Miscellaneous Subsurface Methods 587 



information derived from many wells and integrate the whole into an 

 orderly and plausible picture, the knowledge of the extent and direction 

 of the deviation in the various wells is of the greatest value. 



If tlie elimination of difficulties in drilling is considered, well sur- 

 veying of some sort is of paramount importance. As stated before, most 

 contracts for vertical holes specify that the deviation at no point in the 

 hole shall be greater than 3 or 5 degrees. Aside from the fact that some 

 measure of bottom spacing is thereby specified, a mechanically correct 

 hole is assured. Wells that are allowed to become crooked with "dog 

 legs" or sharp kinks in them are harder to drill, more liable to cause 

 mechanical failures in the drilling equipment, and more difficult to case 

 and cement. Production problems are simplified in a straight well as 

 wear on the pump, abrasion of sucker rods on tubing, and excessive use 

 of power required for pumping are minimized. Down-time with its conse- 

 quent loss of production is reduced. Many correctly drilled directional 

 wells with great deviations actually are cheaper to produce than some 

 so-called straight wells which deviate very short distances but which are 

 crooked. 



A continuous survey of a well as it is drilled is often of greatest value 

 when least expected. Occasionally a well will get out of control, exhaust- 

 ing gas and oil from the formation and sometimes igniting to form a 

 great fire hazard. Relief wells to choke the flow of such wild wells are 

 drilled much more easily if the original hole has been surveyed and the 

 point from which the well is producing is located accurately. 



A twist-off or a stuck drilling string is not an uncommon occurrence 

 in drilling. Fishing jobs are often long and very expensive operations. 

 Many times it is less troublesome and costly to set a cement plug on 

 top of the "fish" and sidetrack and redrill around that portion of the 

 hole filled with lost tools. Surveys made as drilling proceeds pay off 

 in a situation of this kind; the new hole may be drilled in such a direction 

 that there is positive assurance that the "fish" will not be encountered 

 again. 



Directional holes have been sidetracked unintentionally in soft for- 

 mations while running in the hole with a sharp bit or during reaming 

 operations. Because of the excellent survey that must be kept on a direc- 

 tional well, it has often been possible by skillful deflection of the bit to 

 break back into the original hole. Thus thousands of feet of drilled hole 

 have been saved that ordinarily might have been lost. In a very few in- 

 stances casing or tools permanently lodged part of the way up the hole 

 have been cemented to hold them in position; then the well has been 

 sidetracked around the "fish" and back into the original hole below. In 

 deep holes the bottom footage is very costly. An attempt of this kind 

 is very worth while, provided the original hole was well surveyed so that 

 the sidetracked hole can be directed very accurately to intersect the old 



