2. Water Wells
&
Well Construction
Target Group: WRIE 4th
Water Wells
 Water well is a hole or shaft, usually vertical, excavated into the
earth for bringing groundwater to the surface.
 Groundwater is broadly defined as the water present in the
saturated zone below the ground. The zone of saturation is
technically called ‘aquifer’ which are significantly porous and
permeable to supply water to wells and springs.
 The objectives of water well is to:
 Provide water of good quality
 Provide water in a sufficient quantity
 Provide water for a long time
 Provide water at a low cost
Classification of Water Wells
 There are many ways to classify water wells such as
based on;
 Well depth,
 Method of construction,
 Type of aquifer,
 Entry of water into wells,
 Type of formation (unconsolidated and consolidated
formations).
Cont’d
Classification of Water Wells
 Broadly, water wells can be classified into four groups according to
their functions;
 Water Supply Wells,
 Recharge Wells,
 Drainage Wells, and
 Monitoring Wells.
 Based on their design and method of construction, Water supply,
recharge and drainage wells can be further classified as;
 Open wells and
 Tube wells
Classification of Water Wells
Cont’d …
Open Wells
 Open wells, also known as dug wells, are the most convenient
and cost effective way of harnessing groundwater present in
shallow and low yielding unconfined aquifers for small scale
water supply

(e.g., domestic and small scale irrigation purposes).
 Open wells may be either circular or rectangular in shape.
 Open wells are of large size with the diameter usually ranging
from 2 to 5 m, though the diameter may be as large as 20 m under
special circumstances.
Open Wells
Cont’d
 The open wells of larger size and rectangular in shape are
preferred in hard rock formations to facilitate larger amount of
groundwater inflow into the well.
 The depth of open wells varies from a few meters to about 50 m.
 Open wells can be of four types;

Unlined open wells,

Open wells with pervious lining,

Open wells with impervious lining, and

Dug cum bore wells.
Open Wells
Cont’d
 Open wells dug for purely temporary purposes are normally not
protected by lining of their walls.
 The depth of unlined open wells is limited to about 6.5m in order
to ensure stability.
 However, open wells dug for permanent purposes in loose and
unconsolidated formations require lining to prevent the collapse
of side walls and are usually lined with dry bricks or stone masonry.
 Pervious lining is suitable when the water bearing formation consists
of coarse sand and/or gravel.
Open Wells
Cont’d
 Impervious lining such as permanent masonry lining (laid in cement
mortar) are normally used in the open wells constructed in alluvial
formations.
 The depth of open wells with impervious linings is generally
larger than the two types described above, but the depth usually
does not exceed 30 m because of excessive construction cost beyond
the 30 m depth.
 Open wells with reinforced cement concrete (RCC) lining are also
sometimes used, especially for greater depths.
 RCC collar wells (also called ‘ring wells’) are used in some shallow
water table regions mainly for domestic water supply.
Cont’d
Open Wells
b
a
(a) Unlined open well, (b) an open well lined with pervious lining and
(c) Open well lined with permanent masonry lining
c
Cont’d
Open Wells
 On the other hand, the open wells in hard rock areas are excavated
pits through the rock and are lined only a couple of meters from
top because the rocky formation ensures the stability of side
walls.
Open well in a hard rock formation
Open Wells
Dug cum Bore wells
 Sometimes dug wells are provided with a vertical
borehole to augment their yields; such open
wells are called Dug cum bore wells.
 The small borehole of size ranging from 4 to 15
cm in diameter is drilled through the bottom of
the dug well up to the water bearing formation
lying below the well bottom.
 Note that dug cum bore wells are hydraulically
superior to ordinary dug wells and provide
higher yields compared to ordinary dug wells.
 However, their success depends on the availability
of a good confined aquifer at a reasonable
depth below the bottom of the dug well.
Tube Wells
 Depending on the availability of aquifer layers and the quantity of
desired water supply tube wells are classified as:
 Shallow tube wells and
 Deep tube wells
 Some special types of tube wells are known as;
 Bore wells and
 Cavity wells.
 On the other hand, monitoring wells or observation wells are small
diameter (usually 1” to 2”) tube wells for monitoring groundwater
levels and taking groundwater samples for exploring water quality.
Tube Wells
 Tube wells are wells consisting of pipes ranging in size from 6 to
45 cm in diameter and sunk into an aquifer.
 Tube wells are constructed by installing a pipe below the ground
surface passing through different geological formations
comprising Water bearing and non water bearing strata.
 Blind pipes (casing pipes) are placed in the non water bearing
layers and well screens are placed in the water bearing layers.
 The type of tube well to be constructed depends on:
Type of geological formation,
Intended use of the well and
The availability of fund.
Tube Wells
Cont’d
 Tube wells are also classified based on the depth, method
of construction, entry of water into the wells and the
type/nature of the aquifer.
 Based on the depth of the well, tube wells are classified as
shallow tube wells or deep tube wells.
 Shallow
tube wells are of low capacity and their average
depth is normally less than 35 m. They mostly tap one
aquifer.
 Deep tube wells are of high capacity and their depth usually
ranges from 60 to 300 m. They often tap two or more
aquifers.
 Based on the method of construction, tube wells are classified
as bored tube wells, drilled tube wells, driven tube wells and
jetted tube wells.
Tube Wells
Cont’d
 However, tube wells in hard rock formations are known as bore wells,
because the borehole remains stable for most of its depth and the tube
is placed only in the upper weathered soil zone.
 No strainer/screen or gravel pack is required for bore wells.
 Tube wells in unconsolidated formations generally consist of blind
pipes, strainers and gravel pack (if necessary).
 Moreover, tube wells are also classified as fully penetrating tube wells
or partially penetrating tube wells depending on whether the well
screen penetrates the saturated thickness of the aquifer fully or
partially.
 In some special hydrogeologic situations, the drilled hole is
terminated at the top of the confined aquifer without penetrating
it, and hence no strainer is required; such wells are called cavity wells
or non penetrating wells.
Tube Wells
A typical tube well in an
unconsolidated formation
Tube Wells
Cont’d
Cavity Wells
 Cavity well is a shallow tube well drilled in an alluvial
formation.
 If a relatively thin impervious formation consisting of stiff clay,
conglomerate or stone is encountered at a shallow depth
underlain by an extensive thick sandy confined aquifer, then it
is an excellent location for constructing a cavity well.
 A hole is drilled using the hand boring set, and casing
pipe is lowered to rest firmly on the stiff clay layer.
 Water enters the cavity well through the bottom only and
screens are not used in such wells.
 Thus, the cavity wells do not penetrate the aquifer, and
hence they are also known as non penetrating wells.
Tube Wells
Cont’d
Cavity Wells
 Cavity wells have usually a shorter lifespan and the failure is
caused mainly due to the collapse of the clay roof. Therefore, an
essential requirement for a cavity well is that it should have a
strong and reliable roof.
 Since the depth of the cavity well is usually small, deep well
pumps are not necessary.
 Thus, the capital costs of construction, development and pump
set installation for a cavity well are low, and hence cavity wells are
very economical compared to other tube wells.
Cavity Wells
Schematic of a cavity well
Advantages of Open Wells Over Tube wells
 Storage capacity of water is available in the well itself.
 They do not require sophisticated equipment and skilled persons
for constructions.
 They can be easily operated by installing an ordinary centrifugal
pump or by using a manual water lifting device.
 They can be revitalized by deepening by vertical boring or by blasting
at the bottom, or by creating horizontal or inclined bores on the sides
of the well to intercept water bearing formations.
Disadvantages of Open Wells
 Large land space is needed for open wells and for the excavated

