bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydro-Geomechanical Observations During Multistage Hydraulic Stimulation at the Bedretto Underground Laboratory, Switzerland
Authors: Bröker K. , Ma X. , Gholizadeh Doonechaly N. , Hertrich M. , Hansruedi M. , Giardini D. , _ _ , Rinaldi A. P. , Clasen Repollés V. , Obermann A. , Wiemer S. 
Published: September 2023

ABSTRACT
A series of hydraulic stimulation experiments were performed in the Bedretto Underground Laboratory for Geosciences and Geoenergies in Switzerland to answer questions about the creation of an engineered geothermal reservoir in crystalline rocks. A 400 m long stimulation borehole was divided into 15 intervals by a multi-packer system. In this work, we present preliminary results of interval 8 in which two injection phases were performed with a 3.5 months gap in between. The two phases differ in the injected volume and injection protocol (pressure vs. flow rate controlled). Within the interval, we mapped a cluster of sub-parallel pre-existing open fractures that are reasonably well oriented for reactivation in the estimated stress field. The interval pressure and flow rate data from the injections reveal a reactivation of the pre-existing fractures, associated with a large increase in injectivity. A comparison of the expected stress field around the stimulation interval with the observed reactivation pressure indicates that the fractures were likely reactivated by hydraulic shearing. The reactivation is also supported by other data sets from the extensive monitoring network, e.g. distributed temperature and strain sensing.

INTRODUCTION
Engineered geothermal systems (EGS) have received increasing interest in recent years because they are considered a low emission, renewable energy source (Lu, 2018; Aghahosseini and Breyer, 2020). An EGS aims to extract geothermal energy from crystalline basement rocks with low permeability. The permeability is enhanced either by hydraulic shearing of natural fractures or shear zones, or by hydraulic fracturing of intact rock, or by a mixture of both (McClure and Horne, 2014). This permeability enhancement is often linked to induced seismicity, which can reach damaging levels if large fault zones are reactivated (e.g. Deichmann and Giardini, 2009; Evans et al., 2012; Ellsworth et al., 2019). To address this challenge, several scaled-down in situ hydraulic stimulation experiments have been conducted in underground research laboratories in representative crystalline rock types (e.g. Amann et al., 2018; Zimmermann et al., 2019; Schoenball et al., 2020; Fu et al., 2021).
Real-Time Seismic Wave Velocity Prediction for Accurate Source Location in Underground Mines Based on Machine Learning
Authors: Mukhamedyarova Z. , Suorineni F. , Maksut Z. , Meiramov R. , Yazici A. 
Published: September 2023

ABSTRACT
The objective of this study is to develop machine learning techniques to forecast seismic wave velocities in real-time amidst the constantly changing conditions of underground mining. As human-induced seismicity in underground mining can negatively impact productivity, safety, and operating costs, it is crucial to have an accurate predictor for the source of microseismic events. To simulate the dynamic conditions of underground mining, laboratory experiments using AE systems and concrete blocks mimicking homogeneous rocks were conducted. The concrete blocks were of various sizes with different hole diameters and lengths representing variations in extraction ratio with mine maturity. Stress-induced fractures were produced using a static cracking agent. The blocks were tested with the voids empty and filled with various cement to sand ratios representing backfill in mining. The data collected from AE measurements, such as seismic wave velocity, arrival time, AE hits, and energy, were utilized to train different machine learning models, including linear regression, neural networks, Random Forest Decision Tree, and Gradient Boosted Decision Tree. The Gradient Boosted Decision Tree model demonstrated the highest accuracy with a mean absolute error of 7.15 m/s. The capability to predict seismic wave velocity in real-time would lead to better identification of the location of seismic events, ultimately improving the safety and efficiency of underground mining operations.

