Technical Manual for Drilling Works for Technical Support Plan for the Drillers in DDCA (2013)

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

3.5 BIT CONTROL AND REPARING FOR MUD DRILLING (TA CODE 4-5)

Rotary bits shall be correctly controlled and the proper repair and/or replacement is required. The

excessive use of bits over their lifetime brings about the following problems:

Under gauge of the hole which causes the wearing of bit and/or tool stucking.

By the wearing of bearings of roller bits, cones falls into the hole.

Buttons or pieces of tooth fall into the hole.

For the drag bits, periodical repairing on their blades and gauges by welding is needed.

Drillers are required to conduct proper bit record and repairing/replacement using the log sheet as

shown in Table 31 .

Table 31 Example of Bit Log Sheet

BIT LOG SHEET

Type:

Bit Size:

Part No.:

Bit No.:

Date of Issue:

To Rig No.:

Date of Return:

From Rig No.

Date

Metrage

Times

Diameter or

Type of Formation

Remark Service Record.

Drilled

Sharpened

gauge after

Penetrated

w/Bit

re-sharpened

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3.6 AIR CONTROL FOR DTH DRILLING (TA CODE 4-6)

It can be observed that drilling with Megadrills and Megabits do by far not reach the performance

recommended by the manufacturer of the tools. Low penetration rate may result from problem of

different nature of operation of Megadrills and bits such as:

 Air supply is not according to requirement resulting in not adequate air pressure in the

Megadrill or air volume is not less than 1,200 m per minute or air pressure required for A

53-15 Megadrill not less than 9.0 to 10.3 bar.

 The drill bit is not sharpened properly

 The Megadrill is worn-out, clearance of piston and piston case sealing O- rings worn-out etc.

 Bits are very dully because of overrunning

 The necessary bit weight is not on the bit or there is too much load on the bit (for A 53-15

Megadrills 680 kg minimum weight and 1,600 kg maximum weight (is recommended).

 Rotation of bit is not according to the geological formation and to the expected penetration

rate per revolution. Ideally the bit should penetrate 3/8"into the formation of the drill pipe.

Generally acceptable revolution per minute are considered with 15rpm to 30rpm

 No use of water injection will create problems of “collaring” or bridging caused by scopage

of small amounts of formation water into the hole. To be avoided by injecting 2 to 5 CPM of

water into the air stream.

 The “back pressure” created by considerable formation water influx may reduce extremely

the penetration rate. To overcome this problem form has to be used in quantities.

Drillers are required to understand the mechanism and function of the air-compressor and the DTH

using the operation manual of the manufacturers. They have to consider the static water pressure,

back-pressure, annular velocity necessary to remove the cuttings from the borehole and conduct

proper operation of the air-compressor.

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3.8 CASING FOR DTH DRILLING

(TA CODE 4-8)

The boreholes in hard rock formation are

normally drilled by DTH drilling methods in

three stages, i.e. surface hole drilling,

conductor hole drilling and production hole

drilling. In general the shallow part in hard

rock

formation

unconsolidated

overburden and is collapsible during air

drilling. Therefore, down to

5 to 30 m,

sometimes even to 60 m, this overburden

shall be drilled by the mud drilling and the

conductor casing shall be installed. Figure

23 show an example of the casing program

for DTH drilling borehole.

The surface casing is required when:

 Surface water must be sealed off

 Unstable formations interfere with

drilling, or

Figure 23 Example of the

 Artesian flows are possible. in this case the

Casing Program for DTH Drilling

surface casing must be cemented

Borehole

The purpose of surface casing is to isolate

freshwater zones so that they are not contaminated during drilling and completion. The surface

casing is also necessary for the smooth work around the borehole during the drilling.

PVC casing and screen pipes are used for most of the boreholes in Tanzania. Please refer

Technical Item 6-1 for the specifications of PVC casing and screens and Technical Item 6-3 for the

installation procedures.

The conductor casings are in general of steel and with flush joint. In many cases they are

temporary and are to be removed after the completion of the drilling work. The preparation of the

conductor casing with sufficient number on site is quite important to obtain the smooth progress of

the drilling works by DTH. Please refer to Technical Item 2-5 for the specifications of steel

casing pipes.

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3.10 BIT CONTROL AND REPARING FOR DTH DRILLING (TA CODE 4-10)

DTH bits shall be correctly controlled and the proper repair and/or replacement is required. The

excessive use of bits over their lifetime brings about the following problems:

Under gauge of the hole which causes the wearing of bit and/or tool stucking.

Buttons or pieces of tooth fall into the hole.

Progress of drilling decreases when the buttons of bits are worn.

Periodical sharpening shall be conducted to keep the good drilling progress. Please refer to

Technical Item 2-3 for the repairing of DTH Bit.

Together with Bit Log Sheet (Technical Item 3-5), DTH tool shall be controlled using the DTH log

sheet as shown in

Table 32 Example of DTH Log Sheet

DTH LOG SHEET

Model:

No. of Tool

Date of Issue:

To Rig No.:

Date of Return:

From Rig No.:

Date

Hours

Metrage

Type of Formation

Remarks, Cleaning Servicing Tool

tool/Run

Drilled

Penetrated

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4 BOREHOLE LOGGING (TA CODE 5)

4.1 BOEREHOLE LOGGING INSTRUMENTS (TA CODE 5-1)

4.1.1 GENERAL INFORMATION ABOUT BOREHOLE LOGGING

Many of the geophysical survey methods for groundwater exploration, which are carried out on the

ground-surface, can also be used within a borehole in vertical direction.

 Resistivity well logs - RES

Resistivity logging, usually called electric logging, provide a useful tool, and the information

gained increases in general the effectiveness of the well design. A good log gives a detailed

picture of the character and thickness of the various formations at the well site and an indication

of the water quality by measuring the apparent resitivity of the subsurface material

cross-sectioned in the borehole. Electric logging offers several important advantages, such as

locating the top and bottom of each distinct layer, determining relative water quality, and

differentiating fresh hard rock layers from fractured and weathered parts. A limiting factor in

electric logging is that the method can only be done in boreholes that do not have casings and are

filled with drilling fluid or water. The method is therefore best to be carried out in rotary mud

circulation boreholes.

Please note that in low-yield boreholes in hard rock formation, it is advised to carry out borehole

logging the other morning after drilling was completed to allow the water level to rise for one

night due to low recharge conditions.

 Spontaneous Potential (SP) Logs

Self-potential or spontaneous potential logs are always run in conjunction with the electric logs.

Spontaneous potentials are naturally occurring electrical potentials (voltages) that result from

chemical and physical changes at the contact between different types of formation material. In

a borehole, potentials also occur between the drilling fluid in the borehole and the fluid in the

formation and also between the drilling fluid and the filter cake on the borehole wall.

As in the case of drilling DTH in Swaziland, where fluid in the borehole is the same groundwater

as in the formation, there cannot be a difference in the potential of both waters (fluids). In

general SP logs make only sense in boreholes filled with drilling fluid (drilling mud).

To measure SP at various depths, an electrode is lowered into an uncased borehole filled with

drilling fluid as one electrical terminal. The terminal of the arrangement is connected as a

ground terminal at the surface, which is often placed in the mud pit. The down-hole electrode

is usually negative with respect to the surface electrode. Any current in the circuit, which

results from electrochemical action between the drilling fluid and the formation or formation

water, is conducted to the surface through the drilling fluid column. The milli-voltmeter

connected between the electrodes, therefore, measures the drop (difference) in potential in the

drilling fluid column between the down-hole electrode and the surface electrode.

As the down-hole electrode is moved up and down in the borehole, the meter registers variations

in spontaneous potentials of the different formations. A curve showing these potentials plotted

against borehole depth provides what is called the SP log. Although the SP log may indicate

the permeable zones, there is no definite relationship between the magnitude of the SP

deflection and the permeability and porosity of the formation. Variations shown by the SP

curve are interpreted along with variations in apparent resistivity shown by the resistivity curve.

The two curves together constitute what is usually called the electric log.

The SP log is plotted on the left-hand of the curve sheet, where it can be compared easily with

the resistivity log on the right-hand side.

 Natural Gamma Ray (GR) logs

In gamma logging, measurements are made of naturally occurring radiation coming from the

materials encountered in the borehole. The record of gamma radiation is used as a qualitative

guide for correlation of formations and permeability of formations.

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Gamma radiation is emitted from certain elements in geologic materials that are unstable and decay

spontaneously into other more stable elements. Gamma rays are similar to X-rays in that having a

great ability to penetrate other materials (for example even steel casings), but gamma rays have a

shorter wave length.

