Geomechanics for Energy and the Environment最新文献

Methane hydrate extraction from unconsolidated reservoirs can face challenges due to excessive sand production in the wellbore. Sand production has long been a concern in petroleum engineering and has been extensively studied by researchers. This study investigates sand production in gas-water two-phase flow through numerical simulations. The simulations incorporate the discrete element method (DEM) and resolved computational fluid dynamics (CFD) to model the solid-fluid interaction，which allows for simulating the particle movements and capturing the variations in hydraulic properties of the granular sample at a particle scale. Additionally, a volume of fluid (VOF) method is employed to simulate the two-phase flow. The numerical model provides insights into the gas movement process within the granular matrix and visually depicts the microscopic mechanisms of particle migration during methane hydrate extraction. The results of the study demonstrate that the model incorporating gas injection, which involves injecting a predetermined volume of gas at the inlet to the fluid model, yields a higher mass of produced sand compared to the model without gas injection. Furthermore, as the volume of gas injection increases, the produced mass initially rises and then declines. In addition, parameter analysis shows that the pattern of sand production differs between the model with a higher fines content and the model with a lower fines content. With the increase of hydraulic gradient, the produced mass increase.

Post-mortem analysis of earthquakes induced by fluid extraction or injection is often complicated by the uncertainty in the location and geometry of the causative fault. The 2011 Lorca earthquake in southeast Spain is believed to be triggered by long-term groundwater withdrawal, causing slip along the Alhama de Murcia Fault (AMF) dipping northwest. However, the regional InSAR deformation data can be equally fit by AMF and an unmapped fault located approximately 5 km west of AMF and dipping southeast, which creates an ambiguity in the causative fault that hosted the earthquake. Here, we show that the assumptions of elastic dislocation, undrained deformation, and decoupling between flow and deformation processes contributed to the ambiguity, which can be resolved by conducting a fully coupled analysis that provides additional constraints on the problem. We test that hypothesis and propose that the Lorca earthquake was likely caused by the rupture of a southeast dipping fault plane, which is antithetic to AMF. We build a mechanistic model of groundwater withdrawal over the time period of interest (1960–2010) that includes pressure diffusion, aquifer contraction, crustal unloading, and basement expansion mechanisms. The model identifies the difference in pumping-induced loading of the two faults: poroelastic compression and down-dip shear on AMF vs. tension and up-dip shear on the antithetic fault. We demonstrate that two-way coupling between flow and deformation processes plays a crucial role in the natural selection of the earthquake-inducing fault and holds the potential to detect hidden faults in the case of anthropogenic triggering.

The cessation of hard coal mining in the Ruhr Basin in 2018 marked the region's transition to the post-mining phase. Controlled mine water rebound induces changes in the subsurface stress conditions, as pore pressure increases locally. Presently, mine water rebound is observed in the eastern Ruhr Basin (water province “Haus Aden”) along with associated microseismicity. Furthermore, post-mining challenges might comprise the potential risk of fault reactivation, which is addressed in this study by conducting a fault slip assessment. Based on subsurface coal seam mapping data, a 3D structural model for the NE part of the “Haus Aden” water province has been constructed to serve as the basis for identifying the most vulnerable fault trends and types of the structural inventory. Slip tendency analysis, considering normal faulting conditions, revealed NW-SE to NNW-SSE trending normal faults to be most susceptible to reactivation. Probabilistic fault slip assessment, focused on NW-SE to NNW-SSE trending normal faults mapped within the “Heinrich-Robert” colliery, show no fault reactivation potential for a mine water rebound up to a level of 640 m below ground. Assuming hydrostatic conditions in the vicinity of the faults, friction coefficients are only partially exceeded for high differential stresses. In addition, a novel workflow is used to model the spatial variability of the frictional fault strength as input for a fault stability analysis, exemplified for a selected NNW-SSE trending normal fault. For considering hydrostatic pore pressure, results show that the fault consists mainly of stable, but also unstable, horizontally elongated patches. These findings question the conventional simplified approach of using a single constant friction coefficient for fault stability analysis.

