bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory Strategies to Evaluate Enhanced Geothermal Systems (EGS) in Scale Model Experiments
Authors: Villaquiran-Vargas A. P. , Opperman N. , Knippel E. , Xiong Q. , Sutton C. , Zahasky C. , Hampton J. C.
Published: August 2024

Enhanced Geothermal Systems (EGS) is an emerging energy technology with increasing attention due to its potential to be developed in most places on Earth, helping to accomplish net zero carbon emissions. To comprehensively understand EGS complex environments and reach its commercial application, pilot demonstration projects, modeling, and laboratory tests are needed. Laboratory-scale tests can assess critical knowledge gaps by conducting research under controlled conditions, allowing to understand mechanisms and then extrapolate them at the field scale, especially those contributing to, and controlling, flow heterogeneity. Particularly, block samples are useful to study EGS because they enable the evaluation of interactions between wells, networks, and circulation schemes at reservoir conditions, especially heat/flow properties. Different practices can be performed at this scale regarding wells configuration. It is possible to create a fracture and then locate it aided by nondestructive evaluation methods and interpolations, after that, a production well can be drilled intercepting the fracture plane. Likewise, it is possible to drill the injector and producer wells at the beginning if fracture caging is intended. This under-stress experiment uses a large granite specimen of 30x30x45cm that was placed in a polyaxial frame to fracture and monitor fluid flow. To do this a fracture was created through hydraulic fracturing. Different multiphysics such as acoustic emission sensing and fiber optic cable, were used to monitor fracture creation and characterize fracture flow.

1 INTRODUCTION

According to The Office of Energy Efficiency and Renewable Energy of the United States EERE (2022), geothermal resources have the confirmed ability to generate 90 GW of electricity by 2050, becoming a key component to face climate change. The main contributors to achieve this goal are Enhanced Geothermal Systems (EGS), unconventional reservoirs with significant stored thermal energy and low hydraulic connectivity i.e., Hot Dry Rocks, that can be found anywhere in the world. To unlock EGS potential, a certain number of challenges associated with reaching deep rock targets and creating large flow paths (fractures) in tight rocks, need to be solved (Villaquiran Vargas et al., 2023). In addition, a detrimental flow pattern such as flow channeling might occur in EGS, leading to premature cooling of the fractures that carry the fastest and largest volumes of fluid. By increasing the injection-production well spacing, the production life of a geothermal reservoir might be extended (Fu et al., 2015).
Digital Representation of Microstructures of Cretaceous Formation Rock Cuttings in the Tarim Basin
Authors: Liang H. , Luo J. Q. , Wen T. , Yan H. , Feng W. X. , Jin Y. , Xia Y.
Published: August 2024

The Cretaceous Baxigai formation and Shushanhe formation in the Tarim Basin are characterized by the development of high-maturity hydrocarbon source rocks, and the extensive development of tectonic and lithologic traps, which have good prospects for oil and gas exploration. However, it is in the deep-ultra-deep zone, where complicated accidents occur frequently in drilling, logging is difficult to carry out, and the lack of complete cores is not conducive to rock mechanics-related research. In this paper, we use AMICS to form a pseudo-color map of mineral distribution, complete the denoising step based on the image segmentation of RGB images, then use the "8-neighborhood method" to obtain the edge coordinates of the mineral particles, and finally fit the edges by the "least-squares method", and then digitally reconstruct the microcosm of the rock chips. Finally, the edges are fitted by the "least squares" method to digitally reconstruct the microstructure of the rock chips. The algorithm established in this paper solves the problem of missing cores in the Cretaceous strata of the Tarim Basin, realizes the digital characterization of rock microstructures, and provides a digital geometric model for the subsequent numerical simulation work, based on which the related research can be carried out.

1. INTRODUTION

With the development of oil and gas industry, it has become the main trend of conventional oil and gas exploration and development to advance to the deep and ultra-deep neighborhood. The Tarim Basin is rich in oil and gas resources, and in recent years, there have been continuous breakthroughs in exploration and development. The natural gas of the Tarim Basin is mainly enriched in the depression at the periphery of the basin and in the Paleozoic carbonate rocks, among which the tertiary reserves of natural gas in the Kuche depression exceed one trillion cubic meters, and it is the main source of gas for China's "West-to-East Natural Gas Pipeline" project (Ke et al., 2014).
Influence of Specimen Shape on New Simple Shear Test Using Rock Prism Specimen
Authors: Sato I. , Togashi Y. , Kotabe H. , Hatakeyama K. , Osada M.
Published: August 2024

Rock masses are subjected to simple shear mode deformation during earthquake. Currently, there is no standardized simple shear test method for rocks in Japan. The authors propose a new test method, the simple shear test of a prismatic rock specimen using torsional shearing. In this test, prism specimens are radially installed on the pedestal, the cap is placed on the specimen tops, and then specimens are torsionally sheared by a torque with fixed axial displacement of the cap. In this study, to investigate the influence of radial shear load distribution by the applied torque on stress-strain relationships, proposed tests were conducted by varying the length/width ratio of the prismatic Berea sandstone specimens from 1 - 2.5. The results demonstrated that the more smooth stress-strain relationship, the shorter specimen length. On the other hand, the longer specimens showed more complex failure modes, and the strain decreased with increasing torque and did not increase monotonically.

