bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigating the Energy Balance of Two Mining Methods Set in a Deep Underground Metal Mine in the U.S.
Authors: Kim B. H. , Emery T. M. , Armatys M.
Published: August 2024

Hecla Mining Company (Hecla) operates the Lucky Friday Mine since 1958, which is an underground silver, lead, and zinc mine near Mullan, Idaho, USA. In the mid-1980s until 2020, the company relied on the Lucky Friday Underhand Longwall (LFUL) method for seismic control to mine (first) the Lucky Friday and (then) the Gold Hunter ore bodies. However, engineering challenges related to high in-situ rock stresses, squeezing ground conditions and seismic occurrences continued to increase as the production levels deepened to depths greater than 2,000 m below ground surface. In 2020, Hecla developed a new mining method called UCB (Underhand Closed Bench) which proactively induces fault slip in proximity of the mining front, improving safety and productivity at the mine. UCB was fully implemented at the Gold Hunter in 2021. Although preventing faults to slip at their critical load was identified as the main seismic control measure, the contribution of fragmented ore presents another component capable of reducing the seismic energy release measured at the mine. As part of the seismic hazard research initiative, the National Institute for Occupational Safety and Health (NIOSH) collaborated with Hecla to develop a series of numerical models using a 3-dimensional distinct element method (3DEC) to quantitatively investigate and compare the differences in the energy balance characteristics between the LFUL and the UCB methods. As a result, the numerical models were sensitive enough to capture the differences between the mining methods and were in good agreement with the field observations, recognizing the influence of blasted ore in seismic control.

1. INTRODUCTION

As part of the project, managing ground support for long-term stability, the National Institute for Occupational Safety and Health (NIOSH), is researching more effective seismic energy analysis methods and improved forecasting of induced seismicity around mining areas. The Lucky Friday Mine (Hecla) has recently implemented a new mining method, Underhand Closed Bench (UCB), that has yielded favorable results regarding seismic energy release and control when compared to the Lucky Friday Underhand Longwall method (Board et al., 2022; Armatys, 2023). This collaborative opportunity was realized and leveraged NIOSH's modeling expertise and Hecla's proprietary mining method, which is beneficial for both parties.
Modeling a Deep Coaxial Closed-Loop Vacuum Insulated Tubing (VIT) Completion in a Geothermal Research Test Well Using FEFLOW
Authors: Chen G. , Wright C. , Liu J. , Gomez C. , Garcia A.
Published: August 2024

An innovative geothermal research test well was successfully drilled and completed in a drilling test facility in Navasota, Texas in 2020. This vertical test well reached 11,518 ft (3510.7 m) total depth and set a 6-inch casing to 11,503 ft (3506.1 m) with a DTS/DAS fiber optic cable permanently installed on the outer diameter of the 6-inch casing and cemented in place. At the time, a vacuum-insulated-tubing (VIT) completion was installed from surface to ∼11,369 ft (3465.3 m) to pilot-test a deep coaxial closed-loop geothermal system. The test well was flowing down annulus and up tubing with filtered freshwater being the working fluid. Selected flow rates were 150 gal/min (gpm), 75 gpm and 37.5 gpm. A three-dimensional (3D) FEFLOW finite-element borehole heat exchanger (BHE) model was developed to model the impact of different key parameters such as formation and cement thermal conductivities, flow rates and inlet temperature after the model is calibrated against the field data. The model can be used to simulate energy output and heat production forecast for similar geothermal completions such as BHEs and borehole thermal energy storage (BTES).

1. INTRODUCTION OF THE TEST RIGS AND THE TEST FACILITY

The NOV STC (Springett Technology Center) test facility is located in Navasota in Grimes County, Texas. The geothermal test well was drilled with the automated Ideal Prime 1 drilling rig (1500 hp) and completed with a 5C mobile completion rig (200 kips or 100 US tons static hook load capacity).

The Prime 1 rig consists of an automated Iron Roughneck (ST-100) and 3 permanently installed Robots for automated pipe handling during tripping. The first floor Robot (L1) handles pipe tailing between the well center and the setback area as well as picking up a single joint from the Pipecat. The second floor Robot (L2) handles the ancillary work which includes operating the mud bucket and a combo of the doping head and stabbing guide. the third robot is located above the finger board to handle the top of the pipe stands between the top drive elevator and the finger traps. At the time of this paper being written, the drill cabin has been removed from the drill floor to the ground level for over nine months with non-interrupted rig operations and testing.
Application of Supervised Learning Algorithms to Predict Engineering Characteristics of Soft to Strong Rock Masses Using Actual TBM Performance Data
Authors: Samadi Hanan , Hassanpour Jafar , Rostami Jamal , Khatti Jitendra
Published: August 2024

