Fracture Stage Research Articles

Assessment and optimization of maximum magnitude forecasting models for induced seismicity in enhanced geothermal systems: The Gonghe EGS project in Qinghai, China

Seismic activity induced during the development of Enhanced Geothermal Systems (EGS) is frequent and poses significant hazards. This study aims to accurately forecast the maximum magnitude (Mmax) of induced earthquakes to effectively manage seismic risks. Focusing on the EGS project in Gonghe County, Qinghai Province, we evaluated and optimized various widely-applied Mmax forecasting models, while also endeavoring to directly forecast maximum magnitudes in the post-closure phase. Initially, advanced deep learning models (such as PhaseNet and GaMMA) were employed to process seismic data, coupled with VELEST and HypoDD methods for earthquake relocation. Subsequently, four currently widely recognized maximum magnitude (Mmax) forecasting models (H14, NRBE, V16, and G17) were utilized to forecast and assess Mmax during nine hydraulic fracturing stages, six post-closure stages exhibiting tailing effects, and the entirety of the 2019–2021 period in the Gonghe EGS project. The findings indicate significant disparities in the efficacy of different forecasting models during hydraulic fracturing stages, with no model fully aligning with the complex physical mechanisms of induced seismicity. NRBE and G17 models tend to overestimate Mmax forecasting, potentially escalating production costs, whereas H14 and V16 models yield results closer to actual values but are susceptible to the influence of real seismic breakthroughs. Furthermore, distinct discrepancies were observed in the Mmax forecasting performance of the same model between hydraulic fracturing and post-closure stages. Attempts to directly forecast Mmax post-closure achieved certain efficacy, likely due to the cumulative injection volume exerting a degree of control over induced seismic activity in both stages. Lastly, to overcome limitations in current Mmax forecasting models, a hybrid model Y24, integrating the advantages of four forecasting models, was proposed, demonstrating higher accuracy and reliability in forecasting during both hydraulic fracturing and post-closure stages. The study's findings provide crucial technical support and decision-making basis for the seismic risk management of EGS projects or shale gas development projects employing hydraulic fracturing, underscoring their significance in ensuring the safety and sustainability of new energy and resource development endeavors.

Dynamic prediction of fracture propagation in horizontal well hydraulic fracturing: A data-driven approach for geo-energy exploitation

Accurate and efficient prediction of hydraulic fracturing fracture propagation is of utmost importance for unconventional reservoir development. Traditional numerical simulation methods require specialized domain knowledge and technical expertise, and machine learning approach can be an alternative predictive tool for fracture propagation. Additionally, existing neural networks cannot be directly applied to hydraulic fracturing scenarios influenced by multiple coupled factors. Thus, this study presents an innovative approach, “AE-ATT-ConvLSTM”, that integrates an additional Convolutional Layer, Autoencoder, and an Attention Mechanism Feature Fusion Layer into the architecture of a Convolutional Long Short-Term Memory (ConvLSTM) sequential image prediction network. This approach aims to predict fracture propagations in different fracturing stages of horizontal wells. The proposed model is trained on a sample dataset consisting of 5000 instances of hydraulic fracturing in horizontal wells. The dataset includes crucial data such as fracture propagation images, wellbore perforation images, natural fracture images, pumping schedules, and reservoir properties. The model achieves remarkable results, with an MSE less than 15 × 10−5, a maximum SSIM of 0.93, and an average FMAE less than 48. The research findings demonstrate that this method significantly enhances prediction efficiency and provides new insights for predicting fracture morphology and optimizing fracturing design.

A nomogram for predicting residual back pain after percutaneous vertebroplasty for osteoporotic vertebral compression fractures

