The study of reservoir seal formation characteristics is vital to the success of carbon
sequestration projects. The unique properties of these formations allows for the safe
long-term storage of carbon dioxide. These intrinsic properties also give rise to numerous
experiment complexities outside of the realm of traditional core characterization
techniques. Samples were obtained to represent the main classes of cap rocks; shales
from both a quarry in the UK and a Spanish carbon storage pilot site, anhydrite from
UK extraction mines, and a evaporite sample from a reservoir located in the Middle East.
An apparatus has been constructed capable of measuring the permeability and capillary
threshold pressure of reservoir cap rocks. The pressure decay technique was used
to measure the permeability relationship of clay-rich and evaporite samples with varying
applied stresses was measured. Unique trends are observed for each geologic sample
exhibiting minimums in permeability. The initial reduction of permeability as effective
pressure was increased was due compaction and the subsequent increase at high stresses
was due to the opening of micro-fractures. The capillary threshold pressures of each
sample were determined using three different techniques. A novel technique takes advantage
of the pressure decay permeability measurements technique in quantifying extremely
small fluid volumes during initial sample drainage. Capillary threshold pressures were
shown to also be dependant on applied system stress. The capillary threshold pressure
was observed to decrease dramatically following the increase in permeability with further
increasing effective pressure.
Imaging capabilities were also explored, ranging from core scale to nanometre scale
techniques. Computerized micro-tomography was used in plug sample evaluation, and
in the observation of fractured system behaviour under varying stress. Scanning electron
microscopy paired with focused ion beam milling was used to extract the 3D pore space
of the ceramic allowing for permeability estimates from numerical simulations.