bluuebunny/crossref_metadata_2025 huggingface dataset:
A Three-Dimensional, Finite Element-Based Study of the Effect of Heterogeneities on Thermo-Hydro-Mechanical Deformation During Cold Fluid Injection
Authors: Chaiwan P. , Burtonshaw J. E. J. , Thomas R. N. , Paluszny A. , Zimmerman R. W.
Published: September 2023

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

INTRODUCTION

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

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

INTRODUCTION

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

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

INTRODUCTION

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

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

INTRODUCTION

Since roughness is an important property of rock joints that affects their mechanical behavior, it should be investigated to analyze the stability of rock masses. To measure roughness, many different types of devices can be utilized to capture surface geometry of joints. Barton comb is a widely used tool to get 2D profiles of rock surfaces and more recently, laser and optical scanners are employed by many researchers to obtain their 3D geometries.

When quantifying the degree of roughness using various devices, measurers often do not consider their resolution. However, this can lead to over- or under-estimation of effective roughness since resolution determines how many details are captured in the acquired data. That is, when resolution is too low, asperities that enhance the shear strength might not be detected resulting in under-estimation of roughness. Conversely, when it is too high, very small asperities that may not affect the shear strength will be captured leading to over-estimation of effective roughness. Thus, measurers need to know what is the appropriate resolution for measuring joint roughness. To gain knowledge about it, it would be helpful to know about the effect of small asperities on shear behavior of rock joints.
Investigation on Radial Crack of Cement Sheath During CO2 Injection Using a TM-XFEM Coupled Model
Authors: Gu Chenwang , Su Feiyu , Feng Yongcun , Li Xiaorong , Deng Jingen
Published: September 2023

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

INTRODUCTION

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

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

INTRODUCTION

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

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

INTRODUCTION

The intermittency of renewable energy resources has created an urgent need for energy storage. Deployment of energy storage options will accelerate flexibility in grid operations and provide energy that can be applied to a diverse portfolio of industries. It can also provide environmental benefits by improving the overall efficiency of the power grid and providing a basis for the broader adoption of renewable energy thus reducing harmful emissions to the atmosphere (Uliasz-Misiak et al., 2022). According to Tarkowski & Uliasz-Misiak (2022), H2 is a reliable energy carrier that can play an important role in decarbonizing our current energy system. Hydrogen storage can be used to supplement energy demands associated with seasonal heating needs and peak load (Laban, 2020). The challenge with hydrogen however is that it has a higher energy per unit mass than any other liquid fuel. As an energy carrier, H2 has a low density of 0.089 kg/m3 at standard conditions. As such, it is difficult to store large volumes using chemical and physical storage methods (Lord, 2014). Currently, H2 storage can be stored on a small scale as compressed gas at around 5076 – 13778 psi in type 2, 3 or 4 tanks. In order to store gas at such high pressures, the capital and operational expenditures are significant. On medium scale, it can be potentially stored as a gas in spherical vessels at low pressures of ∼290psi thus requiring larger volume (Papadias & Ahluwalia, 2021).
Study on the Influence of Hydraulic Fracturing Operation on Local Fault Slip Under Non-Communication Condition Based on Numerical Simulation
Authors: Wang Kongyang , Han Yaotu , Xu Gang , Zhang Hui , Chen Bin , Jia Lixin , Xiao Yao , Yu Qinxin
Published: September 2023

