Characterization of the Ductile and Brittle Behavior of Shale Through Plastic Strain, Mineralogy and Gas Flow

Summary Brittleness of reservoir rocks is one of the key rock properties essential for placement of horizontal wells and hydraulic stimulation to propagate fractures and create complex fracture network. This study presents a comprehensive method for characterizing the shale brittleness by analyzing the magnitude of plastic strain from rock mechanics tests, mineral content and benchmarked against gas flow of wells. Laboratory rock mechanics tests, including multi-stage and triaxial tests, were conducted to measure the plastic deformation characteristics of shale samples. These results were integrated with mineralogical data obtained from X-ray diffraction (XRD) and total organic carbon (TOC) analysis to quantify the magnitude of a fit for purpose brittleness. The ductile to brittleness transition was normalized and validated against gas flow from hydraulic fracturing in wells placed in different clay content intervals. Finally, this validated workflow was applied to a geologically analogous shale in a separate basin, enabling the identification of brittle intervals for optimal lateral well placement. The correlation between plastic deformation, mineralogical composition, organic content and brittleness were successfully calibrated with hydraulic fracturing performance, highlighting the critical impact of quartz, clay, and organic content on shale behavior. Quartz content was positively correlated with higher brittleness, while increased clay and organic matter content contributed to more ductility. The workflow enables reliable identification and quantification of brittle zones for hydraulic fracturing and lateral well placement, minimizing the risk of targeting ductile lithologies. Application of this methodology to a similar shale in another basin demonstrates its effectiveness as a benchmarking tool for unconventional reservoir characterization. This integrated approach enhances decision-making for efficient and sustainable hydrocarbon recovery. This study introduces a unique methodology that directly quantifies brittleness by linking plastic deformation measurements with mineralogical composition and validates the approach with hydraulic fracturing outcomes. Unlike traditional brittleness indices that rely solely on elastic properties or mineralogy without direct quantification, this approach incorporates the role of ductile deformation mechanisms, providing a more robust characterization of shale behavior.