Development of Wells: 6 Procedures

The procedures usually adopted for well development are as follows: 1. Over-pumping 2. Backwashing 3. Mechanical surging 4. Air surging and pumping 5. High-velocity jetting 6. High-velocity water jetting combined with simultaneous pumping.

Procedure # 1. Over-Pumping:

In the over pumping method, the well is pumped at a discharge rate higher than the discharge rate of the well during its normal operation. The logic of the method is that any well which can be pumped sand-free at a high rate can be pumped sand-free at a lower rate. It is the simplest method of developing wells. However, the development by this method is not effec­tive, and the developed well is seldom efficient. The aquifer material is also not fully stabilized.

This incomplete development is due to the following reasons:

(i) Water flows in one direction only and some sand grains may be left in a bridged condition. The formation is thus partially stabilized.

(ii) Most of the development takes place in the most permeable zones of the aquifer which are usually closest to the top of the screen. Therefore, lesser development takes place in the lower layers of the aquifer.

Besides, this method usually uses the pump intended for regular use during the normal operation of the well. Pumping of silt-laden water at higher rates can reduce efficiency of the pump.

Procedure # 2. Backwashing:

Reversal of flow through the screen openings will agitate the aquifer material, remove the finer fraction and rearrange the remaining aquifer particles. These effects will usually cause effective development of well. To minimise the chances of sand-locking the pump, the discharging rate of the pump should be gradually increased to the maximum capacity before stopping the pump.

During this process, the well is occasionally pumped to waste to remove the sand brought to the well by surging action of this method of well develop­ment. As in the case of over-pumping method, the surging action may be concentrated only in the upper layers of the aquifer.

Besides, the surging effect is not vigorous enough to cause maximum benefits. When compared with other methods of well development, the overall effectiveness of backwashing as well as over-pumping methods in case of high capacity wells is rather limited.

Procedure # 3. Mechanical Surging:

In this method, a close-fitting surge plunger, moving up and down in the well casing, forces water to flow into and out of the well screen. The initial movements of the plunger should be relatively gentle so that the material blocking the screen may go into suspension and then move into the well.

To minimise the problem of fine materials going back to the aquifer from the well, the fine material should be removed from the well as often as possible. Surging method is capable of breaking sand bridges and produces good results. However, it is not very effective in developing filter-packed wells because the water movement is confined up to the filter pack only and the aquifer remains unaffected by the surging action:

Procedure # 4. Air Surging and Pumping:

This method requires two concentric pipes: the inner pipe is known as air-line and the outer one is known as pumping pipe. The assembly of these pipes is lowered into the well. In air surging, compressed air is injected through air-line into the well to force aerated water up through the annular space between the air line and the pumping pipe.

As this aerated water reaches the top of the casing, the air supply is stopped so that aerated water column starts falling. Air-lift pumping is used to pump the well periodically to remove the sand brought into the well as a result of air surging. The compressed air produces powerful surging action. This method is used to develop wells in consolidated and unconsolidated formations.

Procedure # 5. High-Velocity Jetting:

This method consists of shooting out high-velocity jets of water from a jetting tool to the aquifer through the screen openings. The equipment for this method consists of a jetting tool provided with two or more equally spaced nozzles, high-pressure pump, high-pressure hose and connections, and a water supply source.

The forceful action of high-velocity jets loosens the drilling mud, and agitates and rearranges the sand and gravel particles around the well. The loosened material is removed by pumping. In this method of development, the entire surface of the screen can be subjected to vigorous jet action by slowly rotating and gradually raising and lowering the jetting tool.

This method has the following advantages:

(i) The energy is concentrated over a small area with greater effective­ness.

(ii) Every part of the screen can be developed selectively.

(iii) The method is relatively simple.

The method of jetting is particularly successful in developing highly stratified and unconsolidated water-bearing formations.

Procedure # 6. High-Velocity Water Jetting Combined with Simultaneous Pumping:

The method of high-velocity water jetting results in very effective develop­ment of wells. But maximum development efficiency can be obtained by combining high-velocity water jetting with simultaneous air-lift pumping or some other suitable pumping method.

The method requires that the volume of water pumped from the well should always be more than the volume of water pumped into the well so that the water level in the well is always below the static level, and there is continuous movement of water from the aquifer to the well. This will help in removing some of the suspended material loosened by the jetting operation.