ALBERT

Description: Hydraulic fracturing is a widely used technique applied in unconventional reservoirs to generate large fracture networks. Interactions between hydraulic fracture (HF) and natural fracture (NF) can impact the fracture topology and thus the subsequent productivity. Despite a large number of studies on HF–NF interactions, the HF propagation path is normally judged based on ad-hoc criteria to decide whether crossing or deflection occurs and the mechanism behind has not yet reached a unified understanding. Here, we use a phase-field model (PFM), which is based on a unified fracture propagation criterion, to investigate the influence of in-situ stress, fracturing operational parameters and NF orientation and strength. We analyze the mechanism behind different propagation patterns resulting from different kinds of NFs—non-cemented and cemented ones under different conditions. In particular, we compare the total energies between the symmetric propagation and asymmetric propagation to verify the minimum energy propagation path. Our results indicate that a higher stress anisotropy more likely leads to HF–NF crossing and a less fracture complexity. Injection rate influences propagation speed and fracture complexity. Within a certain range (30°, 45°, 60° in this study), the larger the approaching angle is, the more complex the fractures become. With the increasing strength contrast between NF and rock matrix, the material heterogeneity increases, encouraging HF to form complex fractures. Opening more strongly cemented NFs, which act as a barrier for propagation, consumes more energy than HF propagation outside the interface. Lower stress anisotropy and higher injection rate lead to higher initiation pressure, requiring more energy for propagation.

Description: Drift-bounce resonance between ultralow frequency (ULF) waves and ions is essential for ion energization in the magnetosphere. Here, we present the first comprehensive study of drift-bounce resonance in the dayside outer magnetosphere, where off-equatorial magnetic field minima would strongly distort ions' bounce and drift motion. A generalized theory is proposed, in which the effects of off-equatorial minima, time-evolving fields and ion bounce motion are taken into account. In consequence of these effects, ion pitch angle distributions undergo dramatic changes. In the presence of off-equatorial minima, the time-of-flight effect of ion bounce motion forms latitude-dependent dispersions besides “paw-track shaped” structures, while evolving wave fields cause time-dependent phase shifts in “paw-tracks.” All the predicted signatures have been confirmed by 5 years of Magnetospheric Multiscale spacecraft data and numerical simulations. These results allow us to better understand the interactions between ULF waves and thermal ion species in global magnetospheric dynamics.

Description: In this study, we investigated the phase stability of Al-free and Al-bearing superhydrous phase B (shy-B) up to 55 GPa and 2500 K. In comparison with Al-free shy-B, the incorporation of 11.7 wt.% Al2O3 in shy-B expands the stability by ∼400-800 K at 20-30 GPa. The determined dehydration boundary for Al-bearing phase D indicates that it could be present even at normal mantle geotherm conditions at 30-40 GPa. Up to 23.8 mol.% Al2O3 can be dissolved into the structures of akimotoite and bridgmanite as a result of the decomposition reactions of Al-bearing shy-B and phase D between 20-40 GPa. Results of further experiments indicate that δ-AlOOH is the stable hydrous phase coexisting with Al-depleted bridgmanite at pressures above 52 GPa. This study shows that the incorporation of Al in dense hydrous magnesium silicates can have a profound impact on our picture of the water cycle in the deep Earth.

Description: Hydraulic transport properties of fractures not only control production flow rates in geo-energy reservoirs, but also affect potential leakage in waste/energy storage reservoirs. Here, we performed shear-seepage tests on tensile fractures in sandstone and shale samples under varying effective normal stress conditions. The experimental results show that hydraulic transmissivity of sandstone fractures decreases with imposed shear stress, which may be caused by elastic-plastic deformation of local asperities on the fracture surface. For shale fractures, hydraulic transmissivity stays almost constant at the initial elastic loading stage, followed by a rapid increase until reaching peak shear stress. We interpreted it as a result of brittle damage accumulated on the shale fracture surface. When progressive sliding persists and shear stress remains nearly constant, the corresponding transmissivity is found to be dependent on applied normal stress for both sandstone and shale fractures. This is possibly due to competition between fracture dilation and development of impermeable gouges. The computed tomography analysis reveals that there is a positive correlation between final fracture transmissivity and final sandstone and shale fracture volumes. The comparison of 3D topography analysis of fracture surfaces before and after shearing demonstrates that the sandstone fracture surface gets smoother locally, whereas the local shale fracture surface becomes rougher. In addition, the wear area of sandstone fracture surface is notably larger than that of shale fracture surface under shearing conditions. Our experimental results highlight that shear-induced transmissivity evolution of a tensile fracture depends on the deformation-damage mode of asperities and on applied effective normal stress.

Description: The WHU-GRACE-GPD01s models are the latest monthly gravity field solutions recovered from GRACE intersatellite geopotential difference (GPD) data processed at the School of Geodesy and Geomatics, Wuhan University, China. The intersatellite GPDs are estimated from GRACE Level-1B (RL03) data based on the improved energy balance equation and remove-compute-restore (RCR) technique, and the background models are consistent with GRACE Level-2 processing standards document (RL06). Further details are presented in Zhong et al. (2020, 2022). The WHU-GRACE-GPD01s models include two sets of GRACE monthly solutions: one is the unconstrained monthly solutions with the maximum degree and order of 60, the other is the constrained monthly solutions up to the maximum degree and order 96 with Kaula regularization constraint, and the optimal regularization parameter is determined using variance component estimation (VCE). This work is supported by the National Natural Science Foundation of China (No. 41974015, 41474019, 42061134007) and the Project Supported by the Special Fund of Hubei Luojia Laboratory (Grant No. 220100004).

Description: In order to understand the effect of fluid-induced alteration on the Sm-Nd isotope systematic in apatite, a series of fluid/apatite reaction experiments, which involve reacting the well-characterized Durango fluorapatite with CO2 ± CaCO3-, NaF- or HCl ± CaCl2-bearing solutions with a known 143Nd/144Nd ratio, were conducted at 800 or 600 °C at 200 MPa. In experiments involving CO2-H2O ± CaCO3, the fluorapatite grains did not react with the solution, such that the Sm-Nd isotopic system was undisturbed. In experiments involving NaF, the fluorapatite grains were partially to completely altered. During the alteration process, REE mobilization was retarded via the coupled substitution Na+ + REE3+ = 2Ca2+ due to the high activity of Na in the fluid. Because the REE were not mobilized, the 147Sm/144Nd ratios remained constant. However, the 143Nd/144Nd ratios were slightly altered due to small degrees of Nd isotopic exchange between the fluid and fluorapatite. In experiments involving HCl ± CaCl2, the fluorapatite grains were partially altered, and the REE were variably leached from the altered fluorapatite. Leaching of REE was accompanied by an increase in the 147Sm/144Nd ratio, which is related to the higher compatibility of Sm in the fluorapatite structure and the lower mobility of Sm in Cl-bearing fluids. Although the 147Sm/144Nd ratios were strongly affected, the 143Nd/144Nd ratios experienced only a small change, which is related to the slow rate of transport for Nd between reaction-front fluid and bulk fluid. In general, the experimental results indicate that fluid chemistry is the main factor controlling the response of the Sm-Nd isotopic system to fluid-induced alteration. The 147Sm/144Nd ratio of apatite can be highly modified, and in turn the Sm-Nd isotopic system is disturbed when the fluids are rich in ligands that are able to facilitate REE mobilization and fractionation. Therefore, a thorough evaluation of the fluid-rock history, along with the conjectured fluid chemistry, is necessary before using apatite Sm-Nd isotopes as geological indicators.