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material.
Construction of open wells is slow and laborious.
They are subjected to high seasonal fluctuations of water table.
They are very susceptible to drying up in the years of drought or
even during the later part of the dry season.
They involve high cost of construction as their depth increases,
especially in hard rock regions.
Deeper aquifers cannot be economically tapped by open wells.
There is an uncertainty of getting good quality groundwater.
They are vulnerable to contamination unless they are provided with
suitable sanitary protection and are sealed from surface water ingress.
Advantages of Tube wells over Open Wells
 They do not require much land space and can be constructed






even in a limited open area.
They can be constructed quickly due to the use of mechanized
equipment.
They can provide sustained supply of water even during drought
years. In other words, tube wells provide the only source of water
supply during emergencies (i.e., natural and anthropogenic calamities).
They are economical and more reliable, especially when deep
and extensive aquifers are encountered.
They can also serve as flowing wells under special hydrogeologic
conditions. In this situation, no water lifting device and energy are
required.
They usually provide good quality groundwater.
They are relatively less vulnerable to contamination.
Disadvantages of Tube wells
 They often require costly and sophisticated drilling





equipment.
They need skilled personnel and great care for drilling,
completion, and maintenance.
Costly pumps are required for lifting groundwater from
bore wells.
There is a possibility of missing fractures, fissures and joints in
hard rock regions, thereby resulting in many dry bore wells.
Rehabilitation of tube wells/bore wells is generally very
expensive and requires skilled manpower.
Cost of pumping is normally higher than the open wells.
Summary on types of wells
~
Construction of Water Wells
Selection of Well Site and Type of Well
 The following factors should be carefully studied before selecting suitable sites
for constructing wells:
 Topography;
 Climate;
 Vegetation;
 Geology;
 Porosity, permeability and alteration of rocks;
 Joints and faults in rocks;
 Folded strata;
 Outcrops in the area (if any);
 Proximity of surface water bodies (e.g., tanks, rivers, springs, lakes, unlined
channels, reservoirs, etc.); and
 Depth and yield of the existing tube wells/open wells in the vicinity.
Selection of Well Site and Type of Well
Cont’d
 Apart from the above factors, satellite images and hydrogeological
maps of the area are very helpful in making a rapid
reconnaissance of the area, where a largescale well construction
program is to be implemented.
 Also, some well known facts should be kept in mind while selecting well
sites. They are:
 Wells located at the lowest level in valleys generally have a greater
possibility of yielding large amount of water than the wells located
on slopes or ridges; and
 The wells located close to rivers/streams, or within the influence of
other surface water bodies like lakes, ponds/tanks and reservoirs will
have better yields and will ensure reliable water supply.
 Once the preliminary assessment of well sites has been made, and there
is no constraint of money and time, geophysical methods of
groundwater exploration are also employed, of which electrical
resistivity method has been found to be quite helpful in the
selection of well sites.
Selection of Well Site and Type of Well
Cont’d
 In addition, subsurface exploration can be done by test drilling and
logging techniques can be used to explore various rock formations at
different depths and their water bearing properties.
 However, the use of subsurface exploration techniques is essential and
economically justified for large water supply projects only.
 After determining the purpose and the quantity of water required, the
type of well suitable for the purpose can be selected.
 The following information is helpful in identifying a suitable type of
well:





Availability of land space,
Stratigraphy and hydrogeologic characteristics of the subsurface formations;
Seasonal fluctuation of groundwater levels;
Cost of well construction and that of water lifting devices; and
The economics of groundwater pumping, which can be ignored if there is no
other reliable source of potable water in an area.
Methods of Well Construction
 Construction methods are many and varied ranging from
simple digging with hand tools (hand augers) to high speed
drilling with sophisticated equipment.
 Well construction, in terms of operations, basically includes:
 Drilling operation
 Casing Installation
 Gravel packing and well screen Installation
 Grouting and well head construction
 Developing the well to insure sand free operation at
maximum yield
 Installation of Pumps
Methods of Well Construction
 There are different equipments and drilling methods
available for drilling bore holes.
 Selection of drilling equipment depends upon:
 The hydrogeology of the formation,
 Diameter and depth of the pumping well,
 Availability of fund,
 Maintenance and spaces,
 Production capacity,
 Volume of work,
 Operating crew and easy movement of the drilling rig or
drilling machine.
Commonly used methods for the construction of shallow wells
