A special spudding bit may also be used to drill enough hole by spudding to 

 allow the rotary drill string to follow into the deflected hole. Also in soft forma- 

 tions, a special jet bit may be used that is constructed so that a strong jet or 

 stream of drilling fluid is directed against the side of the hole when the bit is 

 facing in the proper direction. The force of the jet is sufficient to drill a hole at 

 an angle to the main hole and allow a drill string to pass later into the deflected 

 hole. This last technique also has the advantage that no whipstock is required, 

 and it is thus cheaper and faster than the standard method in areas where it 

 will work. 



APPLICATIONS OF Perhaps the most spectacular application of 



DIRECTIONAL DRILLING directional drilling to modern problems is in 



the drilling of a relief well to control a well 

 that has blown out of control. Such a well which is spoken of as blowing wild, 

 has frequently caught on fire and formed a sizeable crater around the surface 

 well location. Well A in Figure 32-4 represents a typical well out of control. 

 From location B a relief well is directionally drilled to intersect well A at a 

 point shortly above the high-pressure zone which is causing the trouble. This 

 surface location at B is far enough away from A so that the rig operations of 

 the relief well will not be endangered by the wild well. Pressure-control materials 

 then can be introduced through well B into well A and the well brought under 

 control. The accurate drilling of such a well is a tribute to the ingenuity and 

 skill of the directional-drilling engineers, particularly when the small size of 

 the target to be hit is considered. 



Other oil-field operations involving directional wells are usually less 

 spectacular, but they are far more common and bring a much greater return 

 to the well operator. At the present time in the United States much attention 

 is being directed toward the search for oil on the continental shelf areas 

 beneath the Gulf of Mexico and the Pacific Ocean. There are many engineering 

 problems not encountered on land which have to be solved in order to exploit 

 these off-shore reserves. 



One of the prime off-shore problems is the establishment of a suitable foun- 

 dation structure to accomodate the drilling rig and its attendant facilities. This 

 problem is generally solved (1) by using a mobile drilling barge which can be 

 floated to the location and anchored in place, (2) by constructing a platform 

 which is supported by pilings anchored to the ocean floor, or (3) by building 

 a man-made island in moderately shallow water. The elaborate self-contained 

 drilling structures, which are currently being built by drilling contractors and 

 oil companies for use in deep water, are essentially barges with retractable 

 pilings or legs which can be let down to anchor the structure solidly on the ocean 

 floor. 



687 



