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An onsite mud-logging system was developed to avoid possible alterations in gas samples during shipment to laboratories. Compensation was made for the large gas contribution of the drilling mud entering the hole, for the rate of drilling, and for lag time of the drilling mud. Location of gas anomalies is more apparent with the modified system.
Several wells in the DJ basin were compared to establish a pattern of sediment gas vs. lithology or geologic formation. Gas content of the drilling mud throughout the hole showed that large changes occur in the absolute concentrations of methane through butanes and also showed an erratic pattern of the component ratios. These compositional changes should be taken into account in surface exploration for gas.
Other gases in the well column were also monitored. Hydrogen and helium were found in most wells. Their concentrations varied widely from well to well and in a single well. Carbon dioxide also showed large variations. Carbon isotope ratios of carbon dioxide did not correlate with the carbon isotope ratios of carbonate cements in the same samples.
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