 Shallow tube wells are constructed by boring, driving and
jetting methods, and the wells constructed by these methods are
designated as bored wells, driven wells, and jetted wells,
respectively.
1. Boring Method
 In this method the hole is constructed by the use of a selected
diameter hand or power drilling auger which is turned to bore
the hole to the designed depth.
 Cuttings are removed by pulling and emptying the auger.
 It can drill up to 30 m or more in soft sand & formations that
are free of rocks.
Augers
Hand-driven augers
~15 m depth
< 20 cm diameter
Power-driven augers
~30 m depth
< 1 m diameter
Power Auger
 Auger drilling is done with a helical
screw driven into the ground with
rotation; cuttings are lifted up the
borehole by the screw
~ 30 m depth
< 15-90 cm diameter
< 500 m3/day
Hand Dug Groundwater Wells
Cont’d .…
2. Driving Method
 In this method the hole is constructed by forcing a casing (well
pipe) equipped with a drive point into the ground by a series
of blows either manually or machine delivered on the top of
the casing.
 Driven wells should be installed only in soft formations that
are relatively free of cobbles or boulders.
 A special device called a cap or drive head protects the top
of the pipe during driving operation.
 After each length of pipe is hammered into the ground the
top is removed and additional sections are attached and
drive as required.
WELLS BEING
DRIVEN
CASING
DRIVER
Cont’d .…
3. Jetting method
 A jetted well is a well which is constructed by means of
boring equipment using water jetted under high pressure
to facilitate rapid boring.
 Jetting is pumping water down the pipe and out through
the well point where the force of the water losing the
surrounding soil materials.
Next Time …
Methods of Deep Well Construction
Based on Drilling Equipment's
Methods of Deep Well Construction
Based on Drilling Equipment's
 Construction of ‘deep wells’ (wells with depths more than
15 m) having high capacity as well as large diameter and
depth is generally accomplished by using drilling
methods.
 Various drilling methods used for constructing deep wells
can be classified as:
 Cable tool drilling (also known as ‘Percussion drilling ’),
 Rotary drilling and
 Rotary-Percussion drilling (or ‘Rotary-cum-Hammer
drilling’).
Cont’d …
 Each method has particular advantages under favorable
hydrogeologic conditions; experienced drillers can easily
select a suitable method for a given hydrogeologic setting.
 The construction procedure of a successful well is
dependent on local conditions encountered during drilling,
and hence the construction of each well should be treated
as an individual project.
Cont’d.
 The two main types of drilling machines are the cable tool
and the rotary drill.
 There is just one basic cable tool rig, but there are several
variations of rotary rigs.
1. Cable tool drilling type
 Are earliest drillers that have been used for about 400 years
 Some times it is also called percussion or walking beam driller
rigs
 Uses a heavy bit that is repeatedly lifted up and dropped down
that crushes and breaks the formation material of the aquifer.
Cable Tool Drilling Method
Cont’d
 The cable tool method consists of repeatedly raising and
dropping a chisel-edged bit to break loose and pulverize
material from the bottom of the hole.
 A small amount of water is kept in the hole, so that the excavated
material will be mixed with it to form slurry.
 Periodically the percussion bit is removed, and a bailer is
lowered to remove the slurry containing the excavated material.
Cable Tool Drilling Method Cont’d
 In cable tool or percussion drilling there are basically three major
operations:
i.
Drilling of the hole by chiseling or crushing the rock, clay, or
other material by the impact of the drill bit,
ii.
Removing the cuttings with a bailer as cuttings accumulate in the
hole; and
iii.
Driving or forcing the well casing down into the hole as the drilling
proceeds.
 Well casing is applied in most percussion- type drilling operations
and is used to help the well bore from collapsing and to prevent
surface or subsurface leakage of water or contaminants in to the
well bore.
Cable Tool Drilling Method
Cont’d
 The cable tool bit (drill bit) is a shaped steel bar, generally 4 to 8 ft long.
 The drill bit is suspended from a cable called the drill line, which is
struck over a pulley at the top of a near vertical mast erected over the
hole. Sharper bits are used in hard rock drilling.
 Cable tool drilling rigs may be most appropriate for boreholes
up to 50 m deep and 200 mm diameter which are drilled into
unconsolidated and semi-consolidated formations.
 Usually drilling is started with a large diameter & the
diameter is reduced telescopically after drilling certain
depths.
Cable Tool Drilling Method Cont’d
 On the lower end, a bit with a relatively sharp chisel breaks the
rock
 Capable to drill 8 to 60 cm in diameter through consolidated
materials to a depth of 600m and least effective in
unconsolidated sand and gravels
 A full string of cable tool equipment consists of five components;
i.e. Drill bit, drill stem, drill jars, swivel socket, and cable.
Cable Tool Drilling Method Cont’d
Components a full string cable tool equipment :
Cable Tool Drilling Method
Cont’d
1. The drilling bit: is usually heavy and massive with a
sharp edge at the bottom. Four functions