Knowing accurate values of rock engineering parameters in hard rock condition is the key in estimating and adjusting TBM performance. Therefore, this paper has tried to predict the rock engineering factors using some indicators related to machine performance, mechanical specification, and TBM operational parameters. In this study, TBM penetration per revolution (Pr) as driving parameter, TBM operational parameters including cutterhead torque (CT), thrust force (TF), cutter load (Fn), cutterhead rotational speed (RPM), and also cutterhead diameter as a mechanical machine specification are used to predict geomechanical parameters based on reverse analysis in different types of soft to strong rocks (carbonate, volcanic, metamorphic). Soft computing methods are trained using operating and driving data as well as rock engineering parameters gathered from several tunnelling projects in Iran which were excavated in hard and soft rock (UCS = 0-200 MPa) condition using TBM. Among the data collected during the pre-construction and construction phases of the project, the dataset was classified into several zones (107 sections), and the reasonable distribution intervals of the main tunneling factors corresponding to each zone were defined (80% for training and 20% for testing). The results of the proposed models indicate an acceptable and reliable accuracy.

1. INTRODUCTION

The tunnel boring machine (TBM) is widely utilized for the construction of long tunnels due to its high efficiency and cost-effectiveness (Liu et al. 2016, Wu et al., 2019). The performance of the TBM during tunnel excavation is significantly influenced by the rock mass parameters. However, obtaining accurate values of these parameters through direct observation and in-situ testing of the working face is limited in tunnel boring machines (Yamamoto et al. 2003, Farrokh and Rostami 2009, Hassanpour et al. 2015, Hassanpour et al. 2019).

In recent years, researchers have sought to establish correlations between TBM operational parameters and rock mass specifications. These studies have predicted rock mass parameters based on monitoring data of TBM operation using back analysis methods. Farrokh et al. (2010) investigated the influence of ground conditions on machine performance based on information obtained from the Ghomroud tunnel, which is 36 km in length.
Nucleation of Instability on Granitoid Faults Under Hydrothermal Conditions: Implications for Fluid Injection-Induced Seismicity
Authors: Huang Rui , Zhang Fengshou , An Mengke , Elsworth Derek
Published: August 2024

Typical in the development of enhanced geothermal systems (EGS), fluid injection for hydraulic stimulation and fracturing hosts the potential for induced seismicity by reactivating deep faults. We use granite cores from the Pohang EGS site in low velocity shear experiments on simulated fault gouges at confining stresses of 110 MPa, temperatures of 100-250 °C and fluid pressures of 21-80 MPa. These experimental conditions are representative of deep geothermal reservoirs and allow the influence of variations in temperature and effective stress to be explored on the nucleation of instability. Our observations document a transition from velocity-strengthening to velocity-weakening response when both the temperature was raised from 100 to 250 °C and the effective confining pressure was reduced from 89 to 30 MPa. Shear deformation localizes in a narrow shear zone with this increased temperature and a transition from fault compaction to dilation evolves with reduced effective stress – congruent with the transition to velocity weakening. These results suggest that high temperature and low effective stress both favor nucleation of earthquake ruptures during fluid injection. Thus, controlling fluid overpressures and being aware of anomalously high thermal gradients potentially enable important controls to be applied in mitigating such injection-induced seismic risks.

1. INTRODUCTION

Fluid injection into the deep subsurface is capable of activating nearby faults and triggering seismicity. This phenomenon has been widely reported in numerous underground projects - including for enhanced geothermal systems (EGS), wastewater disposal and shale gas development (Elsworth et al., 2016; Grigoli et al., 2018; Walsh & Zoback, 2015; Bao & Eaton, 2016). For mature faults present in such projects, the frictional properties of the fault typically control fault rupture and seismic response (Ikari et al., 2011; Niemeijer & Collettini, 2014). Thus, detailed characterizations of the evolution of fault strength and stability under hydrothermal conditions are crucial in understanding and mitigating such seismic risk for induced earthquakes.
Casing Force Analysis During MPC Waiting Setting Stage Considering the Cement Hydration and Heat Release Process
Authors: Liu Jinlu , Li Jun , Li Yingjie , Li Hui , Yang Hongwei , Liu Gonghui
Published: August 2024

Casing force and deformation during MPC (managed pressure cementing) waiting setting stage in deep and ultra-deep wells significantly impacts wellbore integrity. To accurately analyze casing force, the cement hydration and heat release process during waiting setting of cement is initially considered, followed by the establishment of a prediction model for Casing-Fluid-Formation temperature field. Subsequently, a diagram illustrating casing stress is constructed. Based on the predicted temperature field results, the comprehensive influence of temperature on axial force of the casing, column pressure of cement, and casing gelling suspension force are taken into account to establish a prediction model for casing force during cement stone hardening. Using hook load data from a well A in Sichuan Basin as an example, the model is verified with a prediction error of less than 5%. Key parameters during the cementing process are analyzed. The findings indicate that the casing temperature field initially decreases before increasing and then decreasing again over time. Due to changes in the temperature field, both fluid column pressure and suspension force of the casing undergo constant variations while the cement is hydrated. When casings experience stresses exceeding their strength limits, plastic deformation occurs which compromises wellbore integrity. The results of this study can provide theoretical guidance for wellbore integrity during MPC waiting setting stage.

