When the core is rotated to all possible orientations, the normal describes a 

 double cone. As an example, we shall assume that hole A is plunging 45 degrees 

 on azimuth 220 degrees. Measured dip in the core is 30 degrees. Hole B is 

 plunging 60 degrees on azimuth 110 degrees, with measured dip of 40 degrees. 

 The distinction should be kept in mind between plunge of a borehole, measured 

 from the horizontal, and well deflection, measured from the vertical. 



The first step in solving the problem is to pass a plane through the axes 

 of the two boreholes. After marking N on the stereogram sheet, we plot the 

 plunges of A and B (fig. 25-14). By procedure 2 the required plane is deter- 

 mined. The sphere is rotated to bring A and B to the position A' and B', 

 and now the axes of the two double cones of bedding plane normals will lie 



Figure 25-13. The double cone of 

 oriented core (Phillips). 



possible positions of bedding plane normals in un- 



547 



