water wells.ppt

wekks

1. Water Wells
Unit 4

2. Water Wells
Awaterwellisusuallyaverticalhole
intheearthforbringinggroundwater
tothesurface.
Sometimeswaterwellsareusedfor
otherpurposesaswellsuchas
◦subsurfaceexplorationandobservation,
◦artificialrechargeand
◦disposalofwastewater.

3. Water Wells
Therearemanymethodsforconstruction
ofwells.
Theselectionofaparticularmethod
dependson
Purposeofthewell
Quantityofwaterrequired
Depthtogroundwater
Geologicconditionsand
Economicfactors

4. Water Wells
Shallowwellsaredug,bored,drivenorjetted.
Deepwellsaredrilledbycabletoolorrotary
methods.
Attentiontoproperdesigncanensureefficiency
andlonglifeofthewells.
Afterthewellhasbeendrilleditshouldbe
completed,developedforoptimumyieldand
tested.
Wellsshouldbesealedagainstentranceof
surfacepollutantsandshouldbegivenperiodic
maintenance.

5. Methods for construction of
shallow wells
Shallowwellsaregenerallylessthan
15metersindepthandcanbe
constructedby
Digging(DugWells)
Boring(BoredWells)
Drivingor(DrivenWells)
Jetting(JettedWells)

6. Dug Wells
Depthofdugwellsmaygoupto20metersormoredependingupon
thedepthtowatertableandthediametermayvaryfrom1to10
meters.
Theirlargediameterhelpsinthestorageoflargequantitiesofwater
iftheirdepthissomedistancebelowthewatertable.
Thesewellsarenormallyusedforindividualwatersupply
mostlyinareashavingunconsolidatedglacialoralluvial
sediments.
Dugwellsaremostlyexcavatedbyhand,howevertheuseof
blastingtechniquesmaybeemployedwhiledigginginhardrock
formations.
Thedugwellmaybejustaholeinthegroundoritmaybelinedwith
acasingofbrick,rock,concreteormetal.

7. Dug Wells

8. Bored Wells
Wherethewatertableexistsatshallowdepthsinanunconsolidatedaquifer
,boredwellscanfurnishsmallquantitiesofwateratminimalcost.
Boredwellsareconstructedwithhandoperatedorpowerdrivenearth
augers.
Hand-boredwellsarerarelymorethan15metersindepthand20cmin
diameter.
Powerdrivenaugersmaygouptoadepthof30metersandthediameter
maybeupto1meter.
Theaugerconsistsofacylindricalsteelbucketwithacuttingedge
projectingfromaslotinthebottom.
Thebucketisfilledbyrotatingitintheholebyadriveshaftofadjustable
length.
Whentheaugerisfullitistakenoutoftheholeandtheexcavatedmaterial
isremovedthroughthehingedopeninginthesideorbottomofthebucket.

9. Bored Wells

10. Driven Wells
Adrivenwellconsistsofaseriesofconnectedlengthsofpipedrivenbyrepeatedimpacts
intothegroundbelowthewatertable.
Waterentersthewellthroughadrivepointatthelowerendofthewell.
Diametersofdrivenwellsaresmall,mostlyfallingintherangeof3to10cm.
Depthsaregenerallylessthan15metersbutfewmayexceed20meters.
Thewateristakenoutfromthesewellsbyasuctionpump,thereforethewatertablemust
beclosetothegroundsurfaceforacontinuouswatersupply.
Forbestresultsthewatertableshouldbewithin3to5metersdepthsfromtheground.
Drivenwellsarebestsuitedfordomesticssupply,fortemporarywatersupplyandfor
explorationandobservation.
Drivenwellsarelimitedtounconsolidatedformationcontainingnolargeboulderor
gravelwhichmightdamagethedrivepoint.

11. Driven Wells

12. Jetted Wells
Jettedwellsareconstructedbythecuttingactionof
downwarddirectedstreamofwater.
Thehighvelocitystreamwashestheearthaway,whilethe
casingwhichisloweredintothedeepeninghole,conducts
thewaterandcuttingsupandoutofthewell.
Smalldiameterholesof3to10cmareformedinthismanner
andthedepthsmaygoupto15metersormore.
Jettedwellshavesmallyieldsandarebestsuitedfor
unconsolidatedformations.
Becauseofthespeedofjettingawellandtheportabilityof
theequipment,jettedwellsareusefulforexploratorytest
holesandobservationwells.

13. Jetted Wells

14. Methods for construction of
deep wells
Mostlarge,deepandhigh-capacitywells
areconstructedbydrilling.
Thedrillingcanbedonebycable-tool
methodorbyoneoftheseveralrotary
methods.
Eachmethodhasaparticularadvantage
soexperienceddrillershavedrilling
equipmentsavailablefordifferentdrilling
approaches.

15. Cable tool method
Wellsdrilledbycabletoolmethodareconstructedwithastandardwell
drillingrig,percussiontoolsandbailer.
Themethodiscapableofdrillingholesof8to60cmindiameterthrough
consolidatedrockmaterialtodepthsof600meters.
Drillingisaccomplishedbyregularliftinganddroppingofastringoftools.
Onthelowerendofthetoolisabitwithsharp,chiseledgewhichbreaks
therockbyimpact.
Fromtoptobottom,astringoftoolsconsistsofaswivelsocket,asetof
jars,adrillstemandadrillbit.
Thetotalweightofthetoolmayreachuptoseveralthousandkilograms.
Toolsaremadeupofsteelandarejoinedtoeachotherbyboxandpin
screwjoints.