Increase in surface roughness by corrosion processes has long been neglected as potential factor influencing pile setup. However, recently there has been an increasing number of studies who referred pile setups largely or solely to corrosion and sand incrustation. Only limited research has been conducted to assess the potential impacts of corrosion directly on pile capacity development. Therefore, we sampled steel and crust surfaces from a steel monopile having been aged for ∼four years in sand. Surface roughness measurements and interface direct shear testing were performed to quantify changes for friction angles. The impact of friction angle changes on pile capacity were calculated using ICP-05 and UWA-05 for a large- and small-diameter geometry and referenced by field data. We can show that corrosion can significantly contribute to temporal pile capacity gains. Evidence have been found that the maximum and critical interface friction angles evolve differently considering the same changes in roughness. Also, differences in shearing behavior to literature were observed, being potentially a result of the naturally corroded surfaces sheared in our study. A strong, maybe exaggerated sensitivity of the capacity prediction approaches to pile diameter was observed. Effects causing an increase in surface roughness, should be reconsidered as an important factor influencing pile setup.

Global warming and climate change significantly affect ground temperature and flow patterns. Moreover, areas prone to cracking experience intensified temperature and moisture variations. Therefore, the aim of this study is to investigate ground temperature and moisture dynamics considering soil-atmosphere interaction through a coupled thermo-hydraulic analysis. Heat transfer, advective, and non-advective fluxes were simulated using CODE_BRIGHT finite element program to study water flow and energy transfer within the soil. Statistical analyses were conducted using an existing dataset to match the crack geometry with previous studies and find the best distribution for the width-to-depth ratio of cracks ($C_R$) as a dimensionless parameter. The results indicated that $C_R$ variations follow a lognormal distribution. Numerical modeling scenarios were developed using statistical analysis results. The findings indicate that temperature variations decrease exponentially with depth, while surface soil temperature shows higher uncertainty due to atmospheric temperature fluctuations. Collecting various temperature trends in cracked soil at different time intervals, defined a limited region as the maximum range of temperature variations ($∆T$). Results reveal that $∆T$ in cracked soil can vary up to 4 times higher than intact soil. For the prediction of $∆T$, considering the impact of climate variations on cracked soil, a 3D boundary surface was developed based on two variables: soil depth ($z$) and crack depth ($C_D$). Furthermore, an equation for estimating $∆T$ for uncracked soils was proposed. Additionally, cracked soil showed approximately 1.4 times higher desiccation rates than uncracked soil. Deeper cracks exhibited even more severe desiccation rates, being about 1.2 times higher.

Stimulation is a must for commercial development of tight sandstone hydrocarbon reservoirs. Cryogenic fracturing using liquid nitrogen (LN) is a promising clean technique for efficiently stimulating reservoir rocks given its waterless nature. We developed a fully coupled thermo-mechanical (TM) model that incorporates strain-based damage theory for simulating LN cryogenic cracking in tight sandstone. Particularly, the compressive and tensile strengths, Young’s modulus, and thermal expansion coefficients and conductivity are designated as dynamic functions of the damage variable during the TM coupling process. Then the initiation, propagation, and cessation of multiple cracks from a borehole within a 2D heterogeneous tight sandstone plate were systematically scrutinized. Cryogenic cracks are found to emerge in short and long forms. In accordance with experiments, multiple long cracks emanate radially from the borehole along the maximum horizontal stress direction. In the investigated parameter ranges, the fracture morphology, including numbers, lengths, and coverage, is susceptible to changes in in-situ stress, Young's modulus, and thermal conductivity, but relatively insensitive to the variations of heat transfer coefficient and sandstone density. These results deepen our understanding of cryogenic shock on tight sandstone and provide a theoretical reference for designing cryogenic treatment operations.