penetrates,

crushes, and

reams the aquifer material and

mixes the cuttings with water
 Selection variety of bits depends on Formation
material of the aquifer and diameter of the well (for
size selection)
Drilling bit cont’d
Hammer bit
Cable Tool Drilling Method Cont’d
2. The drill stem: is a long steel bar that adds weight and
length to the drill bit and it helps the bit to cut rapidly and
vertically.
3. Drilling jars: consists of a pair of linked heat treated steel
bars
4. The swivel socket: attaches the drilling cable to the string
of tools and allows the cable to unwind.
5. The drill cable: impart an up and down motion to the
cable and drill bit. It also controls the motion of all the tools
Cable Tool Drilling Method
Advantages of the Cable-tool system
 The major advantages of the cable-tool system as opposed to other
drilling systems are listed below.
1. Relatively cheap and ease to operate & maintain
2. Better cuttings of sample, easily make well drillers log, (a more
accurate sample for formation can be obtained)
3. Easy identification of water bearing strata.
4. Lesser amount of water is required during drilling operations
5. Minimum contamination of production zones
6. Water can be tested immediately, for quality & yield from each
water bearing stratum
7. Rate of groundwater can be measured
8. Better ability to seal off undesirable zone.
9. Capability of drilling any formation
10. The well driller need not be as skilled as his counterpart in
rotary drilling.
The major disadvantages of the Cable-tool system
 The major disadvantages of the cable tool method
1. Slower drilling rate in hard formations.
2. Limitation on depth
3. Lack of control over fluid flow from penetrated formations
4. The need to case the hole as drilling progress, i.e., lack of
control over bore hole stability, the need to use temporary drill
casing in overburden drilling to line a hole in soft formations.
5. Frequent drill-line failure
6. Difficulty in pulling casing from deep wells
Hydraulic Rotary drilling (or Rotary Direct
Circulation) Method
 This method uses a rotary bit to cut the rock and a
circulating drilling fluid to flash rock cuttings to the surface.
 The drilling fluid is usually heavy mud which is able to support
the walls of the well and prevent them from collapsing.
 Generally, the drilling of bore holes by the hydraulic rotary
method requires a drill bit, a system for rotating the bit, the
means for controlling bit pressure on the formation, and a
medium for removing the material displaced by the bit.
Hydraulic Rotary drilling
.
Cont’d
.
Hydraulic Rotary Direct Circulation
Drilling equipment
Rotary drilling bit (Cutter)
Advantages of Direct Circulation Drilling Method
1. Rapid drilling rate (relatively high penetration rates)
2. The avoidance of placement of a casing during drilling
3. The convenience of electric logging
4. Ability to drill and maintain borehole in a wide variety of
formations to depths in excess of those required for water wells
5. Ability to drill small diameter low cost borehole for
formation sampling & geophysical logging. This information
leads to the final well design. In most cases the pilot borehole is
used for this purpose.
6. Low cost for well construction in soft unconsolidated
alluvium particularly with depth greater than 300 m.
7. Large diameter holes can be drilled more economically by
the rotary method.
Disadvantages of direct Circulation drilling Method
1. A more complex drilling system compared with the cable-tool
2. Relatively high equipment capital cost.
3. Higher bit cost particularly in hard formations
4. Engineering & control drilling-fluid properties (Reynolds number, density,
gel strength, velocities) critical to well logging, completion & development.
5. High noise levels that create operating problems in urban areas.
6. Greater daily operating cost
7. Relatively high makeup water requirements
8. Relatively High equipment transportation cost
9. High cost for drilling karstic formations
10. The need to remove mud cake during well development
11. Not suitable for boulder formation and requires more water, repair &
maintenance.
Direct versus Reverse Circulation rotary drilling
.
Conventional (Direct)
Drilling pipe
circulation
 The drilling fluid circulates from
the drill pipe and then flows up
the annulus between the outside of
the drill stem and borehole wall.
Reverse circulation
 The direction of flow of drilling
flow is opposite to that of direct
circulation drilling. Drilling fluid
flows from the annulus between
the drill pipe and hole wall to the
drill stem
Hydraulic rotary drilling with reverse circulation
Reverse Circulation Rotary Drilling Method
 A modification of direct circulation rotary method is known as reverse

