groundwater exploitation well construction

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Groundwater Exploitation

• Today

– Well Drilling

– Well Completion

– Well Development

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For deeper wells,

more intricate methods are needed,

as we will review here.

Fletcher Driscoll, 1986,

Groundwater & Wells,

Johnson Div.

National Ground-water Association

http://www.ngwa.org/

Good resources:

Australian Drilling Industry

Training Committee Ltd., 1997,

Drilling: The Manual of Methods,

Applications, and Management,

Lewis Publishers.

How are wells constructed?

• Drilling

• Completion (casing, screen,

surface features)

• Development

For shallow wells/piezometers(total depth <100 ft):

• Hand digging

• Augering

• Drive point

• Jetting

Well Construction

WaterAid /Jim Holmes

www.wateraid.org

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http://coastlinemachinery.com/

Drilling


bbwater.com http://en.wikipedia.org/wiki/Water_well

Completion w. screen

dnrc.mt.gov/wrd/water_op/bwwc

Cable tool drilling Rotary drilling

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(Harlan et alii, 1989)

Mast

Cable Tool Drilling

Well construction: drilling

http://en.wikipedia.org/wiki/Water_well

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Advantages:• Low cost

• Minimal alteration of permeability or water quality

• Doesn’t require large amounts of water

Disadvantages:• Slow (especially for deeper wells) 100 ft/d (good), but 10 ft/d (poor)

• Slow in soft sediment

• Casing loss (casing must typically be used to support the

hole; it might not be possible to recover this)

Cable Tool Drilling

http://coastlinemachinery.com/This method is disappearing.

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Mud pitMud pit

Rotary Drilling

(Harlan et alii, 1989)Well construction: drilling

http://www.youtube.com/watch?v=Y_dEzSa6I4E

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(Todd, 1980)

(Driscoll, 1986)Well construction: drilling

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Advantages:• Fast drilling rate

(300-500 ft/d if soft; 30-50 ft/d in very hard rock)

• Little loss of drilling rate with depth

• No casing loss (fluid keeps hole open)

Disadvantages:• High cost of rig

• More labor intensive

• Drilling mud can clog formation, change water quality

• Can lose fluid circulation

(caverns in limestone, lava tubes in basalt)

• Development time is high

Rotary Drilling


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Bowman Irrigation WellDrilled with mud rotary

12 inch diameter, 116-ft deep

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Reverse Rotary Drilling

Mud has a higher velocity

through the drill string

than it does in the annular

space around the drill

string—it can thus lift

coarser particles

This is ideal for

formations that form large

clasts; helps prevent

clogging in general

(Harlan et alii, 1989)Well construction: drilling

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Air Rotary Drilling

The same principle as

rotary drilling, but uses

air as the drilling fluid:

often it is actually air with

a foaming agent

Can’t be used in

materials that collapse or

materials that form

coarse particles(Harlan et alii, 1989)


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Similar to air rotary drilling, but uses a hammer action instead of

rotary action

Pneumatic (air hammer) Drilling

Advantages:• Fast drilling rate in hard rock (50-100 ft/d)

• No plugging (or water quality change)

Disadvantages:• Most expensive method

• Only good in hard rock

• Can’t use in high permeability intervals

below the water table (can’t lift water)


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13(Harlan et alii, 1989)

Drilling with Auger

Augering:

hollow stem

or solid stem

(Harlan et alii, 1989)

A fast and cheap

method for

unconsolidated or

poorly-consolidated

sediments.

Using a hollow-stem

auger allows core

sampling.

The auger will bounce

off boulders, so this

method is not ideal for

alluvial fan sediments.


http://www.geology.sdsu.edu/

classes/geol552/hollowstem.htm

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“Mobile B-59 is a versatile medium-duty drill rig. It can run hollow stem augers or perform

using mud rotary, air rotary or down-the-hole hammer drilling techniques. It is

accompanied by one of six available late-model support trucks which can carry all of the

support equipment needed to complete your project. This drill rig is mounted on a 1993

Ford F800 Series truck, has 12,000 foot pounds of torque enabling it to drill with up to 12

V4-inch diameter hollow stem augers capable of sampling soils and rock coring up to a

depth of 1,000 feet, installing 2-inch and 4-inch diameter monitoring wells and recovery

wells to 10-inch diameter. This rig is supported by a 1995 GMC Topkick 9400 Series truck

with a 24-foot box to handle all supplies necessary to complete projects.”