Certain radioactive elements occur naturally in igneous rocks (granites, gabbros) and metamorphic

rocks (slate, mica-schist, gneiss) and as depositional particles in sedimentary rocks. Clays and

shale contain high concentration of radioactive isotopes, usually potassium. Sands and gravel on

the other hand contain primarily silica, a stable substance, and therefore emit only very low levels

of radiation.

So gamma ray curves of silica rich, light colored, acidic rocks, such as granites, gneiss and

sandstones are showing deflections in the curve to the left.

Gamma ray logging has a fundamental advantage over electrical logging. It can be done either in

cased wells or in open boreholes containing air, water, or drilling fluid. Therefore with gamma

ray it is possible logging existing wells, where logs have been lost or were not carried out. The

gamma probe is very simple, having a detecting element, which is measuring the pulses given off

by the radioactive materials in the different formations. The radiation extensity is expressed as

the average number of counts per second (cps).

The minerals normally found in sedimentary materials such as clay, silt, sand, or sandstones

contain small amounts of radioactive potassium-40, and decay products of uranium and thorium.

Potassium is an important constituent of clay minerals, mica, feldspar, and shale. Quartz sand

contains no potassium or radioactive potassium-40. Quartz sand formations emit gamma-rays at

extremely low levels. Normally the gamma logs show more cps at depths, corresponding to clay

or shale layers and few cps at depths corresponding to sand or sandstone layers, if the sand is

mostly consisting from quartz.

4.1.2 OPERATION OF BOREHOLE LOGGING

Components of the equipment of the Geologger 3030:

 Power winch 3895

 Geologger 3030 machine

 Combination Probe (GR, SP, RES)

 Sheave, sheave stand and supporting legs



2 Batteries 12 V



2 Surface electrodes

 Power supply cords

 Cable for Geologger 3030 to power winch

 Cable for Geologger 3030 to sheave

Connection of the equipment:

1. Join up the components of the probe (GR + SP/RES) then seal the joint with insulation

tape

2. Connect slowly the winch connector to the probe turning slowly until there is a click

sound, and then lock the link

3. Connect the battery to the power winch

4. Sheave stand is then put over the borehole and sometimes there might be a need for the

sheave’s stand additional / support legs in case, when the temporary casing is more than

30 cm above the ground

5. Then wind the cable from the winch, while the probe lies on the ground, to the sheave

wheel and the direction of the wheel will be decided by the winding of the cable. The

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winding of the cable should be in a cross manner and sometimes, just wind it straight.

Then use the lock to prevent any slippage. Lock the probe cable with the lock knob

from the wheel to avoid any slippage of the cable from the wheel and getting damaged

6. Connect the cables from power winch and sheave to connector panel of Geologger

7. Connect the earth electrodes to the connector panel and then to the ground with the

B-near (black) the borehole- and the N-30m (red) maximum away from the borehole and

they should be connected to wet ground.

8. After all the connection from the connector panel has been completed and the setting of

the sheave then the probe is put inside the borehole. Then connect the cable from the

Geologger to another battery.

Operation of the equipment:

Set the probe into the borehole and knowing the casing top above ground level, you will know

exactly the top of the spring of the probe would set level with ground level.

Set the power switch “ON” and the menu will be displayed at the LCD display. As the menu

items are displayed, they will respond to function keys shown to the left of the menu, F1 to F4.

First step

For the display and the setting of date and time, observe the following procedures:

 Choose date and time by pressing F1

 Setting the date by pressing the key (*) star. This enables you to set the date, “YY MM

DD”, by putting in the figures from the keyboard.

 Set the time by pressing the hash key (#). This enables you to set the time, “ HH MM SS”,

by putting in the figures from the keyboard. Then enter.

Second step:

 Choose system by pressing F4

 System check by pressing F1

This enables the machine to check that everything is functioning well and if it is in order. It will

let you know in case, which part of the system is not ok.

Note: If there is an error, for example with the floppy disk drive, it will tell you where the error is,

and all you have to do, is to check, if the floppy disk is inside and then slightly press or move it

sideways. Then cancel and restart system check.

Third step:

 Choose measure by pressing F3

 Measure by pressing F1

Depth input will appear, and then change depth to zero and then press enter. Sign change due to

the direction of probe movement from sheave by pressing F1, if necessary - then press enter.

 Then set the gamma range, which is normally 0. 2K cps by pressing F3 - then press enter

 The ampere range is automatically set.

 Input sampling interval is normally every 10 cm, but can be change to other measuring

interval.

 On the display will appear >>Reset data & start. Just press enter.

 After measuring press the enter key.

 Enter ID No. of the borehole. Then enter.

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 Print out click play back on F2

 Input of ID No. This helps to know the file, in which the recorded data are stored on the

floppy disk. This is entered with three figures e. g. M2-10-2, ID No. is 001 when

measuring down and 002 when measuring up. With more reference to the recorded data,

there is a sheet that needs to be filled for ID No. and borehole No.

 Depth scale selection is normally 1/500, but select by pressing F4.

 Selection of gamma scale can be selected from the keyboard from 1 to 9.

 Selection of resistivity scale can be selected from the keyboard from 1 to 9.

 Selection of Spontaneous Potential (SP) scale can be selected from keyboard from 1 to 5.

Please note for the scale selection of the different methods, it is important to observe constantly the

measuring keyboard, while driving the probe down. Then you know the scale in which the

measured values, ohmmeter for RES, mV for SP and cps for GR, are lying and subsequently you

choose the appropriate scale for the print out process. The pictures of Figure 25 shows the above

procedures.

2. Preparation of the Loging Equipment

1.Measuring of the water level before

Logging

Outlining the principles of the

4. Explaining the installation of sheave stand

borehole-logging methods

on top of the borehole

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4.2 INTERPRETATION OF BOREHOLE LOGGING RESULTS (TA CODE 5-2)

4.2.1 INTERPRETATION OF BOREHOLE LOGGING RESULTS

 Interpretation of electric logs

The electric log cannot be used to qualitatively identify the material encountered in the borehole,

because the measured resitivity is a function of various different parameters, such as composition

of the drilling mud or the fluid in the borehole, fluids in the formation, diameter of the borehole

and the distance of the electrodes within the measuring probe. Depth related rock samples

recovered during the drilling (drilling cuttings) are required for positive identification of specific

geological formations. Dry formations are poor electrical conductors and show very high

resistivities as well as fresh and dense igneous, metamorphic and volcanic rocks, such as

granites, granodiorites, amphibolites, gneiss, dolerites, basalts and ryolites. Saturation of a

formation reduces its resistivity. The reduction again is partly controlled by the porosity of the

formation.

The type of material is only factor, which is influencing the resistivity. Water in the pore space

is always mineralized differently due to the material of the formation and it’s chemical

composition. So various different factors are influencing the resistivity and experience is an

important factor in the interpretation of electric logs. Knowledge of the general trends and the

spectrum described above are also very important. In the hard rock formation of Swaziland

high resistivities are usually indicating dense and dry hard rock types, whereas curves changing

to lower resistivity values are indicating fractures and fissures and weathered formations, which

can be filled with groundwater.

 Interpretation of SP logs

Interpreting SP logs is generally very difficult and it makes only sense to analyze logs which

were carried out in an uncased borehole filled with drilling fluid and in a borehole having

distinctive clay layers to provide a so called baseline (clay line). Please note here that SP logs

published from oil-field works are completely different from SP logs run in water-wells. It is

important to understand the differences between oil-well and water-well SP curves. In general

groundwater associated with oil is salt water. The electrical conductivity of this water is

extremely high in comparison with the conductivity of the water in the drilling fluid.

Groundwater suitable for drinking water purposes has low dissolved solids, on the other hand,

and therefore has a much lower conductivity than oil-field brine. Its electrical conductivity

may be about the same as, or even less than, the conductivity of water in the drilling fluid.

Thus, the electrochemical reaction between the formation water and the drilling fluid is quite

different, depending on whether the formation water is considerably more salty than the drilling

fluid (oil-field condition), or whether the formation water has about the same salinity as the

drilling fluid (water-well condition). When a permeable formation (aquifer) contains salt water

and the drilling fluid is made with fresh water, the SP normally shows a relatively large

deflection to the left in relation to the clay baseline. The SP deflection opposite the same

formation containing fresh water, however, would be relatively small. Another way to describe

the difference is to note that the formation with salt water shows a high negative potential in

relation to clay layers, whereas the formation with fresh water shows only a slight negative

potential. Some helpful observations in interpreting SP logs for formation with fresh water:

 It is often difficult to interpret a SP curve at shallow depth. SP deflections are more

pronounced in moderately deeper to deeper wells because, as depth increases, the

ground-water tends to become more highly mineralized.

