design of an efficient well

DESIGN OF AN EFFICIENT WELL

By

MARIO P. SANDOVALPresident

AQUA-DYNE TECHNOLOGICAL SERVICE, INC.

GENERAL OBJECTIVES

1. Highest yield with minimum drawdown2. Good quality water with adequate protection3. Sand-free water4. Long life of well5. Reasonable cost

WELL DESIGN ELEMENTS

• Depth• Borehole diameter• Casing Diameter and materials• Type, length and placement of screens• Gravel pack specifications• Sanitary seal

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

CASING DIAMETER

• Large enough to accommodate pump

• Create uphole velocity less than 1.5 m/sec

CASING MATERIALS

• Steel pipes, seamless, spiral welded or ERW

• Stainless steel pipes• PVC• Fiberglass reinforced plastic pipes

PHOTOS OF CASING MATERIALS

• B.I. pipes• Stainless steel pipes• Pvc• Fiberglass reinforced plastic pipes

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

TYPES OF INTAKE STRUCTURES

• Photos of well screens• Perforated pipes• Louver type • PVC screens

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

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

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.

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

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.