Fluid Inclusion Stratigraphy (FIS) is a method currently being developed, with CEC funding, for use as a geothermal well logging tool to identify fractures and fluid types. This paper is the fourth in a series of papers on the development of FIS. Fluid inclusion gas geochemistry is analyzed and plotted on well log diagrams. The working hypothesis is that select gaseous species and species ratios indicate areas of groundwater and reservoir fluid flow and reservoir seals. Analyses have shown that it is possible to not only identify fluid types but also fractures. Analyses are performed by a commercial laboratory, Fluid Inclusion Technologies.

We developed a standard method of plotting bulk fluid gas analyses performed on systematically down-hole samples of core or cuttings. It can be applied to both Fluid Inclusion Technology analyses and our own quantitative fluid inclusion gas analyses. We plot gas ratios that suggest magmatic, meteoric, evolved, meteoric, and steam heated waters in a special manner on mud log type plots. For examples ratios of N2/Ar, Ar/He CO2/CH4 and (N2/Ar + CO2/CH4) / (Propane/Propene) are plotted to indicate reservoir fluids. These ratios are plotted in a manner that makes clear the amount of a magmatic component. A N2/Ar ratio > 105 suggests a magmatic fluid component. Therefore for a given analysis if N2/Ar > 105 we plot the quantity (N2/Ar -105), and if N2/Ar s < 105 we plot 0. Other ratios are plotted in a similar manner.

This plotting method is applied to Fluid Inclusion Technologies analyses of four Coso wells, and to 4 Karaha-Telega Bodas wells. Interpretations of well fluid types are confirmed by COC Ltd personnel, and the Karaha-Telega Bodas interpretations agree with vein mineralogy. The advantage of these plots is that FIT data can be plotted in minutes and are easily interpreted. Fence diagrams made from the fluid inclusion gas data interpretations are plotted for both systems and show a rudimentary fluid stratigraphy. The Karaha-Telega Bodas system shows a plume of magmatic volatiles near the volcano.

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