Choosing the Right Drilling Rig

Drilling type Soil type Comments

Rotary drilling

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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.

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What is Crawler Mounted Water Well Drilling Rig and Why Do We Use Them?

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.

While there are different types of drilling rigs, these rigs obviously share many similarities since the tasks that they perform are identical. In particular, all modern hydrocarbon rotary rigs contain five main systems. These systems are:

• the Power System
• the Hoisting System
• the Rotary System
• the Circulation System
• the Well Control System (Blowout Prevention System)

These systems are shown in Figure 9.01. In addition, Figure 9.02 shows a more detailed schematic diagram of a rotary table, land rig.

Figure 9.01: Major Systems in a Modern Rotary Rig

Source: Serintel: Oil and Gas Portal Drilling Technologies

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Figure 9.02: Sub-Systems in a Modern Rotary Rig

1. crown block
2. mast
3. monkey board
4. traveling block
5. hook
6. swivel
7. elevators
8. kelly
9. kelly bushing
10. master bushing
11. mousehole
12. rathole
13. drawworks

14. weight indicator
15. driller's console
16. doghouse
17. rotary hose
18. accumulator unit
19. catwalk
20. pipe ramp
21. pipe rack
22. substructure
23. mud return line
24. shale shaker
25. choke manifold
26. mud gas seperator

27. degasser
28. reserve pit
29. mud pits
30. desander
31. desilter
32. mud pumps
33. mud discharge lines
34. bulk mud components storage
35. mud house
36. water tank
37. fuel storage
38. engines and generators
39. drilling line

Source: Serintel: Oil and Gas Portal - Drilling Technologies