Pulsating fracturing, as a new technology for unconventional oil and gas exploration, enables to enhance stimulated reservoir volume (SRV) effectively, which further helps to improve well performance. It is of great importance for the evaluation of fracturing performance and optimization of fracturing parameters by accurately calculating variables from formation impairment during pulsating fracturing treatment. Based on the principle of conservation of energy, a novel theoretical model describing the evolution of rock damage was proposed by analyzing energy evolutionary characteristics from the hysteresis loop of rock stress‐strain curve while the treatment. This model was in a good agreement with experimental data. In this paper, our study indicates that the rock damage is caused by the accumulation of damage in each cyclic loading and unloading process during pulsating fracturing. Moreover, the cumulative rock damage would increase with the increment of the number of cyclic loading and unloading. Conversely, the rock strength is negatively correlated with cyclic number. The cumulative damage variable approximates to one as the rock breaks. Additionally, the frequency and the stress level of pulsating fracturing have an obvious impact on the evolution of rock damage. The optimization of these parameters can help to accelerate the rock damage and reduce the corresponding rock strength. The speed of rock damage can be accelerated with the enhancement of the stress level at the later period of the step loading, which facilitates the increment of cumulative damage variable. Our new model provides a guideline for predicting the initial rock damage during pulsating treatment.

Acidizing, as an essential approach for well stimulation of sandstone or carbonate reservoirs, greatly affects the brittleness of the rock mass. Therefore, it is of great significance to develop a scientific brittleness evaluation methodology for the acid-corroded rock. In this paper, firstly, a damage constitutive model considering the compression hardening process of the acid-corroded sandstone under uniaxial loading is established and verified. Then, the evolution formulae of the relevant mechanical and fitting parameters are derived, and the stress-strain curve of the sandstone subjected to acid corrosion with soaking time is predicted. Finally, a theoretical model for evaluating the brittleness index (BI) of the acid-corroded sandstone based on energy evolution theory and damage constitutive relation is proposed. Based on this model, the BI of the sandstone subjected to acid corrosion is calculated and analyzed, and the BI of the acid-corroded sandstone with the soaking time is predicted. Results show that the BI of the sandstone is negatively correlated with the soaking time, and the rate of descent of the BI decreases with the increment of the soaking time. In addition, the decline degree of the BI has a negative correlation with the pH value. On the other hand, the temperature (25°C, 50°C, and 75°C) has greater weakening effects on the BI compared with the impact of the pressure (5 MPa, 10 MPa, and 15 MPa). Besides, days 50 and 120 are two turning points where the decreasing rates of the BI change from rapid to slow and slow to almost constant, respectively. Furthermore, a coefficient (⁠ $θ$⁠) is proposed to quantify the effect of the acid corrosion, and some suggestions are provided for the application of the acidizing treatment.