IDENTIFICATION OF SOME CHEMOPOROELASTIC PARAMETERS OF A REACTIVE SHALE FROM EXPERIMENTAL DATA

Summary This paper is concerned with the experimental identification of some chemoporoelastic parameters of a chemically reactive shale from data obtained in pore pressure transmission-chemical potential tests. The parameter identification is carried out by matching the observed pressure response with a theoretical solution of the experiment. This solution is obtained within the framework of Biot theory of poroelasticity, extended to include physico-chemical interactions. EXPERIMENTAL ISSUES The so-called pore pressure transmission-chemical potential test is used in the petroleum industry to evaluate the osmotic membrane efficiency of a shale in contact with a drilling fluid [10, 8]. It is motivated by the need to assess the capacity of improving the stability of a borehole in a chemically active shale by increasing the salt concentration of the drilling fluid [4, 5, 9]. In this test, a saturated cylindrical sample of shale is subjected sequentially to a hydraulic and a chemical loading at the upstream end of the sample (z =0), with the downstream end (z = L) connected to a closed reservoir. The hydraulic loading consists of applying a pressure pm at z =0with the solution used during the saturation phase. In the chemical loading the upstream end is placed in contact with a solution of a different salt concentration but at the same hydraulic pressure pm. This experimental program was conducted with a two-fold objective: (i) check the relevance of the theory by its ability to be consistent with the observations; (ii) provide data to allow identification of the parameters of the model