these techniques are time consuming and expensive. They are excellent research 

 tools but commonly play a minor role in competitive exploratory and production 

 drilling. Paleontological analysis has been successful in many areas, but again 

 the method is too expensive for small operators and can be applied only if 

 microfaunas are present. Clay-swelling analyses are useful but are definitely 

 limited for correlative purposes. Radiation analysis is a new and inexpensive 

 method that holds considerable promise as an aid in correlation problems, but 

 it seldom can be considered sufficient in itself. 



At the present time differential -thermal analysis (DTA) approaches the 

 practical solution to the problem of analyzing cuttings to give a maximum 

 amount of information on mineral composition at a minimum cost. DTA pro- 

 vides a means of determining — by machine— compound and mineral composi- 

 tion, qualitatively and semi-quantitatively, with automatic recording of the re- 

 sults in the form of a differential-thermal curve. These curves, when determined 

 for regular periodic depths of cuttings and prepared in log form, provide an 

 excellent basis for correlating drilled sections. Results, which are a direct min- 

 eralogical picture of formation material, are not altered by the physical character- 

 istics of the zone, the fluids present, and the temperature and pressure environ- 

 ment, as are results obtained by in-the-hole logging methods. Results from DTA 

 can be obtained within a short time after drilling, or they can be delayed for 

 years until the need arises, provided the cuttings have been cleaned and stored 

 properly. 



As early as 1947 the need for subsurface correlation by DTA was recog- 

 nized and propounded by Florent H. Bailly (1952), who initiated and developed 

 its use on a volume basis in the exploration for oil. Many previous investigators 

 (Berkelhamer, 1944; Grim and Rowland, 1942 and 1944; Norton, 1939; Speil, 

 Berkelhamer, Pask, and Davies, 1945), have shown the value of DTA for the 

 identification and study of clays, aluminous minerals, and hydrous materials, 

 but it remained for Bailly to adapt the method to the production of logs with 

 the specific goal of achieving correlation of subsurface formations. Techniques 

 have been improved greatly and speed of determination increased many fold. 

 Thousands of samples have been tested and DTA logs prepared for numerous 

 wells and the correlation results have been most encouraging. 



DEFINITION OF DTA is a measurement of the physical and 



DIFFERENTIAL-THERMAL chemical reactions induced in a substance or 

 ANALYSIS mineral assemblage by change in temperature 



at either constant or variable pressure, a meas- 

 urement in terms of the gain or loss of heat energy. These reactions include 

 changes of state such as melting and evaporation, loss of water of hydration and 



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