Figure 7-4. Compounding a differential-thermal curve. Data obtained from ditch cuttings. 



C, showing largely dolomite, plus small amounts of minerals present in B. Curve 



D, the complete sample, shows each of the various separated minerals, each re- 

 duced in intensity according to its concentration, and with consequent reduction 

 in peak temperature. The temperature of certain almost instantaneous reactions 

 not affected by small changes in atmospheric pressure, i.e., the quartz inversion, 

 will not be altered appreciably because of concentration and will remain essen- 

 tially constant unless a simultaneous reaction is heating or cooling the sample 

 at this point. 



SUBSURFACE DTA As mineral assemblages become more and 



CORRELATION more complex, it becomes increasingly diffi- 



cult to analyze the minor compounds present. 

 Nevertheless, the complex profile of the DTA curve is an accurate reflection of 

 all thermally active minerals present and can be used for identification of or 

 comparison with other mineral assemblages. This is the basis for correlating 

 subsurface formations. 



Figure 7-5 presents a schematic drawing of two wells penetrating a hypo- 

 thetical formation. One of the wells crosses a fault along which downward dis- 



126 



