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DIFFERENTIAL- 

 THERMAL 

 ANALYSIS 



George B. Mangold 



A major source of information on subsurface geology during the drilling 

 of an oil well is the cuttings. Each successive stratum is represented ; the samples 

 are obtained without extra cost; and represent an actual part of the penetrated 

 formation. 



Failure to make full use of the cuttings has been due to (1) the belief that 

 the samples are always contaminated, (2) the belief that depth identification and 

 stratigraphic position are inaccurate, and (3) the lack of an inexpensive method 

 of providing a meaningful mineralogical analysis of the cuttings. With the ad- 

 vent of drilling-mud control and careful formation logging, and through the 

 use of differential -thermal analysis, these objections, for the most part, are no 

 longer valid. If the drilling fluid is properly maintained, sloughing of the hole 

 is virtually eliminated, and contamination of cuttings from other depths becomes 

 insignificant. Through continuous regular determination of lag time, depths 

 can be assigned to the cuttings with an accuracy almost comparable to that of 

 cores. 



Many methods have been used for analyzing cuttings. The simplest, of 

 course, is examination through a binocular microscope. A competent geologist 

 can make detailed descriptions of the cuttings at regular depth intervals; how- 

 ever, the results are dependent largely upon the human element. 



Thin-section analysis, X-ray analysis, and chemical analysis provide dif- 

 ferent types of information, each of which lends itself to correlation; however, 



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