16. Cable tool method
Themostimportantpartofthestringoftoolsisthebitwhichactuallydoesthedrilling.
Drillcuttingsareremovedfromthewellbyabailerorsandbucket.
Duringfrillingthetoolmakes20-40strokesperminute,rangingfrom40to100cmin
length.
Afterthebithascut1to2metersoftheformation,thestringtoolisliftedtothesurface
andthedrillcuttingsareremoved.
Thecabletoolmethodishighlyversatileandcanbeusedfordrillinginavariety
ofgeologicconditions.
Howeverthemajordrawbacksofthemethodaretheslowdrillingrate,itsdepth
limitation,theneedtoputthecasingalongwiththedrillinginunconsolidated
formations.
Thesimplicityofdesignandtheeaseofmaintenanceandrepairoftherigandtools
areimportantadvantagesinisolatedareas.

17. Cable tool method

18. Rotary method
Arapidmethodofdrillinginunconsolidatedformationistherotarymethod.
Deepwellsupto45cmindiameterormorecanbeconstructedusingthis
method.
Themethodconsistsofahollowrotatingbitthroughwhichamixtureofclayand
waterordrillingmudisforced.
Materialsdrilledbythemethodiscarriedupwardonthesurfacebytherisingmud.
Nocasingisnormallyrequiredasthemudformsaclayliningonthewallsofthe
welltherebypreventingcollapseofthewell.
Drillbitsareavailableindifferentdesignsthatgrindandfracturethroughtherock.
Thecommonstringoftoolsconsistsofadrillbit,adrillcollar(toaddweight)anda
drillpipethatextendsuptothegroundsurface.

19. Rotary method
Drillingmudconsistsofasuspensionofwater,bentonite(clay)andotherorganic
substance.
Rotarydrillingisemployedforoilwellsanditsapplicationtowater-welldrillingissteadily
increasing.
Advantagesaretherapiddrillingrate,theavoidanceofplacementofcasingatthetimeof
drilling.
Disadvantagesincludethehighequipmentcost,morecomplexoperationandtheneedto
removethemudcakeduringwelldevelopment

20. Air Rotary Method
Rotarydrillingcanalsobeaccomplishedwith
compressedairinplaceofdrillingmud.
Thetechniqueisrapidandconvenientforsmall-
diameterholesinconsolidatedformationswherea
clayliningisunnecessarytosupportthewalls
againstcaving.
Drillingdepthcanexceed150metersunder
favorablecircumstances.
Animportantadvantageofthismethodisitsability
todrillthroughfissuredrockformationswithlittleor
nowaterrequired.

21. Air Rotary Method

22. Rotary-Percussion Method
Arecentdevelopedrotary-percussionprocedure
usingairasthedrillingfluidprovidesthefastest
methodfordrillinginhardrockformations.
Arotatingbit,withtheactionofpneumatic
hammer,delivers10to15impactspersecondto
thebottomofthehole.
Penetrationratescanbeashighas30cm/min.
Wherecavingformationorlargequantitiesof
waterareencountered,achangetoconventional
rotarydrillingwithmudusuallybecomes
necessary.

23. Rotary-Percussion Method

24. Well Completion
Afterthedrillinghasbeenfinished,
thewellmustbecompleted.This
caninclude
Placementofcasing
Cementingofcasing
Placementofwellscreensand
Gravelpacking
Howeverwellsinhardrock
formationscanbeleftasitisand
thesecomponentsmaynotbe
required

25. Well completion: Casing
Wellcasingservesasaliningtomaintainan
openholefromthegroundsurfacetotheaquifer.
Itpreventsthesurfacewatertoenterthewell
andalsoprotectsthewallofthewellfrom
collapsing.
Thecommonmaterialusedforcasinginclude
wroughtiron,steelandPVCpipes.
Casingscanfurtherbedividedinto2types
◦Surfacecasingand
◦Pumpchambercasing

26. Well completion: Casing
Surfacecasingis
installedfromthe
groundsurfacethrough
theupperstrataofthe
unstable,weatheredor
fracturedmaterialinto
relatively stable
material.
Pumpchambercasing
comprisesallcasing
abovethescreenin
wellsofuniform
diameter

27. Well completion: Cementing
Thespaceleftbetween
theboredholeandthe
casingisnormallyfilled
withcementtoprevent
thecorrosionofthe
casingandtostabilizethe
cavingrockformation.
The cement grout
consistsofamixtureof
cementandwaterand
canbeplacedbyadump
bailerorbypumping.

28. Well completion: Screens
Inconsolidatedformationswherethematerial
surroundingthewellisstable,groundwater
candirectlyenteranuncasedwell.
Inunconsolidatedformationhoweverwellsare
equippedwithscreens.
Thescreenstabilizesthesideofthehole,
preventssandmovementinthewelland
allowsthemaximumamountofwatertoenter
thewell.
Screensareavailableinarangeofdiameters
andtheselectionofthescreendiameter
shouldbemadeonthebasisofdesiredwell
yieldandaquiferthickness.

29. Well completion: Gravel
packs
Agravelpackedwellisonecontaining
anartificiallyplacedgravelscreenor
envelopesurroundingthewellscreen.
Agravelpackstabilizestheaquifer,
minimizessandpumping,permitsuse
ofalargescreenslotwithamaximum
openareaandprovidesanannular
zoneofhighpermeabilitywhich
increasestheeffectiveradiusand
yieldofthewell.

30. Well development
Afterthewellhasbeencompleted,itmustbe
developedtoincreaseitsspecificcapacity
andobtainmaximumeconomicwelllife.
Theseresultsareobtainedbyremovingthe
finermaterialfromthenaturalformations
surroundingtheperforatedsectionsofthe
casing.
Developmentprocedurearevariedand
includepumping,surging,useof
compressedairhydraulicjetting,addition
ofchemicals,hydraulicfracturinganduse
ofexplosives.