Mechanical Properties of Lamellar Shale Considering the Effect of Rock Structure and Hydration from Macroscopic and Microscopic Points of View

It is well known that the effect of shale hydration causes wellbore instability due to water phase invasion drilling fluid lamellar rich formations. This because mechanical properties (compressive strength, elastic modulus, etc.) surrounding borehole, which in clay minerals, will decrease significantly after hydration. In this study, using continental stratum southern Ordos Basin, were studied by compression tests considering structure and from a macroscopic point view. addition, mechanism was discussed combined with CT scanning results microscopic The demonstrate following points. Lamellar has stronger anisotropy than bedding shale, compressive strength (deviatoric stress) modulus are both lower those it more prone tension fracture. With increase angle (?) between lamina axial direction 0° 90°, decreases when ? < 30° then increases, greatly tends flatten. time, gradually decrease, rates their decrements reduce. affected shale. leads formation new fractures expansion existing junction area laminae rock matrix, resulting easy fracture along