Water well design, installation and completion Flashcards Preview

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Flashcards in Water well design, installation and completion Deck (24):
1

Requirements for designing a water well

Need to know both current and future uses of the water well

2

Before water well field investigations

a) geophysical surveys
b) test drilling -- wells drilled to better delineate the aquifer
c) log the cuttings to create a stratigraphic log

3

After water well field investigations

a) down hole geophysics
b) pump tests

4

Considerations in choosing a well location are:

1. Geology of the area/ aquifer
2. location of contaminant sources
3. minimal distances - buildings, septic tanks
4. accessibility for cleaning, testing, monitoring, maintenance and repair
5. ground slope in immediate vicinity of the well

5

4 types of water wells:

1. Dug - by hand
2. Driven or jetted - pushed or hydraulic
3. Bored - auger wells
4. Drilled - rotary

6

4 general components of a water well

1. casing
2. intake design
3. annulus fill
4. surface considerations - mounding caps

7

Casing

1. solid pipe - steel or plastic
2. large enough diam to have pump
3. casing must extend > 20cm above ground
4. casing must be > 60 cm higher than record flood
5. if non-metallic, must be protected by steel casing

8

Intake design:

1. allow water not sediment in
2. only placed across from the aquifer section of the well

9

2 main types of screens

1. wire-wound stainless steel well screen for sand or gravel
2. slotted or perforated liner for caving bedrx

10

Size of openings in the screens

Use a slot size that allows 60% of the aquifer material to pass through the screen during the development phase

D60

11

Annulus fill

Annulus is the area b/t the borehole and the well casing

12

2 main types of annular fill

1. annular seal
2. filter pack/gravel pack

13

Annular seal and its purpose

Annulus must be filled with impermeable, chemically inert material from the surface to immediately abve the perforated zone or screen

Prevent surface contaminants from entering the well
prevents fluids from poor quality or contaminated zones from entering the aquifer

concrete, bentonite, grout mix

14

Filter pack/gravel pack and its purpose

Often gravel, clean quartz sand or glass beads
Placed in the annulus of finer-grained aquifers to improve well yields

15

Surface considerations

1. Mound around the well
2. water wells must be securely covered
3. pump house must contain only the water well and pump
4. pump house made so water will not pool on floor

16

Well completion tasks

1. well development
2. well disinfection
3. yield test

17

Well development purpose

1. remove any fine sediments and drilling mud from around the well screens
2. to remove water introduced to the aquifer (surface h2o, other aquifers)

18

Methods used to develop a well

1. over pumping - pump water out of the well until its clear - 1 direction of flow
2. Jetting - blowing high P water or air through the screens
3. surging - Water surged in and out through the openings, pump used to remove sediment ladened H20 - 2 direction flow

19

Naturally developed well

Development methods used remove the fine material leaving the coarse material behind, directly in contact with well screens -- Non-cohesive sediments

20

Gravel packed well

Sand or gravel is placed in the annulus after drilling. NOT material from the area -- BED RX

21

Well disinfecting

Done after all eqpt has been installed. Chlorine at a min [] of 200 mg/l in the well for 12 hours

22

yield test

1. Minimum of 2 hoours or until the well is back to 90% of it original level
2. determines rate at which to pump the well and where to put the pump

23

Pump must not lower wtr level below

1. top of aquifer
2. top of perforations
3. top of pump intakes

24

Submissions to AEP

1. General stratigraphic log
2. Well construction and design details