To construct percutaneous vertebroplasty for predicting osteoporotic vertebral compression fractures (OVCFs) nomogram of residual back pain (RBP) after percutaneous vertebroplasty(PVP). Clinical data of 245 OVCFs patients who were performed PVP from January 2020 to December 2022 were retrospectively analyzed, including 47 males and 198 females, aged from 65 to 77 years old with an average of (71.47±9.03) years old, and were divided into RBP group and non-RBP group according to whether RBP occurred. Gender, age, comorbidities, fracture stage, body mass index (BMI), bone mineral density (BMD), visual analogue scale (VAS), Oswestry disability index (ODI) and other general information were collected; anterior vertebral height (AVH), anterior vertebral height ratio (AVH), anterior vertebral height ratio(AVHR), Cobb angle, intravertebral vacuum cleft (IVC), thoracolumbar fascia (TLF) injury, paravertebral muscle steatosis, injection volume and leakage of bone cement, bone cement dispersion pattern, anterior vertebral height recovery ratio (AVHRR), Cobb angle changes, etc. imaging parameters before operation and 24 h after operation were collected. Univariate analysis was performed to analysis above factors, and multivariate Logistic regression model was used to investigate independent risk factors for postoperative RBP, and Nomogram model was constructed and verified;receiver operating characteristic(ROC) curve and calibration curve were used to determine predictive performance and accuracy of the model, and Hosmer-Lemeshow (H-L) test was used for evaluation. The area under curve (AUC) of ROC was calculated, and Harrell consistency index (C index) was used to evaluate the predictive efficiency of model;decision curve analysis (DCA) was used to evaluate clinical practicability of model. There were 34 patients in RBP group and 211 patients in non-RBP group. There were no significant differences in gender, age, comorbidities, fracture stage, BMI, BMD, VAS, ODI, AVH, AVHR and Cobb angle between two groups (P>0.05). Univariate analysis showed 6 patients occurred IVC in RBP group and 13 patients in non-RBP, the number of IVC in RBP group was higher than that in non-RBP group (χ2=5.400, P=0.020);6 patients occuured TLF injury in RBP group and 11 patients in non-RBP group, the number of TLF injury in RBP group was higher than that in non-RBP group (χ2=7.011, P=0.008);In RBP group, 18 patients with grade 3 to 4 paraptebral steatosis and 41 patients in non-RBP group, RBP group was higher than non-RBP group (χ2=21.618, P<0.001), and the proportion of bone cement mass in RBP group was higher than non-RBP group (χ2=6.836, P=0.009). Multivariate Logistic regression analysis showed IVC (χ2=4.974, P=0.025), TLF injury (χ2=5.231, P=0.023), Goutallier grade of paravertebral steatosis >2 (χ2=15.124, P<0.001) and proportion of bone cement (χ2=4.168, P=0.038) were independent risk factors for RBP after PVP. ROC curve of model showed AUC of original model was 0.816[OR=2.862, 95%CI (0.776, 0.894), P<0.001]. The internal verification of model through 200 bootstrap samples showed the value of C index was 0.936, and calibration curve showed predicted probability curve was close to actual probability curve. H-L goodness of fit test results were χ2=5.796, P=0.670. DCA analysis results showed the decision curve was above None line and All line when the threshold value ranged from 6% to 71%. IVC, TLF combined injury, paravertebral muscle steatosis with Goutallier grade> 2, and bone cement diffusion with mass type are independent risk factors for RBP after PVP. The risk prediction model for RBP after PVP established has good predictive performance and good clinical practicability.

Competition among simultaneously stimulated multiple hydraulic fractures: Insights from DEM simulation with the consideration of fluid partitioning

AbstractStimulating long and persistent fractures from multiple perforations in horizontal wells plays a vital role in enhancing the recovery of hydrocarbons from unconventional reservoirs. However, interaction among fractures may lead to dramatic nonuniformity, but the mechanism that drives the competition still eludes explanation. We proposed an improved two‐dimensional discrete element model to simulate fluid competition and stress interaction among perforations in the same fracturing stage. The fluid partitioning is implemented by dynamically dividing the injected fluid into different perforations to maintain pressure consistency and fluid conservation. The model is validated by comparing the induced stress, fracture aperture, and the evolution of the fracture height and the injection pressure with theoretical models. The influences of the perforation friction, fluid viscosity and injection rate are examined systematically. Simulation results reveal that fluid competition tends to stimulate one dominant fracture with other perforations suppressed. The effect of increasing the perforation friction for promoting the fluid partitioning is not remarkable while using more viscous fracturing fluid helps to initiate more fractures at the perforations. With a higher injection rate all fractures can propagate to the borders but the asymmetrical fracture pattern cannot be avoided. Four typical fracture patterns are distinguished by changing operational parameters.

