Table 1.

Mineralogy and porosity data from the Mercia Mudstone Group determined by X-ray diffraction and Hg intrusion porosimetry

Depth (m):300.0300.4301.5302.6307.5309.3AverageStandard deviation
Sample number:M1M2M3M4M5M6
Quartz %31.844.232.643.747.765.544.212.3
Illite %39.915.617.933.837.14.224.814.3
Chlorite %5.74.44.14.64.91.54.20.9
K-feldspar %15.911.511.67.78.76.510.33.4
Plagioclase %1.91.72.30.60.11.01.30.9
Calcite %3.40.50.20.20.11.00.91.3
Dolomite %1.48.312.49.21.43.56.04.6
Gypsum %0.013.818.90.10.016.78.39.2
Total silt minerals49.557.446.552.056.473.055.89.4
Total clay minerals45.619.922.038.542.15.729.015.5
Total pore-filling cements4.822.731.59.51.521.315.211.7
Clay/(clay + silt) %47.925.832.142.542.77.333.115.0
K-feldspar/(plagioclase + K-feldspar) %89.386.983.292.898.986.589.65.5
Porosity %7.410.310.79.19.79.59.41.2
Mean pore throat radius (nm)19664621291185038
Threshold capillary entry pressure (p.s.i.)2475984176105338980
Potential column height (m)54013019039023070258176
Calculated permeability (m2)1.1 × 10−204.2 × 10−202.8 × 10−201.2 × 10−201.7 × 10−207.8 × 10−203.1 × 10−202.6 × 10−20
  • The total silt mineral content is the sum of the quantities of quartz, K-feldspar and plagioclase. The total clay mineral content is the sum of illite and chlorite (as there are no other clay minerals present in these samples). Total pore-filling cements is the sum of the calcite, dolomite and gypsum. The mineral total equals 100%. The porosity is the final component of these rocks; this is microporosity as it is largely not visible with light optics. Threshold capillary entry pressures were calculated for CO2–H2O, assuming an interfacial tension of 28 mN m−1 and a contact angle of 40° (Chiquet et al. 2007a, b; Chalbaud et al. 2009). Potential column heights assume a CO2 density of 700 kg m−3 and a brine density of 1020 kg m−3. Permeabilities were calculated from pore-size distribution data using a modified version of the method of Yang & Aplin (1998).