New results from continuous gasometric determinations of carbonate in cuttings and cores from drill holes

Abstract

Continuous gasometric determination of carbonate in cuttings has been succesfully used by the Mobil Oil AG in the Weser-Ems area since 1954. It is used to check changes in rock composition (facies development) during drilling and to compare the results with those of adjacent drillings. Cuttings are taken at intervals of 1 to 2 m at the site of drilling; they are washed, dried, and ground. The amount of CO2 is determined with the "Scheibler- asometer" (described in MüIlet,1967) by treating 1/2 gr of the sample with HCl. Absolute carbonate content and the approximate calcite/dolomite ratio can be estimated if the first reading is taken after 30 seconds, the second after 1 minute (sometimes after 5 minutes) and the final reading after the gas development is completed (to 21 minutes). The resulting "carbonate-log" can be compared with those of adjacent drill holes during drilling operation. Such logs are very useful for exploring carbonate reservoirs and for stratigraphic correlation of sections strongly influenced by tectonics and of rocks lacking fossils.