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 into secondary migration require new methods and techniques to characterise the composition of organic fluids obtained from reservoir rock samples. Ideally the composition of residual petroleums should be compared with the mineralogical and petrophysical properties from the same sample. This requires a non-destructive extraction procedure that keeps the rock in its natural state. We have developed a flow-through extraction system capable of efficiently extracting core plugs while preserving the pore system of the sample. Extractions can be performed sequentially 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 the 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 Darcyʹs 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/rock interaction in the subsurface.