plastering action of the fluid spiraling against the wallof the well, prevent the wall from caving-in. Theconsistency of the mud must permit the cuttings to beheld in suspension in the hole, yet permit them to settleout in the surface pits. Although some local clays willmix to an acceptable consistency, many do not. Acommercially prepared clay, such as Bentonite, must beadded to improve the density of the mud.Kelly-Drive Rotary Drilling OperationsIn well drilling, details of setting up the rig will vary,depending on the rig used. Well drilling rigs can beskid-mounted, trailer-mounted, truck-mounted, or evenself-propelled. In any case, it is necessary that the rig islevel and cribbed with dunnage before operations begin.Keeping your rig level helps to keep the hole straightduring the drilling operation.While the rig is being leveled, part of the crew canexcavate the mud pits (fig. 9-10). The size of the pitdepends on the water supply, depth of drilling, and thetype of material drilled. A fluid return ditch should bedug from the drilled hole to the settling pit and from thesettling pit to the main pit. The ditches enter and leavethe settling pit in such a reamer that the flow of fluid isreversed and causes the cuttings to settle, thus keepingthem from flowing into the main pit. The pits are linedand sealed with drilling mud and then water is added.Once the mud pits are full of water, the drilling mud canbe added and mixed to the right viscosity with themixing hose. The suction-hose screen is then placed inthe main pit at the opposite end of the return ditch. Thesuction hose is submerged at all times but does not lieon the bottom.Keep the circulating fluid as clean and free fromabrasives as possible to protect the pump parts. Thesettling pit should be cleaned when 75% full of cuttingsso that cuttings will not be placed in circulation. The pitis cleaned when the rig is stopped for a drill pipe change,or drill bit cleaning.A water supply is essential when drilling wells bythe rotary method. There is no set rule as to the amountof water required to drill any one hole. In some cases,where the formations are compact, 3 to 4 gallons ofwater per foot of hole drilled is sufficient. In other caseswhere formations are loose and extremely porous, alarge supply of water is required. For ordinary purposes,750 to 1,000 gallons of water per 8-hour shift is needed.Skid-mounted and canvas tanks are usually apart of thedrilling outfit.Figure 9-10.-Mud pits.Even holes spaced only a short distance apart andin the same soil formation may require different drillingtechniques. The drill supervisor must be capable ofselecting the best bit for penetrating a particular for-mation. Some examples of rotary drilling bits are shownin figure 9-11. Either the roller or the cone type of rockbit can be used to penetrate moderately hard to hardformations; a fishtail, three way, or pilot bit can be usedto penetrate soft formations and overburden material.Figure 9-11.-Drill bits.9-9
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