1. INTRODUCTION

With the growth of human demand for oil and gas resources, oil and gas extraction is gradually developing in the direction of deep and ultra-deep wells (Liu, et al., 2023). The harsh natural conditions as well as low reserves and hard-to-explore oil and gas reservoirs require low-cost, efficient and safe cementing technologies. Meanwhile, with the increase of well depth, the construction process is more and more facing the problems of HPHT (high temperature and high pressure), narrow density window, narrowing of wellbore flow channel, long bare hole section, et al. The increasingly complex construction conditions bring new challenges to the cementing (Xu, et al., 2019). For cementing in complex formations, overflow is easily induced by pressure, in addition. If the pressure is increased excessively during the construction, it may also lead to downhole leakage, all of which may result in failure of cementing and bring very big hidden dangers to the cementing construction. As the cementing process is complicated and involves many links, the MPC (managed pressure cementing) technology has become extremely urgent (Rostami, et al., 2017; Wilson, et al., 2018). The research on MPC technology will greatly reduce the cost of cementing, improve the quality of cementing, reduce the occurrence of accidents, and ultimately further improve the level of oil and gas drilling and completion (Thibodeaux, et al., 2018; Teoh, et al., 2019).
Study on Wellbore Stability of the Intrusions in Manshen Block, Tarim Basin
Authors: Tang Bin , You Zhi , Gao Haiyang , Liu Sen , Xiao Guilin , Li Hongda , Lu Yunhu
Published: August 2024

A set of intrusions is developed in the deep Ordovician in Western China. However, the complex coexistence of losses, collapse and jamming during drilling seriously restricts the exploration and development of deep oil and gas resources. Aiming to solve the problem, this article first conducted geophysical and engineering characteristics analysis on the drilled wells that encountered the intrusions in the field, then carried out the physical and mechanical experiment with the intrusions and performed numerical simulation of the intrusions, to clarify the wellbore instability mechanism and controlling countermeasures of the intrusions in the block. The results of the experiment show that the existence of microfractures significantly reduces the overall strength of the intrusions, and provides a channel for drilling fluid intrusions. The results of the numerical simulation show the existence of the weak plane effect of microcracks plays a main role in controlling the wellbore instability of the intrusions. For the intrusions with high degree of breakage, within the safe drilling fluid density range, the impact of density changes has little influence on the wellbore instability, while the plugging property has great influence on the wellbore stability. The research achievements are helpful to guide similar strata to improve wellbore instability.

1. INTRODUCTION

As global energy consumption continues to increase, achieving efficient development of deep and ultra-deep resources has become an important goal to continue conventional oil and gas resources and increase oil and gas production. However, according to statistics, the phenomenon of wellbore instability widely exists in the exploration and development of deep and ultra-deep resources in major oil and gas fields around the world. It is currently the most important complex problem plaguing the drilling engineering community (Chen et al., 2008; Jin and Chen, 2012). The Manshen block studied in this article is located in the hinterland of the Taklimakan Desert and in the Aman transition zone of the northern depression of the Tarim Basin. It has abundant oil and gas reserves and huge development prospects. The strata below the Ordovician in this block are affected by diabase intrusions. During the drilling process, losses and collapse are prone to occur, resulting in frequent downhole obstructions, which seriously restricts safe and efficient drilling.
A Numerical Solution to the Flow-Induced Vibration of a Hanging String in a Storage Cavern
Authors: Chieslar J. D.
Published: August 2024

A hanging string is the center pipe or tube in a storage cavern. It is situated inside of a cemented casing and, in conjunction with the cemented casing, is used to move product (crude oil, propane, natural gas, etc.) into and out from the storage cavern. When the injected fluid exits the hanging string, it exerts a back-pressure, causing the string to vibrate. Above a certain injection flow rate, the vibration becomes unstable. Before this condition, however, the string may bend and even break due to fatigue. Recently a field test (Reitze, A. 2019) was conducted at four different injection rates to assess the tendency for the hanging string to vibrate. This provided the opportunity to validate closed form solutions (Ratigan, J. 2004, 2017). The purpose of this communication is to provide a numerical solution to this problem. The numerical model produced results within the minimum and maximum vibration amplitudes recorded in the field test, at all four flow rates. Furthermore the numerical solution affords the opportunity to capture effects not normally addressed in closed form solutions.

