Multi-stage water permeability measurements on claystone by steady and transient flow methods

Abstract The present paper deals with the comparison of permeability measurements between steady flow and transient flow tests (pulse decay test). We submitted one sample to a series of four sequences of one pulse test followed by one steady flow test. This whole multi-stage test lasted approximately 120 days. The pulse tests were interpreted with an inverse method proposed by Giot et al. (2011) allowing assessment of mechanical and poromechanical parameters in addition to intrinsic permeability. Overall, the pulse test measurements showed that the claystone progressively turned into mud, exhibiting constant decreases in permeability and Young's modulus and a constant increase in the Biot coefficient. In contrast, the steady flow tests exhibited constant permeability corresponding to the final value assessed by the pulse test. These results are explicated by the evolution of the claystone fabric with wetting and call into question the representativeness of permeability measurements by the steady flow method on these kinds of materials.