 The first step in interpretation is to establish a clay baseline (shale baseline) on the log.

If clay layers are not present, the SP log add little information to the interpretation. For

many wells, the SP curve may be of little value, because variations in the curve may be

insignificant.



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 Note deflections to either the left (negative) side or the right (positive) side of the clay

base-line. Formations having deflections to the left, generally indicate groundwater

having higher chemical activity than formations having deflections to the right. These

deflections indicate the positions and thickness of aquifers containing fresh water.

Deflections in the SP curve may be insignificant unless the formation has at least a

thickness of 1 - 1. 5 m.

 Conclusions drawn from the SP curve will generally correlate with data from the

resistivity curve, although the SP curve will usually move in opposite direction.

 The clay baseline may shift gradually or abruptly at increasing depth for no apparent

reason.

 SP curves should always be used in conjunction with resisitivity or other logs, because it

may be particularly difficult to interpret the curves.

 Interpretation of Gamma Ray (GR) logs

In the hard rocks, we can say simply that silica rich, light colored, acidic rocks like granites,

gneiss, contain less radioactive decaying minerals and showing less cps, than rocks with less

silica content, but high in micas, dark colored, basic rocks, like diorites, gabbros, amphibolites,

shales contain more radioactive decaying minerals, showing more cps.

A problem of interpretation is related to the borehole diameter. As we know, gamma ray can

only be detected around the borehole wall into the formation with a distance of about 0. 3 m.

Where caving clay or shales are encountered and a wash-out occurs, the gamma ray log will

indicate low cps opposite of the enlarged section of the borehole. Thus the log will appear to

indicate a sand- or granite formation. Borehole samples, the driller’s log, and a caliper log can

be used to minimize this difficulty in interpretation.

4.2.3 DETERMINATION OF SCREEN POSITION

After having successfully carried out the borehole-logging operation, the casing plan has to be

established. As described earlier, in certain low-yielding wells it might be suitable to carry out the

logging the other day, allowing the low recharging water table to rise to the static level. The

following information is necessary to establish a sound casing plan:

 Situation of the static water level after completion of drilling

 Depth of various or single water strikes

 Description of the drill cutting samples

 Penetration rate records

 Measurements of water quantities at various depths

 Information about the stability of the borehole wall

 Drillers general observation of fracture zones and water strikes

Generally, high yielding water wells with distinctive, groundwater producing fractures zones need

only a limited quantity of screen length opposite of the fractures. Low yielding wells however, or

wells with a certain number of micro fractures need a longer screen length to exploit groundwater

as much as possible from every fracture present. In order to achieve a hydraulically good

connection between the well and the aquifer(s), it is good practice to install one screen section only,

for better inflow conditions of the groundwater into the well.

For a more safe installation of the well assembly into the well, it is common practice to drill some

1-3% deeper than the depth, at which it is intended to place the bottom cap of the casings. The

following pipe-lengths are available to install within the project:

 Plain casing length of 5.72 m

 Plain casing length of 2.81 m

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 Plain casing length of 0.93 m

 Plain screen length of 2.81 m

The depth calculation of the casings and screens to be installed into the borehole should start from

the bottom to the top of the borehole, indicating as well the portion of casings, which is going to

stand over the ground surface. Knowing from the records the height of the drilling table of the

drilling rig above ground surface, it is possible to indicate exactly the casing depth.

Screens need to be placed opposite of groundwater bearing zones (aquifers) and not shallower than

the first water strike, which was reported during drilling. The project is not allowing the installation

of screens at a shallower depth than 20 m below ground surface.

Generally on top of the bottom cap (lowest part of the well) a so called sedimentation pipe or sump

pipe has to be installed, being a plain casing pipe with 2.81 m length.

Centralizers have to be installed around casing and screens in the depth where gravel pack is

intended to be placed, in order to keep the pipes centrically in the borehole and allowing the gravel

pack to be placed evenly around the screen pipes.

Figure 26 shows the example of logging results and casing program for a borehole in sedimentary

formation in Kisarawe region. Figure 27 shows the one for a borehole in hard rock formation in

Bagamoyo region. Principally, resistivity shows the high value at the position of the aquifer in

sedimentary formation. On the contrary the resistivity of the aquifer in hard rock formation

becomes higher than the formation with lower water contents.

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5 GRAVEL PACKING (TA CODE 7)

5.1 DETERMINATION OF GRAVEL SIZE (TA CODE 7-1)

Various parameters shall be considered for the design of gravel pack such as aquifer

characteristics,screen size, discharge rate, hole diameter and so on. The size of the gravel shall be

principally less than the size of the slot of the screen. The velocity shall be considered upon the

decision of the hole diameter so as not to cause the sand production.

The steps necessary to design a gravel pack are as follows (Refer to Figure 28):

1. Read off the 25 % and 75 % grain

size values of the percentage of

material passing and multiply them

by 4 and 5, and 4 and 6 respectively.

Plot these results on the graph.

2. Draw connecting lines through 4X

and 4Y and 5X and 6Y.

3. Transfer the position of the

90 %

passing to the 10 % passing position

for the same graph size. This point

then becomes Z.

4. Complete the line 4Y - 4X -Z.

Source: National Waterwell & Drilling Association of Australia

An envelop has now been defined

Figure 28 Example of Gravel Pack Design

(shaded area). The gravel pack

analyses should fall within this

envelop (except at its extreme ends). Search around for suitable rounded gravel which

will fall within this envelop or can easily be adjusted (by addition or subtraction of sand

or gravel) into the envelop, e.g. broken curve - natural gravels of the ideal type are

difficult or time consuming to find, hence the envelop.

Select a screen size to pass 10 % of gravel pack and round up to nearest 0.1 mm (100

micron).

To sieve analyse a sand sample (Refer to Figure 29):

1. Select a sand sample and thoroughly dry it ( a clean BBQ plate is ideal for drying).

Extreme heat should be avoided since it may cause breakage of the grains. The sample

quantity can be any amount, but about 0.8 to 1.0 kg is convenient.

2. Weight the sample.

3. Arrange sand sieves according to aperture, largest opening at the top, smallest at the

bottom, and place pan on bottom. Pour in sand sample and shake sieves.

4. Weigh the quantity trapped on each size (largest to smallest) and the bottom pan.

5. Add the individual quantitie and compare the figure with the original smaple weight. If

less than 5 % difference) proceed with calculation. If greater than 5 %, look for and

correct the mistake, or start again.

6. Complete cumulative percentage retained as per Sieve Analysis sheet.

7. Plot sieve size versuscumulative percentage passing on Sieve Analysis sheet.

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5.2 CALCULATION OF GRAVEL VOLUME (TA CODE 7-2)

Drillers are required to acquire the calculation method of the volume of gravel including the safety

factor to be considered according to the conditions of

each borehole. The miscalculation of the gravel

volume will bring about the interruption of the

drilling work. Furthermore, insufficient volumeof

the gravel can be the cause of the turbidity of the

pumped water after the delivery to the client.

This section gives an example of the gravel

calculation for a borehole design shown in Figure 30.

The borehole was drilled down to 100 m and casing

was planned to be installed down to 90 m. The top

of screen is 40 m and the gravel is to be packed up to

Figure 30 Example of the Gravel

30 m from the ground level. The volume of the

Calculation

gravel is calculated as described below:

1) Bore Volme

The gravel is to be packed in two parts of the borehole, i.e. the uncased bottom from 90 m to 100 m

and the annular space between 12” hole and 6” PVC casing. With the consideration of the

enlargement of the drilled hole according to the geological conditions, safety factor of 1.2 is taken.

The total gravel volume is calculated as 4,583 L.

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5.3 GRAVEL PACKING (TA CODE 7-3)

5.3.1 GRAVEL PACKING PROCEDURES

When the well assembly is successfully installed into

the borehole and the assembly is still hanging in the

hole, the annular space between casing and screens and

the borehole wall has to be filled with filter gravel.

The filter gravel is also called gravel pack or formation

stabilizer. The gravel is normally well graded in

relation to the grain size of the aquifer material and is

to filter the entering groundwater and holding back

fine material from the formation to enter the well.

For borehole drilled into rock formation, a gravel pack

with a grain-size of 3-5 or 3-6 should be installed.

