Abstract
The knowledge of stress dependence of rock elastic properties (e.g., wave velocities) plays an important role in broad practical scenarios such as seismic data processing in stressed formations, pore pressure prediction, hydrocarbon reservoir exploration and time-lapse monitoring. The classic acoustoelasticity (CAE) model is suitable to describe the stress dependence of rock elasticity within the limited stresses; however, its prediction for elastic properties is divergent without limit at the high-stress regions due to the internal linear stress-strain relationship. To address this problem, we first consider the continuous loading process to propose a nonlinear stress-strain relationship as an integral function of stress-dependent bulk compressibility and applied stress, and incorporate this new relationship into the acoustoelasticity model to improve its behavior at high stresses. The improved acoustoelasticity (IAE) model contains no additional adjustable parameters and provides the convergent predictions for wave velocities and moduli of dry and saturated sandstones at high stresses. The predicted results have a good agreement with ultrasonic laboratory measurements for dry and saturated sandstone samples in a wide stress range. Further, the IAE model is employed to establish a workflow to reveal the natural link between the microscopic pore properties and rock elasticity in combination with the pore structure model. The crack density and porosity are found to be approximately linearly correlated with the confining stress-induced elastic strain. This finding can be potentially used to characterize the microscopic crack properties with the macroscopic rock deformation directly. Our model and results help improve the understanding of seismic wave propagation in stressed subsurface fields, which has potential applications in rock mechanics and geophysical exploration.
Paper Information:
Chen Fubin, Zong Zhaoyun*, Yin Xingyao, 2024. Rock elasticity and crack property descriptions using an improved acoustoelasticity model with nonlinear stress-strain relationship. Geoenergy Science and Engineering, 241, 213211.https://doi.org/10.1016/j.geoen.2024.213211
