PRIVATE WATER SYSTEMS - Completion - Gravel Pack

Gravel Pack

In naturally developed wells, fine formation material around the screen is removed by a developing process to create a more permeable zone. Certain conditions, however, favor the construction of an artificial gravel pack or the addition of a formation stabilizer.

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PRIVATE WATER SYSTEMS - Completion - The Development Process

The Development Process

The objective of well development is the removal of fine sand, silt, and other such materials from the zone immediately surrounding the well to increase the permeabilty of the zone. Another purpose is to correct any clogging or compacting of the formation resulting from drilling operations. Development also grades the aquifer material around the screen to achieve maximum yields of sand free water.

There are several well-development methods in use, but three of the most effective and commonly used are mechanical surging, high-velocity jetting, and backwashing.


Mechanical Surging

Mechanical Surge Plunger Mechanical Surge Plunger Mechanical Surging is the most widely well-development method used. A plunger is operated up and down in the casing slowly at first, then gradually picking up speed. Occasionally, the plunger is stopped, and the sand in the screen is bailed or pumped out.

When the aquifer contains many clay streaks or clay balls, the action of the plunger can cause the clay to smear over the screen surface and reduce the yield. Also, the surging caused by the plunger can cause high differential pressures in the well which could collapse the screen, unless a sufficiently free flow of water has been established in the well before surging is begun. Care should be taken if the overlying formation is soft clay, fine sand, or silt.


High-Velocity Jetting

High-Velocity Jetting is the most effective development method. It has the following advantages: The procedure consists of operating a horizontal jet inside the well in such a way that the high-velocity streams of water shoot out through the screen openings. The jet is rotated and moved up and down.

The jet washes fine materials out of the water-bearing formation and the turbulence created by the jet washes the material into the well. When possible, lightly pump the well during jetting operations.


Backwashing

The surging effect or reversal of flow required to develop the formation can be produced by 3 or 4 backwashing methods. Two of these are referred to as rawhiding the well.

Rawhiding Deep Wells

Using a deep well turbine pump without foot valve, water is lifted to the and then shut off. The water then falls back down the well. The pump is started and stopped as fast as the power unit and starting equipment will allow. The effect is to raise and lower the water level in the well which produces inflow and outflow through the well screen.

Some wells respond to this, but the surging action is not vigorous enough to obtain maximum results in most cases.

Rawhiding Shallow Wells

Where the static water level high enough to permit pumping by suction, another backwashing scheme using a centrifugal pump which can take water from inside the well and recirculate inside the well can be set up.

A string of pipe let down in the well to about its full depth is connected to the discharge of the pump. Water is then pumped from the well and circulated back into the inside the screened section. The turbulence thus created inside the well screen assists in developing the well.

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