A Review of Fracturing and Enhanced Recovery Integration Working Fluids in Tight Reservoirs

Tight reservoirs, characterized by low porosity, low permeability, and difficulty in fluid flow, rely on horizontal wells and large-scale hydraulic fracturing for development. During fracturing, a significant volume of fracturing fluid is injected into the reservoir at a rate far exceeding its absorption capacity. This not only serves to create fractures but also impacts the recovery efficiency of tight reservoirs. Therefore, achieving the integration of fracturing and enhanced recovery functions within the working fluid (fracturing-enhanced recovery integration) becomes particularly crucial. This study describes the concept and characteristics of fracturing-enhanced recovery integration and analyzes the types and features of working fluids. We also discuss the challenges and prospects faced by these fluids. Working fluids for fracturing-enhanced recovery integration need to consider the synergistic effects of fracturing and recovery; meet the performance requirements during fracturing stages such as fracture creation, proppant suspension, and flowback; and also address the demand for increased recovery. The main mechanisms include (1) enlarging the effective pore radius, (2) super-hydrophobic effects, and (3) anti-swelling properties. Fracturing fluids are pumped into fractures through pipelines, where they undergo complex flow in multi-scale fractures, ultimately seeping through capillary bundles. Flow resistance is influenced by the external environment, and the sources of flow resistance in fractures of different scales vary. Surfactants with polymerization capabilities, biodegradable and environmentally friendly bio-based surfactants, crosslinking agents, and amino acid-based green surfactants with outstanding properties will unleash their application potential, providing crucial support for the effectiveness of fracturing-enhanced recovery integration working fluids. This article provides important references for the green, efficient, and sustainable development of tight oil reservoirs.

On Defect Evolution in EBM Additively Manufactured Ti-6Al-4V via In Situ Investigations.

This study concerned the in situ investigation of the defect evolution and fracture mechanism of additively manufactured (AM) Ti-6Al-4V under uniaxial tensile tests. In order to achieve this, microstructure characterization was initially carried out in order to identify the defects within the matrix of the candidate material. In situ testing was then performed, focusing on the spherical defect to observe its evolution under tensile loading. It was found that, before the fracture stage, the geometric evolution of the spherical defect towards an ellipse shape was dominated by the load in the tensile direction. In addition, the slip band density was found to be aggravated near the spherical defect due to the geometric discontinuity-induced stress concentration. During the fracture process, the defect geometry evolved as an irregular shape, which was mainly attributed to the micro-void-induced localized multi-axial stress state. The fracture analysis indicated that defects play a key role in crack initiation, leading to the fracture of LPBF materials.

Influence of Interaction between Microcracks and Macrocracks on Crack Propagation of Asphalt Concrete.

This paper aims to reveal the interaction relationship between microcracks and macrocracks and the influence of the interaction on the crack propagation behavior. A theoretical model of asphalt concrete was established for the interaction between microcracks with different crack densities and a macrocrack. And a meso-structure model of AC-13 dense-graded asphalt concrete was established by combining the Talyor medium method and the DEM (discrete element method). Macro and micro parameters, such as the stress-strain characteristics, crack evolution parameters, and crack tip stress field, were obtained through a semi-circular bend virtual test and used to study the characteristics of crack propagation under the interaction between microcracks and the macrocrack. The results indicate that the interaction has an effect throughout the process of asphalt concrete damage, and shows shielding and acceleration effects as the microcrack density changes. When the microcrack density is low (f3 ≤ 0.8), the crack propagation process, which is affected by the interaction effect, exhibits significant differences, and the interaction effect shows the shielding effect. When the microcrack density is high (f3 > 0.8), the fracture stage is mainly affected by the interaction effect, which shows the acceleration effect. The results provide a predictive theoretical and numerical model for low-temperature cracking of asphalt pavement, and theoretical support for the design, maintenance, and upkeep of long-life pavement.

Molecular dynamics simulation of CoCrFeMnNi with twin boundaries under high-speed impact

Based on the hybrid modeling framework of atomic scale and continuum, molecular dynamics (MD) was the method to study the shock wave, elastic-plastic dual-wave, and microstructure of CoCrFeMnNi high entropy alloy (HEA) with twin boundary under high-speed impact. The interaction between dislocation and twin interfaces is significant to the plastic deformation of HEA, but research on them as initial defects is still limited. Therefore, this article simulates and analyzes the impact velocity and twin spacing and proves that HEA with twin boundaries can synergistically improve strength and flexibility by comparing the wave simulation process and variation of spalling strength between HEA with TB and crystal Ni. The simulation results show that TB affects the propagation of shock waves in HEA and provides deformation sites for the generation of dislocations. Unlike single-crystal HEA, there is a smoother impact response process, and the maximum tensile stress during the fracture stage can reach 41 GPa, which is about 34.12% higher than that of single-crystal HEA. The research results may contribute to a better understanding of HEA with TB and help apply complex load scenarios such as explosive loads.

