Evaluation of hydration of Permian basalt and tuff in Sichuan Basin based on S-wave spectrum, nuclear magnetic resonance integral area, and effective porosity

Hydration of rock during drilling will lead to wellbore instability. The wellbore stability can be effectively improved by accurately evaluating the hydration damage of rocks. However, there are few studies on the hydration damage of volcanic rocks. Based on the S-wave frequency domain, nuclear magnetic resonance and effective porosity, this article establishes a hydration damage variable, and discusses the influence of hydration on the microstructure, acoustic properties and mechanical properties of basalt and tuff. The results show that volcanic rocks produce new cracks during soaking, accompanied by mineral spalling and clay expansion. The correlation between the new hydration damage variable and the existing hydration damage variable is greater than 0.8. At the same time, the stress-strain curve simulated by the hydration constitutive model is in good agreement with the results of uniaxial compression experiments, and the average relative error of the elastic parameters of the two is small. The average relative errors of the peak stress, peak strain, and elastic modulus of basalt are 2.45%, 1.07%, and 1.72%, respectively, and the average relative errors of tuff are 1.49%, 0.45%, and 3.55% respectively. This study provides a new idea for evaluating the hydration damage of volcanic rocks.