Rock damage evolution model of pulsating fracturing based on energy evolution theory

Abstract

Abstract 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.

Keywords

• dissipative energy
• elastic energy
• energy evolution
• pulsating fracturing
• rock damage