The volume of the gravel to be poured into the well has

Figure 31 Installation of Gravel

to calculate accurately. The gravel pack shall be

Pack

installed at least 10 m above the depth of the highest

screen. The drilling diameter of

½” equals a

volume of 36.59 l/m. The volume of the PVC pipe

with a diameter of 165 mm equals 21.37 l/m has to be

deducted from the volume of the drilling diameter.

The volume of the annular space comes then to 15.22

l/m. One sack of filter gravel has a volume of about 30

l. With one bag of filter gravel almost 2 m of annular

space between pipes and borehole wall can be filled.

It is always good practice to have some 20 % more

gravel on site than calculated, because some parts of

the formation could have washed out fractures or has

been caved out by the drilling process.

Figure 32 Measurement of Gravel

The installation of the gravel has to be done slowly and

Top

in careful manner to allow the gravel to pour into the

borehole with a most even flow rate (See Figure 31).

This is to avoid bridge building of the gravel pack,

which can have serious results, when not noticed and

corrected. Should a gravel bridge being developed,

then pump with some pressure clear water into the well

pipes, which will enter through the screen openings

into the annular space and will lift up the gravel bridge

and allow it to settle down.

During the pouring of gravel mea sure the gravel level

from time to time to avoid overfilling and bridging.

After the installed level of the gravel pack has been

Figure 33 Installation of clay

confirmed by measuring (See Figure 32) and after

pellets

allowing for certain additional time to have been

settled fully, a clay sealing is installed on top of the gravel pack (See Figure 33).

There are commercial clay (bentonite) pellets available, which are poured into the annular space

the same way as the gravel has been installed. When the clay pellets are coming into contact with

water, they are expanding their volume (of up to 45%) and therefore sealing off the annular space

completely. The sink velocity of clay pellets is about 25-30 m/min.

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6 WELL DEVELOPMENT (TA CODE 8)

6.1 WELL CLEANING AFTER DRILLING (TA CODE 8-1)

After the well-construction has been completed and the surface cementation could be hardened for

more than 24 hours, the water well should be developed.

The well was dug into the ground and while the water well was completed, the surroundings of the

well became certainly disturbed by the drilling process. Well development is the operation to

re-generate the previous free-flow situation of the groundwater, in spite the fact that well pipes and

artificial filter gravel has been installed into the ground. The development and pumping test team

shall be equipped with the following equipment:

 An air-compressor with 8 bar pressure and 125 l/s air-volume

 Air injection pipe, which for 4” to 6” wells is usually a PE hose with a diameter of 40 mm to

50 mm and a length of 100 m with connection subs to the air-lift tool and to the compressor

 Airlift-tool, which is generally a metal pipe with diameter of 40 mm as well, and is Closed at

the bottom end and having about 40 holes of diameter 4 mm around the length of the

circumference of this pipe

 water level indicators with a length of 150 m



1 metal bucket with a content of 20 l for measurements of water discharge rates



1 outflow pipe of 1 m length with yield adjustment valve



1 Pick Up truck for transportation of personnel and material

There are various well development procedures

carried out due to special requirements, special

hydro-geological situation, well diameter and

depth of the wells. For the rather shallow and

slim wells drilled with depths of 100 m and 6”

PVC well assembly installation with

½”

drilling diameter in hard rock formation only, a

direct airlift procedure without the use of special

conductor pipes, will be sufficient(Figure 34).

The fine material can be removed from the

fractures or contact zones (aquifers) and from the

gravel pack. The development normally takes

duration of 4-8 hours, which can be prolonged

until the well will be free of sand. Compressed

Figure 34 Development by

air to develop wells is widely used in

Single-Tube Air-Lifting

unconsolidated, loose, sedimentary formation, as

well as in hard rock formation.

In air surging (or flushing) the air is injected into the well directly through a single air injection

pipe (the well pipes are then quasi conductor pipes) to lift the water to the surface. When the

water reaches the top of the casing on the ground, the air supply is shut off, allowing the aerated

water column to fall. Air lift pumping

(continuous airlifting) is used to pump the well

periodically to remove fine material from the screen, gravel pack and from the borehole.

Air development should begin by determining that the groundwater can flow freely into the screen.

Application of too much air volume into the borehole, when the screen and formation are still

clogged by fine material can result in a collapsed screen. So in the beginning of air development

the initial pumping rate has to be minimized and the air-injection pipe should be placed at a rather

shallow submergence. Once the uninhibited flow of groundwater into the screen has been

established, the injection pipe can be lowered close to the bottom of the well. Before blowing any

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water out of the well with a sudden large injection of air, the airlift should be operated at a reduced

rate.

Airlifting from the well has to continue until the water is virtually free of sand. Normally the

entire length of the screens has to be developed. The air-injection pipe is raised through the

screen length by certain intervals. From time to time and at least at the end of the development

the injection pipe has to be lowered again to the bottom of the well to blow out the last fine

material which has been accumulated in the sump (sedimentation) pipe on top of the bottom cap.

Patience, intelligent observation, and the right tools are requested to develop a well correctly. Well

development is not expensive, considering the often remarkable results that can be obtained in

improving yields and eliminating sand- and fine material pumping.

Similarly, aquifer

development is often overlooked an effective way to increase yields substantially.

For the other various methods of the development, please refer to Section 13-2.

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6.3

DOUBLE-TUBE METHOD AIR LIFTING (TA CODE 8-3)

The double-tube method requires more complexed equipment compairing to the single-tube

method (See Figure 36). However, there are several advantage for this mehod as follows:

 The shock upon the commencement is less than the one of the single tube method. As the

air going up between the outer educator pipe and the inner air pipe.

 It is possible to measure the discharge rate and the dynamic water level if the proper air-lift

manihold is used.

The disadvantage is that the crane truck is necessary to handle the pipes, as steel pipes are needed.

The selection between the single-tube method and the double-tube method is examined according

to the well design and geological conditions.

Figure 36 Double-Tube Air-Lifting Method

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7 BACK-FILLING&SURFACE CEMENTING (TA CODE 9)

7.1 BACK-FILLING (TA CODE 9-1)

After having confirmed the top of the clay sealing by measurement, the annular space on top of the

clay sealing has to be backfilled with drill cuttings up to a depth of 5 to 10 m below ground surface

as required by the specification. It is not allowed to backfill using organic material. Also this

backfilling has to be carried out slowly and carefully.

Water Resources Division (WRD) of Ministy of Water prepared the government specifications and

regulations applicable to water well drilling and installation. The work specification of back

filling is shown in this document. The document is distributed to all government agancies and

private drilling companies which have registered to the drilling permit. The application of this

document is necessary for DDCA to duly follow it. The full document is shown in Figure 37.

TO: ALL GOVERNMENT AGENCIES, PRIVATE WATER WELL DRILLING

COMPANIES, CONTRACTORS AND NON-GOVERNMENTAL ORGANIZATIONS

GOVERNMENT SPECIFICATIONS AND REGULATIONS APPLICABLE TO

WATER WELL DRILLING AND INSTALLATION IN TANZANIA

MAINLAND

All water well drilling operations in the country are to be undertaken by registered

companies, contractors and NGOs with a water well drilling permit and certified drillers.

A Water Well Drilling Permit will be issued to a registered company, contractor, executive

agency or NGO upon satisfying the following requirements:

(i)

Making application letter listing equipments, drill rigs and accessories as well as

CVS of personnel should be attached.

(ii)

Physical inspection of the listed items and scrutinizing of personnel by Officers

from the Ministry of water, Water Resources Division.

(iii)

Certification of drillers.

Upon satisfying the Ministry requirements, a water well drilling permit will be

issued.

The Drilling Water Well Permit is of six months or one (1) year duration and is renewable

upon continuing to meet the above requirements and showing satisfactory performance in

the past year.

Any registered company, public executive agency or NGO with Ministry Water Well

Drilling permit before embarking on water well drilling will make an application and be

issued with Borehole Identification Number (s) for new water wells to be drilled.

No drilling activity in the country is to be undertaken without a Hydrogeological and

Geophysical survey, the Technical Report of which must be submitted to the Basin Water

Officer of the respective Basin and a copy to the Ministry of Water, Water Resources

Division.

Upon submission of the said Hydrogeological and Geophysical Technical report, a Water

Well Drilling Clearance Permit will be issued by the Basin Water Officer to the prospective

client. No client will be allowed to have a water well drilled in his/her property without

such a permit.. A clearance permit will be given within seven days after submission of

the Technical report.

