Experimental study on the impact of perpendicular and parallel bedding planes on the physical and geomechanical characteristics of carbonate rocks

The lithological, textural, acoustic, and geomechanical characteristics of various carbonate rocks from the El-Heiz, Khoman, and Ain Giffara formations in the Bahariya Oasis of the Western Desert, which serve as analogues for reservoirs in the region, were studied. High-strength rocks were identified from the uniaxial unconfined compressive strength (UCS), tensile strength (t), point-load strength (IS50), and Schmidt hammer rebound (SHR) values. Regression analysis was used to derive various correlations between the acoustic and geomechanical properties, and these associations were interpreted in light of the microfacies and diagenetic processes. Petrography revealed a total of 4 lithofacies of dolosparite, dolomicrite, foraminiferal wackestone (FW), and foraminiferal grainstone/packstone (GMF) in the Khoman Formation, and three microfacies of vuggy dolostone, sandy dolostone, and marly dolostone in both of El-Heiz and Ain Giffara formations. The most pronounced recorded diagenetic features in the Khoman, Ain Giffara, and El-Heiz formations are cementation, followed by recrystallization, dolomitization, neomorphism, and micritization. Significant correlations were discovered, particularly between the UCS, SHR, and acoustic velocities. The UCS values of carbonate plugs drilled parallel to the bedding planes in the Ain Giffara, El-Heiz, and Khoman formations were lower than those drilled perpendicular to the bedding planes. These findings suggest that rock failure can occur along bedding planes, which are effective weak planes, and a smaller bedding angle in these rocks is favorable for fracture extension in the direction of SHmax during the hydraulic fracturing process. The tensile strength vs. UCS relationship values do not agree with the typical tensile strength assumption (0.1 of UCS) provided by various authors, so care must be exercised when predicting these values in the geomechanical modeling of carbonate formations. Drilling wells into the subsurface should be performed at a lower attack angle to enable easier drilling and more stable holes. The empirical relationships with moderate/high correlation coefficients established here allow significant rock parameters to be computed using regularly measured parameters, allowing rocks to be evaluated considerably more rapidly and effectively.