1. INTRODUCTION

Rock masses are subjected to simple shear mode deformation during earthquake. Currently, there is no standardized simple shear test method for rocks in Japan (Japanese Geotechnical Society, 2015). Since heterogeneity and anisotropy predominate in rock masses (Togashi et al. 2018; 2021a; 2021b), the deformation mode applied in loading tests has a significant influence on the mechanical behavior of rock masses. Therefore, it is necessary to test the appropriate loading mode for each event, and simple shear mode tests are necessary for rock deformation during earthquake.

Torsion tests on rock have been conducted in a small number of cases (Talesnick and Ringel, 1999; Paterson and Olgaard, 2000). In these tests, the end face of the specimen and the cap were rigidly bonded with adhesive and subjected to high cell pressures of 10 - 50 MPa to transfer shear load. However, using an adhesive strong enough to withstand the shear load of the rock may damage or deteriorate the cap and pedestal. It may not be reusable. It is not suitable for studies where multiple tests are essential, such as estimating failure criteria.

The authors propose a new test method, the simple shear test of a prismatic rock specimen using torsional shearing as shown in Fig. 1 (Togashi et al. 2023). In this test, prism specimens are radially installed on the pedestal, the cap is placed on the specimen tops, normal load is applied to the specimen, and then specimens are torsionally sheared by a torque with fixed axial displacement of the cap. This method enables the reproduction of the simple shear mode deformation experienced by rock masses during earthquakes. Additionally, it is possible to replicate arbitrary rock mass conditions by varying the normal stress.
Numerical Simulation of Wellhole Stability in Cretaceous Fractured Water-Sensitive Formation in Tarim Basin
Authors: Zhou Bao , Zeng Ping , Chi Jun , Xu Kaifeng , Lu Hui , Xia Yang , Jin Yan
Published: August 2024

The Cretaceous Baxigai Formation and the Shushanhe Formation in the Tarim Basin are fractured water-sensitive formation. Wellbore instability is frequent during the drilling process. It's urgent to clarify the mechanism of the fractured water-sensitive formation, and to guide drilling operations. The formation occurrence is determined based on the formation micro-scanner imaging (FMI). And the digital wellbore model is established. Numerical simulation of the fluid-solid coupling process in the digital wellbore model is carried out by 3DEC to analyze the effects of drilling fluid density, fracture permeability, number of fractures and drilling fluid immersion time on the wellbore stability. The results show that: (1) increasing density is beneficial to improve the wellbore stability at the early stage; (2) with the increase of the fracture permeability, the wellbore state becomes more serious; (3) with the increase of the number of fractures and the increase of the immersion time of drilling fluid, the risk of the wellbore instability increases. The model in this paper can be used to study the dynamic process of wellbore instability in fractured water-sensitive formations, reveals the mechanism of wellbore instability in the Cretaceous mudstone of the Tarim Basin, and it can provide opinions and guidance for drilling.

1. INTRODUCTION

With the increasing demand of energy and the exploration of conventional energy, deep well and ultra-deep well drillings are now more widely performed exploratory (Zhang S et al., 2015). However, several problems such as collapse, jamming and leakage are encountered during the drilling process owing to high temperature, high pressure and complex geological conditions, and these wellbore instability increases costs of ultra-deep drilling (Gholami R et al., 2014). In fractured formation, drilling fluids penetrate into formation leads to the reduction of rock strength, decrease in friction angle, especially in water-sensitive formation (Chen X et al., 2002).

A large amount of oil and gas is founded in the Ordovician carbonate formation of the Tarim Basin with buried depth of more than 7200m. Some reservoirs are distributed near the faults and it substantially makes formation fractured (Lai et al., 2021). The upper formation named Cretaceous Baxigai formation and Shushanhe formation is mudstone with a thickness of 150m-300m. Wellbore instability occurs frequently in the progress of drilling mudstone formations. Clarify the mechanism of wellbore instability to ensure safe drilling and reduce drilling costs is prompted recent exploration.
Numerical Stress Computation Around Cavity Using Boundary Element Method for Elastic Material
Authors: Habibi A.
Published: August 2024

Precise estimation of field variable values around a cavity is vital for excavation operation safety. The singular nature of stress around the cavity makes the computations challenging for Finite Element Method (FEM) software. Although the Boundary Element Method (BEM) offers a semi-analytical formulation, it gives rise to a set of new challenges in boundary condition enforcement, allocating the traction variables at corners, integration, solving, and post-processing. In this study, the problem of a small cavity inside a three-dimensional elastic domain has been explored using continuous and semi-discontinuous elements. The results of the BEM code were compared with an analytical solution and industrial software (Abaqus). The comparison of stress values indicates that with much fewer elements, BEM is still capable of providing proper results with a few percent of errors. For remote coordinates, error values are less than one percent; for locations too close to the cavity, with a finer mesh, error values are reduced to one percent with the same simple integration scheme. Additionally, for such simulation, semi-discontinuous elements result in higher error values even at remote locations and low deviation ratios.