Each new water well must be assigned an identification number and its geographical

position given in UTM co-ordinates where possible, previously given to the recommended

borehole site, and should not under any circumstances be changed by the driller.

On completion of the water well, the drilling technology to drill the well, changes in

diameter, depths to each water strike, as well as the static water level from the ground

surface must all be indicated in the completion forms.

Figure 37 Government Specifications and Regulations

(1/3)

Applicable to Water Well Drilling and Installation Method

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If the upper section of a well is in unstable rock formation, temporary or permanent

cementing/casing must be installed for all exploration or production wells respectively. A

proper sanitary seal (or intermediate seals) must be placed to preserve, conserve and

protect groundwater resources (its quality) and reservoir pressure potential. This should

as well effectively prevent contaminated water to enter and mix with aquifer waters.

All boreholes should be well cased and screened to bottom of the borehole and plugged

properly. No open boreholes will be allowed/ permitted.

10.

In order to ensure that no interference occurs between a new well and existing wells or

water body in the vicinity, the distance apart should be at least 300m for unconfined

aquifers and 100m for confined aquifers.

11.

While drilling, a site Hydrogeologist should properly collect drilling cuttings which will be

a representative of depth intervals of 2.0m. Where there is change in rock composition

(in between the said interval), this be noted in driller's report. Drill cuttings are kept in

sample boxes at the drilling site for lithological logging. However, a small portion (250

gm) of each sample be placed in sample bag, properly labeled and sent to the respective

Basin Office for storage and future use. However a water well completion Report

detailing the well lithology should be prepared and a copy sent to Hydrogeology Section.

12.

If any borehole geophysics is undertaken, all relevant details of the exercise be recorded

and a report sent to the Basin Water Officer for further action and again a copy sent to the

Water Resources Division.

13.

All casings and screens to be installed in a production water well have to be properly

chosen to prevent chemical and/or galvanic corrosion and thus guarantee structural

integrity of the well, long life and good quality of water.

14.

The selection of gravel pack material, with pear size grains and rounded shape has to be

installed into the angular space of the drilled well after having been washed and sieved.

The material used has to ensure that well efficiency is not lower than internationally

accepted Standards. The thickness of gravel pack installed shall likewise satisfy the same

conditions.

15.

Internationally accepted methods of well cleaning, development to clear and silt free state

of water and step- draw down pumping test followed by a constant rate pumping test of at

least 24 hours depending on the yield of the borehole shall be followed. Evaluation of

pumping test results shall determine safe production limits and aquifer parameters, though

actual abstraction of water shall not exceed levels set by the granted water right for the

well. All records should be filled in a Completion form and sent to:-

(a)

Water Resources Division

(b)

Basin Water officer

(c)

Well owner

Note:

(i)

This information would later be required when well rehabilitation, maintenance or

Servicing works are due in years of its utility.

16.

Any newly drilled borehole that is not to be put immediately into operation should be

securely capped to protect it from vandalism or damage.

17.

A water well shall be commissioned and put to its intended use after a step- draw down

pumping test followed by a constant rate pumping test of at least 24 hours duration

depending on the yield of the water well and immediately followed by a recovery test until

initial SWL has been attained and thorough physical, chemical and bacteriological analysis

of the water by the Central Water Laboratory or a recognized and qualified laboratory.

18.

No groundwater abstraction shall commence until the well owner has been issued with a

Water Permit by respective Basin Water Office

19.

Water well disinfection must be undertaken after well installations and pumping test has

been completed to ensure that the water will be safe for human consumption where

internationally accepted standards shall apply as well.

20.

Any abandoned drilled water well must be properly and perfectly back filled to protect and

conserve ground water resources as well as to eliminate any hazards to human beings and

Figure

37 Government Specifications and Regulations

(2/3)

Applicable to Water Well Drilling and Installation Method

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animals.

21.

Once a water well has been completed, a Completion Form (copy of which could be

obtained from Water Resource Division or Basin Water Officer) must be filled in. To

certify correctness of information, adherence to professional’s ethics and good

workmanship; it should be signed by the responsible Driller and countersigned by the

Basin Water Officer or his representative. The Driller or Company shall then produce

sufficient number of copies and distribute to the Well Owner, Water Resources Division

and respective Basin Water Officer.

Remarks:

Finally, let it be known that groundwater resources are the Nation’s Property.

They must be conserved and well protected if safe and sustainable water supply in

sufficient quantities and acceptable quality is to be guaranteed for present and

future generations. To safeguard its waters therefore, the Government will not

hesitate to take stern actions against person, institution or company which pollutes,

over pumps a water well or leaves an abandoned water hole not properly

back-filled. It is the responsibility of any water well drilling company or driller

to fully understand National and International Standards applicable in water well

drilling and installation practice which are safe to human, livestock, ecology and

the environment.

The Ministry of Water has in this respect, through the enacted relevant laws and

regulations, the capacity and duty to monitor, supervise, inspect, regulate and

control the water well drilling activities by both Government and non-government

water well drilling companies in TANZANIA MAINLAND.

Figure

37 Government Specifications and Regulations

(3/3)

Applicable to Water Well Drilling and Installation Method

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8 PUMPING TEST (TA CODE 14)

8.1 PURPOSE AND METHODS OF PUMPING TEST (TA CODE 14-1)

8.1.1 PURPOSE OF PUMPING TEST

The capacity of well shall be measured by the pumping test. The pumping test is carried out by

installing electric submersible pump in a well.

The pumping test shall include the following components:

Preliminary pumping test

Step drawdown test

Constant discharge rate test

Recovery test

The purposes and methodology of each test are described below:

8.1.2 PRELIMINARY PUMPING TEST

Preliminary Pumping Test is carried out to grasp the

rough estimation of well yield. It is conducted

generally for the period of 2 to 4 hours by varying

the discharge rate.

From the results of the

preliminary pumping test, the schedule of the step

draw down test is planned.

8.1.3 STEP DRAWDOWN PUMPING TEST

In Tanzania, the step drawdown test with three (3) to

five (5) steps of two (2) hours is conducted. Figure

39 shows an examples of t-dwl (time-dynamic water

level) curve of the step drawdown test.

From the results of step drawdown test, the well loss

Figure 39 Example of Results of Step

can be calculated approximately by the following

Drawdown Tests (t-dwl curve)

quotation:

Swl=CQ²

Swl: well loss (m)

C: well loss constant, (h²/m⁵)

Q: discharge rate (m³/h)

Well loss constant C indicates the resistance of well

structure against water flow from the aquifer. If the

screen or neighbouring aquifer is clogged, C will show

the elevation.

Drillers can detect the clogging of screen by comparing

current C and the past one, if they can obtained the past

step drawdown test data.

Figure 40 shows the plotting of discharge rate and

drawdown on Log-Log paper (Q-s curve). From this

chart, the maximu discharge rate can be estimated.

Figure 40 Example of Results of Step

Because of transition from laminar flow to turbulent

Drawdown Tests (Q-s curve)

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flow depending on the flow velocity, drawdown suddenly increases from certain value. This

discharge rate of the transition is often used as maximum discharge rate. The excessive pumping

over this maximum discharge rate may be the cause of the lowering of water level of a well.

The results of the step drawdown test is used for the decision of the discharge rate of the constant

discharge rate test.

8.1.4 CONSTANT RATE PUMPING TEST

Figure 41 shows the example result of constant

discharge rate test and the following recovery test.

The constant discharge rate test is often omitted for

the purpose of well investigation. The major

purpose of this test is, to verify if a well shows the

same capacity as the analysed discharge rate from

step drawdown test for longer pumping period.

In general, 24 to 48 hours pumping for piped water schemes and 8 to 12 hours for handpump well

is applied for constant discharge rate. However,

more pumping time may be applied for wells of

Figure 41 Example of Results of Step

large-scale water supply schemes.

Drawdown Tests and Recovery Test (t-s

The hydraulic coefficients such as transmissivity,

curve)

storage coefficients etc., can be analyzed from the

results from the constant discharge rate test and recovery test.

It is preferable to conduct constant discharge rate test even if it is for the well investigation.

8.1.5 RECOVERY TEST

The recovery test is continuously conducted immediately after the termination of the constant

discharge rate test. Figure 41 shows the examples of the plotting of time and dynamic water level

(t-dwl curve) of a recovery test together with a constant discharge rate test. This test is to know

how fast the dynamic water level is recovered to static water level. The recovered water level is

an important factor to formulate the daily pump operation plan and also important to detect the

deterioration of well.