1. INTRODUCTION

As early as 2004 SMRI (Solution Mining Research Institute) (Ratigan, J. 2004) has taken an interest in the vibrations of hanging strings in storage caverns by virtue of it's funding research into this phenomenon. A cavern operator would naturally prefer to maximize the flow rate while avoiding any possible damage. Consequently there exists a motivation to definitively characterize this phenomenon. While it may be most common that the hanging string is a 10.75 inch (0.273 meter) diameter pipe, the length of the string beyond the cemented casing as well as the fluids involved would certainly impact the flow rate at which instability develops. To this end SMRI recently funded a field test (Reitze, A. 2019) in which a hanging string was instrumented and motions were measured at four different flow rates. Prior to this McGill University undertook research into this phenomenon which involved the development of analytical models as well as bench-scale testing. This work may be summarized in the thesis of S. L. Minas (Minas, S.L. 2017).
Sonar Surveys/Nurb-Surfaces/Adaptive, Body-Fitted Meshing for Large-Scale Modeling of Multiple Solution Mines
Authors: Chieslar J. D.
Published: August 2024

An adaptive meshing technique is detailed which is suitable for large scale finite element modeling of solution mines. The resulting meshes of "bricks" are fully compatible (portable), that is no hanging nodes result, requiring multi-point constraints to satisfy continuity. The procedure begins with sonar surveys and a corrective process is undertaken to make the resulting geometries suitable for meshing. Oftentimes the sonar surveys have irregularities, not to mention excessive detail which makes meshing cumbersome and time-consuming. Solution mines used for waste disposal are often incomplete since the sonar doesn't penetrate the waste. Solid modeling techniques are used to ‘plug’ holes in incomplete surveys. Non-uniform rational b-splines are subsequently fit to the surfaces of the pre-processed solution mines and a subsequent discretization is made to create a suitably-coarse description while respecting the mine geometry and volume. The voxel characteristic at the cavern wall is removed, resulting in a mesh, composed entirely of bricks, accurately representing the cavern geometry.

1. INTRODUCTION

Sonar surveys of solution-mined caverns, typically situated in salt domes, once read into a visualization application, may have obvious irregularities, may be incomplete, or may have unnecessarily high resolution for meshing purposes. In order to prepare these geometries for meshing, we shall pre-process these, first by fitting a b-spline surface to each, then discretize each to a resolution that both respects the geometry and admits an efficient interrogation for mesh generation purposes.

Once pre-processed a solid model is constructed using the discretized caverns. This model defines not only the modeling domain, but also includes geometries identifying locations for refining the mesh (adapting) and also parses the domain to isolate areas of particular importance for post-processing. Certain post-processing techniques may become excessively slow for interaction and interrogation purposes, if these techniques are extended throughout the modeling domain.

For salt domes hosting multiple caverns, interest has increased in assessing the influence of caverns on each other, particularly when considering that cavern volumes generally increase over time. This is due largely to difficulties in maintaining a fully saturated brine in caverns that are frequently filled and emptied. This ongoing dissolution generally overcomes the natural tendency for the caverns to close due to creep. Adaptive meshing is vital when multiple caverns are considered in a single simulation exercise. This allows suitably ‘small’ elements for cavern walls while simultaneously allowing increasingly larger elements beyond.
Drilling Design and Optimization Technology for Ultra Deep Wells in Tarim Oilfield: A Case Study of Well Take-1, the Deepest Well in Asia
Authors: ChunSheng Wang , ShaoBo Feng , Zhi Zhang , Bo Zhou , XiaoLiang Wang , XiaoGang Lv , JinLong Liu , Bao Zhou
Published: August 2024

The Tarim Basin is a Precambrian superimposed composite basin. The main source rocks are characterized by ultra-deep and ancient characteristics. In 2023, based on the dual goals of oil and gas discovery and scientific exploration, Tarim Oilfield proposed the deepest exploration target in China named Take-1, to explore deeper carbonate oil and gas reservoirs under the Fuman Oilfield, with a designed vertical depth of 11,100 meters. In order to achieve drilling goals safely and efficiently, pioneering work has been done in drilling design. The drilling design is based on comprehensive geological engineering research. The design of the upper casing reaches the deepest depth in the area, and engineering technical measures are adopted to achieve the drilling of multiple sets of strata. The force of wellhead tools on ultra-long and overweight casing is simulated and calculated to avoid the casing entering the plastic deformation state during the running process. Hydraulic parameters and vibration effects shall be fully considered during the design of drilling tool assembly to realize safe drilling. The research and field implementation progress show that the key technology of the drilling design of Take-1 can solve the series of drilling difficulties faced and achieve the goal of the 10,000-meter drilling project.

1. INTRODUCTION

In 2023, the Tarim Oilfield proposed the deepest exploration target in China, with the well number Take-1. One of the purposes is to explore the deeper carbonate reservoirs under the Fuman oil field. The design vertical depth is 11,100 meters, and drilling commenced on May 30, 2023, reaching a depth of 10,000 meters by March 4, 2024.

