Quantitative Characterization of Elastic Parameters and Its Implications for Reservoir Evaluation: A Case Study on High Clay-rich Continental Shale

In recent years, the exploration and development of continental shale in China have garnered significant attention. However, there remains a dearth of research on elastic parameter calculation and sweet spot evaluation for high clay content and strong anisotropy shale. In this study, the elastic parameters C11, C13, C33, C44, and C66 of Gulong shale in the Qingshankou Formation of the Songliao Basin during the Cretaceous period were calculated using five predictive models for elastic coefficients based on core analysis and logging data. The accuracy of the calculation results obtained from different models was subsequently analyzed. First, based on the presence or absence of Stoneley wave patterns in acoustic logging, the estimation models for the five elastic stiffness coefficients can be categorized into two groups: models including ANNIE, M-ANNIE1, and M-ANNIE2 that utilize Stoneley wave logging data, and another group comprising M-ANNIE3 and V-reg models that do not require Stoneley wave logging data. By comparing the predictive performance with the measured values of C11, C13, and C66 from core data, our findings demonstrate that the elastic coefficient derived from the M-ANNIE2 model exhibits superior agreement with experimental results. However, it is worth noting that the V-reg model demonstrates broader applicability in wells lacking array acoustic logging data. The Thomsen parameters, obtained through accurate calculation of elastic coefficients, reflect the strength of anisotropy and indicate that the Young's modulus and Poisson's ratio are reduced under its influence. Therefore, geostress calculations should incorporate an anisotropic model. The present study establishes a novel method for evaluating sweet spots based on rock elastic parameters, and its efficacy is demonstrated through an analysis of horizontal well production. This fast and straightforward evaluation approach holds promise as a valuable reference for other shale formations characterized by high clay content.