Revealing evolution law and failure mechanism of interface damage in concrete-encased CFST columns by acoustic emission technology

Concrete-Encased Concrete-Filled Steel Tubular (CFST) has extensive applications in high-rise buildings and bridge engineering as a high-performance composite structure. The severe bond failure between Concrete-Filled Steel Tubular and the outer concrete poses a significant threat to the integrity and safety of the structure. Considering the concealed and random nature of interface damage, this study proposes a real-time monitoring and evaluation method for Concrete-Encased CFST interface damage based on acoustic emission (AE) technology. Four groups of experiments on Concrete-Encased CFST column interface shear was conducted to investigate the influence of the number of shear connectors on the bond failure mechanism between CFST and the outer concrete. The signal characteristics of three kinds of AE sensors with different operating frequency ranges were analyzed to guide the selection of sensors according to the monitoring targets. The structural damage development trend has been recognized by analyzing the change rule of AE feature parameters. RA-AF correlation analysis has been used to identify the evolution law of cracks and the failure mechanism of the structure. The b-value analysis has been used to evaluate the damage severity of the structure. From the above three aspects, the damage evolution law and failure mechanism of the interface can be revealed. The results indicate that the R3α sensor is suitable for early warning of damage, the R15α sensor can be used for monitoring and warning of structural failure, and the R6α sensor can be used to describe and evaluate the whole process of damage. Based on the features of AE hit rate, cumulative hits, and cumulative energy, the damage process of Concrete-Encased CFST column interface can be accurately divided into the elastic stage, local slip stage, shear connector fracture stage, and slip stage. The RA-AF correlation analysis showed that the shear cracks were detected to develop rapidly before the peak load, and a significant number of tensile cracks caused by cracking of the outer concrete appear around the peak load. The changes of b-value can effectively reflect the magnitude of damage and record the occurrence of major damage.

Assessment of two recent hot dry rock thermal energy production projects

In this paper, we present analyses of laboratory and field data indicating that the current two-well, injection-production system, connected with multiple hydraulic fractures, is a very promising method for extracting heat from hot dry rock (HDR) systems to generate electricity. The current two-well system could be expanded to a three-well system consisting of one injection well and two symmetric producing wells connected via the central hydraulic fracture emanating from the injection well. To improve a uniform distribution of the injected fluid among all hydraulic fracture stages in the injection well, we advocate for field implementation of a newly designed well stimulation technique, the GeoThermOPTIMAL.We first present an analysis of the post-fracturing flow data obtained from an HDR geothermal injection well at the Utah FORGE Enhanced Geothermal System (EGS) research field site. The site is adjacent to the Roosevelt hydrothermal (HT) field. The objective of the study is to assess the effectiveness of well stimulation in extracting heat from the low-permeability, hot dry granitoid rock in the Utah FORGE research site. The study includes interpreting pressure falloff data obtained during the well stimulation process and employing laboratory-measured core data as a major input in the interpretation of the field falloff data. As a confirmation of the robustness of our analysis in Utah FORGE, we reviewed and analyzed the flow test results published for an injection-production doublet at the Blue Mountain EGS (Project Red) commercial site in Nevada. From the analyses of these two field tests, we have concluded that the interpretation and findings of the Blue Mountain EGS pilot test are consistent with the interpretation and findings from the Utah FORGE field research project test results.In summary, our engineering assessments began with laboratory experiments conducted on various core samples, including those from a granite outcrop and the Utah FORGE geothermal reservoir. These experiments aimed to measure key parameters such as matrix and fracture permeabilities, and porosities (km≈10−18m2, kf,eff≈10−15m2,ϕm≈10−1,andϕf≈10−4). These data served as guides and inputs for analytical and numerical solutions used to match the field pressure response of the geothermal wells. While we did not have core samples from the Blue Mountain EGS wells, we successfully applied the Utah FORGE analysis approach to the Blue Mountain site with cautious optimism.

