Figure 19-2. Typical dipmeter computation sheet. 



SELECTION OF LEVELS Widespread experience indicates that the ac- 



curacy of a dipmeter survey depends prin- 

 cipally upon a careful selection of the zones in a well over which the measure- 

 ments are made. It is obvious, too, that numerous dip determinations made at 

 relatively close intervals in a well will more clearly define structural and strati- 

 graphic conditions than a few randomly spaced levels. 



After it has been decided at what depth positions dip determinations are 

 needed, a zone or level from 25 to 50 feet in length is chosen nearby for record- 

 ing the three curves. Each level of such length thus provides a number of bed- 

 ding surfaces on which a dip determination is made; if the dip measurement is 

 made on but one contact surface, a freak dip direction due to minor bedding 

 irregularities might be considered as representing the true formational dip. 



It has been found that the most satisfactory zones for a dipmeter level are 

 those consisting of relatively thin beds, 2 or 3 to 10 feet thick, having sharp 

 contacts with adjacent formations. Such zones for a resistivity-dipmeter level 

 are thin limestones or resistive sandstones interbedded with shale, but for an 

 SP-dipmeter level thin sandstones interbedded in shale are more favorable. 



Thin shale or sandy shale beds, on the other hand, within thick sand sections 

 and thin shale beds or minor resistivity variations within a massive limestone 

 frequently give erratic dip results. Sometimes, too, dipmeter measurements at 



392 