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8.2 PUMPING TEST EQUIPMENT (TA CODE 14-2)

Figure

42 shows the standard setting of

pumping test equipment. Major equipment

necessary to conduct the pumping test is

described below:

8.2.1 SUBMERSIBLE PUMP

Sumbmersible pump is the most important

components of pumping test equipment.

Various types and capacities of pumps are

manufactured by many manufacturers. A

pump consists of pump parts of multi-stage

impellers and casings and submersible

motors. The sumbmersible motor is of

three phases power of 200 or 400 V or single

phase of

200 V. They are classified by

diameters of casings which they are to be

applied. Each pump has a range of the total

head and discharge rate. The pump is

connected to the generator on the ground by

submersible cables. Two-cores single cable

is used for single phase pump. Three-cores

single cable and three-cores double cables

are respectively used for the starting methods

of direct start and star-delta start for three

phases pumps.

Figure 42 Standard Setting of Pumping

8.2.2 CONTROL PANEL

Test Instruments

The control panel is an important instrument

to control the pump. It is connected between the pump and the generator. It consists of the

electrical circuit for on/off operation, safety cut/off for the over/under voltage and current,

operation control by water level, pressure etc. The knowledge and skills of the operation and

maintenance of the control panel is important for the drillers in charge of pumping test.

8.2.3 RISER PIPE

Riser pipes are threaded or franged pipes which conducts water from the pump to the ground or to

the water tank. In general galvanized steel 1-1/2” to 6” pipes are used. For the permanent

setting purpose, stainless riser pipes are used, too, as they are anticorrosive.

8.2.4 PUMP HEAD MANIHOLD

The pump head manihold consists of small pipes,

elbows, reducers, valves, pressure gauges,

air-release valve etc.

This is important

component to conduct proper control of the

discharge rate for the test measurement.

8.2.5 NOTCH TANK

Source: Australian Drilling Industry Training Committee Ltd

The discharge rate shall be correctly measured.

For large discharge rate, the notch tank is used.

Figure 43 Structure of Notch Tank

The discharge rate is calculated from the

measured height of overflow from the weir(Figure 43). Table 34 shows the conversion table

from the measured height to the discharge rate.

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8.3 SELECTION OF SUBMERSIBLE PUMP (TA CODE 14-3)

8.3.1 PUMP SPECIFICATIONS

Drillers in charge of the pumping test shall be acquired the proper knowledge of the submersible

pump for the selection of the suitable for each test. Principally, pump shall be selected according

to the discharge rate and the total head. Table 35 shows the specifications of the series of

submersible pump of SP17 manufacture by GRUNDFOS.

“17” of “SP17-10” means it is

designed for pumping of 17 m³/h of discharge rate.

“10” is the number of stages of impeller.

More number of stages produces hiegher pressure and needs more power. An option of ppower

supply can be selected from voltages of 230 V or 400 V and from single phase or three phases.

Diameter of the pump is important as well. The selected pump shall be of the diameter which can

be smoothly installed into the casing pipes of the well, with the consideration of power cables.

8.3.2 PUMP CAPACITY CURVE AND SELECTION OF SUBMESIBLE PUMP

Figure 44 shows an example of the calculation of total head. In this example, the pump transmits

the water of 10 m3/h up to the water tank of which the difference of the elevation down to the

dynamic water level of the well is 82.5 m. In order to decide the total head of the submersible

pump, head loss through the riser pipe and transmission pipe shall be calculated. The head loss of

each diameter of the pipe can be calculated by using the pressure loss nomogram (See Figure 45)

According to the nomogram, unit head loss for each diameter of the pipes for 10 m³/h are obtained

as follows:

2” GS:

0.0350 m/m

2-1/2” GS:

0.0182 m/m

3” GS

0.0048 m/m

If 50 m of 2”GS is used, the head loss is calculated as 0.0350 m/m x 50 m = 1.75 m. For the type

B in the example, 2” riser pipes and 3” transmission pipes are used. In this case the total head loss

is calculated to be 6.89 m. The difference of the elevation between the dynamic water level and

the tank is 82.5 m. Therefore the necessary pump head is calculated as 6.89 m + 82. 50 m = 89.39

m. Consequently the submersible pump with the discharge rate not less than 10 m³/h and the total

head not less than 89.39 m shall be selected.

Figure 46 shows the pump capacity curve of SP17 series submersible pumps. The suitable pump

can be selected by using the pump capacity curve according to the discharge rate and the total head.

From these examinations, the submersible pump SP17-9 was selected.

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8.4 INTERPRETATION OF TEST RESULTS (TA CODE 14-4)

8.4.1 RECORD OF PUMPING TEST

DDCA normally conducts the constant

discharge rate pumping test and the

recovery test after the completion of

the drilling works.

The step

drawdown tests are conducted when

the client specially requests. Figure

48 is the DDCA’s record form for the

constant discharge rate test and Figure

49 is the one for the recovery test. A

challenge related to the pumping test

records of DDCA is that the summary

of the pumping test including the

preliminary pumping test, step

drawdown pumping test, constant

discharge rate pumping test and

recovery test is not included in the

record forms. This series of test shall

be summarized as the example shown

in Figure 47.

Figure 47 Example of Form of Summary of

Pumping Test

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Figure 49 DDCA’s Record Form of Recovery Test

8.4.2 INTERPRETATION OF PUMPING TEST RESULTS

There are various interpretation methos of pumping test. They are categorized in two major

methods of non-equilibrium method and equilibrium method. The equilibrium methods are used

to calculate the hydraulic coefficients of aquifer such as transmissivity, storage coefficient etc.

These methods are based on Theis’ formula. The non-equilibrium methods are used to calculate

the well capacities and efficiency by calculating the parameters such as well loss and aquifer loss

coefficient, specific capacity.

This section describes the simplified non-equilibrium method to determine the recommended

discharge rate of the well to decide the pump capacity and position. This is one of practical

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interpretation methods for drillers. An example of the pumping test data and intrpreptation are

given in Figure 50 to Figure 53. The data of well is as follows:

Completion Date

14-Oct-08

Well No.

CO 596/2008

Borehole No.

MKR-2-BH2

Pumping Test No.

PT-025

Village

Mwandege

Region

COAST

Contractor

DDCA

Static Water Level (m)

1.3

Blown Yield (m3/h)

4.2

Screen Position (m-m)

55.35-61.10, 69.68-72.54

Casing Depth (m)

Date of Step Drawdown Test

From

17-Oct-08

18-Oct-08

Date of Constant Discharge Rate Test

From

19-Oct-08

20-Oct-08

From the results of the step drawdown test, discharge rate, dynamic water level, drawdown and s/Q

are summarized and Q-s curve is plotted as shown in Figure 52. Then the recommended

discharge rate is determined from the Q-s curve as to be 4.25 m³/h with the consideration of safety

factor of 0.85. Accordingly, dynamic water level is estimated to be 45.70 m. The pump setting

depth can be determined from this dynamic water level and several meters for seasonal fluctuation.

All the pumping test results, interpretation and pump setting plan are summarized as shown in

Figure 53.

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9 WATER QUALITY (TA CODE 15)

9.1 PURPOSE OF WATER QUALITY ANALYSIS (TA CODE 15-1)

9.1.1 IMPORTANCE OFSAFE WATER QUALITY

Access to safe drinking-water is important for health, basic human right and development at

national, regional and local levels.

In some areas, it has been found that investments in water

supply can support a net economic benefit such as reductions in adverse health effects and

health-care costs outweigh the costs of undertaking the interventions.

It has also shown that the

improvement of access to safe water confers benefits to the poor in particular, whether in rural or

urban areas, and can be an effective part of poverty alleviation strategies.

According to above aspects, water quality analysis is required to be confirmed not only at drilling

but also at rehabilitation.

9.1.2 WATER QUALITY PARAMETERS

Table 36 and lists suggesting water parameter to be analised in Tanzania, pollution sources and

effects respectively.

Categories of the tableare based on Tanzania Temporary Standards (TBS,

1974).

Table 36 Water Quality Parameters and each Pollition Sources and Effects

Name of

Pollution Source

No.