INTRODUCTION
This study specifically examines seismicity caused by underground mining operations. A seismic event refers to the sudden release of energy from the Earth crust, which leads to the propagation of seismic waves. In the mining industry, this release of energy can result in damage to equipment, injury, or even fatalities, in which case it is referred to as a rockburst (Feng et al., 2019). The impact of rockbursts and seismicity on mine safety, productivity, and costs is substantial. Despite this, predicting rockbursts remains a challenging task due to limitations in current knowledge and technology (Trifu and Suorineni, 2009). To address this issue, the implementation of microseismic monitoring systems in deep underground mines has become vital in managing mining-induced seismicity. These systems are critical in the management of seismic hazards, thus enhancing worker safety and mining productivity.
A Three-Dimensional, Finite Element-Based Study of the Effect of Heterogeneities on Thermo-Hydro-Mechanical Deformation During Cold Fluid Injection
Authors: Chaiwan P. , Burtonshaw J. E. J. , Thomas R. N. , Paluszny A. , Zimmerman R. W. 
Published: September 2023

ABSTRACT
This paper investigates the effects of the injection of (relatively) cold CO2 into a saline aquifer, focusing on the effects that local heterogeneities may have on the geomechanical changes observed during injection. Representative properties of the Smeaheia site, a full-scale carbon storage site in the North Sea, are used in the simulation. The geometry of the Smeaheia site is represented by a simplified three-dimensional geometric model containing four rock layers, and a fault that spans multiple layers. Thermo-poro-elastic deformation is modeled using a finite element approach, with the coupled solution of fluid flow, heat transfer, and mechanical deformation of the Smeaheia site. The boundary conditions are based on in situ conditions at the Smeaheia site, along with fixed injection temperature and flow rate. The effects of injection rates, injection periods, injection temperatures, heterogeneities, fault, and fracture properties are investigated. The results show that the changes in temperature, pressure, and stresses are concentrated in the vicinity of the injection point, with a limited effect on the caprock away from the injection well. Thermal stresses dominate the overall stress reduction, shifting the stress state towards the failure condition. The flow rate causes a localized effect on the pressure field, due to the high permeability of the reservoir. Heterogeneity in the Young's modulus yields variations in deformation which are of comparable magnitude to the effects of cold injection.

INTRODUCTION
Cold fluid injection is a topic of interest in future sustainable technology for both geological carbon storage and geothermal energy. Fluids injected into the subsurface often have lower temperatures than in situ reservoirs (Li et al., 2021; Salimzadeh et al., 2018a). The temperature difference can induce thermal stresses, thermally driven fracture, and contraction of the rock caused by heat transfer between the fluid and reservoir fractures and rock matrix (Celia et al., 2015; Jeanne et al., 2014; Rutqvist, 2012; Taylor & Bryant, 2014).
A Split-Node Method for Modeling Pulse and Hydraulic Fracturing
Authors: Meng C. , Fournier A. , Jin W. 
Published: September 2023

ABSTRACT
Reservoir stimulation is akey technology to enabling carbon and renewable resources recovery from the subsurface. The combination of pulse- and fluid-driven fracture propagation has great potential to revolutionize the hydro-fracturing industry. In this study, we present a novel method that extends the existing traction-at-split-node method to allow mode-I fracture propagation in both dynamic and quasi-static time frames. We implement this method in an open-source code, Defmod, that adaptively alternates between quasi-static and dynamic governing equations. We introduce a quasi-linear weakening failure criterion that allows irreversible tensile failures. To couple the fracture development and fluid flow inside and outside the fracture, we introduce a method to modify the fracture's neighboring elements by an anisotropic permeability as a function of fracture width. To ensure mass conservation, we balance the fluid-injection volume with the fracture-opening volume, by defining virtual fluid sources in the neighboring elements. We first compare an example of two-dimensional (2D) pulse-driven fracturing with experimental results. Then we compare an example of 3D penny-shaped hydraulic fracture, developing from a pressurized borehole, against the analytical Kristianovich-Geertsma-de Klerk (KGD) solution.