1. INTRODUCTION

Stress concentration near a cavity and its higher values compared to the remote stress values at the boundary is a well-established subject. This stress intensity could impact the stability of rock during an excavation operation. A precise estimation of stress values using analytical solutions or numerical software can reduce the chance of rock failure. Yet analytical solutions are a proper basis for code and software error evaluation, they just address a set of specific problems and geometries.

Boundary Element Method (BEM) is a numerical tool for engineers to approximate stress and displacement values by scattering elements over boundary surfaces. In this study, direct BEM formulation has been used which includes singular integrands and discontinuous boundary-imposing challenges (Aliabadi, 2002; Crouch et al., 1983; Gao & Davies, 2002; Hall, 1994; Leng, 2007). Among many methods for dealing with discontinuous Boundary Conditions (BC), non-conforming elements have been extensively utilized. Semi-Discontinuous Element (SDE) is one of the methods that simplify the BC imposing by introducing new nodes to differentiate degrees of freedom (Aliabadi, 2002; Dyka & Millwater, 1989; Mi & Aliabadi, 1992; Mitra & Ingber, 1993; Parreira, 1988; Yan & Lin, 1994). A simpler method, referred to as Unique Traction (UT) in this work, neglects all challenges. Both UT and SDE have been utilized in this study.
Characterization of Water-Rock Interaction in Water-Sensitive Tight Oil Reservoirs and its Mitigation Method with Pilot Tests
Authors: Xie Bobo , Wang Bin , Wang Mingxing , Teng Jinchi , He Bingxian , Liang Tianbo
Published: August 2024

The injection of fracturing fluid into water-sensitive reservoirs can cause a rapid pressure decline during production, and the estimated ultimate recovery (EUR) of the well is only 1/4 to 1/3 of that in neighboring plays without water sensitivity. Laboratory experiments are conducted to analyze the impact of water-sensitive minerals on the rock matrix, and quantify the in-situ damage during the shut-in and production. Furthermore, water-sensitive inhibitors are developed, whose effectiveness is then examined in field pilot tests. The composition change of reservoir cores is analyzed using XRD, and their microstructure change is analyzed using SEM before and after interacting with the fracturing fluid in the mimicked reservoir condition. After water-sensitive inhibitors are developed, their effectiveness on mitigating the rock damage is characterized using the in-situ CT scans. The oil production rate and types of stabilizers of 34 oil wells in P3w1 pay zone and 29 oil wells in P3w2 pay zone are summarized. Finally the effect of stabilizer on oil production rate is investigated. The smectite ratio is over 70% in clay minerals. When the rock sample is submerged in the stabilizer solution, no clay swelling is observed. The in-situ CT scans show that the porosity decreased by 0.99% after interacting with the fracturing fluid. While when stabilizers are used in the fracturing fluid with concentration of 2%, the damage of rock permeability is reduced by 49.35%, and porosity increases by 0.66%. No obvious difference in well production is noticed when the KCl solution is used in the field. On the contrary, well production increases 40% because of the use of stabilizer. An in-situ characterization method is proposed based on a coreflood in a micro-CT, which can show the real-time change of pore structure and permeability of a rock sample. An effective water-sensitive stabilizer formula is developed, which can be a promising tool to develop water-sensitive tight oil reservoirs based on current fracturing techniques.
Experimental Study on Permeability and Desorption of Tectonic Coal Under Mechanical Vibration
Authors: Li K. C. , Hou B. , Zhai Z. W.
Published: August 2024

Coalbed methane (CBM) is one of the unconventional oil and gas resources. The potential of CBM resources in the north of Qinshui Basin is good, but it has not reached the scale of industrial exploitation. CBM mining not only can obtain energy, but also has important significance in reducing coal mine safety accidents and reducing greenhouse effect. In this paper, according to the characteristics of low porosity, low permeability and soft structure of coal reservoirs in the study area, the permeability and desorption of tectonic coal samples collected from different mining areas are measured and analyzed under mechanical vibration. The experimental results show that the low frequency mechanical vibration has obvious effect on the permeability of tectonic coal samples. Increasing the mechanical vibration frequency can promote the large amount of methane desorption in coal reservoirs with more primary fractures and increase the production of CBM. This study can provide a technical reference for the mining of tectonic CBM.

