Well Development Techniques Part (3)

Well Development Techniques Part (3)

Air Development (air surging and pumping)

Several techniques for the air development of wells exist. However, all inject air into the borehole such that aerated slugs of water are lifted irregularly out the top of the well casing. Air pressure may be cycled on and off to create a surging action desirable in well development. Sufficient air pressure will result in a continuous flow of aerated water out the top of the well, removing sediment and fine particles from the borehole.

For small wells, air may be injected down the drill stem into the formation. For larger diameter wells a separate airline and eductor pipe are inserted into the borehole. The size of the eductor pipe and airline depend on air pressures and volume available as well as the casing diameter. Numerous sources caution drillers that under some conditions the use of air development approach can create aquifer air locks, in such cases a development with water is a wiser choice. Even so air as a development is probably the most popular and widely used method of well development today.

The type of discharge produced from a well during air development depends on the air volume available, total lift, submergence, and annular area. In practice, two different flow conditions can be recognized when air is used when air is used for water well development although other flow regimes may exist at much lower or higher velocities in smaller diameter pipes. The picture above provides an illustration of how multiphase flow (water and air) occurs in the casing during air development. The percent submergence, total lift, and capacity of the compressor will control the relative proportion of air and water for a particular well.

A. Introduction of a small volume or air under high head causes little change in the water level in the well. In this case, the air pressure available is just sufficient to overcome the head exerted by the water column.

B. As air volume increases, the column becomes partly aerated. Displacement of the water by the air causes the water column to rise in the casing. Drawdown does not change because no pumping is occurring.

C. Further increases in air volume cause aerated slugs of water to be lifted irregularly out the top of the casing. Between surges, the water level in the casing falls to the near the static level.

D. If enough air is available, the aerated water will continually flow out the top of the well. With average submergence and total lift, the volume of air versus water is about 10 to 1. Higher air volumes may increase the pumping rate somewhat, but still higher rates may actually reduce the flow rate because flow into the well is impeded by the excessive air volume.