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
circulation rotary method.
In this system, the drilling fluid with cutting return inside the drill
string & is discharged into a settling tank or pit.
Downward flow is in the annulus between the drill string &
borehole.
The clear water returns to the borehole by gravity flow.
The reverse-circulation rotary method has become increasingly
popular for drilling large-diameter boreholes in unconsolidated
geologic formations
In fact, it is the most rapid drilling technique available for
unconsolidated formations
The system components are similar to those of the direct rotary except
for rotation.
Reverse Circulation Rotary Drilling method
 As the diameter of the drill pipe is relatively small, the
velocity of the drilling fluid in the pipe is high. This results
in two advantages:
1.
There is no need for the rotary bits to crash the formation
at the bottom of the hole into pieces.
2.
There is no need to use heavy drilling fluid for bringing
the cuttings to the surface & clear water can be used. Thus
the problem of clogging of the aquifer around the well by
mud intrusion is greatly reduced.
 It is probably the most rapid method of drilling and
hence it has become increasingly popular:
Advantages of Reverse Circulation Rotary
Drilling method
1. Lower capital cost than equivalent-capacity direct rotary equipment.
2. Good for drilling large diameter holes in soft, unconsolidated alluvial
formations.
3. Formation sampling is more accurate than with direct rotary.
4. High return velocity lowers drilling fluid viscosity requirement.
5. Lower noise levels with insulated compressors
6. Lower transportation costs than equivalent-capacity direct rotary.
7. Simpler and less costly circulating system.
8. Lower bit costs than with direct rotary.
9. Lower development pumping time where water without additives is
used as drilling fluid.
10. The boring is done without a casing and hydrostatic pressure is used to
support the walls of the bore-hole during construction
Disadvantages of Reverse Circulation Rotary
Drilling method
1. Drilling efficiency declines rapidly below 250 to 300 m.
2. Large water supply requirements. It requires five times the amount
of water required for direct rotary drilling.
3. The system is not suitable for drilling large boulders,
consolidated rock formations, and karstic formations. When drilling
long sections of clay and shale, drill fluid additives must be used.
4. Difficult to use where the static water level is less than 5m.
5. Boreholes smaller than 18’’ can not be drilled due to the eroding effect
of the higher velocity fluid down the annulus.
6. Maintaining borehole alignment is more difficult than with direct rotary
because of the relationship of the drill collar diameter & weight to the
large diameter borehole.
7. Resistivity logs are not reliable where water without additives is used as
the drilling fluid. It is unsuitable for exploratory test drilling.
Down–the-hole Hammer Drilling Method
 In this method pneumatic hammer operated at the lower end of the
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drill pipe is used. It combines the percussion effect of cable tool
drilling & the rotary action of rotary drilling.
In hard rock, compressed air can be used to blow out cuttings.
This method is often used in conjunction with a special bit that has a
hammer action as it is rotated.
This method is called down-the–hole (DTH) -hammer drilling and is
commonly used to bore through crystalline rocks.
In hard formation the DTH hammer is most effective but becomes
less so as the rock strength reduces.
DTH hammer drilling is the technique of drilling where by hammering
action at the bottom of the well is incorporated to the conventional
rotary action.
With such drilling method penetration of about five meters per hours
in hard formation is possible.
Down–the-hole Hammer Drilling Method
 Percussion and rotary methods of well drilling are usually
uneconomical in water well drilling in hard rock formations due
to the slow penetration rate, high bit rate, and high maintenance
cost of the machinery.
 Air-operated down the hole hammer (DTH) drilling method has
proved to be the best for the construction of water wells in hard
rock areas.
Down-the-hole Hammer (DTH) Drilling Method
The following table summarizes the performance of these drilling techniques in diverse
geologic formations.
.
Drilling Fluid
 Drilling fluid can simply be defined as the combination of
fluids and solids required in certain drilling processes to
facilitate the production and removal of cuttings from a
borehole.
 The conveying of the drilled cuttings to the surface is still
an essential requirement but in addition, the drilling fluid must
perform other functions such as:


