Interpretation of Hydrocarbon Shows Using Light (C1-C5) Hydrocarbon Gases from Mud-Log Data

Chromatograph analysis of hydrocarbon gases as reported on mud logs is the first indication of a reservoir’s fluid characteristics. Ratio calculations of these data can enhance the interpretational value of this information, giving the well-site geologist an immediate indication of zones of interest that need further testing. It was found that for an effective interpretation of mud-log gas data, the results must be plotted on a depth log, which can be easily integrated with other data. Thus, a new method of interpreting ratio calculations of C1-C5 gas data is proposed. This method can be used at the well site during drilling to give an initial evaluation of the reservoir fluid type, and in post-well evaluation to enhance wireline and mud-log data.