Practical Aspects of Geobarometry
Fluid inclusions provide a good tool to determine pressure at the time of fluid inclusion entrapment, but the ability to use this tool is extremely dependent on the fluid inclusion assemblage (FIA) preserved and the state of knowledge of the composition and P-V-T properties of the fluid system trapped in the inclusions. The best method for using inclusions to determine true pressure of entrapment requires that FIAs preserve a record of gas-water immiscibility. Without this petrographic evidence of immiscibility, guesses must be made about the temperature of fluid inclusion entrapment to estimate the pressure of entrapment. For some fluid inclusions, the best that one can accomplish reliably is to determine a minimum pressure of fluid inclusion entrapment, and there are several possible approaches. Many of the methods developed in the previous chapter to determine entrapment temperature have parallels for determining entrapment pressure. Another approach using the intersection of isochores from petroleum and water systems (Narr and Burruss, 1984) is not covered in this text because recent work suggests a need for careful reevaluation of its theoretical and practical basis (Burruss, 1992).