Porosity, Permeability and Capillary Pressure Properties of the Kimmeridge Clay Formation of the North Sea using Pore Size Distribution Method

Olufemi Jokanola
University of Newcastle upon Tyne U.K, Newcastle, United Kingdom

In the Kimmeridge Clay Formation (KCF), porosity and permeability decreases with depth from 24%-3% and <10-0.09nD between 1.5-5.0km depth of burial. The upper 2.3 km showed porosity and permeability decreasing with depth from 24-19% and 5-1.5nD respectively. Between 2.3-3.4 km, abnormally high porosity and permeability (20% and 2-9nD) occur due probably to reduced effective stress implying abnormal pore-pressure. The atypical pore size distribution pattern of the mudstones within this regional also suggests presence of coarse grained materials thought to have come from incising alluvial fans. At 3.5km, the KCF is lithologically similar, and reached mechanical compaction equilibrium resulting in best-possible pore sorting with porosity and permeability being <10% and 0.3-09nD respectively. The 3.5km also defines the critical depth of burial (CDB). Compared with existing mudstone data, the KCF porosity-permeability data plots in the lowest portion of the porosity -permeability profile, similar to values extrapolated from previous organic poor, fine- grained mudstones. Capillary pressure measurements shows that if "water wet", the KCF at >3.5km could support >5km and >1.7km oil and gas respectively. Conversely, geochemical data suggest that this source rock may be "oil-wet" and may not be good capillary seals but behave more like a "permeability barrier". At the 2.3-3.4km band, where the KCF appears overpressured, it may be a good pressure seal. The upper 2.3 km is thought to be "water wet" and would make a good capillary seal, capable of holding up to 3.5 km and 1.3 km of oil and gas respectively.