PERMEABILITY TO RESIDUAL WATER SATURATION IN OIL SATURATED PLUGS

ABSTRACT A series of laboratory experiments have been conducted to determine the permeability of brine close to irreducible water saturations with varying rock types, capillary pressures, saturations and permeabilities. X-ray tomography (CT) was used in one experiment as a quality assurance measure, visualizing the distribution of the flow of S wi phase in the sample. Water-saturated plugs attached to a water-wet ceramic membrane were drained by oil to S wi . Oil was then substituted by water at the inlet keeping both the water-and the oilsaturations in the plug constant. This was done in order to allow for water to flow through the plug and the membrane. A subsurface analogue to this laboratory experiment is a hydrocarbon-filled reservoir that is leaking water through a cap rock or a fault -keeping the hydrocarbons in place. The CT scan images showed that, although the overall flow rate was very low, the injected water moved quickly through the S wi -phase. Only a small fraction of the S wi volume contributed to this flow. The CT experiment also revealed some experimental artefacts such as spontaneous imbibition and gravity effects, which warrants further investigation. The result of the experiments verified that water could flow through different core plugs with varying S wi -phase permeability without forcing the oil through the membrane or changing the water saturation. The residual water permeability was dependent on the water saturation (S wi ) and the core plug permeability. Lowering the absolute permeability does not give a similar reduction in water permeability at S wi . The water permeability at S wi ranged from 0.02 µD to 1 µD. The absolute permeability for the different plugs ranged from approximately