PRIVATE WATER SYSTEMS - Completion - Gravel Pack

Gravel Pack

Four of the most common conditions where construction of a gravel pack is warranted are when aquifers consist of:

  1. Fine Uniform Sand
  2. Thick Artesian Aquifers
  3. Extensively Laminated Formations
  4. Loosely Cemented Sandstone

Fine Uniform Sand

If the slot openings to be selected on the basis of a naturally developed well are less than 0.01 inches wide, construction of a gravel-pack should be considered. With a gravel pack, the slot openings can then be much wider, improving the efficiency of the well.

If the water is extremely alkaline (incrusting), a lower limit of 0.015 tp 0.02 inches may be used.

It is also helpful to remember that experience may dictate a much different set of limits. For example, on the Coastal Gulf Plain, experience has shown that the best design width for naturally developed wells is 0.006 inches.


Thick Artesian Aquifers

In thick artesian aquifers where a long screen is required and the pump is to be positioned above the screen, a smaller diameter screen can be centered in the borehole, and the annulus filled with gravel. This is preferable to using a shorter screen of a diameter about the same as that of the borehole

Extensively Laminated Formations

In formations exhibiting extensive lamination or alternating layers of fine and coarse material, it is difficult to determine the precise position and thickness of each individual layer and to choose the proper length of each section of a multiple-slot screen corresponding to the stratification. Designing the well for a gravel pack reduces the chance of making an error. The size of gravel-pack material should be based on analysis of the finest material in the water-bearing portion of the aquifer.

Loosely Cemented Sandstone

In boreholes in loosely cemented sandstones, sand particles tend to slough from the walls of finished open holes. Since most sandstones are fine-grained, 0.005 inch or smaller screen openings may be called for. Providing a gravel-pack will allow wider screen openings.

Another reason for installing a gravel pack is that in loosely cemented sandstones, the formation material usually provides little or no lateral support for the screen - the formation does not readily cave or slump against the screen as in unconsolidated formations. Instead some void spaces are left around the screen leaving open the possibility that chunks of material could fall off and damage the screen.

Back ArrowReturn to Artificially Gravel-Packed Wells © Copyright