At present, there is only one well with a vertical depth of over 10,000 meters drilled on land worldwide, which is the SG-3 well drilled by the former Soviet Union in 1989. The completed drilling depth is 12,262 meters (Claesson et al. (2000)). The well was drilled in four sections with a 36-inch pilot hole and an 8 1/2-inch borehole, and took 23 years to complete. The Tiber well, which was completed at a depth of over 10,000 meters in the deepwater basin of the Gulf of Mexico, USA, was drilled to a depth of 10,685 meters (1,259 meters of water depth) using a seven-opening structure (Naranjo, J. C. et al. (2011)). In October 2022, Abu Dhabi National Oil Company of the UAE set a new record for the world's deepest well in the UZ-688 well on the artificial island of the Upper Zakum field, which was completed at a depth of 15,240 meters in a horizontal well (El Sabeh, K.et al.(2023)).
Surrogate-Based Hydraulic Fracture Propagation Prediction Using Deep Neural Network Proxy
Authors: Li Fan , Zhang Yayun , Xiao Cong
Published: August 2024

Reliable prediction and uncertainty quantification of hydraulic fracture propagation behavior are crucial aspects of unconventional reservoir development, however, their implementations are largely restricted by the huge computational cost of the high-fidelity model simulations. We present a deep autoencoder neural network proxy workflow that allows us to rapidly visualize subsurface fracture morphology (e.g., fracture width, fracture height and fracture length) given pumping schedule and rock properties (e.g., Poisson ratio, Young module, leakage coefficient, etc). Nevertheless, the training process becomes inefficient due to the large output dimensionality. To overcome this issue, an autoencoder network is initially employed to uncover lower-dimensional features that effectively represent high-dimensional fracture morphology images. In our methodology, the regression model is trained to forecast lower-dimensional features instead of directly constructing original fracture image. During the prediction phase, the trained regression model initially predicts the latent variables based on wellhead pumping data, formation characteristics, and rock geomechanic properties. Subsequently, these latent variables are utilized as inputs for the trained decoder to generate fracture morphology images. In addition, a fast self-developed full-physics fracturing simulator is used to efficiently simulate a large set of training samples related to the fracture morphology. Some preliminary results based on a simple illustrative example, i.e., single-fracture propagation, are used to demonstrate the accuracy and efficiency proposed approach. The proposed deep-learning-based visualizations model should be a fast emulator for quantitative characterization and monitoring of hydraulic fracturing stimulation. Further research is required to verify its applicability to field-scale reservoir models with complex fracture network.

1 INTRODUCTION

Horizontal wells hydraulic fracturing is a key technology for unconventional oil and gas development (Daneshy et al, 2011; Barati et al, 2014). In order to improve the degree of reserve utilization, North American oil companies are continuously exploring volume transformation technologies to reduce well spacing and fracture spacing. Onsite fiber-optic temperature monitoring and acoustic monitoring indicate that in the case of small spacing renovation, there are issues such as uneven liquid injection in multiple clusters of cracks, and the proportion of liquid injection in each cluster is closely related to factors such as perforation parameters and stress distribution in each cluster (Wheaton et al, 2016). To improve the balanced expansion of multi cluster fractures and optimize the design of multi cluster fracturing schemes, it is urgently necessary to establish an efficient simulation method for multi fracture propagation coupled with wellbore perforation fracture (Chen et al, 2022, 2022).
Helium Gas Release by Rocks Undergoing Crushing
Authors: Kibikas W. M. , Paul M. J. , Wilson J. E. , Kruichak-Duhigg J. N. , Broome S. T.
Published: August 2024

Geogenic gases often reside in intergranular pore space, fluid inclusions, and within mineral grains. In particular, helium-4 (4He) is generated by alpha decay of uranium and thorium in rocks. The emitted 4He nuclei can be trapped in the rock matrix or in fluid inclusions. Recent work has shown that releases of helium occur during plastic deformation of crustal rocks above atmospheric concentrations that are detectable in the field. However, it is unclear how rock type and deformation modalities affect the cumulative gas released. This work seeks to address how different deformation modalities observed in several rock types affect release of helium. Axial compression tests with granite, rhyolite, tuff, dolostone, and sandstone - under vacuum conditions - were conducted to measure the transient release of helium from each sample during crushing. It was found that, when crushed up to 97500 N, each rock type released helium at a rate quantifiable using a helium mass spectrometer leak detector. For plutonic rock like granite, helium flow rate spikes with the application of force as the samples elastically deform until fracture, then decays slowly until grain breakdown comminution begins to occur. Both the rhyolite and tuff do not experience such large spikes in helium flow rate, with the rhyolites fracturing at much lower force and the tuffs compacting instead of fracturing due to their high porosity. Both rhyolite and tuff instead experience a lesser but steady helium release as they are crushed. The cumulative helium release for the volcanic tuffs varies as much as two orders of magnitude but is fairly consistent for the denser rhyolite and granite tested. The results indicate that there is a large degassing of helium as rocks are elastically and inelastically deformed prior to fracturing. For more porous and less brittle rocks, the cumulative release will depend more on the degree of deformation applied. These results are compared with known U/Th radioisotopes in the rocks to relate the trapped helium as either produced in the rock or from secondary migration of 4He.
Sensitivity Analysis of a Dynamic Subsidence Prediction Model for Longwall Extraction
Authors: Maldonado E. , Benitez J. D. Romero , Agioutantis Z.
Published: August 2024

