Permeability, compressibility and porosity of Jurassic shale from the Norwegian–Danish Basin

Abstract

The Fjerritslev Formation in the Norwegian–Danish Basin forms the main seal to Upper Triassic–Lower Jurassic sandstone reservoirs. In order to estimate the sealing potential and rock properties, samples from the deep wells Vedsted-1 in Jylland, and Stenlille-2 and Stenlille-5 on Sjælland, were studied and compared to samples from Skjold Flank-1in the Central North Sea. Mineralogical analyses based on X-ray diffractometry (XRD) show that onshore shales from the Norwegian–Danish Basin are siltier than offshore shales from the Central Graben. Illite and kaolinite dominate the clay fraction. Porosity measurements obtained using helium porosimetry–mercury immersion (HPMI), mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) techniques on the shale samples show that MICP porosity is 6–10% lower than HPMI or NMR porosity. Compressibility, from uniaxial loading, and elastic wave velocities were measured simultaneously on saturated samples under drained conditions at room temperature. Uniaxial loading tests indicate that shale is significantly stiffer in situ than is normally assumed in geotechnical modelling. Permeability can be predicted from elastic moduli, and from combined MICP and NMR data. The permeability predicted from Brunauer–Emmett–Teller (BET)-specific surface-area measurements using Kozeny’s formulation for these shales, being rich in silt and kaolinite, falls in the same order of magnitude as permeability measured from constant rate of strain (CRS) experiments but is two–three orders of magnitude higher than the permeability predicted from the 1998 model of Yang & Aplin, which is based on clay fraction and average pore radius. When interpreting CRS data, Biot’s coefficient has a significant and systematic influence on the resulting permeability of deeply buried shale.

Static and dynamic pressure sensitivity anisotropy of a calcareous shale

“…This R is always > 1.5 in the direction perpendicular to the bedding planes. This contrasts with the other observations in sandstones and shales in which the value R ß1 only upon the initial depressurization of the material (e.g., Mbia et al (2014)). The recent study of Holt et al (2015a) too is of interest in this context.…”

“…This contrasts with the other observations in sandstones and shales in which the value R ∼1 only upon the initial depressurization of the material (e.g., Mbia et al . ()). The recent study of Holt et al .…”

“…Ruiz Pena (1998) also made direct comparisons of linear stiffnesses on a suite of dolomitized shales from Venezuela with the dynamic easily exceeding the static in all cases. More recently, Mbia et al (2014) made ultrasonic and strain measurements on oriented cylinders taken from Jurassic shales cored from the Norwegian-Danish Basin over depths from 1000 m to 4600 m. Their samples were subject to uniaxial loading to 25 MPa while maintaining a constant ratio of 0.38 between the uniaxial stress and the biaxial side pressures. Their static compressibilities always exceeded those determined dynamically except early in the depressurization stage.…”

Permeability in Rotliegend gas sandstones to gas and brine as predicted from NMR, mercury injection and image analysis

“…4 is controlled by smaller pores. Other authors match the cumulative curves (Mbia et al, 2014). For samples whose NMR and Hg-curves have different shapes, M A N U S C R I P T…”

“…Several authors combined NMR with Hg injection to estimate an effective 5 (Coates et al, 1999;Dastidar et al, 2006;Mbia et al, 2014).…”