Symbol

Effects

Constituent

(Indicators)

Toxic

Lead

Rust of lead pipes

Health effects

Arsenic

Geological condition

Health effects

Selenium

Geological condition

Health effects

Geological condition or effluents

Chromium

Health effects

from industries

Cyanide

Effluents from industries

Health effects

Cadmium

Effluents from industries

Health effects

Barium

Geological condition

Health effects

Mercury

Effluents from industries

Health effects

Silver

Geological condition

Not specified

Affecting Human Health

Fluoride

Geological condition

Tooth decay and fluorosis

Fertilizers, sewage, faeces or

Cause of hemoglobinemia (blue

Nitrate

NO3

decaying organic matters

babies) and support algae growth

(Fertilizers, sewage, faeces or

Cause of hemoglobinemia (blue

Nitrite

NO2

decaying organic matters)

babies) and support algae growth

Organoleptic

Color

Metals or organic matters

Appearance

Turbidity

Soil particles

Appearance

Geological condition, seawater,

Taste

effluents from industries or algae

Taste

growth

Sewage, effluents from

Odor

Odour

industries or algae growth

Salinity and Hardness

Sewage, effluents from

Attack metals (e. g. pipe rust)

industries or algae growth

Total

Filterable

Minerals from geological

Taste and appearance

Residue

condition and dissolved matters

Total Hardness

CaCO3

Geological condition

Taste and soap consuming

Calcium

Geological condition

Not specified

Magnesium

Geological condition

Not specified

Magnesium

Sewage, effluents from

Mg-Na2

Na: taste

Sodium sulphate

industries or seawater

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Name of

Pollution Source

No.

Symbol

Effects

Constituent

(Indicators)

Geological condition or effluents

Sulphate

SO4

Taste and smell

from industries

Sewage, effluents from

Chloride

industries, seawater or

Not specified

geological condition

Less-toxic Metals

Effluents from industries and

Iron

Taste and appearance

mining / Pipe or pump rusting

Manganese

Geological condition

Taste and appearance

Copper

Rust of copper pipes

Taste

Zinc

Geological condition or pipes

Taste and appearance

Organic Pollution of Natural Origin

Cause of water born diseases and

BODs( 5 days)

Organic matters

decaying water

PV (Oxygen abs.

Cause of water born diseases and

Organic matters

KMnO4)

decaying water

Cause of water born diseases and

Ammonium

NH3

Faeces

disinfectant consuming

Total

Nitrogen

Sewage or effluents from

Algae growth

Exclusive Nitrate

industries

Organic Pollution Introduced Artificially

Surfactants ABS

(Alkyl

Benxyl

Organic matters

Odour

Sulphonates)

Organic matter as

carbon

Organic matters

Cause of water borne diseases

chloroform

extract)

Phenolic

substances

Effluents from industries

Health effects

phenol

Bacteriological

Coliform

count

Sewage

Cause of water borne diseases

per 100ml at 37℃

E. coli count per

Faeces

Cause of water borne diseases

100ml at 44℃

Source: Guideline for Drinking-water quality (WHO, 2004) and Tanzania temporary standards (TBS, 1974)

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

9.2 ITEM OF WATER QUALITY ANALYIS (TA CODE 15-2)

9.2.1 GUIDELINE/STANDARD OF WATER QUALITY

There are two types of guideline for drinking-watre in Tanzania; Guideline for Drinking-water

Quality (WHO, 2004) and Tanzania temporary standards (TTS) (TBS, 1974). WHO guideline is

for urban water suppies and large water supplies, and TTS is for domestic water supplies and small

rural water supplries.

Therefore, is is necessary to instruct which guideline/standard is adopt for

water at drilled boreholes to customers and laboratories.

9.2.2 PARAMETERS OF WATER QUALITY ANALYSIS

Table 37 lists WHO guideline and TTS values, and drinking water quality should be less than the

valuses in both Tables.

Table 37 Values of WHO Guideline and TTS

No.

Name of Constituent

Symbol

Units

WHO guideline

TTS

Toxic

Lead

mg/l

0. 01

Arsenic

mg/l

0. 01

0. 05

Selenium

mg/l

0. 01

0. 05

Chromium

mg/l

0. 05

Cyanide

mg/l

0. 07

0. 20

Cadmium

mg/l

0. 003

0. 05

Barium

mg/l

0. 7

1. 00

Mercury

mg/l

0. 001

Silver

mg/l

Not mentioned

Affecting Human Health

Fluoride

mg/l

1. 5

1. 5 - 4. 0

Nitrate

NO3

mg/l

10 - 75

Nitrite

NO2

mg/l

Not mentioned

Organoleptic

Color

mg/l

15 TCU

15 - 50

Turbidity

mg/l

5 NTU

5 - 25

Taste

Not objectionable

Odor

Not objectionable

Salinity and Hardness

6. 5-8. 5/9. 5

6. 5 - 9. 2

Total Filterable Residue

mg/l

1500

2000

Total Hardness

CaCO3

mg/l

Not mentioned

600

Calcium

mg/l

200

Not mentioned

Magnesium

mg/l

150

Not mentioned

Magnesium + Sodium sulphate

Mg-Na2

mg/l

Not mentioned

Sulphate

SO4

mg/l

400

600

Chloride

mg/l

600

800

Less-toxic Metals

Iron

mg/l

Manganese

mg/l

0. 4

1. 5

Copper

mg/l

3. 0

Zinc

mg/l

Organic Pollution of Natural Origin

BODs( 5 days)

mg/l

6. 0

PV (Oxygen abs. KMnO4)

mg/l

Ammonium

NH3

mg/l

0. 5

Not mentioned

Total Nitrogen Exclusive Nitrate

mg/l

0. 1

Organic Pollution Introduced Artificially

Surfactants ABS

mg/l

(Alkyl Benxyl Sulphonates)

Organic matter as carbon in

mg/l

0. 2

0. 5

DDCAP Technical Manual for Drilling Works

For Technical Support Plan for the Drillers in DDCA

No.

Name of Constituent

Symbol

Units

WHO guideline

TTS

chloroform extract)

Phenolic substances as phenol

mg/l

0. 001

0. 002

Bactriological

Coliform count per

100ml at

Acceptable

Allowable

1-3

37℃

1-3

E. coli count per 100ml at 44℃

Nil

Source: Guideline for Drinking-water quality (WHO, 2004) and Tanzania temporary standards (TBS, 1974)

9.2.3 TIMING OF WATER ANALYSIS

Water is analysed after pumping tests

(after water become likely clean) and rehabilitations.

Moreover, regular water analysis is needed for both rural water supply and urban water supply in

order to ensure safe drinking-water in boreholes.

Therefore, DDCA should advise to customers

to analyse water regularly.

Table 38 and Table 39 respectively show frequency of sampling for

rural water supply and urban water supply.

Table 38 Frequency of Sampling for Rural Water Supply

Type of Source/Population served

Up to 1,000

Up to 2,000

Up to 5,000

Borehole deeper than 8m

6 months

4 months

3 months

Source: National Environmental Standards Compendium (TBS, 2003)

Table 39 Frequency of Sampling for Urban Water Supply

Max interval between successive

Minimum number of samples to be

Population served

samples

taken from whole distribution

Less than 20,000

1 month

20,000 - 50,000

2 weeks

1 sample / 5,000 people / month

50,000 - 100,000

4 days

More than 100,000

1 day

1 sample / 10,000 people / month

Source: Design Manual for Water Supply and Wastewater Disposal (MoWI, 2009)

9.2.4 SAMPLING AND TRANSPORTATION METHODS

Sampling is a very important process in order to get the true value of water quality.

Therefore,

following processes are required for sampling.

 To clean the working

 To wash hands

 To avoid dust and draughts in the working area

 To use clean and dry containers washed by proper methods

- those rinced by distilled water for general parameters

- those sterilized by ethanol etc. for bacteriological parameters

- those washed by solution of hydrochloric acid and rinced by distilled water for heavy

metals

 To rinse containers three times by water sample if they are wet by a different water sample

 To sterilize an intake of a tap or a pump by ethanol or fire in order to sterilize and to prevent

biological contamination

 To avoid touching any part of the container dishes and sampler

 To keep samples cold

Contents

1 INTRODUCTION

12 TOOL FISHING (TA CODE 12)

12.1

Tool Fishing Plan (TA CODE 12-1)

12.2

Fishing Tools (TA CODE 12-2)

13 WELL REHABILITATION (TA Code 13)

13.1

Phenomenan and Causes of Well Deterioration (TA CODE 13-1)

13.2

Methods of Well Rehabilitation (TA CODE 13-2)

13.3

Usage of Well Camera (TA CODE 13-3)

Tables

Table 1 Identified Technical Areas Covering Drilling Works of DDCA

Table 2 Technical Area / Item Covered by Teaching Guidance and Manuals

Figures

Figure 1 Analysed Image of Fallen Material

Figure 2 Decision Tree of Fishing Tool Selection

Figure 3 Fishing Tools (1/2)

Figure 4 Fishing Tools (2/2)

Figure 5 Mechanical Cleaning (1/2)

Figure 6 Mechanical Cleaning (2/2)

Figure 7 Installation of Chemical Cleaning

Figure 8 Sedimentation Removal Method

Figure 9 Double-Casing Method

DDCAP Technical Manual for Tool Fishing and Well Rehabilitation

For Technical Support Plan for the Drillers in DDCA

1 INTRODUCTION

The baseline survey on DDCA’s drilling organization was conducted in the course of the Project,

for the purpose to reveal the current status of drilling works and the technical level of drillers in

DDCA. The results of the baseline survey were compiled in the Technical Support Plan for the

Drillers in DDCA (hereinafter referred to as “TSP”) which was formulated in January 2013. This

plan identified

15 technical areas which cover the drilling works of DDCA including eight

technical areas necessary to be enhanced and two new technical areas to be needed, as shown in

Table 1.

