Capillary Pressure measurements are made on rock samples to characterize the fluid filling behavior of a rock sample. This is useful to both model the initial hydrocarbon filling event of a reservoir (and hence determine the theoretical hydrocarbon in place) as well as determining the height above free water for each sample which allows a more realistic determination of formation saturation.
There are three main methods for determining Capillary Pressure and in general they form a cost/quality/turnaround time relationship
- Porous Plate: the sample is desaturated over a ceramic Porous plate, this is a longer term test but more closely replicated the actions of the initial reservoir filling. This test is more appropriate for setting conditions where there is a consistent saturation profile across the entire sample
- Centrifuge: the sample is desaturated in a centrifuge, this is a quicker method and the saturation is calculated at the end face of the sample as there will be a pressure gradient across the sample during testing. This test is more appropriate when only capillary pressure is needed.
- Mercury Injection: the sample in intruded with Hg and increasing pressures (up to 60,000 psi). This is a quick efficient (although destructive) method of demining Capillary pressure across the full range and permeability’s found in both reservoir and Cap rocks. MICP is also a very useful screening tool for choosing a representative suit of sample for further testing