Sediment consolidation via microbial induced carbonate precipitation (MICP) aligns with the principles of sustainable development in resource utilization. This study aimed to explore the solidification potential and mechanisms of integrating nano-SiO₂ as a supplementary material in MICP-treated sediment under various conditions, employing permeability, unconfined compression strength (UCS), X-ray diffraction (XRD), scanning electron microscopic (SEM), and adsorption techniques. The results demonstrated a reduction in permeability and an increase in UCS in sediment treated with ≤0.1% nano-SiO₂-assisted MICP. The factors contributing to solidification potential followed a specific order: Ca²⁺ concentration > OD₆₀₀> nano-SiO₂ dosage > biochemical reaction time. When combined with MICP, nano-SiO₂ at concentrations below 0.05% promoted the transformation from aragonite to calcite. Furthermore, nano-SiO₂ triggered the creation of early-stage C-S-H gels, aged viscous-like silicate gels, and spurrite [Ca₅(SiO₄)₂CO₃] to cement the sediment. Additionally, the micro filling of nano-SiO₂, minerals, and gel phases significantly bolstered the sediment's strength. Finally, the impressive adsorption capacity of nano-SiO₂ for Ca²⁺ (q_m = 0.26 mol/g) alleviated the toxicity of excessive Ca²⁺ on urease activity, thereby facilitating urea hydrolysis and CaCO₃ nucleation. The synergistic effect of nano-SiO₂ with MICP, involving cementation, filling, nucleation, and mitigation of Ca²⁺ toxicity, provides valuable insights for the sediment reinforcement applications.

It is crucial to comprehend soil thermomechanical behavior while designing underground energy structures to ensure safety. Studies on the soil response to thermal cycles in terms of the generation of thermal-induced volume change and pore water pressure are rare, and relevant research on how these responses might affect soil consolidation parameters and shear strength is very limited. To experimentally investigate the effect of thermal cycling under drained and undrained conditions on the isotropic consolidation parameters and triaxial shear strength of lateritic clay, this paper employs a temperature-controlled triaxial apparatus to conduct a series of isotropic mechanical consolidation and thermal consolidation tests, as well as undrained triaxial shear tests. The thermal response in volume change and pore water pressure are discussed, and the changes in the consolidation parameters, the preconsolidation pressure, and the shear strength are identified. It is concluded that increments of irreversible contraction of lateritic clay are observed during thermal cycling under drained conditions and further lead to a slight increase in the preconsolidation pressure. Nevertheless, thermal cycling hardly affects the swelling and compression index. The shear strength increases after being subjected to thermal cycling under drained conditions, which can be attributed to the increase in cohesion. When drainage is not allowed during thermal cycling, the generation of pore water pressure occurs during temperature variations and completely dissipates after the thermal cycling phase, and its reversibility is unaffected by the stress level and number of cycles. Furthermore, thermal cycling has little effect on the consolidation parameters, preconsolidation pressure, and shear strength. This study provides new insights into the mechanisms controlling the response of clay to thermal cycling.

Creep is an important mechanical property of fractured rock. To explore the creep mechanical properties and damage evolution law of surrounding rock mass under long-term external load during freezing construction, triaxial graded loading creep and CT tests are conducted under a freezing environment (−10 °C) on sandstone with different fracture dip angles. The test results reveal that the prefabricated fracture have a significant impact on the creep of sandstone under freezing environment. As the fracture dip angel increases, the creep duration, creep deformation, and long-term strength all decrease first and then increase, with lower values at 15° and 45°. At 0°、 15° and 45° dip angles, the rocks exhibit integrated shear through failure, whereas rocks with a dip angle of 75° and 90° exhibit the mode of tensile shear through failure. Notably, no microcracks or secondary cracks are observed in the rock samples. Finally, a nonlinear viscoelastic–plastic constitutive model of fractured sandstone is established via fractional calculus. Fitting the experimental curve with the theoretical model reveals that the proposed creep damage model could accurately describe the creep behavior of fractured sandstone under freezing, especially in the accelerated creep stage, which validates the reliability of the parameters.

In this paper, the one-dimensional rheological consolidation characteristics of multilayered saturated soil foundations under time-dependent loading and heating are investigated by considering the semi-permeability and the interface thermal resistance. By introducing the fractional derivative model and the thermos-elastic theory, a thermo-mechanical coupling model is established to describe the rheological properties of saturated soils. Semi-analytical solutions for strain, temperature increment, pore water pressure and settlement were derived through the Laplace transform and its inverse. The accuracy of the solutions proposed in this paper has been verified by comparing with existing solutions. The effects of different thermal contact models of the interface on the rheological properties of saturated soils under semi-permeable boundary are discussed, and the effects of fractional derivative order, constitutive material parameters, and thermal conductivity of soil on the thermal consolidation process are investigated. The results show that: neglecting the thermal resistance effect can result in an overestimates of the impact of rheological properties on the thermal consolidation process of saturated soils under semi-permeable boundaries; As the thermal resistance coefficient increases, the influence of soil thermal conductivity on settlement decreases.