"The data on the Progress Chart are shown with respect to time and depth. A convenient vertical scale is 100 ft. to 1 in. The depths drilled per day here shown would be unusual for anything but illustra tion. Progress in drilling is plotted from the daily tour records. It is not necessary, for plotting, to figure corrections between depths below surface and depths below stratigraphic datum. A graphic scale may merely be placed in such a position on the chart as to allow automati cally for the distance of the derrick floor above or below the stratigraphic datum line.
"At the left end of the Progress Chart is a composite graphic log of formations between stratigraphic datum and the bottom of the strati graphically deepest well in the group.
"All lines of correlation are horizontal on the Progress Chart. Dril ling operations in any well, plotted as the work progresses, can be referred across the chart to the composite log for a check on the forma tional progress of the work.
"As formations penetrated in certain wells may not be logged (al though present) in a well being drilled, the summarizing of conditions (such as water sands, caves, shells, etc., in all wells of a group) into a
composite log is a useful guide, although it should not displace the ordinary cross-section for accurate work.
"In preparing cross-sections, where the correlations are definitely known, stratigraphic datum can be used as the base line, instead of sea level. As on the Progress Chart, this will make the lines of correlation horizontal, and is a convenient method for comparison of relative depths, thickness of formations and other inter-related features.
"The Progress Chart gives a graphic history of operations in all the wells of a group. For example, reading up the vertical line for August 1, 1917, on the attached Progress Chart, it is easy to tell how many wells in the group were completed or in the oil sand at that date, also what wells were drilling or standing cemented.
"The Progress Chart could be used to advantage in the comparison of drilling records, either as to personnel of crews or methods of drilling. A comparison under this system would be more accurate, because of more nearly equal formational conditions, than a comparison by plotting to depths below surface."