A NOVEL SEQUENTIAL EXTRACTION SYSTEM FOR WHOLE CORE PLUG EXTRACTION IN A SOLVENT FLOW-THROUGH CELL - APPLICATION TO EXTRACTION OF RESIDUAL PETROLEUM FROM AN INTACT PORE-SYSTEM IN SECONDARY MIGRATION STUDIES

The rapidly developing field of reservoir geochemistry and studies int o secondary migration require new methods and techniques to characteri se the composition of organic fluids obtained from reservoir rock samp les. ideally the composition of residual petroleums should be compared with the mineralogical and petrophysical properties from the same sam ple. This requires a non-destructive extraction procedure that keeps t he rock in its natural state. We have developed a flow-through extract ion system capable of efficiently extracting core plugs while preservi ng the pore system of the sample. Extractions can be performed sequent ially to obtain various oil phases present in the pore system, i.e. '' free'' or ''mobile oil'' can be obtained separately from residual oils adsorbed onto mineral or organic matter surfaces. The ''free'' and '' adsorbed'' residual oils exhibit marked compositional differences due to fractional adsorption effects and maturity variations. Monitoring t he pressures at the inlet and outlet positions of the extraction cell allows the measurement of pressure gradients across the core, enabling the calculation of the relative permeability of the sample according to Darcy's law. Application of the sequential flow-through extraction method gives a substantial increase in information on the rock sample, allowing a better understanding of fluid flow and fluid/roek interact ion in the subsurface. (C) 1997 Elsevier Science Ltd.