Wellbore Stability: The Impact of Specimen Size and Ionic Solutions on the Mechanical Properties of Berea Sandstone

Mechanical properties of sandstone such as the compressive strength, Young’s modulus, and Poisson’s ratio are commonly used in the design of geotechnical structures and simulation of oil and gas reservoirs. An accurate characterization of sandstone’s mechanical behavior under loading conditions is imperative when assessing the stability of geotechnical structures such as wellbores. During laboratory testing, the specimen size needs to be carefully selected in order to obtain reliable results. Also, the impact of ionic solutions on sandstone’s mechanical behavior needs to be fully assessed. This work showed that the native mechanical parameters of Berea sandstone decreased as the diameter of the specimen decreased. Therefore, it is recommended to use proper specimen size for testing purposes. Data also showed that generally there was a reduction in compressive strength and Young’s modulus of Berea sandstone after exposure to ionic solutions, while there was an increase in Poisson’s ratio when exposed to the same solutions. It was further observed that KCl solution had the least impact on the compressive strength of Berea sandstone, especially for small samples, while NaCl and CaCl2 solutions had a greater impact. This may have to do with the suppressive and inhibitive role that potassium ion plays in clay swelling and subsequent mechanical degradation. It is recommended to examine the impact of ionic solutions on the mechanical properties of the drilled formation in order to avoid premature wellbore failure.