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The Well / Aquifer Model
The Well / Aquifer Model Imprimir
Martes, 10 de Mayo de 2011 00:49
INTRODUCTION
 
1.1 General Background Leading to Development of the Well / Aquifer Model Today, more than ever, energy plays a vital role in the planning and operation of any water resources development project. Providing safe, reliable ground-water supplies at the lowest possible cost requires careful design of all factors affecting the pumping and transportation water, from its source in the aquifer to its final destination and use.
 
Minimizing energy consumption can result in huge operational savings over the lifetime of any water resources project. One example of energy waste is the head loss associated with the entrance of ground water into the well. Minimizing this head loss requires careful consideration of the relationships between aquifer and gravel pack materials, well screen characteristics and location, and pumping rates.
 
Understanding the laws and principles governing these interrelationships is the subject of extensive research currently being conducted by Roscoe Moss Company of Los Angeles. The need for a study of this type and magnitude has long been overdue in the ground-water profession. Too often, critical factors affecting the design and construction of water wells are being obtained from unverified general assumptions, outmoded techniques, or application of methods and values which clearly do not apply. Consequently, many wells continue to be improperly designed, with results ranging from marginal to complete well failure.
 
1.2 Specific Objectives of the Investigation
 
The purpose of this investigation is to study interrelationships between well screens, gravel packs, and aquifers, using both theoretical and experimental techniques, and to deduce the basic laws governing these relationships. The original objectives are summarized as follows:
 
1. Determine the physical hydraulic relationships between screen entrance velocity, sand transportation, and gravel pack design. In conjunction with this, test the validity of the "opinion" by Bennison (page 26) that entrance velocities must be between 0.1 and 0.25 ft/ sec.
2. Determine the effect of gravel pack design criteria on stabilization of aquifer materials and well development (e.g., void ratio, grain size and shape, uniformity coefficient, and percentage passing for various screen openings).
3. Verification of Peterson’s basic design criteria (CL/D>60 for minimum frictional head losses (page 29) on a large r scale than his original test apparatus and with consideration to aquifer materials. This will also determine the effects of partial penetration and the resulting converging flow field.
4. Determine velocity distribution along the well screen length and check the validity of Peterson’s statement (page 29) that most flow takes place at the discharging end of the screen through a length such that CL/D>6.
5. Demonstration of the principle of increased drawdown (and higher pumping lifts due to partial penetration effects even though CL/D>6.
6. Determine the importance of screen open area and geometry in development of the gravel pack and surrounding aquifer material.
7. Investigate the effects of different types and density distribution of screen openings on stabilization of gravel pack and well efficiency.
8. Develop well loss criteria for a practical range of commercially available well screens and compare well efficiencies of these screens for different gravel pack / aquifer ratios.
9. Investigate the structure of the gravel pack immediately adjacent to the well screen for various types of screens(louver, wire wound, etc.), and determine whether screen geometry affects entrance velocities and well efficiency.
10. Investigate the build-up and methods for removal of incrustations with various types of commercially available well screens.
 
 
ENVIADO POR RAÚL CAMPILLO U., HIDROGEÓLOGO.