drilling school located at NCTC, Port Hueneme, usesthe second method when circulation is lost duringdrilling operations; however, to regain circulation theschool recommends dropping into the holeapproximately a yard of 3/4-inch to 1-inch cleanaggregate to regain circulation. The amount of cleanaggregate used depends on the size of the area in whichcirculation is lost. If circulation is lost in cavernouslimestone, the fluid level in the hole is checked andtested for fresh water.A cheap, abundant supply of water is often thedetermining factor between a straight well hole and aloss of time, labor, and equipment.Much depends on the experience and ability of thedriller when drilling through difficult formations. Thedriller will have to use the capabilities of the machineand experience to keep the hole straight. The harderformations, especially those which are dipped and thosethat are broken and crevice, present many difficulties.Use only a roller and three- or four-wing drag bits forthis type of drilling. Fishtail and some of the single-coneroller bits are not suitable for any except the softestformations.Crooked HolesOne way to detect crooked holes during drilling isto watch for wear on the drill pipe. If wear occurs at aset distance from the top of the ground, it indicates thehole was deflected at this point. When drilling, detectionof deflections of the bit and drill pipe is not easy becausethe hole can be quite crooked without noticeablyaffecting the operation of the rig. The driller must bealert to any indication that the hole is going crooked.To avoid crooked holes, make sure that the bits areof a form and size that prevent undue eccentricity duringrotation. They must be sharp and dressed to propergauge. The drill collar that holds the bit to the lower endof the drill pipe must be large enough in diameter to holdthe pipe centrally in the hole and to prevent the bit fromworking off to one side. Avoid excessive bit pressures.Another difficulty sometimes encountered is thesticking or freezing of the drill pipe. An inexperienceddrill operator can cause the drill pipe to stick by notcirculating mud in the hole. The drill pipe is kept free inthe hole by simultaneously rotating the pipe andcirculating a mud-laden fluid. If either operation stops,only a short time should elapse, depending upon theformation being penetrated before pulling the bit intothe casing (or out of the hole altogether, if no casing hasbeen installed). Failure to do this often causes the drillpipe to become stuck due to sand and cuttings settlingaround it.The drill pipe may also stick in some formations iflost mud is replaced with water and not mud. Formationsare often encountered that drain off or absorb a certainamount of the drilling mud. If this mud is replaced withclear water to keep up the fluid level in the hole, thewater thins the mud to a point where the mud exerts acutting action on the walls of the hole and causesextensive caving around the drill pipe, fastening itsecurely in the hole.Inadequate equipment may cause the drill pipe tostick; for example, a mud pump with insufficientcapacity would not keep circulation moving fast enoughto prevent drill cuttings from settling out and jammingthe drill pipe.Balling up may also cause the drill pipe to stick.Balling up is the accumulation of soft, sticky shale orclay around the drill collar and bit. Occasionally, mudcollars are formed that are forced up the hole by thepump action. This balling, if allowed to continue, formsa coating around the drill collar that sticks to the drillpipe securely when it is raised off the bottom. The usualcause of balling up is a high rate of penetration,combined with a speed of rotation insufficient to mixthe drill cuttings thoroughly. To overcome theseconditions, the drill operator should raise the pipefrequently by raising it off the bottom 4 or 5 feet andthen drop the pipe while it is rotating rapidly. If this isdone and if the rate of penetration is held to a speed thatgives the circulating fluid time to mix the drill cuttingsthoroughly, this source of trouble can be held to aminimum.As mentioned before, loss of circulation may resultin a stuck drill pipe. Loss of circulation is especiallytroublesome in porous limestonethat contains muchwater. When one of these porous zones is penetrated bythe drill, the pressure of the drilling mud causes it todrain off rapidly into the formation. The sudden reversalof circulation in the hole deposits the suspended drillcuttings around the drill pipe. This often happens sosuddenly that there is no time to remove the drill pipe.Recovery of Stuck Drill PipeEvery precaution should be observed to prevent thedrill pipe from sticking as only extreme scarcity of drillpipe justifies extensive recovery operations in drillingshallow wells; however, there are a few things that canbe done successfully with the equipment at hand,9-14
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