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Drilling methods
- 1. Various techniques implementedfor drilling purposes
- 2. Introduction Well drillingis the process of drilling a hole in the ground for the extraction of a natural resource such as ground water, brine, natural gas, or petroleum. Drilling is also used to obtain very detailed information about rock types, mineral content, rock fabric and the relationships between rock layers close to the surface and at depth. The samples of the rocks are obtained in the form of cylindrical cores or rock fragments.
- 3. Various Types OfDrilling Methods Auger drilling. Air-rotary drilling Rotary-percussion drilling. Cable tool drilling. Mud rotary drilling Diamond core drilling. Direct push rigs. Hydraulic rotary drilling. Sonic drilling Reverse circulation rotary drilling.
- 4. Auger Drilling • Augerdrilling is done with a helical screw which is driven into the ground with rotation; the earth is lifted up the borehole by the blade of the screw. • Hollow stem auger drilling is used for softer ground such as swamps whereas solid flight augers/bucket augers are used in harder ground construction drilling. • It is restricted to generally soft unconsolidated material or weak weathered rock. • It is cheap and fast.
- 6. Air-Rotary Drilling • Thisis a quick and economical method of producing a sample. • Compressed air is forced down the drill pipe and, as it returns to the surface, it carries with it rock chips made by the rotating bit. • This method is used in soft rock materials to about 150m deep, or to drill through the top layer of decomposed rock and soil to get a fresh rock sample from the bedrock below.
- 8. Rotary-Percussion drilling • Thismethod is used for penetrating hard rock types to a depth of around 300m. • Rather than a rotating bit, a hammer bit is forced through the rock by compressed air. • As in air-rotary drilling, rock chips are brought to the surface by the returning air.
- 9. Cable Tool Drilling Cable tool rigs are a traditional way of drilling water wells. It is still the most practicable drilling method for large diameter, deep bedrock wells, and in widespread use for small rural water supply wells. The impact of the drill bit fractures the rock and in many shale rock situations increases the water flow into a well over rotary. Cable tool rigs are simpler and cheaper than similarly sized rotary rigs, although loud and very slow to operate. Since cable tool drilling does not use air to eject the drilling chips like a rotary, instead using a cable strung bailer, technically there is no limitation on depth.
- 11. Mud Rotary Drilling •This method is used for drilling through soft rocks, sand and clay layers especially in the search for coal, oil or gas. • A special mix of clay and water is forced down the drill hole turning a rotary bit, with rock chips returning in the mud slurry. • This method is used for holes up to 3km deep and can be done from ships or offshore platforms especially in the search for oil or gas.
- 12. Diamond Core Drilling. •Thismethod involves a pipe encrusted in industrial diamonds being used to drill through rock layers, with a "core" of rock being left in the centre of the pipe. • This core is recovered and gives information not only about the rock types, but also about the relationships between the rock layers in detail. •Drilling of 1200-1800 meter is common and this method is very expensive.
- 14. Direct Push Rigs •Direct push technology includes several types of drilling rigs and drilling equipment which advances a drill string by pushing or hammering without rotating the drill string. • It is typically limited to drilling in unconsolidated soil materials and very soft rock and are also used for recovery of shallow soil samples. • It uses hydraulic cylinders and a hydraulic hammer in advancing a hollow core sampler to gather soil and groundwater samples. • The speed and depth of penetration is largely dependent on the soil type, the size of the sampler, and the weight and power of the rig • The advantage of direct push technology is that in the right soil type it can produce a large number of high quality samples quickly and cheaply. Rather than hammering, direct push can also be combined with sonic (vibratory) methods to increase drill efficiency.
- 16. Hydraulic Rotary Drilling It consists of a large, heavy machinery that is used to dig deep into the earth. It utilises tri-cone roller, carbide embedded diamond- impregnated drill bits to wear away at the cutting face. This is preferred because there is no need to return intact samples to surface because the objective is to reach a formation containing oil or natural gas. Rotating hollow drill pipes carry down bentonite and barite infused drilling mud to lubricate, cool, and clean the drilling bit, control down hole pressures, stabilize the wall of the borehole and remove drill cuttings. The mud travels back to the surface around the outside of the drill pipe, called the annulus. Examining rock chips extracted from the mud is known as mud logging.
- 18. Sonic Drilling • Asonic drill head works by sending high frequency resonant vibrations down the drill string to the drill bit, while the operator controls these frequencies to suit the specific conditions of the soil/rock geology. • The frequency is generally between 50 and 120 hertz and can be varied by the operator. • Resonance magnifies the amplitude of the drill bit, which fluidizes the soil particles at the bit face, allowing for fast and easy penetration through most geological formations.
- 19. Reverse Circulation RotaryDrilling •RC drilling is similar to air core drilling, in that the drill cuttings are returned to surface inside the rods. •It utilizes much larger rigs and machinery and depths of up to 500 meters are routinely achieved. •RC drilling is slower and costlier but achieves better penetration than RAB or air core drilling; it is cheaper than diamond coring and is thus preferred for most mineral exploration work. •Reverse circulation is achieved by blowing air down the rods, the differential pressure creating air lift of the water. • Although RC drilling is air-powered, water is also used, to reduce dust, keep the drill bit cool, and assist in pushing cutting back upwards, but also when “collaring” a new hole. • It helps in drilling large diameter holes in unconsolidated formation.