rock physics, acoustic emission, CT, in situ, tomography, FEM, DEM, FDEM, finite discrete element, hydraulic fracturing, DFN, earthquakes, fault, roughness, 声发射, 层析成像, 有限元离散元, 实验室地震, 水力压裂模拟, 岩石节理,结构面, 粗糙度, 颗粒形貌
Our recent collaboration with Prof Wei Hu on the acoustic emission in granular material under shear deformation has been published in PNAS. The high-time resolution observation of acoustic emission and dilation/compaction revealed intriguing similarities in fast and slow earthquakes. Read more.
Under quasi-static shear loading, the fault surface experiences local dynamic seismic activities. We found that the seismic activity is related to the stress concentration on interlocking asperities. This interlocking behavior (i) causes stress concentration at the region of contact that could reach the compressive strength, and (ii) produces tensile stress up to the tensile strength in the region adjacent to the contact area. Thus, different failure mechanisms and damage patterns including crushing and sub-vertical fracturing are observed on the rough surface. Asperity failure creates rapid local slips resulting in significant stress perturbations that alter the overall stress condition and may trigger the slip of adjacent critically stressed asperities. Read more.
We explore the systematics of frictional behavior, deformability and dilatancy of proppant-filled fractures to define the complex response to different fracture roughnesses and proppant mass loadings. We found a systematic transition in shear behavior from fracture-roughness-dominant to proppant-dominant caused by increased proppant mass loading that is augmented by increased proppant grain size. Read more.
We implemented grain based modelling (GBM) in the combined finite-discrete element method (FDEM) to study the mechanical behaviour of crystalline rocks. GBM in FDEM honours grain petrological properties and explicitly models grain boundaries. The simulation results demonstrated that GBM in FDEM predicted more realistic microscopic and macroscopic response of rocks than conventional FDEM models. Read more.
We conducted semi-circular bending (SCB) tests and monitor the AE activities during loading. We investigate the influence of pre-existing cracks on AE characteristics. Read more
We use FDEM to simulate an asteroid impact.
We conducted a laboratory study to investigate fault slip induced by injecting cold water into a hot fault under geothermal conditions, and we employ a 2D thermal-hydro-mechanical (THM) coupled hybrid finite-discrete element method (FDEM) to improve the understanding of the laboraory results. We show that slip will occur on stressed fault even if the overall stress condition is in the stable regime, and the slip is aseismic around the injetion point (Read more).
We conducted a in situ shear experiment on a sand column under micro-CT. We identified 15,961 individual particles and tracked their motion. We use FDEM to reproduce this experiment and investigate the granular shear behaviour at the microscopic scale (Read more).
In situ chemical oxidation processes: 4D quantitative visualization of byproduct formation and deposition via micro-CT imaging. We observe the chemical reaction process and the deposition of the byproduct in multiphase fluid (Read more).
A rotary shear apparatus (ERDμ-T) was designed, assembled, and calibrated to study frictional behavior, in situ and in operando, under X-ray micro-computed tomography (μCT). This technology allows us to observe how the sample deforms without perturbing the experimental conditions (e.g., pressure, temperature, and sample position) (Zhao et al., 2017).
A set of rotary shear tests were conducted on a rough rock surface to investigation the evolution of a laboratory fault. We (1) identified real contact areas on the fault surfaces and estimated sizes of contact patches by means of μCT image analysis, (2) observe the formation and evolution of off-fault fractures created by interlocking and breakdown of large asperities, and (3) quantitatively assess the complete energy budget (Zhao et al., 2018 ; Zhao et al., 2020).
ML methods artificial neural networks (ANN) and support vector machine (SVM) can provide effective and accurate approaches for relocating seismic events in a medium with unknown velocity structures. We conduct a laboratory fault slip experiment, and record acoustic emission (AE) events occurred during slipping. The locations of these events can be accurately assessed using machine learning methods. (a) ANN model results. (b) SVM model results. Figures show AE distribution overlaying on the photograph of the fault surface taken after the experiment. Circles indicate locations of AEs calculated by the ML models (note how they align with areas with white powder, i.e., gouge). Insets: locations of the two strongest events indicated by stars (AGU 2019 Poster ; Zhao and Glaser, 2019).
The rock surfaces are digitized using 3D surface scanner and surface roughness can be quantitatively assessed with spectral analysis method. Read more
Simulation of of laboratory rock failure tests showing the influence of in-situ stress on seismic activities (acoustic emissions) (Zhao et al., 2015).
Two hydraulic fracturing (HF) simulations were carried out to investigate the influence of reservoir geological conditions, including bedding planes and discrete fracture network (DFN), on the HF stimulation performance. HF induced fractures penetrate into the bedding planes and zigzag through the DFN (Zhao et al., 2014).
Simulation of dynamic loading test using Split-Hopkinson pressure bar (SHPB). The propagation of stress wave, compaction, and grain crushing are successfully simulated. Read more
We investigate the characteristics of progressive rock failure at different stress conditions using a laboratory experiment, coupled with ultrasonic tomography (UT) and numerical simulation. A time-lapse 2D UT observation was conducted on a granite slab under uniaxial compression. This test was then reproduced numerically by the combined finite-discrete element method (FDEM). This innovative combination of technologies depicted the entire deformation and failure processes at macroscopic and microscopic scales. Read more