Table 1 Identified Technical Areas Covering Drilling Works of DDCA

New Areas

Areas to be

No.

Technical Area

All Areas

to be

Enhanced

Needed

Site Mobilization

✔

Drilling Tools and Equipment

✔

Drilling Drawbacks

✔

Drilling Control

✔

Borehole Logging

✔

Casing Program / Installation

✔

Gravel Packing

✔

Well Development

✔

Back-Filling & Surface Cementing

✔

Site Demobilization

✔

Well Investigation

✔

15 Water Quality Analysis

✔

This Technical Manual for Tool Fishing and Well Rehabilitation was prepared according the TSP

and covers two new technical areas to be needed. This manual is expected to be utilized by the

senior drillrs in DDCA in order to acquire the necessary technical knowledge and the proper work

procedures. Furthermore, it forms a part of materials for the teaching guidance which is used for

the technical instruction to both private drillers and DDCA’s drillers. In the TSP, the technical

areas were further divided into details namely technical items. Technical areas and items are the

important basic units for the activities of technical training and guidance in the Project, in the

respects of the manual formulation, training plan, technical evaluation and so on. They are

commonly used between three major training related documents i.e. the Teaching Guidance, the

Manual for Drilling Works and the Manual for Well Rehabilitation and Tool Fishing, as shown in

Table 2.

Table 2 Technical Area / Item Covered by Teaching Guidance and Manuals

Manual for Well

Teaching

Manual for

TA Code

Technical Area / Item

Rehabilitation and

Guidance

Drilling Works

Tool Fishing

Site Mobilization

✔

1-1

Site Preparation and Drilling Machine Setting-Out

✔

Drilling Tools and Equipment

✔

2-1

Selection of drilling bit and drilling method

✔

2-2

Rotary Bits

✔

2-3

DTH and DTH Bit

✔

2-4

Rig Accessory

✔

2-5

Casing Tools

✔

2-6

Drilling Equipment

✔

2-7

Drilling Calculation

✔

2-8

Weight of drilling tools

✔

2-9

Rotary bit rotation speed and weight on bit

✔

2-10

DTH Bit rotation speed and weight on bit

✔

DDCAP Technical Manual for Tool Fishing and Well Rehabilitation

For Technical Support Plan for the Drillers in DDCA

Manual for Well

Teaching

Manual for

TA Code

Technical Area / Item

Rehabilitation and

Guidance

Drilling Works

Tool Fishing

Drilling Drawbacks

✔

3-1

Countermeasures against lost circulation during mud

✔

drilling

3-2

Countermeasures against lost circulation during DTH

✔

drilling

3-3

Countermeasures against bore wall collapse during mud

✔

drilling

3-4

Countermeasures against bore wall collapse during DTH

✔

drilling

3-5

Countermeasures against jamming of drilling tools

✔

Drilling Control

✔

4-1

Mud control

✔

4-2

Mud Pump Operation

✔

4-3

Casing for mud drilling

✔

4-4

Drilling operation for mud drilling

✔

4-5

Bit control and repairing for mud drilling

✔

4-6

Air control for DTH drilling

✔

4-7

Air compressor operation

✔

4-8

Casing for DTH drilling

✔

4-9

Drilling operation for DTH drilling

✔

4-10

Bit control and repairing for DTH drilling

✔

Borehole Logging

✔

5-1

Borehole logging instruments

✔

5-2

Interpretation of borehole logging results

✔

Casing Program / Installation

✔

6-1

PVC casing, screen pipe

✔

6-2

Casing Program

✔

6-3

Role of centralizer

✔

6-4

Casing, screen pipe installation

✔

Gravel Packing

✔

7-1

Determination of gravel size

✔

7-2

Calculation of gravel volume

✔

7-3

Gravel packing

✔

Well Development

✔

8-1

Well cleaning after drilling

✔

8-2

Single-tube method air-lifting

✔

8-3

Double-tube method air-lifting

✔

Back-Filling & Surface Cementing

✔

9-1

Back-filling

✔

9-2

Surface cementing

✔

Site Demobilization

✔

10-1

Precautions upon site demobilization

✔

Well Investigation

✔

11-1

Necessary information of well rehabilitation plan

✔

11-2

Well rehibilitation plan

✔

Tool Fishing

✔

12-1

Tool fishing plan

✔

12-2

Fishing tools

✔

Well Rehabilitatation

✔

13-1

Phenomenan and causes of well deterioration

✔

13-2

Methods of well rehabilitation

✔

13-3

Usage of well camera

✔

Pumping Test

✔

14-1

Purpose and methods of Pumping Test

✔

14-2

Pumping test equipment

✔

14-3

Selection of Submersible Pump

✔

14-4

Interpretation of test results

✔

Water Quality Analysis

✔

15-1

Purpose of Water quality analysis

✔

15-2

Item of water quality analysis

✔

DDCAP Technical Manual for Tool Fishing and Well Rehabilitation

For Technical Support Plan for the Drillers in DDCA

12 TOOL FISHING (TA CODE 12)

12.1 TOOL FISHING PLAN (TA CODE 12-1)

For wells with fallen tools and/or materials which disturb the proper installation of alternative

pump, such obstacles in a well shall be at first removed from a well by “Tool Fishing”.

Prior to the formulation of tool fishing plan, the following preliminary investigation shall be

conducted:

12.1.1 DATA COLLECTION

 Collection of well and water supply scheme.

 Detailed specifications of fallen materials such as diameters, lengths, shape, materials.

 If the fallen material is a pump, specifications of auxially tools such as riser pipes and cables

shall be obtained too.

 The remaining parts of fallen materials are also the important information source. In case

the riser pipe of the pump is cut at certain point on the riser pipe, the length of the fallen

pump and riser pipes in the well can be calculated by measuring the remaining parts of the

riser main. Furthermore, the observation of the cut point is important to estimate the shape

of the top of the fallen riser pipe.

 Well structure information such as depth, diameter, length, materials and whether or not

production hole is cased.

With the integral analysis of the above information, the proper tool fishing plan shall be prepared.

12.1.2 DOWN-HOLE INVESTIGATION

After the maximum efforts to collect the data, the

condition of the top of the fallen materials shall be

Borehole Dia. 12-1/4"

investigated by following measures:

Power Cable

3" Steel Riser Pipe w/ Socket

 Confirm reachable depth by water level sensor

Water Level 28.5m

32.1m

 Confirm reachable depth by pipes or rods

38.5m

Slot Screen

 Run into the hole, investigating device such as

45.2m

Casing 49.3 m

plate with nails

8" Mild Steel

50m

 Run into the hole, well camera

Fallen Pump

and Riser Pipes

From the collected data and the results of the above

down-hole investigation, the illustration of the

down-hole situation of the fallen material shall be drawn

Figure 1 Analysed Image of Fallen

up as shown in Figure 1 and suitable tool fishing plan

Material

shall be prepared.

12.1.3 WELL CLEANING

If a well is not cased, collapsed bore wall may be sedimented above and/or around fallen materials.

Prior to tool fishing works, such sedimentation shall be removed by the following measures:

(1) Removal of sedimentation above fallen material

Air-lifting, bailing, reaming with rotary bit etc are used.

(2) Removal of sedimentation around fallen material

Sedimentation shall be reamed by casing pipes. If the fallen material leans one side of the hole, it

must be straightened up using spud.

Technical Manual for Drilling Works for Technical Support Plan for the Drillers in DDCA (2013) - page 2