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using: (3.2)
Φ = Vb − Vma
Vb

In here, the bulk volume Vb = π D2Lc is derived from the diameter and the length of the plugs, assuming
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a perfect cylinder. Multiple measurements of these dimensions reduced the possible errors.

3.3.2 Permeability

For samples with a permeability that reflect typical hydrocarbon-bearing rock — from O few millidarcy
up to O two darcy — a Ruska gas- or liquid permeameter can be used (Wolf, 2010). Both methods
measure flow rate and the pressure drop over the core. Together with the viscosity of the used fluid and
the core dimensions, the permeability can be determined with Darcy’s law:

Q = −k ∆p Ac (3.3)
Lc µw

In here, k is the permeability [m2], ∆p the pressure drop [Pa], Lc the length of the core [m], Ac the

cross-sectional area of the core Ac = π D2 [m2] and µw the viscosity of water [Pa s].
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The Favignana samples, though, have a too high permeability to use this apparatus. A liquid permeameter
uses a small reservoir with water, making it possible to let a fixed amount of water flow through a sample.
Several canisters are available to vary the volume of the water to flow trough the samples. The largest
canister available had a volume of 10 ml, and with only a very small pressure drop the time it took for
this amount of water to be entirely pushed trough the sample was too short to accurately measure. First
attempts to measure permeability with these permeameters resulted in values of O tens of darcy. With a
gas permeameter, it was not even possible to build up a high enough pressure drop over the core to obtain
reliable measurements. Even with the highest possible rates, gas was flowing in such an unrestricted way
that no pressure increase was observed in the upstream part of the apparatus.

In order to overcome the problems regarding the high permeability of the samples, an alternative set-up
had to be created. An experimental set-up using a falling-head pressure differential was designed to
eliminate the problem with the high pressure drop. The sample is fixed at the end a transparent PVC
tube with a known diameter. An inner tyre of a bicycle placed around the sample restricted the flow
only trough the core. The bottom end of the tube is placed in a large tank of water. Figure 3.3 gives a
schematic overview of the set-up.

In order to perform the measurements, a vacuum pump is installed at the top. This serves two purposes:
1) it ensures that the core will be completely water-saturated; and 2) it will fill ensure that the tube is
entirely filled with water. Appendix E.1 provides a detailed workflow with both the preparation of the

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