Air Drilling

Air Drilling Associates is a world leader in applying air-, mist-, foam-, aerated fluid and other underbalanced techniques for petroleum and geothermal drilling projects.

The company is led by a management team with over thirty years of experience running such projects on all continents of the world. Our equipment fleet has an average age of only two years, making it among the youngest and most modern in the industry.

All this is backed up by our strong commitment to quality, safety, health and the environment through adherence to the strictest regulatory and ISO requirements.


Air/Mist/Foam Drilling

The main reason for using air for drilling purposes is to reduce the hydrostatic pressure in the wellbore. The “lightest” form of drilling, using only gas (air, nitrogen, or natural gas) to circulate with results in an equivalent specific gravity (s.g.) of close to zero. This can be then be “weighted” to about 0.2 by injecting small amounts of fluid, a method called “Mist Drilling”. Conversely, a fluid (water, oil-based mud, etc) can be lightened down to an s.g. of about 0.6 by injecting gas, a method also called “Aerated Drilling”. By injecting small amounts of surfactant the gas/fluid mixture can also be foamed to create a circulating fluid with an s.g. in the range 0.2 – 0.8. These circulating systems are shown in the graph below:

Air Drilling is a technique used in areas where formations are "Dry", i.e. there is no influx of water or liquid hydrocarbons. High volumes of low-pressure air are used in place of conventional drilling fluids to circulate the well bore clean of cuttings. This method is also called “Dusting” due to the clouds of finely ground rock cuttings that blow away from the return line, also called the “Blooie Line”.

The main advantages of Air Drilling are as follows:
  • Increased Penetration Rates over other air assisted systems and drilling fluids, in many cases 2 - 3 times higher. This can often be increased even more using air hammers.
  • Elimination of Lost Circulation into low-pressured formations.
  • Continuous Well Test when drilling into gas zones; a real time indication of contact with the pay zone.
  • Formation Damage is minimized since to the lack of hydrostatic pressure prevents rock cuttings from being injected into the rock matrix.
  • Extended Bit Life since the compressed air cools the bit and quickly transports the cuttings away from the drill bit’s cutting structure.

The disadvantages of Air Drilling are its inability to handle formation fluids or to contain sloughing shales, thus reducing its application to consolidated “hard rock” country applications where there is little to no fluid influx.



Mist Drilling


Mist Drilling is used when the rock formations begin to produce small amounts of water (10 to 100 bbls per hour) during air drilling operations. Air volumes are increased and a Mist Pump is used to inject small quantities of a solution of water and foaming agent. This solution entraps the water influx and enables the air phase to lift the cuttings and influx to surface. Without the addition of surfactant, wet cuttings may coalesce and form a “Mud Ring” in the annulus, usually just above the drill collars where velocities are reduced, resulting in lost circulation, stuck pipe, and/or downhole combustion. The same advantages as for Air drilling also apply to Mist Drilling, though the increased air volume requirement for mist drilling will involve the 30-40% additional compression equipment.


Foam Drilling


Foam Drilling is especially suitable for drilling large holes in formations that are prone to lost circulation. Foam is generated at the surface by mixing the air from the compressors with a foaming solution from the mist pump. The consistency of this “fluid” is much like shaving cream with an interlocking bubble structure of encapsulated air providing a lifting capacity superior to that to any drilling fluid. The adjustment of the Foam Quality (gas/fluid ratio) in conjunction with a back pressure valve allows the operator to produce a bottom hole pressure equivalent to a circulating fluid weight in the range 0.2 to 0.8 s.g.




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