INTRODUCTION
Numerically modeling tensile fracture propagation is of great interest in reservoir engineering (Chuprakov et al., 2011; Dahi-Taleghani and Olson, 2011; Jiang et al., 2015). Under in-situ stress conditions, natural rock failures are mostly in shear modes, such as fault activation, while tensile failures are sometimes attributed to magma/dike intrusions (Rivalta and Dahm, 2006; Aydin et al., 2006; Rutqvist et al., 2008). Induced tensile failure, typically hydraulic fracturing, has been widely used to enhance tight reservoirs’ permeability and greatly made unconventional hydrocarbon and geothermal resources accessible (Rubinstein and Mahani, 2015; Li et al., 2019). Several numerical methods have been applied to model hydraulic fracturing, such as the cohesive-zone method, extended finite-element method, and boundary-element method (Chen et al., 2021; Jin, 2018). We extend a well established traction-at-split-node (TSN) method, which has a strong track record for modeling dynamic fault ruptures (Day et al., 2005; Dalguer and Day, 2007), to model tensile failures.
Evolution of Wellbore Strain in Horizontal Wells for Production Evaluation
Authors: Ou Yuhao , Sharma Mukul M. , Zheng Shuang 
Published: September 2023

ABSTRACT
The azimuthally resolved wellbore strain and geometry change provides a direct measure of the wellbore locations that are depleted due to production. As pore pressure decreases due to production, the stress field around borehole changes resulting in casing deformation which can be measured by field-scale downhole tools with high azimuthal resolution. It is shown that the shape of the wellbore is different in producing sections/clusters and non-producing sections/clusters along the well. A pad-scale geomechanically fracturing-flow simulator is used to perform life-cycle simulation of a horizontal well, from dynamic fracture propagation to long term pressure depletion. High levels of mesh refinement are used to obtain very fine meshes in the near wellbore region to simulate the deformation of the rock and the casing along the wellbore. Axial and radial strain is obtained as a function of space and time. The results show: a) the total stress around the casing is larger than the wellbore pressure, which leads to compressive deformation of the casing. The magnitude of the casing deformation is different along and around the casing due to the non-uniform pore pressure distribution; b) producing sections/clusters of the wellbore deform less but show larger ellipticity; c) resolution needed in the deformation measurements lies in the precision range of current downhole tools; d) bending deformation can occur due to non-symmetric fracture geometry or pressure depletion. Measurement of the ellipticity of the borehole as a function of measured depth should allow us to identify sections of the wellbore that are depleted (producing fluid) and sections that are not.

INTRODUCTION
The application of hydraulic fracturing in horizontal well contributes to the production of hydrocarbon resources from unconventional reservoirs with ultra-low permeability in the past decade. In contrast to vertical wells generally stimulated with only one single fracture, horizontal wells have many fractures created in a sequence of stages. During the stimulation treatment of each stage, multiple perforated clusters are fractured simultaneously along the horizontal wellbore, creating high-conductivity pathway between the tight rock matrix and wellbore. Therefore, the surface area available for the transport of hydrocarbon is increased by 3 orders of magnitude, leading to a corresponding rise in production rate.
Effect of Micro-Scale Asperities on Shear Behavior of Artificial Rock Joints
Authors: Lee S. , Jeon S. 
Published: September 2023

ABSTRACT
Various devices such as Barton comb, optical and laser scanner are used to record surface geometries of rock joints for roughness measurement. Measurement resolution of the used device can vary significantly depending on settings and the nature of device. Ignoring the effect of resolution may result in misestimation of effective roughness because resolution determines how precise details are captured by the measurement. To improve our understanding on the proper resolution for roughness measurement, effect of micro-scale asperities on the shear behavior of rock joints is investigated in this study. Plaster joint specimens having regular sawtooth asperities of 0.4 and 0.8 mm lengths were generated using high quality 3D printer and silicone molds. Direct shear tests at four different normal stresses were conducted on them and the results show that the 0.8 mm asperities significantly increase the shear strength of joint specimens while 0.4 mm asperities do not. Together with the test results, main factors contributing to the results are also discussed.