For unconventional reservoirs, hydraulic fracturing is a common development method. Casing deformation occurs frequently during fracturing operations. Severe casing deformation will block the fracturing tool from reaching the designed position, due to the subsequent fracturing operation between the casing deformation position and the fracturing stage cannot be carried out. According to the statistical results of various oilfields, at least half of casing deformation cases are related to the faults across the well trajectory. Classic theory presumed that the normal stress and friction coefficient of the fault surface will decrease after the high-pressure fluid of the fracturing operation flows into the fault. When the friction stress is less than the shear stress of the fault surface, the fault is activated to slip and cause deformation of the casing passing through the fault. However, the research results based on numerical simulation in this paper show that even if the fracturing fluid does not communicate the fault, the change of the shear stress field at the tip of the artificial fracture also can cause the local fault to slip, especially those faults which the shear stress and friction stress are relatively close. This result can better explain some casing deformation cases far from the fracturing operation stage. In this paper other results indicate that: (1) Unlike the classical theory that the fluid flow into the fault causes the slip of all the fault area, the change of local shear stress field by fracturing operation will only cause the local fault slip; (2) Because only local fault slips, the influence of fault length on fault slip is not obvious, but the fault length and fault slip are still in a positive correlation; (3) The short fault located in the extension line area of the artificial fracture can make the artificial fracture more inclined to propagation to the fault area, and the length difference between the half artificial fracture length of the same fracturing stage is about 20%. Based on the research results, the fault area intersected by the artificial fracture extension line is the most dangerous fault. For the well trajectory that must cross fault, adjusting the design scheme to cross the area with a small fault slip is one of the feasible means to reduce the fracturing casing deformation probability.
Assessing the Feasibility of Geological CO2 Storage in a Depleted Gas Field with Multi-Scale Coupled Reservoir Geomechanics Simulation
Authors: Pan Yuanwei , Lee Daegil , Lee Haeseon , Kim Jongsoo , Wang Xiao , Cho Jaekyoung , Qiu Kaibin , Lee Hoseob
Published: September 2023

Korea National Oil Corporation (KNOC) is now leading the nation's 1st large-scale carbon capture and storage(CCS) demonstration project using a depleted gas reservoir in the East Sea of offshore Korea. The Donghae-1 gas field, first discovered in 1998, came online producing gas and condensate in 2004 putting the country in the list of hydrocarbon producers worldwide. The field shut down in 2021, and is now considered as one of the most immediate candidates for geological CO2 sequestration. As a candidate CO2 storage site, the geomechanical risks are vital to the injectivity, containment, and long-term sustainability which must be assessed and dealt with before field operations. To this end, cap rock integrity and well completion integrity evaluation of CO2 injection and storage are required for the feasibility study.

In an effort to evaluate the integrity of CO2 storage in Donghae-1 gas field, a thorough geomechanics study workflow was established. Core laboratory tests were firstly carried out to delineate geomechanical characteristics for both reservoir and cap rocks. The degradation of rock stiffness and strength was taken into consideration by treating core samples with CO2. 1D mechanical earth model (MEM) for a few selected wells was constructed honoring core testing results and logging data, and then the 3D MEM modelling was performed in full-field scale and in near wellbore scale. For the full field scale, the gas production was numerically simulated and history-matched before coupled reservoir geomechanics simulation for CO2 injection and plume migration was performed. To elevate the study to a comprehensive level, different CO2 operation scenarios were considered, covering different potential injection wells and maximum allowable injection conditions. Cap rock integrity was assessed by the failure criteria derived from core laboratory tests. As significant physical processes occur near wellbore, a well-centric and fine-grid sector model was built to delve more into hydraulic-mechanical coupled behavior in terms of rock integrity and well completion integrity.

This study indicates that it is less likely to damage the storage and cap rocks given the formation properties and the safe injection rate, and the potential risks of CO2 leakage are under control. Besides, multiple layers of shale above the target storage zones provide additional containment assurance. The workflow proposed in this study can be utilized to understand long-term behavior of CO2 storage, which is helpful to many similar CCS projects worldwide.
Study on High-Pressure Treatment of Unconventional Reservoirs with Water-Based Fluids
Authors: Zayas I. C. , Meegoda J. , Kolawole O. , Pinkert S. , Zhang D.
Published: September 2023

