4. Monitor the pulldown and top-head drivespindle rotation pressure gauges to avoid overthrust andmonitor the air line pressure to avoid a plugged bit.5. When the drill hole is complete, shut down theair and repressurize before “tripping out” the hole.Down-Hole-Drilling (DHD) (fig. 9-4):1. Use the percussion button bit.2. Use the holdback regulator to control feedforces.3. Switch on the DHD line oiler before operatingthe DHD. (A air line lubrication system injects adetermined rate of oil into the flushing hose to lubricatethe DHD hammer when air hammer drilling.)4. Use the DHD line oiler regulator to adjust the oilflow and check the oil flow by placing a piece ofcardboard under the spindle sub and inspect the pattern.5. Monitor the DHD frequency and cuttings todetermine proper feed force.Setting Casing:1. Retract the top-head drive and unpin and swingout the forward centralizer.2. Replace the centralizer bushing with casingclamps.3. Install the choker sling on the first casing, andhoist the casing above the drilled hole.4. Lower the casing into the hole until the top isabout 1 foot above the worktable.5. Close the centralizer and pin it shut.6. Remove the choker sling and attach it to the nextcasing. Hoist the second casing above the first.7. If the casing is plastic, install the collar andcement joint. If weld type, join shoulders and weld. Andif thread type, clean threads and dope and tighten witha chain wrench or breakout wrench.8. Set the screen and rest of casing.9. Unpin and swing out centralizer.10. Gravel pack and grout as to the constructionspecifications.DRILLING DIFFICULTIESLost circulation is one difficulty you may encounterwhen drilling. Sometimes it occurs in zones of highporosity that usually contain large supplies of water. Atest of the well should be made whenever circulation islost. Formations that draw off or absorb all or part of thecirculating fluid offer problems, ranging from minorinconveniences and loss of time to extreme conditionsthat render rotary drilling impossible.Formations that contain joints and fissures, such asquartzite, sandstone, limestone, and dolomite, presentproblems arising from caving, abrasion, and completeloss of circulation.Shale that is jointed and fissured seldom draws offan excessive amount of circulating mud; however,drilling fluid that is absorbed causes the shale to swelland heave, filling up the drill hole. This has beenovercome by the use of special drilling fluids. ‘Thiscondition is rare, and satisfactory drilling progress canusually be made by using a drilling fluid of highviscosity and weight.Sands and gravel often absorb enough drilling fluidto hinder drilling progress. Fluid loss, which, in mostcases, will be continuous, should be replaced with mud,not water. Water, when used to maintain sufficientvolume for circulation, soon lowers the viscosity andweight of the mud-water mixture, and caving results.Two methods are used to regain lost circulation. Thepreferred method is to drill through the zone of lostcirculation and to set a string of conductor casingsbelow the porous zone. The chief requirement for thisprocedure is a plentiful supply of water to circulate thecuttings away from the bit and into the formation. Mudis desirable but the quantity needed usually precludes itsuse. When using water to carry off the drill cuttings,always remember to continue to operate the pump for afew minutes after drilling has stopped. This flushes thecuttings out of the hole and prevents the drill pipe fromsticking when it is stopped to make a connection. Inextreme cases where it is necessary to drill as much as100 feet or more through a formation in whichcirculation is lost, a small quantity of mud is spottedaround and above the bit while an additional joint of pipeis installed in the drilling string. This prevents excessivesettling of the drill cuttings and consequent stickingwhile the drill pipe is standing. When the bottom of thezone has been reached, drilling is continued into theunderlying formation for about 50 feet to give room forcementing the casing. When the casing has been run andcemented, the ordinary rotary drilling procedure isresumed.In the second method, circulation can usually beregained by mixing a clay-type material with the drillingfluid that can be bought commercially. The water well9-13
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