1. INTRODUCTION

Qinshui Basin is located in the central and southern part of Shanxi Province, China, which is rich in coal reserves and also contains a large amount of coal-bed methane (Zhou, 2013). The northern part of the basin is mainly coal-bearing strata of Upper Carboniferous Taiyuan Formation and Lower Permian Shanxi Formation (Wang et al., 2006). CBM mainly exists in the form of adsorption in the coal body, and its production is a complex process of adsorption/desorption, diffusion/seepage (Yi, 2007). At present, the main methods used to increase production are hydraulic fracturing (Jiang et al., 2016; Johnson et al., 2002; Hou et al., 2022), heat injection (Wang et al., 2015; Wang et al., 2023; Goraya et al., 2019), gas injection (Jessen, et al., 2008; Mazzotti, et al., 2009), vibration (Tanuwijaya, C., & Ariadji, T. 2009; Cui et al., 2024) and other mining methods. In order to explore a technology suitable for the combined extraction of CBM from surface and underground of shallow mid-level tectonic coal in northern Qinshui Basin, the permeability and desorption of tectonic coal samples collected from different mining areas were measured before and after mechanical vibration. The influence of vibration frequency on permeability and desorption of tectonic coal is studied, which provides a technical reference for vibration mining of tectonic coal bed methane.
The Influence of Stress Heterogeneity on Hectometer Scale Hydraulic Stimulation Experiments
Authors: Bröker K. , Valley B. , Gholizadeh Doonechaly N. , Rosskopf M. , Hertrich M. , Giardini D. , BedrettoLab team _ , Rinaldi A. P. , Clasen Repollés V. , Obermann A. , Ma X.
Published: August 2024

From 2022 to 2023, a series of hydraulic stimulation experiments were conducted at the Bedretto Underground Laboratory in Switzerland (BedrettoLab) to study the creation of an engineered geothermal reservoir in crystalline rock. A 400 m long stimulation borehole was divided into 14 intervals using a multi-packer system. During the volume characterization, an azimuthal rotation of borehole breakouts was observed, indicating a stress perturbation caused by a major fault zone intersecting the experimental volume. In this study, we present the seismo-hydromechanical observations from seven hydraulic stimulations in four selected intervals. This is the first systematic comparison of repeated stimulations in different intervals at the BedrettoLab. Two of these intervals are neighboring the fault zone, while the other two are located further away. We utilize data from a dense multiparameter monitoring network to show that the stress perturbation affects the reactivation of similarly oriented pre-existing fractures. In our example, the stress perturbation caused by the fault zone prevents the reactivation of structures in the nearby interval, while similar structures are clearly reactivated in the three other intervals. Reactivation pressures from pressure-flow rate plots agree with the pressures encountered at the onset of seismicity. Given that the prevailing fractures are well oriented for shear reactivation within the far field stress field, hydraulic shearing is considered the probable reactivation mechanism.

1 INTRODUCTION

Interest in engineered geothermal systems (EGS) as a low emission, renewable energy source (Lu, 2018; Aghahosseini and Breyer, 2020) has grown since the late 2000s. In Central Europe, EGS reservoirs with sufficiently high temperatures are located at depths of several kilometers, where the permeability of the crystalline basement rocks is insufficient for geothermal energy extraction. Permeability enhancement is achieved through hydraulic stimulation, which can involve hydraulic shearing of natural fractures or shear zones, hydraulic fracturing of intact rock, or a combination of both (McClure and Horne, 2014). This permeability enhancement goes hand in hand with 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 at decameter scale 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).
A Comparison of Tensile Testing Techniques and Predictive Correlations Using Simulated Rock
Authors: Lindenbach E. J. , Foran J. R. , Bearce R. G.
Published: August 2024

The mechanical properties of rock are important parameters in the structural analysis of dams as they help inform an understanding of how a structure is likely to behave under loading. One commonly utilized but difficult-to-obtain engineering parameter is the tensile strength of rock. Direct tensile strength (DTS) testing of rock is rarely performed due to cost considerations and the complexity associated with the testing. The majority of testing is performed using indirect tensile methods, such as the Brazilian Tensile Test (BTS), akin to the splitting tensile strength test typically performed on concrete, or by using correlations to other mechanical properties like the crack initiation strength, mi from Hoek-Brown, or the Mode I fracture toughness. While the BTS is easier to prepare and more economical, significant uncertainty remains in how the test results correlate to the DTS and the actual behavior in situ. All the major organizations that standardize rock testing are in broad agreement on how to run the BTS however, there is still some room for more detailed guidance about platen shape, the use of a cushion, stress concentrations, and how to use the BTS to estimate the DTS. The goal of this research is to perform laboratory testing on stiff and soft simulated rock to improve understanding about the DTS and BTS tests, how different methods compare, and refine correlations between mechanical properties and the DTS.

1. INTRODUCTION

In order for a robust model to be developed, the anticipated range of behavior of rock when subjected to a variety of loading conditions must be understood and quantified. This range of behavior can be defined by a full strength envelope developed from laboratory testing and up-scaled to the problem of interest.

