1956a), and Ca/Mg ratio as reflected in geologic age (Chilingar, 1956b). DTA 

 can be a great help in complementing other lines of research and in presenting 

 new as well as corroborative evidence for more comprehensive stratigraphic 

 evaluations. 



In the study of formation environments, an increasing emphasis on the use 

 of clay-mineral identification is appearing in the literature. W. D. Keller 

 (1956) has pointed out recently the potentialities of this line of approach in de- 

 termining characteristics of source rock and the physical and chemical factors 

 prevailing during the clay deposition. Here again DTA can be an invaluable tool, 

 and it is already widely accepted in certain industries for clay-mineral evalua- 

 tions. In an extensive study of clays from the lone formation, Amador County, 

 California, Pask and Turner (1952) employed various techniques in addition 

 to DTA but found the latter to be relatively simple to use and their most 

 powerful formation-identification and correlation tool. 



DTA can be of great use not only for environmental studies but for immedi- 

 ate practical applications of knowledge of the type and amount of clays in a for- 

 mation. Flood-control projects, canal building, and land drainage are examples 

 of engineering works which may be aided very much through the utilization of 

 clay properties and avoidance of harmful effects of clay hydration and base ex- 

 change. In the petroleum industry, the same factors are involved in waterflood- 

 ing projects, where success or failure may depend on knowledge of the concen- 

 tration of swelling clays and the ability to treat injection waters in order to pre- 

 serve permeability of the formation to water. 



Frequently DTA may explain and corroborate apparent anomalies in core 

 analysis by showing a mineralogical reason for changes not apparent in physical 

 structure. Figure 7-13 illustrates this possibility. Data on 11 consecutive core 

 samples, spaced 1 foot apart, are presented alongside the corresponding differ- 

 ential-thermal curves. Visually there were no appreciable differences between 

 these samples, yet core analysis indicated many decided variations. Similarity 

 of the first two depths, low permeabilities, and high resistivity is explained by 

 the similar thermal curves showing considerable dolomite content. The next two 

 samples are much alike yet quite different from the first pair. Correspondingly, 

 porosity, permeability, and resistivity values have changed radically yet are of 

 the same order between themselves. The sample from 8251 feet contains calcite, 

 which accounts for the low permeability without high resistivity. And again, 

 depths 8255 and 8256 feet appear almost identical on DTA and have almost 

 identical core-analysis values. 



DTA is potentially able to locate position of casing failures by identification 

 of depth corresponding to composition of material being produced through the 

 pipe break. There is an actual instance of this type on record where shale par- 

 ticles were apparently coming from the producing zone but were identified by 

 DTA as formation up the hole opposite a subsequently located casing defect. A 



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