Confocal microscopy of fluid inclusions reveals fluid-pressure histories of sediments and an unexpected origin of gas condensate

We present two examples of how fluid inclusion data can be used to determin e geologic pressure histories and to quantify the compositional evolution o f petroleum in oil reservoirs. Volumetric liquid:vapor ratios generated wit h a confocal laser scanning microscope are used along with pressure-vapor-t emperature (P-V-T) modeling software to estimate the composition, P-T phase envelope, and isochore of single petroleum inclusions in the North Sea's J udy and Alwyn fields. In both cases, the gas condensates currently in the r eservoirs formed by the emplacement of gas into preexisting oil accumulatio ns. Pressure histories of individual units in each field are also revealed, providing the kind of data needed to determine the permeability and fluid flow histories of sedimentary basins.