Well development methods

Well development methods

There are several methods of developing wells, either naturally developed or gravel-packed, some of which are more popular than others, and some of which suit only very special cases and formations.

These include surging, either with a plunger or with air; overpumping; backwashing, by one of several methods; jetting; and the use of chemicals, explosives, and even dry ice.

Perhaps the most common method of developing wells, especially in sand and gravel aquifers, is surging with a plunger.

It will serve best to show what results the driller hopes to get from natural development of the well since the largest number of people use this method.

Gravel-packed wells will be considered later.

One tool used in this kind of surging is easily fabricated in almost any shop; the solid surge plunger consists of two rubber or leather discs between wooden discs on a heavy pipe nipple with steel plate washers under the end couplings.

Different sizes can be assembled to fit reasonably well in different sizes of casing.

Another type of plunger is equipped with valves to give a lighter surging action when desired.

The surge plunger is well adapted to cable tool operation.

The downstroke forces water out of the well and into the surrounding formation.

The upstroke then pulls water back into the well, and with it silt, sand, and anything fine enough to pass through the openings in the well screen.

By forcing water out of the well, the surge breaks up "bridges" of sand particles as well as the "skin" created on the side of the borehole by the drilling process.

A bridge of sand particles can form between two coarser particles of gravel, thus providing an obstruction to water flow into the well, whenever water is pulled into the well only, and the flow is just in one direction.

Forcing water out into the aquifer breaks up these bridges and creates a turbulence which tends to bring all fine particles into the well when the upstroke reverses the plunger's action.

The skin is most often a result of rotary drilling when the mud fluid used in the drilling process clogs the formation and cakes into an impervious skin.

All types of drilling, however, disturb the formation itself along the sides of the borehole to a point where some impediment to free flow of water is formed.

Thus the out-and-in surging action is superior in most cases to those methods which only pull water into the well.

After the first few strokes of the plunger, a deposit of fine sand and silt will have entered the well.

This is removed, usually by a sand bailer, and the amount carefully noted.

As the length of time surging grows longer, and the amount of fines collected by the bailer grows smaller, the job of naturally developing a well in unconsolidated formations approaches its end.

The action has increased the effective diameter of the well by spreading its zone of influence, and the amount of water which can be pumped from the well for each foot of drawdown (known as its specific capacity) also has increased.