Trenton, NJ

http://www.talon.bizland.com/index.html

“Talon installs monitoring wells, production wells, and piezometers using

Air and Mud Rotary, Air percussion rotary, Hollow Stem Augers, ODEX

and Rock coring techniques.”

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(Driscoll, 1986, Groundwater & Wells)


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It is often hard to drill

‘straight’ or ‘plumb’.

Survey the well (vertically)

in order to

determine configuration.

Why?Imagine all calculations we do

(potentiometric mapping, well

test analysis, etc)

that depend on knowing where

the well is located at the depth

of measurement.

(Driscoll, 1986)

Drilling “straight”


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17Well construction: completion

Surface Features

casing

gravel

pack

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Surface Features

(Todd, 1980)

If no precautions are taken, runoff

can move down to the aquifer,

traveling along the outside of the

casing—this can lead to

groundwater contamination, or

casing collapse from erosion

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Unless in hard rock, something

has to keep the hole open at

depth—the casing is typically

steel; in shallow wells, PVC or

some other plastic

Well construction: drillingWell construction: completion

Casing

(Todd, 1980)

Completion with casingJohnson Screen

PVC Monitoring

Well Casing

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In the aquifer, there has to be a

way to let water in to the well;

we must still typically keep the

hole ‘propped’ open, though;

also we don’t want the well bore

to fill up with particulates


Screen

Johnson Screen (Todd, 1980)

bbwater.com

Completion w. screen

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“Home-made screens”—these involve making openings

in regular casing

•torch cut

•knife cut

•shot perforated

These types of screens are cheap, but open area is

low (1-2 %); there is poor control of opening

dimensions.

In many locations and for many purposes handcut

screens are now illegal.


Homemade Screen

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(Nielsen, 1991)

Milled slots: similar to torch cut,

but done with a milling machine

at the factory

2-3 % open area

Good control on slot size


Milled Slot Screen

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ScreenThree patterns of shutter screen, continuous slot, bridge slot, and mill slot screens

Roscoe Moss Company http://www.roscoemoss.com/

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(Nielsen, 1991)

Well construction: completion

Wire Wrap Screen

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Wire Wrap Screen

Johnson Screen

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(Driscoll, 1986)


Screens

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Wire-wrapped screens help prevent clogging

(Driscoll, 1986)


Screens

28Production Well

(Schwartz and Zhang, 2003)

Helps well production

by increasing hydraulic

conductivity around

the screen


Filter (Graval or Sand) Pack

USGS monitoriing well;

pouring & tamping

a sand pack

http://il.water.usgs.gov/nawqa/uirb

Roscoe Moss Company

“Well screen is an important component of well

design. It must be realized that it is not an answer

to all well problems. In a gravel envelope well, it is

the gravel that filters the formation material and not

the screen. The screen simply retains the gravel

pack. Screen selection must be based not only on

theoretical considerations, but on a practical

relationship to the design and construction of an

efficient, durable installation. The best screen

design cannot automatically correct incompleted

gravel installation or well development. Screen can

only facilitate the construction of an efficient well

and help assure its satisfactory operation” Roscoe

Moss Company

http://roscoemoss.com/tech_manuals/gwwc/

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A well is developed to give better production; this is

especially important in wells where drilling mud was used

Development removes fine particles, leaves only particles

that are bigger than the screen opening size

• surge block

• surge pumping

• overpumping

• jetting

• compressed air injection

Well construction: development

Development

Surging one way (leaving sand bridges) v. back-and-forth.

(Driscoll, 1986)(Driscoll, 1986)

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www.nps.gov/hafo/hydrology/stage/stage7.htm

Jetting

Well construction: development

Development

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Centrifugal pump performance curves

PumpsSubmersible (downhole) Pump Turbine PumpCentrifugal Pump

http://www.goulds.com/pdf/Bturbine.pdf

http://www.goulds.com/pdf/BSPMSPH.pdf

http://www.goulds.com/pdf/B5-25GS%201%20.pdf

Turbine pump performance curves

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Bowman Irrigation Well12-in casing, 116-ft deep

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Bowman Irrigation Well12-in casing, 116-ft deep

casing casing

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Well Completion Report


groundwater exploitation well construction

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