Subsurface Logging Methods 471 



Figure 219 illustrates a type of form on which drilling-time data may be 

 tabulated. 



Determination of the time factor from the chart, using the engineer's 

 scale, is made by placing the scale parallel with the long dimension of 

 the chart and at the left of the base line from which the slanting stroke is 

 made. The zero of the scale is then placed at the top side of the depth 

 stroke and the position of the top side of the succeeding depth stroke noted 

 on the scale. The observer can read the scale to the nearest quarter of a 

 division or fifteen seconds of time, and this reading is the time factor for 

 the foot being measured. Because of the type of coordinate paper recom- 

 mended for plotting the log, it will facilitate recording and plotting these 

 time factors if decimals instead of fractions are used, as in figure 219. 



No difficulty will be encountered in thus reading and tabulating the 

 time where there have been no interruptions in drilling. If drilling has 

 been stopped at other than at the completion of an even foot, as at 6,021- 

 6,022 feet in plate 10, the time out must be subtracted from the total time 

 to indicate only the net time consumed in the drilling of the foot. The 

 position of the 6,022-foot stroke on the scale is shifted to the top of the 

 bottom horizontal line, indicating the end of the time out. The position 

 on the scale of the top side of the top horizontal time-out line will be the 

 net total time required in the drilling of this foot. If more than one inter- 

 ruption has been made in the drilling of one foot, this process is repeated 

 for each pair of horizontal lines indicating interruptions. All interrup- 

 tions should be recorded on the tabulation, as in figure 219, and by con- 

 ventional symbols shown on the plotted log, as in figure 220, to prevent 

 false interpretations. Care should be given to the pens so that they are in 

 exact horizontal registry in respect to each other at the top of each chart; 

 otherwise, errors in calculating time-out intervals may be made. 



After the chart has been prepared with the proper depths indicated, 

 any instructed person may make the time determinations and plot the log. 

 Office clerical assistance is used often by geologists supervising the work 

 on several wells being drilled at the same time. When this is done, it is 

 imperative that the original charts be received with the correct depth 

 designations shown. 



Plotting the log starts with the tabulation of data as in figure 219. 

 The selection of the time scale is important and has been discussed and 

 illustrated in previous papers by the writer. The log strip found to be 

 most satisfactory for interpretative work consists of coordinate paper with 

 twenty divisions per inch and cut six to eight inches in width. The head- 

 ing at the top should show the name and location of the well, datum eleva- 

 tions, and the vertical scale used. The name of the observer or plotter may 

 be useful for the record. Referring to figure 220, the depths are given at 

 the left edge of the log at intervals of 10, 25, 50, or 100 feet as determined 

 by the vertical scale used. The time scale is shown across the top of the 

 log in terms of minutes per foot. 