Normal fault reactivation induced by hydraulic fracturing: Poroelastic effects

Numerous surface-felt earthquakes have been spatiotemporally correlated with hydraulic-fracturing operations. Because large deformations occur close to hydraulic fractures (HFs), any associated fault reactivation and resulting seismicity must be evaluated within the length scale of the fracture stages and based on the precise fault location relative to the simulated rock volumes. To evaluate the changes in Coulomb failure stress (CFS) with injection, we conduct fully coupled poroelastic finite-element simulations using a pore-pressure cohesive zone model for the fracture and fault core in combination with a fault-fracture intersection model. The simulations quantify the dependence of CFS and the fault reactivation potential on the host rock and fault properties, spacing between the fault and the HF, and the fracturing sequence. We find that fracturing in an anisotropic in-situ stress state does not lead to fault tensile opening but rather dominant shear reactivation through a poroelastic stress disturbance over the fault core ahead of the compressed central stabilized zone. In our simulations, poroelastic stress changes significantly affect fault reactivation in all the simulated scenarios of fracturing 50–200 m away from an optimally oriented normal fault. Asymmetric HF growth due to the stress shadowing effect of the adjacent HFs leads to (1) a larger reactivated fault zone following the simultaneous and sequential fracturing of multiple clusters compared with single-cluster fracturing and (2) a larger unstable area ([Formula: see text].1) over the fault core or a higher potential of the fault slip following sequential fracturing compared with simultaneous fracturing. The fault reactivation area is further increased for a fault with lower conductivity and a higher opening-mode fracture toughness of the overlying layer. To reduce the risk of fault reactivation by hydraulic fracturing under the reservoir characteristics of the Barnett Shale, Fort Worth Basin, it is recommended to (1) conduct simultaneous fracturing instead of sequential and (2) maintain a minimum distance of approximately 200 m for HF operations from known faults.

Numerical simulation of concrete strength based on microstructure and mineral composition analysis using micro-CT and XRD technology

The investigation of mechanical properties in porous materials, such as concrete, has been a significant area of interest in the fields of civil engineering and architecture. Traditional macroscopic mechanical testing methods are limited due to destructive experimental conditions, time-consuming procedures, and the inability to characterize internal structures. To overcome these limitations, researchers have utilized microscopic factors with micro-CT and simulation models. Different simulation methods demand mechanical parameters to effectively model the constituent materials; however, there exists variability in the amount and standard values of these input parameters, which leads to a decrease in the reliability of the obtained results. In order to tackle this issue, a novel approach is proposed, which integrates mineral component analysis using X-ray diffraction (XRD) and establishes coefficients to minimize the number of necessary input parameters. Simulation results demonstrate excellent agreement with experimental measurements, accurately reproducing the stages of elastic deformation, failure, and fracture in the stress-strain curve of concrete. Our findings reveal that changes in the concrete skeletal structure, microstructure, and mineral composition significantly influence compressive strength. Coarse aggregates and high-mechanical-performance minerals, in particular, have a substantial impact. Additionally, the mechanical properties show a significant linear relationship with the strength reduction coefficient of aggregates and concrete cores. In conclusion, the proposed method, combining CT scanning and XRD with FDEM, proves to be a reliable and practical approach for accurately assessing the mechanical properties of concrete. This methodology simplifies the intricate processes associated with the time-intensive parameter calibration, leading to a more efficient parameter allocation procedure. As a result, this method enhances concrete design, promotes a better understanding of parameter impacts, and enables accurate prediction of concrete behavior across diverse scenarios.

Study on Permeability Evolution Law of Rock Mass under Mining Stress

In order to study the stress–strain–permeability coefficient relationship of overlying strata in a fractured zone after coal mining, taking the Changcun coal mine in the Changzhi basin as an example, the permeability evolution law of coarse sandstone, fine sandstone, siltstone and mudstone during a stress–strain process was analyzed through a triaxial compression permeability test. The generalized model of the rock mass permeability evolution process under mining stress was summarized, and then a coupling model of the stress–water pressure–permeability coefficient of fractured rock was established based on the continuum model of rock mass. The results showed that the maximum permeability coefficient of different coal overburden types was quite different, and the peak strength of the rock mass preceded the maximum permeability coefficient during the rock mass failure process; the permeability coefficient first decreased and then increased, reaching its maximum value after the peak stress, which occurred during the strain-softening stage; the generalized model of rock mass permeability included the compaction stage, elasticity stage, stable fracture stage, unstable fracture stage, macroscopic failure stage and residual strength stage.