Surface ground deformations due to mining are dynamic in nature and depend, among others, on the rate of mining. There are many formulations that can calculate and predict ground deformation due to mining. The majority of these models can accurately predict final deformations, i.e., maximum deformation values at specific surface points. In many instances, dynamic deformation values need to be considered, especially when undermining surface structures that are sensitive to subsidence, differential displacements, and/or tilt. This paper discusses subsidence development (dynamic subsidence) over a longwall excavation in the eastern US, which was recently completed. Measurements include x,y,z coordinates of a number of points (stations) over the longwall panel, which were monitored over a period of time while mining the panel. Dynamic subsidence was modeled for each of these surface points using an empirical formulation based on the influence function method as implemented in the Surface Deformation Prediction System (SDPS) package. Results show that the location of each surface point with respect to panel boundaries affects the calculation of dynamic subsidence values. A sensitivity analysis was completed for some of the parameters that influence dynamic subsidence calculations. These parameters include the edge effect offset and the time factor.

1. INTRODUCTION

Full extraction methods for underground coal mining, such as longwall mining, can result in movements of the surrounding rock layers. When such movements propagate to the surface, surface subsidence may occur. As mining activities progress, movements induced by mining extend from the coal strata through the overburden to the surface (Agioutantis et al., 2018). The study of subsidence in coal mining regions started in Europe during the mid-20th century (Bauer, 2008). Since then, a number of scientific publications regarding subsidence prediction methods have been completed. Currently, a number of final deformation prediction methods are available to model longwall panels and can be applied to different cases with variable features (Whittaker et al., 1989; Kratzsch, 1983).
Rock Mass Failure and Remedial Measures Implemented When Excavating Ultra-Deep Shaft Stations
Authors: Lindsay J. , Hall A. , Cai M. , Simser B.
Published: August 2024

This paper presents several geotechnical challenges experienced while excavating two shaft stations at the depths of 2490 m and 2550 m in highly stressed grounds, along with engineering solutions that effectively reduce exposure and risk associated with the excavations. Proactive measures were completed ahead of beginning the 2490 shaft station excavation; however, adverse conditions further influenced by a nearby fault led to significant rock mass failure and bowling of the station floor. These unanticipated conditions resulted in project delays and increased risk for the operators working at the face. Based on detailed field observations made while excavating the 2490 shaft station, insights from instrumentation and microseismic monitoring data, the methodology for excavating the 2550 shaft station was modified to mitigate the risk of ground failure. Engineering-based modifications introduced for the 2550 station included reducing the size of the initial shaft station blast, and pre-sinking and supporting the shaft below the station floor before the excavation of the shaft station. These modifications and increased distance from the fault resulted in better control of the ground conditions, leading to a 50% reduction in seismic activity and rockburst risk, and no bowling of the station floor. The outcomes not only resulted in cost savings but also provided valuable insights into the geotechnical intricacies and excavation strategies essential for safe mining operations at extreme depths.

1. INTRODUCTION

In the underground mining industry, many operations use shafts to access orebodies. A shaft is a vertical or inclined excavation sunk from the surface or underground. When a shaft is sunk from underground, it is called an internal winze. Operations that utilize shaft infrastructure require the construction of shaft stations. A shaft and its connecting shaft stations are critical infrastructures that provide access for personnel, equipment, material, and the transportation of ore to the surface.

(McCarthy & Livingstone, 1993) determined that a shaft is a more viable option over a haulage ramp when the depth is greater than 650 m and the production approaches 1.2 million tonnes per year. To access deep ore deposits, a ramp is inherently slower and requires the removal of more waste rock than shaft sinking.
Proppant Migration and Distribution Simulation in Tortuous Fractures with Gradually Narrowing Walls
Authors: Yan Pengyin , Wang Zhiming
Published: August 2024

Migration and packing patterns of proppants play a critical role in the conductivity of hydraulic fractures and unconventional oil and gas production. However, the fracture surface is usually tortuous with gradually narrow walls (tortuous - wedge fractures). Existing fracture models only consider tortuosity, and more efforts are needed in this regard. In this study, a numerical model of proppant transport in tortuous wedge-shaped fractures is established based on CFD-DEM method, used to investigate the effects of tortuosity, wedge angle, diameter of proppant, fluid velocity on the migration and placement of proppants. The results reveal that the migration and distribution of proppant in tortuous-wedge fractures exhibit significant disparities when compared with straight fractures or tortuous fractures. Proppant migration in tortuous-wedge fractures is divided into the suspended sand stage, sand bed rapid growth stage and top suspended sand stage according to the main force. The proppant transport distance increases with the increase of the wedge angle. Compared with the tortuous fractures with a wedge angle of 0°, the migration distance of proppant in the tortuous wedge fractures, t = 1 s, wedge angles of 1° and 2° increased by 16% and 29%. However, with the increase of it, the congestion of the proppant may also occur, and there is a critical angle. The greater the tortuosity, the greater the kinetic energy loss of particles and the advancing angle of the dune. Compared with the straight fracture, t=3 s, and the average velocity is reduced by 36%, and 45%. In addition, the proppant migration in tortuous-wedge fractures is non-uniform distribution, and the dune is higher in the tortuous place. This study benefits to understand the migration mechanism of proppant in fractures. It can provide theoretical guidance for the stimulation of unconventional reservoirs.

