drilling school located at NCTC, Port Hueneme, uses the  second  method  when  circulation  is  lost  during drilling  operations;  however,  to  regain  circulation  the school   recommends   dropping   into   the   hole approximately  a  yard  of  3/4-inch  to  1-inch   clean aggregate to regain circulation. The amount of clean aggregate used depends on the size of the area in which circulation is lost. If circulation is lost in cavernous limestone, the fluid level in the hole is checked and tested for fresh water. A cheap, abundant supply of water is often the determining  factor  between  a  straight  well  hole  and  a loss of time, labor, and equipment. Much depends on the experience and ability of the driller  when  drilling  through  difficult  formations.  The driller will have to use the capabilities of the machine and experience to keep the hole straight. The harder formations, especially those which are dipped and those that are broken and crevice, present many difficulties. Use only a roller and  three- or four-wing drag bits  for this type of drilling.  Fishtail  and some of the single-cone roller bits are not suitable for any except the softest formations. Crooked  Holes One  way  to  detect  crooked  holes  during  drilling  is to watch for wear on the drill pipe. If wear occurs at a set distance from the top of the ground, it indicates the hole was deflected at this point. When drilling, detection of deflections of the bit and drill pipe is not easy because the  hole  can  be  quite  crooked  without  noticeably affecting  the  operation  of  the  rig.  The  driller  must  be alert to any indication that the hole is going crooked. To avoid crooked holes, make sure that the bits are of a form and size that prevent undue eccentricity during rotation. They must be sharp and dressed to proper gauge. The drill collar that holds the bit to the lower end of the drill pipe must be large enough in diameter to hold the pipe centrally in the hole and to prevent the bit from working off to one side. Avoid excessive bit pressures. Another difficulty sometimes encountered is the sticking  or  freezing  of  the  drill  pipe.  An  inexperienced drill operator can cause the drill pipe to stick by not circulating mud in the hole. The drill pipe is kept free in the  hole  by  simultaneously  rotating  the  pipe  and circulating a mud-laden fluid. If either operation stops, only a short time should elapse, depending upon the formation  being  penetrated  before  pulling  the  bit  into the casing (or out of the hole altogether, if no casing has been installed). Failure to do this often causes the drill pipe to become stuck due to sand and cuttings settling around it. The drill pipe may also stick in some formations if lost mud is replaced with water and not mud. Formations are often encountered that drain off or absorb a certain amount of the drilling mud. If this mud is replaced with clear water to keep up the fluid level in the hole, the water thins the mud to a point where the mud exerts a cutting  action  on  the  walls  of  the  hole  and  causes extensive  caving  around  the  drill  pipe,  fastening  it securely in the hole. Inadequate equipment may cause the drill pipe to stick;  for  example,  a  mud  pump  with  insufficient capacity  would  not  keep  circulation  moving  fast  enough to prevent drill cuttings from settling out and jamming the drill pipe. Balling up may also cause the drill pipe to stick. Balling up  is  the  accumulation  of  soft,  sticky  shale  or clay around the drill collar and bit. Occasionally, mud collars are formed that are forced up the hole by the pump action. This balling, if allowed to continue, forms a coating around the drill collar that sticks to the drill pipe securely when it is raised off the bottom. The usual cause  of  balling  up  is  a  high  rate  of  penetration, combined with a speed of rotation insufficient to mix the  drill  cuttings  thoroughly.  To  overcome  these conditions,  the  drill  operator  should  raise  the  pipe frequently by raising it off the bottom 4 or 5 feet and then drop the pipe while it is rotating rapidly. If this is done and if the rate of penetration is held to a speed that gives the circulating fluid time to mix the drill cuttings thoroughly,  this  source  of  trouble  can  be  held  to  a minimum. As mentioned before, loss of circulation may result in a stuck drill pipe. Loss of circulation is especially troublesome in porous limestone that contains much water. When one of these  porous zones  is  penetrated  by the drill, the pressure of the drilling mud causes it to drain off rapidly into the formation. The sudden reversal of  circulation  in  the  hole  deposits  the  suspended  drill cuttings around the drill pipe. This often happens so suddenly that there is no time to remove the drill pipe. Recovery of Stuck Drill Pipe Every precaution should be observed to prevent the drill pipe from sticking as only extreme scarcity of drill pipe  justifies  extensive  recovery  operations  in  drilling shallow wells; however, there are a few things that can be  done  successfully  with  the  equipment  at  hand, 9-14