Cooling the drill bit
The maintenance of borehole stability in preventing caving and
sloughing of unconsolidated formation.
Lubrication of the mud pump, bit bearings, and the drilling string
& thus reducing the torque required to turn it.
Drilling Fluid
 Five drilling fluid systems are:-
1. Water base clay mud (e.g. bentonite)
2. Oil base mud
3. Low solids mud
4. Air, gas or moist flush system
5. Low velocity foam system
Drilling Fluid
Cont’d
Water Base Mud
 Drilling mud is a mixture of clay, water & chemicals pumped
down the drill string & up the annulus during drilling in order to
lubricate the system carry away rock cuttings maintain the
required pressure at the bit end and provide an aid to formation
evaluation.
 It consists of
1.
2.
3.
A liquid phase
A suspended-particle(colloidal) phase, and
Cuttings entrained during drilling
 The oldest and probably the most widely used drilling fluid
for water well drilling is a water-based mud.
 In this fluid the continuous liquid phase is fresh water.
Drilling Fluid Cont’d
Oil Base mud
 These are drilling fluids in which oil is the continuous phase
and water is the dispersed phase.
 As with salt water-base muds, the oil base muds are used to
prevent the hydration of the native clays which may reduce
permeability.
 Because of the obvious contamination problem oil-based
muds have no application in water well drilling.
Drilling Fluid
Cont’d
Low Solid Mud
 This is a drilling fluid in which the solids content is less
than 10% by weight or a mud weight of less than 2.6 parts
per liter.
 For water well drilling the continuous liquid phase is
water & the solids are CMC (sodium carboxyl methyl
cellulose), HEC (Hydroxyethyl cellulose) & other
polymers.
Drilling Fluid Cont’d
Air, Gas or Mist Flush system
 Of these, air has the greatest application in water well drilling.
 This may be used for air flush lifting of cuttings from rotary drilled
holes or may be used to operate and flush cuttings from DTH
hammers.
 Air flush drilling is generally very much faster than water or
mud drilling and bit life is extended considerably as a result of the
very rapid removal of drilled cuttings from the face of the bit.
 However, problems arise when water is encountered in the hole.
 It is impossible to restart drilling below a pressure head of water in
the hole which exceeds the air pressure available at the bit.
Drilling Fluid Cont’d
Low velocity Foam system
 This is an extreme low solids system in which a slow moving
column of foam transports the cutting up the hole with the
particles suspended and separated in bubble clusters.
 Very low water & air volumes are required.
 The material used for foam flush drilling is a concentrated
foaming agent with good emulsion and foam stability, which
gives small, tight, thin –walled bubbles.
Class Activity
~ Due date:
…
Water Well Design and Construction
1) State and briefly explain stages of Well design
2) What Geological and Hydrogeological
Considerations should be considered while
designing well?
3) State and briefly explain steps in Well construction
4) What are components of final designed well:
 Drawing
 Functions and/or description of each component
Next Time …
Well Completion
Well Development
Well Rehabilitation
Well Construction Methods ~~~ as Review
shallow depths;
domestic wells;
unconsolidated
formations
Deep municipal,
industrial,
domestic wells;
Unconsolidated and
Consolidated
formations
 Dug wells
 Bored wells
 Driven wells
 Jetted wells
 Percussion (Cable tool)
method
 Hydraulic Rotary method
 Air (Pneumatic) Rotary
method
As Review ~~
 Tests are to be conducted:
every 15m of depth or
 every four circulating hours or
 Whenever conditions appear to have change
or problem arises.
 The driller must maintain current records on the
site at all times to show
 time, depth and results of all mud tests,
and
 all materials added to the system-kind,
amount, time and depth.

