needs to consider the availability of spare parts when buying a drilling rig. It is part of the operating costs. If spare parts are not readily available, it means you have to pay more to get them and it takes longer. All this will definitely affect the profitability of the drilling business.

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