-y^x 



Figure 7-12. Differentiation of volcanics by thermalog. 



and even the type and composition of drilling fluid. These measurements depend 

 upon the sum total of the physical and chemical environment. In contrast, for 

 DTA each mineral must be identified in its own right; no combination of phe- 

 nomena or grouping of properties can "produce" a mineral that is not there. 



Minimum Effect of Human Element 



The human element does not enter into the actual determination of thermal 

 curves. After the samples have been loaded into the holder, control of tempera- 

 ture rise and recording of thermal reactions are automatic. Although identifica- 

 tion of constituents is a matter of experience and training, correlation can be 

 based purely on the similarity or dissimilarity of curve characteristics. 



No Loss in Rig Time 



DTA does not involve cessation of drilling and loss in rig time. The source 

 of material for analysis is always present in the form of cuttings while drilling 

 is in progress. 



Flexibility in Time and Location 



DTA can be determined in a nearby laboratory, or in a laboratory thousands 

 of miles away. It can be done while the well is being drilled or at any later date. 

 If samples are washed and preserved properly, they need not be tested until such 



136 



