156 IRRIGATION AND WATER RESOURCES ENGINEERING
4.10. WELL COMPLETION After drilling a well, the well screen and filter pack (wherever necessary) are to be placed and the casing removed. If the formations are sufficiently strong and stable, ground water may directly enter the uncased well. In unconsolidated formations, however, a casing with perforation (or a well screen) is needed to support the outside material and also to admit water freely into the well.
The installation of the well screen and the removal of the casing is best done by the pull-back method in which the casing is installed to the full depth of the well and the well screen, whose size is smaller than that of casing, is lowered inside the casing. The casing is then pulled back or lifted far enough to expose the screen to the water-bearing formation (Fig. 4.12).