Influence of acoustic emission sequence length on intelligent identification accuracy of 3-D loaded rock’s fracture stage

Accurate prediction of impending disasters in underground projects is crucial and requires the identification of rock fracture stages. Currently, rock fractures are commonly analyzed using microseismic parameter statistics or individual waveform features for engineering disaster early warning systems. However, rock fracturing is a continuous process, and waveform sequences contain a wealth of information on fractures, which is often overlooked by existing research that generally neglects the information within continuous waveforms. In this study, we leverage acoustic emission (AE) data and employ a transfer learning approach with a convolutional neural network (CNN) to identify rock fracture stages under three-dimensional (3-D) stress paths induced by true triaxial compression tests. Failure experiments were performed on seven sandstone specimens under various 3-D stress paths. To fully utilize the characteristics of the crack rupture sequence, we introduce the concept of AE waveform sequence length. This concept integrates the discrete features of AE time–frequency images, thereby improving the CNN model’s performance. Utilizing waveforms of six different lengths (1, 2, 3, 5, 10, and 15) to train the neural networks, our findings reveal that a sequence length of 10 enables the CNN to effectively identify rock fracture stages under 3-D stresses with an accuracy rate of up to 90.4%. This demonstrates that appropriately increasing the sequence length to process the discrete features of AE waveforms structurally is a viable strategy to enhance CNN identification accuracy. Our results underscore that rock fracturing is a sequential process with significant inter-sequence correlations, which critically influence the CNN model’s ability to accurately identify rock fracture stages. These insights offer valuable theoretical contributions to the automatic monitoring of rock fracture stages in deep engineering projects.

Research on the factors influencing the width of hydraulic fractures through layers

The method of segmented hydraulic fracturing in the coal seam roof has proven to be an efficient technique for coalbed methane exploitation. However, the behavior of hydraulic fractures in multilayer formations with significant differences in mechanical properties is still unclear. This paper studied the variation in hydraulic fracture width at the coal-rock interface by employing experimental method with a true triaxial hydraulic fracturing experimental system and numerical simulation method. Results revealed that the hydraulic fracture more likely to expanded along the coal-rock interface instead of break through it with the small horizontal stress difference and low flow rate injection condition. And improving the injection flow rate lager than a critical value, the hydraulic fracture tends to break through the coal-rock interface. Hydraulic fractures in both mudstone and coal beds exhibited a trend of increasing and then decreasing of fracture width at the interface. Since the strength of the coal seam was lower compared to that of the mudstone, maintaining high pressure was no longer necessary when the hydraulic fracture crossed the interface and entered the coal seam, leading to a reduction in fracture width within the mudstone. During the later stages of fracturing, the entry of proppant into the coal seam became challenging, resulting in a phenomenon characterized by excessive fluid but insufficient sand. The time required for the fracture width to traverse the proppant was found to be inversely proportional to the difference in horizontal ground stress and the flow rate of the fracturing fluid. And it was directly proportional to the modulus of elasticity, permeability of the coal seam, and interface strength. The interface strength has the greatest influence on the width of hydraulic fractures. In conclusion, this study provides valuable insights into the behavior of hydraulic fractures in multilayer formations with varying mechanical properties. The findings contribute to a better understanding of the factors affecting hydraulic fracture width within coal seams, which can ultimately enhance the efficiency of coalbed methane exploitation.

Failure evaluation mechanism of cement sheath sealing integrity under casing eccentricity during multistage fracturing

