Development of wells means the stabilization of the walls of a well adjacent to the screen, by processes which remove the fine particles from the formation immediately surrounding the well screen, leaving the coarser particles to contact and surround the screen. Development of walls is necessary in all gravel packed wells and other screened wells, except when the screen is made of fine wire mesh or coir or other closely knot filters, located in a highly permeable aquifer.
The basic principle of well development is to cause reversals of flow through the screen openings, that will rearrange the aquifer particles in order to prevent the bridging of the groups of particles.
The importance of well development as summarized as follows:
- To unclog the water bearing formation of the wells
- To increase the porosity and permeability of the water bearing formation in the vicinity of the well.
- To increase their specific capacity, prevent discharge of sand, and to obtain maximum economic well life.
- To stabilize the sand formation around a screened well, so that the well may yield sand free water.
Common Methods of Well Development include:
Jetting Technique
This method involves operating a horizontal water jet inside the well in such a way that the high velocity water stream shoots out through the screen openings. Fine particles are thus washed out of the aquifer, and the turbulence created by the jets brings these fines back into the well through the screen openings above and below the point of operation. By slowly rotating the jetting tool, and by gradually raising and lowering it, the entire surface of screen can be covered.
Pumping Technique
Overpumping and rewhiding of well are pumping techniques used in well development. Overpumping involves heavy pumping of the well to cause heavy drawdown. Rewhiding involves starting and stopping of pumping intermittently to provide relatively rapid changes in the head of the well. This method is more effectively done with turbine pump installed with a foot valve.
Surging Technique
This method is done with a surge block or surge plunger. In the method, a plunger is worked up and down in the well, so that the water is alternately forced out into the surrounding formation and then allowed to flow back into the well. The outflow portion of the surge cycle breaks down the bridging to loosen the fines and the inflow portion of the surge cycle moves the fines towards the screen and into the well, from where they are removed.
Method of Compressed Air
This is the most common method of well development and it involves two processes: backwashing technique and surging technique.
In the backwashing technique, the well water is forced back into the aquifer by the means of compressed air introduced into the well through the top of the casing after it has been closed. When the pressure forcing the well water back to the aquifer is released, the water will flow back into the well through the screen to bring the fine particles from the area surrounding the well, thus ensuring their removal. The process is continued till no sand is brought in.
In the surging technique, the inrush of compressed air creates a powerful surge within the well, and loosens the fine material surrounding the perforations, which may then be brought into the well by continuous air injection. The operation is repeated at intervals along the screened section of the well, until sand arrival is stopped.
Use of Dispersing Agents
Dispersing agents which are chemicals can help in the removal of mud when added to well water and water used in backwashing. Examples of such chemicals are tetra sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, and sodium septaphosphate. This method is often used to enhance the previous methods that where described.
Disclaimer: The contents in this writeup are not the original thoughts of the author but were shared to advance knowledge.
