Air drilling fluid

A drilling fluid comprising air, water, and a foaming agent (surfactant). These substances travel into a well as a mist, then change into a foam before returning up the annulus. See also Air Drilling Fluid, Stable Foam, Stiff Foam. 

Stable Foam. An oil and gas well drilling fluid foam that contains film-stabilizing additives, such as polymers or clays, and is pre-formed at the surface. See also Air Drilling Fluid, Foam Drilling Fluid, Stiff Foam. 

Chemical additives for gas-based drilling fluids are limited to surfactants (qv), certain polymers, and occasionally salts such as sodium or potassium chloride. An aqueous solution of the additives is iajected iato the air or gas flow to generate a mist or foam. No additives are used ia dry air or gas drilling operations. Gas-based fluids are not recirculated and materials are added continuously. As the fluid exits the well, air or water vapor escapes to the atmosphere, gas and oil are burned, and water and formation soflds are collected into a pit for later disposal. Stable foams must be destabili2ed to separate the air from the Hquid phase for disposal. 

Density. The density of the drilling fluid is adjusted using powdered high density soHds or dissolved salts to provide a hydrostatic pressure against exposed formations in excess of the pressure of the formation fluids. In addition, the hydrostatic pressure of the mud column prevents coUapse of weak formations into the borehole. Fluid densities may range from that of air to >2500 kg/m (20.8 Ib/gal). Most drilling fluids have densities >1000 kg/m (8.33 lb/gal), the density of water. The hydrostatic pressure imposed by a column of drilling fluid is expressed as follows ... 

Air-gas drilling usually increases drilling rate by three or four times over that when drilling with mud as well as one-half to one-fourth the number of bits are required. In some areas drilling with air is the only solution these are (1) severe lost circulation, (2) sensitive producing formation that can be blocked by drilling fluid (skin effect), and (3) hard formations near the surface that require the use of an air hammer to drill. 

Air and natural gas have also been used as drilling fluids in slim-hole-drilling mining operations, special large-diameter boreholes for nuclear weapons tests, and, more recently, in geothermal drilling operations. 

Air and natural gas are often used as a drilling fluid with no additives placed in the injected stream of compressed fluid. This type of drilling is also often referred to as dusting because great dust clouds are created around the drill rig when no formation water was present. However, modern air and gas drilling operations utilize a spray at the end of the blooey line to control the dust ejected from the well. Figure 4-185 shows a typical site plan for air drilling operations. 

In most air and gas drilling operations, open-hole well completions are common. This type of completion is consistent with low pore pressure and the desire to avoid formation damage. It is often used for gas wells where nitrogen foam fracturing stimulation is necessary to provide production. In oil wells drilled with natural gas as the drilling fluid, the well is often an open hole completed with a screen set on a liner hanger to control sand influx to the well. 

Air and Gas. In the regions where air and natural gas are used as the principal drilling fluids, the potential oil and gas production zones usually have low pore pressure, or require well stimulation techniques to yield commercial production. In these production zones, air drilling (or natural gas drilling) is continued into the production zone and the initial produced formation fluids are carried to the surface by the circulating air or natural gas. This is nearly the same situation as in mud drilling, except that in air (or gas) drilling the transit time for the initial produced formation fluids to reach the surface is much shorter. In mud... 

The downhole turbine motor designed to be activated by the flow of incompressible drilling mud cannot operate on air, gas, unstable foam or stable foam drilling fluids. These downhole turbine motors can only be operated on drilling mud or aerated mud. 

The positive displacement motor of the Moineau-type design can be operated with unstable foam (or mist) as the drilling fluid. Some liquid must be placed in the air or gas flow to lubricate the elastomer stator as the metal rotor rotates against the elastomer. Positive displacement motors have been operated quite... 

Air percussion U or C 2000+ M,R,I drilling fluids dangerous with flammable fluids Fast cuttings removal rapid good in consolidated formations... 

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