design of an efficient well
DESCRIPTION
well design and rehab basic procedures.TRANSCRIPT
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DESIGN OF AN EFFICIENT WELL
By
MARIO P. SANDOVALPresident
AQUA-DYNE TECHNOLOGICAL SERVICE, INC.
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GENERAL OBJECTIVES
1. Highest yield with minimum drawdown2. Good quality water with adequate protection3. Sand-free water4. Long life of well5. Reasonable cost
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WELL DESIGN ELEMENTS
• Depth• Borehole diameter• Casing Diameter and materials• Type, length and placement of screens• Gravel pack specifications• Sanitary seal
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WELL DEPTH
• Determined from logs of existing and pilot hole
• Should utilize aquifer thickness to ensure higher specific capacity
• More drawdown should be available for greater discharge
• Sufficient available drawdown during droughts
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CASING DIAMETER
• Large enough to accommodate pump
• Create uphole velocity less than 1.5 m/sec
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CASING MATERIALS
• Steel pipes, seamless, spiral welded or ERW
• Stainless steel pipes• PVC• Fiberglass reinforced plastic pipes
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PHOTOS OF CASING MATERIALS
• B.I. pipes• Stainless steel pipes• Pvc• Fiberglass reinforced plastic pipes
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WELL SCREEN LENGTH
• Should be placed in most permeable layer
• In water table aquifers – bottom 1/3 of aquifer
• In confined aquifers – 80 to 90% of the total thickness of aquifer
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TYPES OF INTAKE STRUCTURES
• Photos of well screens• Perforated pipes• Louver type • PVC screens
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DESIRABLE GRAVEL PACK
• Clean – short development time
• Well –rounded grains have greater porosity and permeability, resulting in smaller drawdown. More effective well development
• Inert grains ensures no dissolution of materials
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GOOD WELL HYDRAULICS-1
• When entire thickness contributes water to well
• For thick aquifers, short screens across entire thickness of aquifer
• For water table aquifers, screens should not extend to top of aquifer
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GOOD WELL HYDRAULICS-2
• Wells should only draw water from bottom of water table aquifers
• Proper well development should allow entry of water through entire circumference of the screen.
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Factors affecting connection between well and aquifer -1
• Well design– Position of screens– Formation damage – Slot sizes– Aquifer collapse due to excessive slot size– Initial clogging of the slots because of
instability of aquifer
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What factors affect connection between well and aquifer -2
• Drilling method – Drilling should minimize formation damage– Selected casing and screen should stabilize
formation and avoid collapse– Mud filtrate should not enter aquifer– Permeable zones should be determined
accurately– Aquifer must be developed to increase
permeability around the screens.