Correlation characteristics and genetic mechanisms between lithofacies and mechanical properties of deep carbonate rocks

To deeply analyze the intrinsic relationship between lithofacies characteristics and the mechanical properties of deep carbonate rocks, the study focuses on the Ordovician Yingshan Formation in the Tahe area of the Tarim Basin. Drilling cores, rock thin sections, and rock mechanics experimental data were comprehensively analyzed to clarify the lithofacies types of the carbonate rocks. Rock components were quantitatively characterized using ImageJ software, and the correlations between different lithofacies and rock mechanical properties were revealed. Three main carbonate rock lithofacies were identified in the Yingshan Formation of the Tahe area: sparry grained limestone, fine-medium crystalline dolomite, and micritic grained limestone. Experimental results revealed significant differences in rock mechanical properties among these lithofacies. Specifically, the fine-medium crystalline dolomite exhibited the highest compressive strength, Young's modulus, and compressional and shear wave velocities, while the corresponding parameters of the micritic and sparry grained limestones decreased successively. The micritic grained limestone had the highest Poisson's ratio, while the sparry grained limestone had the lowest. Additionally, multiple regression models with three linear equations were developed to describe the relationships between lithofacies and rock mechanics, among which Model 2 achieved the best correlation (R²=0.777). The study elucidated the genetic mechanisms underlying the variations in rock mechanical properties across different lithofacies. Grain size and cement content were the main controlling factors. The compressional and shear wave velocities of grained limestone decreased with increasing grain size, accompanied by a corresponding decrease in compressive strength. In contrast, as cement content increased, the shear and compressional wave velocities significantly decreased, and a linear functional relationship was observed between particle size and cement content. The study is expected to predict the mechanical properties of deep carbonate rocks through detailed lithofacies analysis, thereby advancing the geological and engineering integration process of oil and gas production.