INTRODUCTION
Since roughness is an important property of rock joints that affects their mechanical behavior, it should be investigated to analyze the stability of rock masses. To measure roughness, many different types of devices can be utilized to capture surface geometry of joints. Barton comb is a widely used tool to get 2D profiles of rock surfaces and more recently, laser and optical scanners are employed by many researchers to obtain their 3D geometries.
When quantifying the degree of roughness using various devices, measurers often do not consider their resolution. However, this can lead to over- or under-estimation of effective roughness since resolution determines how many details are captured in the acquired data. That is, when resolution is too low, asperities that enhance the shear strength might not be detected resulting in under-estimation of roughness. Conversely, when it is too high, very small asperities that may not affect the shear strength will be captured leading to over-estimation of effective roughness. Thus, measurers need to know what is the appropriate resolution for measuring joint roughness. To gain knowledge about it, it would be helpful to know about the effect of small asperities on shear behavior of rock joints.
Investigation on Radial Crack of Cement Sheath During CO2 Injection Using a TM-XFEM Coupled Model
Authors: Gu Chenwang , Su Feiyu , Feng Yongcun , Li Xiaorong , Deng Jingen 
Published: September 2023

ABSTRACT
Cement sheath integrity is critical to the safety and efficiency of CO2 capture and storage technology. Radial cracking of cement sheath is one of the pathways leading to CO2 leakage. Cement sheath radial cracking has been little studied, and the models usually ignore the effect of fluid temperature, while it is challenging to achieve fracture tortuosity. In this paper, a fully coupled thermo-mechanical (TM) model is developed to simulate cement sheath radial fracture using the XFEM method. The influences of various parameters on the fracture trajectory of cement sheath are studied, including in-situ stress, casing pressure, and fluid temperature. The results indicate that tensile stresses may be generated in the circumferential direction of the cement sheath during supercritical CO2 fluid injection. When the tensile stress exceeds the tensile strength of the cement sheath, radial crack of the cement sheath will occur. The fracture size increases with casing pressure and decreases with fluid temperature. This paper is of great significance in studying the failure mechanism of cement sheath integrity, and has guidance for optimizing cement sheath design to ensure the long-term wellbore integrity.

INTRODUCTION
CO2 geological storage (CGS) is the main approach to solving the greenhouse effect. The major challenge in the operation of CGS project is CO2 leakage (Zhang & Bachu, 2011). The Kansas region of the USA has been severely polluted by the wellbore sealing failure, which led to 3,000 tons of gas leaking into the atmosphere (Metz et al., 2005). Wellbore integrity is critical to maintaining operation safety, operation efficiency, and environmental sustainability for CO2 sequestration. The major functions of the cement are to seal the annular between the casing and formation, prevent the inter-zonal fluid migration, and provide additional support and protection for the casing. As one of the essential physical barrier units in a wellbore barrier system, the sealing ability of the cement sheath is critical for the safe and effective long-term storage of CO2 (Bai et al., 2016; Choi et al., 2013). The sealing integrity of cement sheath consists of two main components: the cement stone sealing ability and the interface sealing ability. Most previous studies focused on the failure analysis of the cement sheath interface (Feng et al., 2017; Gu et al., 2022; Yin et al., 2019). However, during CO2 injection, the cement sheath could develop radial cracks under high pressure and low temperature, seriously affecting the wellbore sealing ability (Hassani et al., 2014). Therefore understanding the development of cement radial cracks under different operating conditions is essential to evaluate wellbore integrity.
Slope Stability Analysis Considering Effective Stress Law and Material Softening During the First Impoundment of a Reservoir
Authors: Zhang Kai , Lyu Qingchao , Liu Yaoru , Zhuang Wenyu , Wang XingWang , Yang Qiang 
Published: September 2023

