3 August 1998
(3) Diameter. The screen diameter shall be selected so that the entrance velocity
through the screen openings will not exceed 0.1 foot per second. The entrance velocity is
calculated by dividing the well yield in cubic feet per second by the total area of the screen
openings in square feet. This will ensure the following:
(a) The hydraulic losses in the screen opening will be negligible.
(b) the rate of incrustation will be minimal,
(c) the rate of corrosion will be minimal.
(4) Installation. Various procedures may be used for installation of well screens.
(a) For cable-tool percussion and rotary drilled wells, the pull-back method may be
used. A telescope screen, that is one of such a diameter that it will pass through a standard
pipe of the same size, is used. The casing is installed to the full depth of the well, the screen
is lowered inside the casing, and then the casing is pulled back to expose the screen to the
(b) In the bail down method, the well and casing are completed to the finished
grade of the casing; and the screen, fitted with a bail-down shoe is let down through the casing
in telescope fashion. The sand is removed from below the screen and the screen settles down
into the final position.
(c) For the wash-down method, the screen is set as on the bail-down method. The
screen is lowered to the bottom and a high velocity jet of fluid is directed through a self closing
bottom fitting on the screen, loosens the sand and allowing the screen to sink to it final
position. If filter packing is used, it is placed around the screen after being set by one of the
above methods. A seal, called a packer, is provided at the top of the screen. Lead packers
are expanded with a swedge block. Neoprene packers are self sealing.