When logs are plotted from the sample examiner's notes, the plot can be 

 made on translucent material, such as vellum. All lettering and symbols are 

 inked, including the inked parts of color symbols within the color column, but 

 no color is applied to this original. Prints on heavy-grade paper are run off 

 the translucent log. The prints are then hand colored. 



A similar method consists in lettering and inking a standard well-log strip 

 as described in the preceding paragraph. A film negative is made from the 

 strip, and duplicate positives are made from the film negative by a continuous 

 photostat process. The column is then colored with pencils. 



All except the color column of a completed and colored strip can be re- 

 produced in the following way: 



Although the column will have to be hand colored on the reproduction, 

 copying of the descriptions is avoided. The color column is cut from a blank 

 log strip. This narrow strip is placed with the proper alignment of depth lines 

 on the colored strip and taped in this position with transparent photo tape. With 

 this as copy, a photographic film negative is made. Prints from the negative 

 are identical to the original, except that the column is a ruled blank. Colors 

 and symbols are copied from the original. 



SUPPLEMENTAL USES OF The lack of exactness in picking stratigraphic 

 OTHER TYPES OF LOGS boundaries and occasionally in the interpreta- 



tion of caved and freshly cut materials can 

 be minimized through judicious use of drilling-time, electric, and radioactivity 

 logs. These aids to detailed sample logging should be employed with restraint, 

 because it is not difficult for the sample man to get into the habit of interpreting 

 lithologies from the mechanical logs instead of the samples. In sections of sand- 

 stones and shales this mistake can actually be made with considerable assurance, 

 but in sections of highly diversified lithologies, particularly in carbonate sections, 

 the examiner must rely principally on his interpretation of the cuttings. 



Drilling-Time Logs 



It is common practice on drilling rigs to maintain a complete record of 

 the progress of the hole. This record may be in the form of feet per hour or 

 minutes per foot. In either case, the rate of penetration can be plotted on a 

 strip log and thus serve as a valuable tool for the sample examiner. Usually the 

 breaks in drilling time correspond to some visible change in lithology (fig. 3-5). 

 Very porous zones in dolomites and limestones normally are drilled at a faster 

 rate than the denser portions. Changes from shale to sandstone, gypsum to 

 shale, and so forth, are frequently reflected in the rate of drilling. However, 

 the manner of change — slow-to-fast or fast-to-slow — is not always the same in 

 similar sequences of rocks. The following example illustrates these relationships : 



52 