A full strength envelope for rock is provided in Figure 1, with the typical laboratory tests used to define the various portions of the curve given on the figure (Hoek and Martin, 2014). The tensile strength of rock defines a cutoff value in the overall shear strength envelope, but as indicated above, this value can be difficult to determine. The significantly more common uniaxial and triaxial compression tests are typically used to define the remainder of the envelope past the tensile cutoff.
Meter-Scale Laboratory Earthquakes Triggered by Fluid Injection and the Role of Background Stress in Mediating Runaway Ruptures
Authors: McLaskey Gregory
Published: August 2024

I present large-scale laboratory experiments where water is injected directly into a stressed fault that is a saw-cut interface in a slab of granite (3 m by 1.5 m and 300 mm thick) in an attempt to examine the earthquake energy budget. The laboratory fault is subjected to 2-10 MPa stress levels, and exhibits slow and aseismic slip within a localized "nucleation zone" prior to rapid dynamic fault rupture. Slow slip associated with the nucleation of dynamic rupture is observed both for cases where water is injected onto the fault and where slip initiates spontaneously due to the external application of shear stress. The 3-m-long sample is long enough that ruptures sometimes arrest within the sample. So, using arrays of sensors, we study the conditions required for rupture arrest, a crucial element in determining whether an earthquake rupture will grow into a large, devastating event, or will remain small and harmless. The rupture can be modeled as a shear crack, and we employ fracture mechanics to explain rupture arrest. Our experiments demonstrate that the initial shear stress plays an important role in an earthquake's size. Another key unknown in earthquake mechanics is the shear fracture energy required to advance rupture. In the lab, we can measure values in the range of 1-10 J/m^2, but it is unclear if shear fracture energy, or, similarly, breakdown work, increases with the rupture size as it propagates into an increasingly rough fault surface. Answering such a scaling question is key to understanding the earthquake energy budget, a major impediment in our ability to accurately model and predict earthquakes.
Utilizing Coseismic Strain in the Modelling of Tunnel Loading in Deep Burst-Prone Mines
Authors: Malovichko D. A. , Rigby A. , Kaiser P. K.
Published: August 2024

Seismic monitoring data acquired at mines can be used to infer the characteristics of coseismic strain, including amount, orientation of principal directions and type (deviatoric, volumetric explosive or implosive). This strain corresponds to plastic strain increment if seismic events represent episodes of sudden deformation in confined environment. If sources of seismic events involve the convergence of excavations, then coseismic strain depends on the amount of the convergence. These peculiarities of coseismic strain are taken into account in the proposed method for its direct incorporation into a numerical stress model. The method is verified using analytical cases of confined inelastic deformation as well as brittle failure around a tunnel. The method can be used to assess the redistribution of stresses and change in the loading of tunnels in seismically active mines. A synthetic mining example is presented to illustrate the impact on tunnel stress.

1 INTRODUCTION

Seismic systems installed at mines record seismic waves radiated by episodes of sudden (i.e., durations on the order of fractions of a second) deformation within the rockmass. The analysis of these recorded waves make it possible to assess the time, location, amount and intensity of deformation, as well as its geometrical characteristics (e.g., direction of principal strains, proportion of volumetric and deviatoric shape change). This information is highly valuable for understanding the overall rockmass deformation induced by mining and the associated redistribution of stresses. It is quite logical that the characteristics of rockmass deformation inferred from seismic data are often utilized when performing numerical stress modelling. There are fundamentally two ways to do this.

Firstly, seismic data can help to improve the input parameters of the stress models. This is often done through qualitative or quantitative comparing of various aspects of seismic data (e.g., location of sources) with the corresponding modelling parameters (e.g., areas of high deviatoric stress) – see, for example, the works of Lachenicht (2001);

Beck and Brady (2002); Beck et al. (2006); Spottiswoode et al. (2008); O'Connor et al. (2010); Arndt et al. (2013); Kalenchuk (2022); Malovichko and Rigby (2024). The improved (calibrated) stress model is expected to deliver more realistic distribution of stresses for the current mining step and should provide better prediction of the stress redistribution for the future planned mining steps.
A Microscale Analysis of Millimeter-Wave Induced Vitrified Basalt for Use in Enhanced Geothermal Energy Systems
Authors: Meltzer E. R. , Stefaniuk D. , Einstein H. H.
Published: August 2024

Extraction of the energy available from geothermal heating in the Earth could provide substantial contributions to energy needs long-term. However, there are major technical limitations with the current geothermal drilling process. A new technology in the field of EGS that uses a millimeter (mm) wave gyrotron, which allows for quicker, more efficient drilling could be a potential way to overcome these limitations. The mm-wave drilling process, a technique developed by Dr. Paul Woskov of the MIT Plasma Lab, has two significant advantages as compared to traditional drilling: 1. The well hole advance is through melting of the rock, which is faster than mechanical drilling. 2. The molten rock then solidifies, creating a vitrified wall support without the need for extra casings. This drilling and casing process can potentially save money, time, and material. The study presented in this paper is aimed at understanding the strength and microscale mechanical and chemical properties of the vitrified material to see what is happening to the rock, specifically Basalt, pre- and post-melting by using a series of experimental and analytical tools.

