Pore network geometry in low permeability argillites from magnetic fabric data and oriented mercury injections

Abstract

The relationship between mineral fabric and pore network geometry anisotropy is studied for representative clay‐rich lithologies from the Callovo‐Oxfordian formation of the Andra Laboratory (Paris Basin, France), sampled from the oblique borehole‐core #EST211. Comparisons between standard magnetic fabric measurements (AMS) that give the mineral fabric, high pressure mercury injections parallel to the AMS axes, that reflect the pore structure parameter and AMS measurement after impregnation with a ferrofluid at different pressures, giving the shape of the pore networks, allow us to propose three pore models. (1) In the silt‐enriched specimens the transfer pathway is found to be controlled by vertical pathways. (2) In the carbonate‐enriched specimens the best transfer pathway is parallel to bedding, and in this plane is almost isotropic in spite of an anisotropic pore structure. (3) In the clay‐enriched specimens, at the site of the Andra Laboratory, the transfer pathway is also parallel to bedding and ∼20% higher parallel to both the magnetic lineation and the pore shape preferred orientation.