A microannulus (MA) is the primary reason for sustained casing pressure in multi-stage fractured-shale gas wells. However, the effect of the casing eccentricity on the long horizontal section has not been considered. In this study, a full-scale integrity tester for cement sheaths is adopted to measure the cumulative plastic deformation. Numerical models are applied to evaluate the development of the cumulative plastic deformation and quantify the MA width considering casing centralization and eccentricity in the context of multiple loading and unloading cycles. Subsequently, the influences of the eccentricity distance and angle, cement-sheath mechanical variables, and different well depths on the cumulative sheath plastic deformation and sheath MA development are explored. The research results demonstrate that casing eccentricity significantly increases the cumulative sheath plastic deformation compared with that of the casing-centered condition. Consequently, the risk of sealing integrity failure increases. The accumulated plastic deformation increases when the eccentricity distance increases. In contrast, the initial plastic deformation increases as the eccentricity angle increases. However, the cumulative plastic deformation decreases after a specific loading and unloading cycle count. Affected by the coupled influence of the internal casing pressure and fracturing stages, the width of the MA in the horizontal section increased from the toe to the heel, and the casing eccentricity significantly increased the MA width at each stage, thus increasing the risk of gas channeling. Finally, an engineering case is considered to study the influence of casing eccentricity. The results show that cement slurries that form low and high elastic moduli can be applied to form a cement sheath when the fracturing stage is lower or higher than a specific value, respectively. The results of this study offer theoretical references and engineering support for the integrity control of cement sheath sealing.

Strike‐slip fault zone architecture and its effect on fluid migration in deep‐seated strata: Insights from the Central Tarim Basin

AbstractThe internal fault architecture is crucial in assessing the significance of faults in fluid migration. The development of overlapping zones between segments and subsidiary structures is characteristic of a strike–slip faults. However, their internal architectures and roles in fluid migration are still poorly understood. The Tarim Basin's recently identified strike–slip faults imply that the petroleum resource is hosted in caves that were formed by subsequent dissolution after the formation of the fault zones in carbonate rocks, indicating that the internal fault architecture may be closely linked to the accumulation of petroleum. We investigated the architecture of the strike–slip fault zone using field, geochemical, seismic and well‐logging data. The results revealed that the strike–slip faults contain flower‐like structures in their vertical profiles and an en échelon and ‘X’ conjugate pattern in their horizontal slices. The fault core may become more complex because of the flower structure as fault breccia, slip surfaces, hydrothermal veins, dissolved pores and caves develop, and the damage zone contains multiple stages of fractures with high dip angles. Compared with ‘X’ pattern conjugate faults, NE‐trending strike–slip faults have a more developed and connected fault zone. The fault core acts as a fast conduit for fluid transport and experiences significant elemental losses, and the elemental variations in the damage zone may relate in long‐term and relatively lower‐level fluid–rock interactions. Three fault zone architecture models were created, namely, a releasing bend, a restraining bend and a single segment, and their controlling impacts on fluid migration were addressed accordingly. Our findings imply that fluid migration and accumulation are more favourable at the releasing bend than at the restraining bend and single segment.

Formational stages of natural fractures revealed by U-Pb dating and C-O-Sr-Nd isotopes of dolomites in the Ediacaran Dengying Formation, Sichuan Basin, southwest China

Deep core (&amp;gt;4.9 km) from Ediacaran Deng IV Member algal dolomites in the Gaoshiti-Moxi block in the Sichuan Basin, southwest China, reveals multiple generations of dolomite-lined and dolomite-filled opening-mode fractures. Three progressive stages of fracture formation are marked by crosscutting relations visible in the core, by acoustic emission experiments revealing evidence of past stress directions, and by fluid inclusions, U-Pb ages, C-O-Sr-Nd isotope patterns, and rare earth element data for dolomite cements in fractures, which document ages and differing thermal conditions and fluid compositions during fracture. In calcite-filled fractures, U-Pb ages and carbon and oxygen isotope signatures vary greatly, indicating that fractures developed with intensified tectonic activity marked by regional structures and with enhanced diagenetic alteration. In stage I, WNW-striking opening-mode fractures formed that contain dolomite deposits precipitated from basinal fluids between ca. 549 Ma and ca. 532 Ma. At this time, the Sichuan Basin experienced Xingkai taphrogenesis (rifting) from the late Neoproterozoic to early Cambrian. The central Sichuan paleo-uplift was undergoing ENE extension, and preexisting ESE- and nearly E-W−striking faults were oblique to the ENE principal stress orientation. This led to a local stress field favoring dextral shear near fault zones accommodated by the fractures. In stage II, ENE-striking fractures that are younger based on crosscutting relations contain dolomite deposits from basinal fluids with ages from ca. 423 Ma to ca. 411 Ma. Contemporaneous with Xuefeng thrusting, the central Sichuan paleo-uplift was in a NNE-striking transpressional stress field, which likely further generated ENE-striking fractures. In stage III, nearly N-S−striking fractures formed in the Gaoshiti-Moxi block. High-temperature fluids related to the Permian Emeishan large igneous province invaded these fractures from ca. 260 Ma to ca. 256 Ma. At this time, the Sichuan Basin was uplifted under the influence of the Emei taphrogenesis in the late Permian, and the central Sichuan paleo-uplift was subjected to E-W−striking extension. In fractures in these carbonate rocks, micro-computed tomography imaging reveals that macropores (&amp;gt;10 μm, 12.1%−21.8%) and small pores (2−10 μm, 76.6%−86.1%) dominate the dolomite mineral deposits, and that there are few (1.6%−1.8%) micropores or nanopores (&amp;lt;2 μm). Medium-sized throats (1−3 μm) are the main connecting channels. We infer that fractures served as conduits for fluid migration, leading to the dissolution of matrix pores adjacent to the fractures. This secondary porosity not only enhances reservoir storage capacity but also augments reservoir connectivity. Our study shows that in situ U-Pb dating and full-diameter rock acoustic emission data can effectively constrain the timing of fractures. By integrating this information with regional tectonic sequences and fracture diagenetic sequences from combined relative timing, geochemistry, and rock mechanics evidence, we clarify the factors controlling fracture formation.

