On the damage constitutive model for hydrated shale using CT scanning technology

• Proposed a novel characterization method for the damage of shale due to hydration.
• The evolution law of damage variable was determined by X-ray CT scanning tests.
• Proposed a novel damage constitutive equation for hydrated shale.
• This constitutive equation could accurately simulate the complete stress–strain curves.
• This novel method could be used to help solve the shale hydration problem for the analysis of wellbore stability..

A novel characterization method for identifying hydrated shale damage characteristics is presented using X-ray CT (computed tomography) scanning technology and damage mechanics. Furthermore, a constitutive damage model was proposed based on the evolution equation of the damage variable for hydrated shale. On this basis, a theoretical method for quantitatively describing the mechanical effects caused by chemical reactions can be obtained via the integration of the aforementioned methods. X-ray CT scanning was conducted on shale samples from the Wufeng-Longmaxi Formation to investigate the internal damage and hydrated shale evolution laws. Uniaxial compression tests were utilized to investigate the complete stress–strain curves during the different hydration stages. The results indicated that the damage variable gradually increases with increasing immersion time. The damage variable growth rate is greater during the initial stage, but it slows with increased immersion time. The complete stress–strain curves simulated by the damage constitutive model are relatively consistent with the experimental results. The results suggest that this model accurately describes the mechanical effects induced by shale hydration. This method could help to improve research methods and chemically and mechanically coupled wellbore stability analyses.

To study the hydrated damage and its evolution laws of shale, a novel quantitative method of damage characteristics during hydrating was proposed by using the X-ray CT scanning technology, the theory of damage mechanics and the digital image processing. On this basis proposed a novel damage constitutive model for hydrated shale, this model could simulate the complete stress–strain curves for hydrated shale.Figure optionsDownload high-quality image (338 K)Download as PowerPoint slide