Characterization of the mechanical behavior of a flawed sandstone, the case of the Huayacocotla Formation, eastern México

This work evaluates the mechanical behavior of a quartz-feldspar sandstone from the Huayacocotla Formation, located in the Tampico-Misantla Oil Province (TMOP), Mexico. Uniaxial and triaxial compressional tests were conducted in samples oriented perpendicular and parallel to the stratification under confining pressures of 0, 30, and 60 MPa, in both dry and wet conditions. Petrographic descriptions of samples, before and after testing, were used to assess deformation mechanisms and microstructural evolution. The results demonstrate that sample orientation, confinement, and moisture significantly influence the crack initiation stress (cs), the peak strength (ps), and the elastic modulus. In uniaxial tests, perpendicular specimens presented higher cs and ps than the parallel samples, while increasing confinement enhanced strength and stiffness, with ps and cs increasing by up to 27 and 26% under 60 MPa. Wetted samples exhibited reductions in Young´s modulus cs and ps by up to 29%, especially in parallel samples, due to decreased surface energy and intergranular cohesion. Failure was brittle in all cases, transitioning from tensile splitting to shear along pre-existing flaws. Petrographic observations allowed us to identify deformation features, such as grain crushing, pore collapse, and en échelon fracture arrays. These findings provide insights about the combined influence of fabric anisotropy, confining pressure, and the influence of water on the geomechanical response of compact sandstones.