1. INTRODUCTION

With global energy consumption on a continual upward slope, there is a growing need for a clean and renewable energy solution. At present, in the United States, geothermal energy constitutes merely 2% of the total renewable energy usage. However, both in the U.S. and globally, the utilization of geothermal energy has been steadily increasing. Tapping into the Earth's heat potential holds the promise of significantly reducing CO2 emissions and making substantial contributions to meet the escalating energy demand worldwide. Nevertheless, significant limitations currently impede the feasibility of this approach in the United States, creating the necessity of alternative methods. Thanks to researchers at the MIT plasma lab, a novel approach was introduced: the utilization of a millimeter – wave (MMW) gyrotron. This technology potentially allows one to drill wells by employing MMW heating, leading to the melting and vaporization of basement rock at extremely high temperatures. The rapid heating and subsequent cooling of the rock result in the formation of a glass-like substance, making it possible for this vitrified material to serve as a wellbore casing for geothermal injection and production wells.
Experimental Study of Underground Heat Storage via Hydraulic Fractures
Authors: Möri A. , Naftalski J. , Liardon T. , Talebkeikhah M. , Lecampion B. , Lu G. , Burghardt J.
Published: August 2024

We present a laboratory setup to test the energy budget of underground heat storage in an otherwise impermeable rock through engineered fractures, a so-called Fracture Thermal Energy Storage (FTES) system. A hydraulic fracture is first created in a cubic specimen of Zimbabwe Gabbro. In the experiment, de-ionized water is circulated under high pressure through an injection steel tubing automatically heated to a target temperature. The fluid adjusts to the tubing temperature during its flow before entering a production well drilled into the 250 mm edge length block. The warm fluid then circulates through the previously created hydraulic fracture at mid-height of the block toward a production well drilled at the block periphery. The production well is equipped with a dedicated completion to allow fluid outflow. External fracture appearances are sealed using an epoxy resin. We demonstrated through the results of a preliminary heating experiment that we can transfer nearly all of the heat from the circulating fluid to the block. An efficient charging of the thermal battery is achieved. This first experiment is currently under further improvement and will ultimately help to better understand the engineering of mid- to large-scale field implementation of FTES systems.

1 INTRODUCTION

Storing excess heat produced during summer or as a byproduct of industrial treatments is of widespread interest in the context of the energy transition. Typically, the peaks in energy production are not aligned with peak consumption. This mismatch is notably observed for inter-seasonal differences in demand and production. Underground thermal energy storage (UTES) systems could provide an efficient mechanism to overcome these limitations. Several types of UTES systems are being used as of today. The most used systems, not including any phase change of the temperature carrier, as of today are Aquifer Thermal Energy Storages (ATES) (Bloemendal et al., 2015). Other systems include the use of a series of boreholes (Borehole Thermal Energy Storage - BTES) or underground caverns (Cavern Thermal Energy Storage - CTES). All of these systems have regulatory, economic, and geological advantages and disadvantages.
“SINTEF-TriPOD” in Underground Design – A Demonstration for Two Projects in Norway
Authors: Trinh N. , Grøv E.
Published: August 2024

Many rock engineering projects today may face rock mechanics challenges such as (a) particularly complicated profile or excavation plan, (b) located near to existing infrastructure and thus pose a high risk to such structures, and (c) complicated geological conditions. In such situations, there may be no similar existing experience to lean on. Empirical methods have limitations and uncertainties in such cases. Therefore, SINTEF has developed a rock engineering tool to deal with the challenges. The tool is a combination of Investigation, Numerical modelling, and Monitoring. We use the term "SINTEF-TriPOD" for the methodology, and through projects it has proved to be a reliable tool. This paper presents the application of the SINTEF-TriPOD for two important infrastructure projects in Oslo, Norway, which are Follo Line metro project (4 billion USD) and a fresh water supply project (approximately 1.2 billion USD).

1. INTRODUCTION

Many rock engineering projects today may face rock mechanics challenges such as (a) particularly complicated profile or excavation plan, (b) located near to and thus cause a high risk to existing structures, and (c) complicated geological conditions. In such situations, there may be no similar existing experience to lean on. Empirical methods have limitations and uncertainties in such cases. Therefore, SINTEF has developed a reliable rock engineering tool to deal with the challenges. The tool is a combination of Investigation, Numerical modelling, and Monitoring:

• Investigation: The investigation can be rock stress measurements before and during construction (hydraulic fracturing from rock surface, 2D and 3D over-coring), different geological surveys, drill holes, and geological engineering mappings to evaluate the rock mass quality. Obtained information is used for the second component of the "SINTEF-TriPOD" – numerical model.

