3 August 1998
(1) A naturally developed well relies on the development process to generate a highly
permeable zone around the well screen or open rock face. This process depends upon pulling
out the finer materials from the formation, bringing them into the well, and pumping them out of
the well. Development work should continue until the movement of fine material from the
aquifer ceases and the formation is stabilized.
(2) Artificial filter packing provides a second method of providing a highly porous
material around the screen. This involves placement of a specially graded filter in the annular
space between the screen and the wall of the excavation. Development work is required if
maximum capacity is to be attained.
(3) Development is necessary because many drilling methods cause increase in the
density of the formation around the hole. Methods utilizing drilling fluids tend to form a mud
cake. Good development will eliminate this "skin effect" and loosen up the sand around a
screen. Removal of fines leaves a zone of high porosity and high permeability around the well.
Water can then move through this zone with negligible head loss.
(4) Methods of development in unconsolidated formations include the following:
(a) Mechanical surging is the vigorous operation of a plunger up and down in the
well, like a piston in a cylinder. This causes rapid movement of water which loosen the fines
around the well and they can be removed by pumping. This may be unsatisfactory where the
aquifer contains clay streaks or balls. The plunger should only be operated when a free flow
of water has been established so that the tool runs freely.
(b) Air surging involves injecting air into a well under high pressure. Air is pumped
into a well below the water level causing water to flow out. The flow is continued until it is free
of sand. The air flow is stopped and pressure in an air tank builds to 700 to 1,000 kilopascals
(100 to 150 psi). Then the air is released into the well causing water to surge outward through
the screen openings.
(c) Over pumping is simply pumping at a higher rate than design. This seldom
brings best results when used alone. It may leave sand grains bridged in the formation and
requires high capacity equipment.
(d) Back washing involves reversal of flow. Water is pumped up in the well and
then is allowed to flow back into the aquifer. This usually does not supply the vigorous action
which can be obtained through mechanical surging.
(e) High velocity jetting utilizes nozzles to direct a stream of high pressure water
outward through the screen openings to rearrange the sand and gravel surrounding the
screen. The jetting tool is slowly rotated and raised and lowered to get the action to all parts of
the screen. This method works better on continuous slot well screens better than perforated
types of screens.
(5) Development in rock wells can be accomplished by one of the surging methods
listed above or by one of the following methods.