Mastering the art: Proficient finite element implementation and robust evaluation of a strain-hardening porous ductile material crack growth prediction model at finite strain

Accurate prediction of crack extension is crucial for ensuring the structural integrity of metal components exposed to diverse loads. While the Gurson model and its extensions are widely accepted for delineating ductile fracture stages, especially in porous materials with a rigid-perfectly plastic matrix, their efficacy diminishes in the presence of strain-hardening matrices. To address this limitation, our study introduces a robust numerical implementation and assessment of Perrin's model. In contrast to Gurson's approach, Perrin's model incorporates two distinct strain-hardening parameters derived from an intricate analysis of a strain-hardening hollow sphere subjected to axisymmetric loading.Moving beyond theoretical discussions, this paper actively engages in the rigorous evaluation of Perrin's model under various scenarios, encompassing isotropic, kinematic, and mixed isotropic-kinematic hardening conditions. The model's effectiveness is convincingly demonstrated through meticulous comparisons between numerical simulations and real-world experimental observations conducted on pre-cracked specimens.Facing challenges related to achieving global elastic-plastic convergence in large-scale simulations, our research introduces a sophisticated approach. Leveraging stiffness tangent moduli ensure the maintenance of quadratic convergence in global Newton method iterations. This not only enhances the reliability of our simulations but also underscores the practical applicability of our findings.The study also focuses on the necking and crack propagation of a cylindrical specimen through meticulous computational modeling. Our mesh captures intricate details and addresses stress gradients, revealing coplanar crack propagation contrary to prior beliefs. The confirmation of the cup-cone fracture effect challenges previous interpretations, emphasizing the critical role of void nucleation. This reinforces the credibility and applicability of our approach in advancing the understanding of material fracture behavior.In summary, this study significantly contributes to existing knowledge in fracture prediction models, offering a robust framework for predicting ductile fracture under substantial deformations. The presented findings pave the way for advancements in structural engineering, providing invaluable insights for optimizing the performance and resilience of metal structures in real-world applications.

Extrinsic-Riveting Friction Stir Lap Welding of Al/Steel Dissimilar Materials.

To obtain high-quality joints of Al/steel dissimilar materials, a new extrinsic-riveting friction stir lap welding (ERFSLW) method was proposed combining the synthesis advantages of mechanical riveting and metallurgical bonding. SiC-reinforced Al matrix composite bars were placed in the prefabricated holes in Al sheets and steel sheets, arranged in a zigzag array. The bars were stirred and mixed with Al sheets under severe plastic deformation (SPD), forming composite rivets to strengthen the mechanical joining. SiC particles were uniformly dispersed in the lower part of the welding nugget zone (WNZ). The smooth transition between the SiC mixed zone and extrinsic-riveting zone (ERZ) ensured the metallurgical bonding. The maximum tensile shear load of the joints reached 7.8 kN and the maximum load of the weld per unit length was 497 N/mm. The fracture occurred at the interface between the rivets and steel sheets rather than the conventional Al/steel joining interface. Moreover, ERFSLW can prolong the service life of joints due to three fracture stages. This method can be further extended to the welding of other dissimilar materials that conform to the model of "soft/hard".