Well Completion
 The drilling of the borehole alone does not complete
the construction of an efficient well.
 Well completion involves: Placement of casing,
 Cementing of casing,
 Placement of well screen,
 Gravel packing, and
 Well head cap construction
Well Completion Cont’d
Well Casing: The provision of casing in wells maintains a stable open hole
from the ground surface to the bottom of the aquifer.
 It seals out surface water and undesirable groundwater.
 It also provides structural support against caving materials
found in the wall of the well. Commonly employed materials
are iron and steel.
 It may be classified as surface casing and pump chamber
casing.
… Cont’d
 Reasons for using casing in water well or
borehole.
1.
2.
3.
4.
5.
6.
7.
To prevent the collapse of the walls of the borehole
serving as a lining.
To exclude pollutants
For conveying the water to the surface.
For conveying the water into the well for injection
purpose
For housing the pump mechanism
For conveying a cement grout in the well for
cementation purpose
Serving as a reservoir for a gravel pack
… Cont’d
Placement of Well Casing
 Basically we have two category of well casing:
Blind casing and


Well screen
Types of casing (based on function)
 Surface casing
 Conductor Casing
 Intermediate Casing
 Pump house casing
COMPONENTS OF A WELL
… Cont’d
Surface Casing
 At upper strata of unstable or fractured
materials.
Used:
 Supporting unstable materials during drilling,
 Reducing loss of drilling fluids
 Facilitating installation or removal of other
casing
 Helping in placing a sanitary seal, and to seal
off the well against the inflow of polluted
surface water
… Cont’d
Conductor Casing
Used to
 To prevent well contamination from the surface
 Stabilizes the upper borehole while drilling as
reservoir for gravel packing
 Conductor Casing
 For high-capacity well design
 installed and cemented to a minimum of 15m, or to the
first impervious formation
Cont’d
Design of Well Casing and Housing pipe
Design includes the selection of


A suitable material,
Diameter
Casing size
(mm)
Actual inside
diameter
102
127
152
203
254
305
Maximum
discharge
(m3/day)
1,090
1,690
2,450
4,250
6,700
9,590
Casing size
(mm)
Actual inside
diameter
337
387
438
489
591
Maximum
discharge
(m3/day)
11,700
15,500
19,800
24,700
36,100
Cont’d
Depth of well and bore size
Bore size
 To facilitate the lowering of the casing pipe the diameter of the
bore has to be at least 5cm bigger in diameter than the casing.
 If gravel pack is to be used, the minimum diameter should be
= 2* thickness of the gravel pack + outside diameter of
the casing pipe.
Depth of well
Depends upon
 Locations of water-bearing formations,
 Desired yields of the well and
 Economic considerations
… Cont’d
Diameter of casing, depth
Diameter of casing Should be at least 5 cm more in diameter
than the nominal diameter of the pump.
 The depth of housing pipe below the ground level is selected
such that the pump is always submersed in water.
 It

must set a few meters below the lowest draw down level
The diameter of the pipe of the well section below the
pump housing is fixed by the permissible velocity (1.5-5m/s)
of water through the pipe. A velocity of order of 2.5-3m/s is
found to be most suitable. The usual practice is to provide
constant diameter pipe.
Well Completion Cont’d
Cementing of Casing:o It is the placement of concrete in annular space
surrounding the casing.
o It has the following purposes.
 Prevent entrance of water of unsatisfactory quality
 Prevent the casing against exterior corrosion
 Stabilize casing rock formation
Types of casings
 Poly Venile Chloride (PVC)
Note:-
Steel (Mild or stain less steel)
Non metallic materials should be used where corrosion or
encrustation by irons bacteria is a problem
- Shallow well
Casing Comparison
PVC
VS.
STEEL
Non-corroding
Corrodes
Lower strength
Higher strength
Fewer water quality
complaints
Rusty water
Rotary construction only
Suitable for any
drilling method
Low cost
High cost
Well Completion Cont’d
 Screens:- Wells in unconsolidated formations are
equipped with screens that will serve the following
purposes.
Stabilize sides of the well
Prevent sand movement into the well
Allow maximum amount of water to enter the
well with minimum hydraulic resistance
 Non ferrous metals, alloys and plastics are often preferred
as a screen material.
 To control the head loss through a perforated well section a
minimum open area of 15% is required. The length of the
screen provided in artesian (confined) aquifer is about 70 to
80% of aquifer thickness. Where as in a water table
(unconfined) aquifers screening the bottom one-third (1/3)
of the aquifer provides optimum design.
Well Completion Cont’d
Gravel Packing:- A gravel packed well is one containing
an artificially placed gravel screen or envelop surrounding the
well screen in a thickness ranging from 8 to 15cm.
 It may have the following purposes.
 Stabilize the aquifer
 Minimize sand pumping
 Permit use of large screen slot with a maximum open area
 Provide an annular zone of high permeability
Grouting / Sanitary Seal
 The drilled hole is usually larger than the well casing.
 Annular space around the well casing should be filled
with grout.
dhole = dcasing + (7-15)cm
o It is also necessary to seal out water of unsuitable quality
strata above a fresh water aquifer.
Well Grouting Cont’d
 Well grouting involves filling the space (usually
between the casing and the wall of the well) around the
pipe or casing with a suitable impervious material.

