In this day and age, the performance of oil and gas wells is severely affected by downhole and reservoir geomechanical problems. The key factor in predicting and solving these problems is a detailed study of the various aspects of the compressive and tensile behavior of the reservoir rock. In this study, the influence of mean sand grain size distribution as an important parameter influencing the petrophysical and geomechanical properties of the rock has been investigated using synthetic sandstone core samples. The results show that increasing the grain size range from 0.1 to 0.2 mm to 0.1–0.8 mm would result in a 23% and 64% decrease in rock porosity and permeability, respectively. However, such an unfavorable trend would be mitigated by the removal of fine particles from the rock composition. According to the results, there is a critical range of sand grains (i.e., 0.2–0.6 mm) above which rock permeability would be severely affected by a change in grain size. At the same compressive stress, the fine sandstones showed a more compressive deformation compared to the coarse specimens. In this regard, a direct relationship between rock compressive strength/Young’s modulus and sand grain size was found. The results also indicate that fracture in the fine specimen initiates at lower stress conditions than in the coarse sample. This implies that the weakest grain to grain boundary (GGB) is weaker in the fine-grained samples than in the coarse-grained specimens.

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