Shales are tight rocks with ultra-low porosity and often contain hydrocarbons (oil and gas). Both the United States and Israel have abundant shale formations containing oil and gas. The majority of shale hydrocarbon production in the United States takes place in Permian basin, Texas, whereas the largest kerogen shale deposits in Israel occur in the Negev area. For the recovery of oil and gas, shale formations are hydraulically fractured by injecting water-based fluids under high pressure. To transition away from fossil fuel use and address atmospheric greenhouse gas levels, sequestration of carbon dioxide (CO2) and hydrogen (H2) storage is now proposed in depleted tight hydrocarbon formations, such as shales. Shales are composed largely of clays and silts, bound by carbonates to form ultra-tight matrices, and containing interconnected nano- to micro- to macro-voids with total porosities of 1-6%. The introduction of fracturing fluids and, potentially, other fluids for storage purposes (e.g., CO2 and H2) may cause changes to the ultra-tight shale matrix, as formations had previously been isolated for millions of years. These changes have been linked to reduced production of oil and gas and may affect possible storage of CO2 and H2. The interaction between artificially introduced fluids and shale formations, leading to softened shale, is attributed to the interlayer expansion of clays and the dissolution of cementing carbonates. This study seeks to investigate of the effects of interaction between various fluids and unconventional reservoir rock at high temperature and pressure for geo-storage implications. Shale-fluid interactions will be quantified through the lens of mineralogical, pore network, and mechanical property changes. of CO2 and H2.

INTRODUCTION

Shale formations have ultra-low porosity and permeability, and when shales contain hydrocarbons, are considered unconventional reservoirs. Large shale gas reserves are popularly located in China, United States, and Argentina; with 31.6, 17.6, and 22.7 trillion cubic meters of reserve, respectively (U.S. Energy Information Administration, 2015). Horizontal drilling and hydraulic fracturing are major methods of extracting the hydrocarbons trapped in these tight formations (Speight, 2020). Once both a vertical and horizontal well is drilled into the reservoir formation, high-pressure fluid is injected at a designed rate. The fluid, often a water-based brine, also contain proppants chosen to withstand the rock closure pressure as fractures propagate out perpendicular to the horizontal well. These new fractures increase the connectivity of formation pores and allow for the hydrocarbons stored within them to be recovered. Depleted unconventional oil and gas reservoirs therefore offer potential uses for nuclear and wastewater disposal, hydrogen storage, and carbon sequestration, due to their existing wells and fracture networks, and otherwise low porosity.
Experimental Fracture Creation in Cores: Permeability and Porosity Measurements of the Fractured Cores and the Use of Such Measurements in Analysis of Pressure Falloff Tests Following Well Stimulation
Authors: Mindygaliyeva B. , Uzun O. , Amini K. , Fleckenstein W. W. , Kazemi H.
Published: September 2023

This paper presents an assessment of the stimulation of an existing, research, geothermal well in a potential enhanced geothermal system (EGS) in Utah, adjacent to the Roosevelt hydrothermal field. The geothermal well has undergone stimulation with the objective to extract heat efficiently from the field's low-permeability granitoid hot rock. This research focuses on deciphering the information content of the stimulated well's pressure transient test using laboratory-measured core data as guides. Specifically, fractures were created in the laboratory in several cores from a non-related granite outcrop and from the Utah FORGE granitoid geothermal reservoir. Matrix and fracture permeabilities and porosities, and pore compressibility were measured and, where appropriate, were used both as guides and input data in the interpretation of the analytical and numerical solutions of flow equations in history matching of the geothermal well measurements. The information obtained from the core experiments was of great value in conventional interpretation of pressure falloff tests. From a pragmatic point of view, our laboratory data suggest that the contribution of the matrix flow to the fracture flow is extremely small, and probably some of the pre-existing natural fractures reopen during well stimulation to provide the main path for fluid flow and, possibly, heat exchange in the stimulated geothermal wells.