• Numerical model: Establish a comprehensive numerical model, normally 3D numerical model is preferred as such model can handle complicated geometry and construction plans and methods. Simulations are to be carried out in certain order with clear objectives for each simulation steps. This is done to follow the planning and construction closely, helping the project team in making correct decisions.

• Monitoring: To improve the numerical model even further, stress and displacement are monitored continuously, and comparing them to the values from the numerical model. The model is calibrated, verified, and improved with the observations made in the surveillance program. This gives project team a reliable tool to help for decision making during implementation of the project.
Progressive Excavation Disturbance Zone Evolution During and Post Mine-By Tunneling (PRECODE) – Insight into a New Underground Research Laboratory for Crystalline Rocks in the BedrettoLab
Authors: Hamdi P. , Achtziger P. , Dickmann J. , Kruszewski M. , Rinaldi A. P. , Villiger L. , Shakas A. , Perras M. , Bahrani N. , Jiang D. , Amann F. , Wiemer S.
Published: August 2024

Development of brittle damage around tunnels is quite common in massive rocks under highly-stressed conditions. Understanding the shape and extent of the Excavation Damage Zone (EDZ) is important, particularly for deep geological repositories (DGRs) for nuclear waste. Within the EDZ, permeability is often increased, and in the context of nuclear waste disposal, this increased permeability may create preferred pathways for the migration of radionuclides. Therefore, a comprehensive assessment of brittle fracture formation in space and time requires multidisciplinary monitoring systems. A new Underground Research Laboratory (URL) in Southern Switzerland in the old Bedretto Gallery is under construction for the purpose of studying the evolution of the Excavation Damage Zone (EDZ) in crystalline rocks. The new experimental tunnel will form a new branch from the existing Bedretto tunnel which will be densely instrumented prior to the excavation with various sensors. The main objectives of the PRECODE experiment are to understand: (1) short-term rock mass behavior and EDZ formation during tunneling; (2) long-term fracture propagation within the EDZ associated with environmental conditions (fluctuations in humidity and temperature); (3) permeability evolution around an open excavation and (4) the impact of tunneling on potential dislocations of nearby fault zones. In-situ data and a series of comprehensive laboratory tests form a hydro-seismo-mechanically coupled reference data set for numerical simulations with the aim to further improve predictive models. This paper outlines an overview of the project objectives, details of the planned monitoring systems, and some preliminary results obtained from a baseline study.

1. INTRODUCTION

Development of brittle fracturing around tunnels in massive and highly stressed rocks is quite common. In crystalline rocks (i.e. granite), the brittle fracturing is depicted through spalling and in a severe case rock bursting (Diederichs, 2007). The fracture initiation and propagation often start during the tunneling process and develop over time. These progressive failures may lead to an interconnected fracture network typically associated with the radiation of micro-seismic signals. Within the excavation damage zone (EDZ), the permeability is often enhanced and – in the framework of nuclear waste disposal – may provide preferential pathways for radionuclide migration.
Characterization of Direction-Dependent Properties of Sierra White Granite: Initial Results
Authors: Kafle L. , Mok U. , Einstein H. H. , Villamor-Lora R. , Germaine J.
Published: August 2024

Most granites have preferred directions ("rift", "grain", and "hardway") that affect the ease with which the rock can be split. In this study, we present a series of uniaxial and triaxial tests on the directional-dependent properties of Sierra White Granite, a rock that has been chosen as a laboratory analog for the FORGE site granitoid. We performed triaxial tests on 1.5" by 3.5" cylindrical cores involving a test program including isotropic compression, cyclic loading, and triaxial compression in three preferred directions under low to high confining pressure. In these tests, we measured stress, displacement, axial and circumferential strain, and P-wave velocity. We found no significant degree of direction dependency in the deformation (stiffness) and strength parameters. On the other hand, the P-wave velocity results show the largest velocity along (equation) (direction perpendicular to plane C) then (equation) and (equation). More tests are needed to accurately quantify the direction-dependent behavior of the given test material.

1. INTRODUCTION

The direction dependence (anisotropy) of granite is often reported in the literature, both in relation to practical engineering and scientific aspects. With respect to practical engineering, the best known are the orthogonally oriented so-called "quarry planes" rift, grain, and hardway, indicating the ease of splitting or cleavage in this sequence (i.e., rift the easiest, and hardway the hardest). In quarrying, this direction dependence is often used to split the rock by a hammer blow in the rift direction.