ABSTRACT
Slope failure near a reservoir area is mainly influenced by reservoir impoundment and rainfall. In this paper, a bank slope on the Lancang River near a hydropower station in Southwest China is studied. The FEM numerical model is established to investigate the deformation and stability of the bank slope, especially the influence of the reservoir impoundment and rainfall. Unbalanced force (UST) and the factor of safety of the potential failure surface are presented to quantitatively evaluate the monolithic stability of the slope. The numerical analysis results show that the slope reaches a critical state after the first impoundment. The maximum deformation is mainly located at the toe of the slope towards the riverbed. The failure mechanism can be explained that the bank slope especially the toe of the slope is softened by rainfall and water impoundment and the effective stress effect makes it easier for the slope to yield, which results in significant deformation or landslide failure. It is also demonstrated that the toe reinforcement has a significant effect on restraining the shear displacements of the slope and preventing the progressive failure of the landslide. This study presented a feasible approach for more accurate analysis of reservoir slope stability during impounding and rainfall, and also provided practical measures for slope reinforcement.

INTRODUCTION
Landslides will cause major threat to both lives and property worldwide, especially in regions of steep terrain and heavy rainfall (Xu et al., 2014). Due to the impoundment of many large reservoir dams, more and more landslides have been triggered and cause serious damage. Water is an important factor that influences the mechanical behaviour of geotechnical materials and is responsible for many engineering hazards (Vásárhelyi and Ván, 2006; Wang et al., 2014). The weakening effects caused by water will significantly influence the stability of the reservoir slope.
Geo-Mechanical Characterization of a Well to Store Hydrogen
Authors: Josephs R. E. , Porlles J. , Tomomewo O. S. , Gyimah E. , Ebere F. 
Published: September 2023

ABSTRACT
Hydrogen storage holds the potential to address the intermittency of renewables in the power sector as well as provide low-cost emissions-free energy. However, hydrogen (H2) as an energy carrier has a low density and low energy per unit volume at standard conditions. This significantly complicates large-scale storage using chemical and physical methods. Aquifers, salt caverns, and depleted/abandoned oil and gas fields are some of the subsurface options that can be used to store hydrogen underground because they possess the requisite volumes to store H2 at higher pressures. In this study, the recent interest in exploiting salt deposits in North Dakota as hydrogen storage sites is addressed. The Pine salt in the Spearfish Formation and the "A" salt in the Opeche Formation are the thickest and most prevalent of these salts, making them the most viable candidates for these types of ventures. We tested the feasibility of storing hydrogen by analyzing the behavior of the salts through geo-mechanical characterization. We estimated the mechanical properties of the rock salt from log data and considered the stresses of the salt formation to aid understanding and determine possible limitations. Geomechanical characterization showed a typical behavior of stresses, Sv&gt;SH&gt; Sh.

INTRODUCTION
The intermittency of renewable energy resources has created an urgent need for energy storage. Deployment of energy storage options will accelerate flexibility in grid operations and provide energy that can be applied to a diverse portfolio of industries. It can also provide environmental benefits by improving the overall efficiency of the power grid and providing a basis for the broader adoption of renewable energy thus reducing harmful emissions to the atmosphere (Uliasz-Misiak et al., 2022). According to Tarkowski & Uliasz-Misiak (2022), H2 is a reliable energy carrier that can play an important role in decarbonizing our current energy system. Hydrogen storage can be used to supplement energy demands associated with seasonal heating needs and peak load (Laban, 2020). The challenge with hydrogen however is that it has a higher energy per unit mass than any other liquid fuel. As an energy carrier, H2 has a low density of 0.089 kg/m3 at standard conditions. As such, it is difficult to store large volumes using chemical and physical storage methods (Lord, 2014). Currently, H2 storage can be stored on a small scale as compressed gas at around 5076 – 13778 psi in type 2, 3 or 4 tanks. In order to store gas at such high pressures, the capital and operational expenditures are significant. On medium scale, it can be potentially stored as a gas in spherical vessels at low pressures of ∼290psi thus requiring larger volume (Papadias & Ahluwalia, 2021).