1. INTRODUCTION

Hydraulic fracturing is an important means of reservoir stimulation and improving oil and gas recovery. By pumping high - pressure fluid, the reservoir is broken and proppant particles are injected to fill the fractures, forming a long - term high conductivity channel for oil and gas in the reservoir. Proppant migration in fractures is a fluid - solid coupling problem among reservoir fluid, proppant particles and fracture walls. The migration and distribution of proppant depend on the physical parameters of particles, fluids and fractures, the distribution of flow field and pressure field in complex fractures, and the mechanism of action is complex. Scholars have carried out a lot of research based on indoor physical experiments and numerical simulation methods.
Stress Corrosion Cracking in Carbonates Initiated by Carbonic Acid, A Reactive Molecular Dynamic Simulation
Authors: Wang Jingru , Liu Yuetian , He Yuting , Liu Xinju , Lin Ziyu , Zhang Bowei , Chai Rukuan
Published: August 2024

As the greenhouse effect gradually intensifies, addressing CO2 as the primary greenhouse gas has become a pressing concern. Currently, the predominant carbon sequestration technique involves storing CO2 in reservoirs or saline aquifers. However, CO2 readily dissolves in water, forming carbonic acid, which can compromise geological formations and lead to stress corrosion cracking. Stress corrosion cracking (SCC), a chemical activation mechanism, involves fluid adsorption on crack surfaces and fluid-assisted crack propagation. While there is extensive research on the stress corrosion cracking of CO2 in quartz crystals, investigations on stress corrosion cracking in gas-water-carbonate rock systems remain limited. Moreover, the carbonic acid formed when CO2 dissolves in water can engage in complex chemical reactions with carbonate rocks, exacerbating the corrosion and cracking of carbonate rocks. This study focuses on carbonate reservoirs, representing them using calcite crystals. Molecular dynamics simulation is employed to investigate stress corrosion cracking in pre-cracked calcite crystals under fluid interaction. By comparing the cracking behavior of calcite crystals in different environments, the intrinsic mechanisms of crack propagation are analyzed. This study indicates that carbonate fluids have a strong impact on the subcritical expansion of cracks. During the stress corrosion cracking process, Ca-O bonds are the first to break. H atoms from the external environment readily form H-O bonds and C-H bonds on the surface of calcite, with H-O bonds binding to Ca atoms, accelerating the fracture of Ca-O bonds. In a carbonate environment, H atoms infiltrate the interior of calcite more rapidly, binding with C and O atoms, creating crystal vacancies, and intensifying the extent of stress corrosion cracking. This study aims to explore the damage to carbonate rock reservoirs during the CO2 storage process and analyze the gas-water-rock interactions in enhanced oil recovery with CO2 injection or during CO2 fracturing processes. These findings contribute to describing the details of rock fracturing and provide insights for the development of effective oil and gas extraction and carbon sequestration technologies.
Simulating Large-Scale Supported Pillar Laboratory Experiments in 3DEC
Authors: Chaurasia A. , Walton G.
Published: August 2024

Underground mine pillars are typically supported using rockbolts, wire mesh, shotcrete liners, or a combination of these methods to enhance stability and maintain their load-bearing capacity. The design of these supports is generally based on field experience, which is often site-specific, making them less applicable to all geological and loading conditions. Advancements in computational power have made it feasible to utilize numerical tools to simulate and analyze complex deformation behavior effectively. Discrete Element Methods (DEM) are more suitable than continuum modeling tools for simulating large displacements and accounting for the influence of rock support. This study employed a bonded block modeling approach in 3DEC to simulate pillar deformation and support behavior under monotonic loading conditions for three different width-to-height ratios (0.5, 1, and 2). These models were calibrated against large-scale laboratory compression test data for a porous limestone with a cross-section of 0.5 × 0.5 m2. The objective was to evaluate the ability of a model calibrated against unsupported pillar test results to reproduce observed ground-support interaction trends for supported pillar tests. The supports, such as grouted rock bolts, face plates, and wire mesh, were explicitly represented using built-in structural elements to resemble the laboratory tests, and their properties were calibrated using a trial-and-error approach until the simulation reasonably matched the laboratory results. The effects of the support systems on the peak strength, residual strength, and deformational behavior of the pillar were evaluated for all three width-to-height ratios.