From the geotechnical viewpoint, one wants to know what causes the direction dependence, if it affects other small- and larger-scale properties, and what these effects are. Moreover, understanding the material reaction to external influences such as stress, temperature, electrical currents, and chemical agents, is also important to better design geotechnical structures. Most researchers agree that the mechanical properties along the rift orientation depend on the orientation of microcracks and fluid intrusions – which in turn are affected by the direction dependence of quartz (see e.g. Douglass & Voight, 1969; Osborne, 1935). The reasons behind the other two directional dependencies are less clear, but most likely involve the effects of foliation, large-scale stress, and/or temperature changes (Osborne, 1935). It should be noted, however, that some granite samples used in laboratory experiments do not show preferred directions (Chen et al., 1999).
The Two-Phase Flow of Oil-Gas Multiple Rounds Injection-Production in the Reconstructed of Gas Storage with Oil-Ring Condensate Gas Reservoir
Authors: Liu Qi , Yao Yuedong , Wang Lian
Published: August 2024

There will be multiple rounds of oil and gas mutual displacement during the operation of the condensate gas reservoir with oil-ring. Up to now, the experimental research on the characteristics of two-phase flow in the industry mainly focuses on gas-water or oil-water mutual displacement. While, the construction and operation of gas storage reservoirs in condensate reservoirs with oil-rings will appear the phenomenon of two-phase flow of oil and gas, the indoor physical simulation method has been used to carry out the two-phase flow characteristics experiments of the actual reservoirs relative to the relatively high, medium, and low penetration cores of each of the eight times of the two-phase seepage characteristics of the mutual displacement of oil and gas. Studies the flow of oil-gas in two phases during the operation of gas storage, analyzes the influence of multiple rounds of oil-gas mutual displacement on the storage capacity of gas storage, grasps the changes of oil-gas flow under different permeability conditions, and optimizes the optimal reservoir suitable for the construction of gas storage.

1. INTRODUCTION

As an important means of developing clean energy, underground gas storage has the characteristics of large capacity and low cost(Yuan et al, 2020). Generally speaking, there are two purposes for the construction of underground gas storage: one is to meet the gas demand and seasonal peak shaving needs of nearby urban residents, and the other is to serve as a strategic resource reserve. The construction and operation of gas storage has been relatively mature abroad, but it is still in the development stage in China(Ding, et al, 2020). For the construction of gas storage, foreign theories cannot be copied, and the construction of gas storages must be carried out based on my country's national conditions and local conditions (Zhang 2018, Yin 2013). During the operation of gas storage, it has the characteristics of alternating strong injection and extraction of gas, high-speed seepage of single well, large flow huff and puff fluid, etc. In order to ensure the normal operation of gas storage after built, it is necessary to study the relative permeability of gas storage fluid.

At present, a large number of scholars have carried out indoor physical model experiments on the two-phase flow rules of gas-water mutual flooding in different types of gas storage, and there are few studies on the relative permeability of oil-gas mutual flooding in gas storage.
Unveiling the Invisible: Mapping Basement Faults Using Microseismic Clouds
Authors: Wang Chaoyi , Sherman Christopher S. , Kroll Kayla W. , Glubokovskikh Stanislav , Alumbaugh David , Morris Joseph P.
Published: August 2024

The Illinois Basin Decatur Project (IBDP) has piloted the process of large-scale injection of CO2 into a deep saline reservoir. During the project, microseismic clouds were observed from locations that were not identified in any previous geological database. Based on the injection depth, it is surmised that the pressure plume reached previously unidentified basement faults, altered their stress conditions, and triggered microseismic events. Understanding the presence and behavior of basement faults is critical for monitoring and managing induced seismic risks. However, basement faults with near-vertical dips can be challenging to detect using conventional seismic imaging methods due to poor incident angles. In this study, sponsored by the U.S. Department of Energy's SMART initiative, we developed a machine learning workflow using Long Short Term Memory (LSTM) recurrent neural network (RNN) architecture that maps basement faults using microseismic clouds. The LSTM-RNN is trained on synthetic microseismic catalogs produced by physics-based geomechanics models that simulate fluid injection into a reservoir above a faulted basement. Microseismic catalogs are passed to the LSTM-RNN to predict the location of the basement faults and shear stress state. The network aims to take real-time microseismic data and progressively produce an updated fault map. Our approach shows the potential of ML-based methods for mapping previously invisible basement faults, providing information to enable rapid decision-making during CO2 injection to prevent and mitigate induced seismic risks. However, there is still much room for improvement in the accuracy of the machine learning model, which we are actively working on.

LLNL Release Number: LLNL-CONF-860823

1 INTRODUCTION

Carbon sequestration is a process that involves capturing CO2 emissions from various sources such as industrial plants and power generation facilities, and storing the captured CO2 in subsurface reservoirs to help mitigate the buildup of greenhouse gases in the atmosphere (Halmann and Steinberg (1998); Pires et al. (2011); Herzog et al. (2000)). As nations and industries strive to reduce their carbon footprints and limit global warming, large-scale carbon sequestration has emerged as a significant, potential contributor toward meeting ambitious net-zero targets (Budinis et al. (2018); Meys et al. (2021)).