Experimental and numerical study of membrane properties and pore pressure transmission of Ghom shale

• Pore pressure transmission test on Ghom shale is conducted.
• Shale pore pressure in response to hydraulic and chemical loading is measured.
• Numerical model is based on a chemo-poroelastic theory and finite element solution.
• The simulation results are in good agreement with the actual pressure measurements.
• This result provides further validation for the theoretical model.

Serious wellbore instability frequently occurs during drilling operations in shale formations. Selection of safe mud parameters to alleviate shale instability problems during drilling operations can benefit from predictive models that consider fully coupled chemo-mechanical phenomena involved in shale-drilling fluid interactions. Although different chemo-poroelastic analyses on these interactions are presented in the literature, only a few experimental measurements and analysis of model predictions are available. In this paper, pore pressure transmission test on Ghom shale is conducted and pore pressure changes in the shale sample under hydraulic and chemical loading is measured. The main outcome of this experiment is the reflection coefficient which is usually used to quantify the osmotic characteristics of the chemically active shale in contact with a water-based fluid. The measured parameter together with other physico-chemical properties of Ghom shale are used to simulate time evolution of pore pressure and solute mass fraction distributions in the sample based on the chemo-poroelastic model of the test and the finite element solution in MATLAB. Comparison with experimental data shows that the simulation results are in good agreement with the actual pressure measurements in the test. This result provides further validation for the theoretical model.