1. INTRODUCTION

Underground mine pillars play a crucial role in providing natural stability to the roof and ensuring safe working conditions for both workers and machinery. Despite engineering design efforts, the challenges of ground falls and pillar failures persist and continue to be concerns in the field. Consequently, support systems such as rockbolts, wire mesh, face plates, and shotcrete are frequently employed to stabilize pillars, limiting the progression of spalling and pillar degradation, and mitigating the associated risks of sudden or violent pillar failure (Kaiser et al., 1996; Mohamed et al., 2016). Therefore, pillar design should consider rock-support interaction in addition to common geological and loading considerations.
Cyclic Loading-Unloading Impacts on Salt Cavern Stability: Implication for Underground Hydrogen Storage
Authors: Chang Kyung Won , Ross Tonya S. A.
Published: August 2024

Underground caverns in salt formations are promising geologic features to store hydrogen (H2) because of salt's extremely low permeability and self-healing behavior. Successful salt-cavern H2 storage schemes must maximize the efficiency of cyclic injection-production while minimizing H2 loss through adjacent damaged salt. The salt cavern storage community, however, has not fully understood the geomechanical behaviors of salt rocks driven by quick operation cycles of H2 injection-production, which may significantly impact the cost-effective storage-recovery performance. Our field-scale generic model captures the impact of combined drag and back stressing on the salt creep behavior corresponding to cycles of compression and extension, which may lead to substantial loss of cavern volumes over time and diminish the cavern performance for H2 storage. Our preliminary findings address that it is essential to develop a new salt constitutive model based on geomechanical tests of site-specific salt rock to probe the cyclic behaviors of salt both beneath and above the dilatancy boundary, including reverse (inverse transient) creep, the Bauschinger effect and fatigue.

1. INTRODUCTION

Hydrogen (H2) is an attractive energy storage medium due to its high specific energy and clean performance [U.S. DOE Regional Clean Hydrogen Hubs Program (H2Hubs)]. However, the low density of H2 requires large-scale, high-pressure endurable storage sufficient to meet the scalable supply and demand. Underground caverns in salt formations can be suitable storage reservoirs due to low permeability and self-healing behaviors of the salt rock. In the United States, domal salts located in the Texas Gulf Coast region are potential targets to store H2 because off their storage volumes, as well as their proximity to critical markets and infrastructure.

Successful salt-cavern H2 storage schemes must maximize the efficiency of cyclic injection-production operation while minimizing H2 loss through adjacent damaged salt. Underground H2 operation can result in three major geomechanical behaviors: (1) cavern volume changes with creep (creep rate will vary depending on operation cycles), (2) potential leakage through damaged caprock nearby the wellbore, and (3) hydraulic and mechanical interactions among multiple caverns, including presence of fractures, stress transfer etc. (Figure 1). However, the salt cavern storage community has not studied these geomechanical behaviors of salt rocks driven by quick operation cycles, which may have a significant impact on the cost-effective storage-recovery performance.
Experimental and Numerical Validation of Cooling-Induced Stress Change Within a Caprock Shale – Seal Integrity Insights from the Northern Lights CCS Project
Authors: Thompson N. , Griffiths L. , Bjørnarå T. I. , Smith H. , Andrews J. S.
Published: August 2024

As Carbon Capture and Storage (CCS) is experiencing rapid growth, there is increased focus on the geomechanical integrity of the storage system(s). In addition to pressure limitations, thermal influences (due to injection of cold CO2 into a warmer subsurface) can play an important role in defining the geomechanical integrity of the caprock seal. Through analytical investigation, Thompson et al. (2021) recognized that undrained pore pressure effects in low permeability caprocks alter the effective stress picture of the caprock, as the caprock may be cooled significantly due to conduction processes. This paper builds on that work and presents laboratory data from specially designed thermal uniaxial strain testing in caprock shale material, as a validation exercise for the analytical investigation. The results of these tests are directly compared to confirm the analytical approach and to determine lab-calibrated parameters that can be used for further simulation and assessment of caprock integrity. Where the experimental and analytical approaches serve as end member descriptions of the effective stress evolutions (drained versus undrained) from cooling, numerical simulations are also performed to quantify additional factors that may affect the effective stress response. All three approaches are found to be consistent, qualifying the analytical approach as a robust means of thermal influence investigation for caprock integrity evaluation.

1. INTRODUCTION

In the challenge to meet net zero ambitions, the Carbon Capture and Storage (CCS) industry is developing rapidly, with a high number of large-scale projects planned and/or coming on stream in the coming years (Global CCS Institute [2023]). Integrity assurance of the subsurface storage systems is paramount and, subsequently, geomechanical characterization and risk assessment is recognized as first-order contribution to storage site feasibility and storage volume potential (Rutqvist [2012]).

Inherent to CO2 injection and storage are changes in pore pressure that need be assessed in terms of geomechanical integrity. Thermal changes can also be equally as important, as the injected CO2 is often significantly colder than the temperature of the storage formations. Such thermal influences may result in significant changes in effective stress both in the reservoir/storage and caprock/seal formations and therefore must be fully assessed in order to fully quantify the geomechanical risk for a given storage project.