Concrete

Sand cement

Neat cement

Bentonite clay
Well grouting …. Cont’d
Reasons for well grouting

To protect entry of contaminating fluids flowing into
aquifers

To prevent undesirable water movement b/n aquifers
(quality).

Protecting entry of unwanted water from the surface
or a subsurface zone.

To protect the casing against exterior corrosive and
also to assure structural integrity of casing against external
pressure and buckling.

To make the casing stay tight in the drilled hole.
Grouting / Sanitary Seal Cont’d
 On completion of gravel pack, seal the upper 5m of the remaining
annulus space with cement
 Before grouting put pure sand (0.3-0.6 mm) on the top of gravel to protect
the cement from moving down to the screen position
Grouting
Well Development
 Following well completion, a new well is developed to increase
its specific capacity, prevent sanding and obtain maximum
economic life.
This is done by removing the finer material from the natural
formations surrounding the perforated sections of the
casing.
 There are various well development methods. The following are
some of them:
Pumping: - this involves pumping the well in a series of steps
from a low discharge to one exceeding the design capacity. At
each step the well is pumped until the water clears. This
irregular and non-continuous pumping agitates the fine material
surrounding the well to be pumped out from the well.
 This development method is recommended after utilizing
the other techniques as a finishing procedure.
Well Development
… Cont’d
Surging:- It is based on the up and dawn movement
of a surge block attached to the bottom of a drill stem.
Initially, surging should begin with a slow stroke at the
bottom of the screen and progress to the top of the
screen.
This should then be repeated with increasingly faster
strokes.
The procedure is completed when material
accumulating in the bottom of the well becomes
negligible.
Well Development Cont’d
 Use of compressed air:- The method involves the release
of compressed air into the well through a pipe. This air is
then loosens the fine material surrounding the well.
 Hydraulic jetting: - Jetting with a high velocity stream of
water is an effective technique in open rock holes and in
wells containing screens with large percentage openings.
Fine grained materials from the formation are carried into
the well by the turbulent flow. The method is particularly
effective in developing gravel-packed wells
Well Development Cont’d
 Addition of chemicals:- Open –hole wells in limestone or
dolomite formation can be developed by adding hydrochloric
acid to water in well.
The solvent action removes fine particles and tends to widen
fractures leading into the well bore Hydraulic fracturing.
Mechanical surging
Air lifting
High velocity Jetting of water
Dispersing agent – chemicals
PUMPING TEST FOR WELL YIELD …
Revision
 Following development of new well, it should be tested to determine its
yield and drawdown.
 The main purpose of pumping test operation is:
 To determine the performance of a well (Well test )
 To determine the hydraulic parameters of the aquifer (Aquifer test)
Specific purpose
To check the well efficiency (construction performance)
To determine the potential of an aquifer and sustainable abstraction
rate (safe yield)
To select the appropriate type of pump and its position in the well
To obtain information about the groundwater quality of the well
 The test is accomplished by measuring the static water level, after
which the well is pumped at a maximum rate until the water level in the
well stabilizes.
Well Rehabilitation / Maintenance
 The performance of a well usually declines after
some years of operation resulting in higher
drawdown, reduced discharge (<25%) and higher
pumping costs.
 Well
rehabilitation:
refers to the treatment of a
production well by mechanical, chemical, or other means to
recover as much as possible the lost production
capacity.
Well Rehabilitation Cont’d
 The major causes of a reduction in well performance are:
o Chemical encrustation or clogging of the screen due to
bacteriological activity
o Plugging the formation around the well screen by fine
particles (clay and sand in the pores)
o Pumping of sand due to poor well design or corrosion of
the well screen
 Maintenance/rehabilitation usually carried out through well
development together with brushing and addition of chemicals.
Well Head Construction
 A concrete, horizontal apron 2mx2m with a minimum thickness of 0.2m
and the well at the center
Prevent
surface water from entering into aquifer
The surface casing shall be cut off horizontally not less than 0.7 cm
above ground level
The observation pipe shall be cut off below the level of the surface casing
but not lower than 0.5 cm above ground level
Well disinfecting and Sealing the Well Head
 Well can be contaminated during construction
 Disinfect a well by applying
a chlorine solution to kill any harmful
bacteria in the well
Sanitary well cap
 To protect external materials from falling into the well the top
of the well has to be secured either by welding or by using nut
and bolt until the permanent pump installed
End of the Chapter