Real-time porosity inversion of rock based on the ultrasonic velocity and its compression-damage coupled model under triaxial compression.

It is of great significance to evaluate the stress state and mechanical properties of deep rock engineering, by inverting the real-time porosity of rocks. In this study, the triaxial compression tests and real-time ultrasonic velocity tests were conducted on siltstone under different confining pressures. Firstly, a nonlinear model for the evolution of rock ultrasonic velocity with axial strain was proposed, based on the characteristic that the ultrasonic velocity rapidly increases and tends to stabilize.

Accurate measurement techniques and prediction approaches for the in-situ rock stress.

The precise calculation and evaluation of the in-situ rock stress tensor is a crucial factor in addressing the major challenges related to subsurface engineering applications and earth science research. To improve the accuracy of in-situ stress measurement and prediction, an improved overcoring technique involving a measurement circuit, temperature compensation, and calculation method is presented for accurately measuring the in-situ rock stress tensor. Furthermore, an embedded grey BP neural network (GM-BPNN) model is established for predicting in-situ rock stress values.

Comparison and evaluation of overcoring and hydraulic fracturing stress measurements.

The stress measurements determined by both the overcoring (OC) and hydraulic fracturing (HF) methods in the Shuichang iron mine and Sanshandao gold mine were compared and evaluated, respectively. The results indicate that the independent OC and HF data in the two mines reveal the same dominant faulting stress regime. The σ orientations derived from the OC and HF methods in the Shuichang iron mine are dominantly oriented in the N81.

Study on Hydro-Mechanical Coupling Failure and Permeability Enhancement Mechanisms for Sandstone with T-Shaped Fractures.

The rise in the connectivity of the fractures is a key task in oil/gas and geothermal exploitation systems. Natural fractures widely exist in underground reservoir sandstone, while the mechanical behavior of rock with fractures subjected to hydro-mechanical coupling loads is far from clear. This paper employed comprehensive experiments and numerical simulations to investigate the failure mechanism and permeability law for sandstone specimens with T-shaped faces subjected to hydro-mechanical coupling loads.