INTRODUCTION

The process of drilling and completion of a pair of parallel injection-production wells in hot, dry rock (HDR) system at 7000-10000 ft depths in the Utah FORGE area is an extensive effort (Moore et al., 2020). Because the permeability and porosity of this HDR system are very small, there is no mobile hot brine in the formation to circulate to sufficiently extract the heat from the formation. The aforementioned injection-production pair shown in Fig. 1 (injector 16A(78)-32 and producer 16B(78)-32) are vertically placed parallel to each other and are intended to be connected by a set of hydraulic fractures (Kumar, D., & Ghassemi, 2019). At this point field attempts have been made to connect the two wells which are 300 ft apart (Allis & Moore, 2019) with three large hydraulic fracture (HF) stages. Each fracture has a relatively large surface area to provide a means of extracting heat from the formation via the injected water flowing through the fracture. However, there is a need for additional surface areas that are perceived as the surface areas of the micro- and macro-fractures in the stimulated volumes between three sets of parallel hydraulic fractures placed in the injection well. One does not know how permeable these smaller fractures are; nonetheless, it is anticipated that some of the innate fractures and the newly created ones provide additional permeability connection to the HDR matrix (Bruce Hill, 2021).
Evaluation of Shotcrete Performance from Full-Scale Load-Deflection Tests Using Numerical Analysis
Authors: Moon T. , Wang E. , Oh J. , Li K. , Ramandi H. L. , Zhang C. , Saydam S.
Published: September 2023

Shotcrete is a support system that is sprayed onto the surface of excavated tunnels and mines to create a self-supporting layer. It is an economic and integral solution to ground support in civil and mining construction projects. To ensure the long-term stability and safety of underground structures, it is essential to understand shotcrete's performance and failure mechanisms and to develop effective design methods. While previous studies have elucidated the performance and failure mechanisms of shotcrete, many unknowns and misinterpretations remain. This study conducted a numerical analysis replicating full-scale load-deflection tests in comparison with field test results. Parametric studies were also performed on the interaction between support elements and shotcrete adhesion under different loading configurations. The simulation revealed that the ultimate capacity of the shotcrete liner is primarily governed by flexural tensile failure mode, and the residual bonded area along the shotcrete panel periphery after the major bonding failure plays an important role in increasing the apparent flexural failure resistance of the shotcrete liner. A new alternative shotcrete design method based on the bending moment coefficient has been proposed and compared with empirical support design methods.

INTRODUCTION

Shotcrete refers to a ground-support system that is pneumatically sprayed, typically onto the exposed surface or an excavation face to produce a compacted self-supporting and load-bearing layer for underground structures. Today shotcrete has become an essential component of an initial ground support system or permanent structural lining that can be an economic and integral solution to a host of applications in civil and mining construction. Therefore, it is crucial to comprehend the performance and failure mechanisms of shotcrete as a ground-support system and to develop practical and effective design methods that can ensure the long-term stability and safety of underground structures.

Many researchers, Barrett and McCreath (1995), Kaiser, and Tennent (2001), and Bernard (2004), have elucidated the performance and failure mechanism of the shotcrete liner. However, many unknowns and misinterpretations remain on the failure process of shotcrete panel, such as: the interactions between shotcrete and rock bolt configuration, and the effect of the shotcrete adhesion, etc. These factors play an important role in the understanding and development of a more practical and suitable shotcrete lining design. Thus, the main objective of the paper is to: 1) investigate the influence of those key factors which could affect the performance and the failure mechanism of the shotcrete, by means of replicating the full-scale load-deflection test using Finite Element Method (FEM) analysis, 2) propose a new method of shotcrete design based on the findings above.
Intelligent Switch Control Algorithm of the Push-The-Bit Rotary Steerable Drilling System
Authors: Shen Xinyu , Liu Sen , Su Qiang , Mi Guangyong , Deng Haibo
Published: September 2023

Push-the-bit rotary steerable system (RSS) is a guide technology that realizes directional drilling by controlling the eccentric mechanism to push against the borehole wall. However, the control effect of push-the-bit RSS is often not satisfactory in many interference factors, such as rock anisotropy and trajectory deviation. An intelligent switch control algorithm based on push RSS is proposed to achieve a smooth trajectory, stable control, and efficient decision-making. Firstly, the control rules of thrust force and thrust orientation are given according to the actual drilling situation. Next, the decision results are substituted into the borehole trajectory prediction model to achieve an accurate prediction of the trajectory to be drilled. Finally, the intelligent switch and mechanical control effect are simulated using field data, and the control precision, trajectory complexity, calculation time, and other aspects are analyzed comprehensively. The results show that the on-off control algorithm can effectively overcome the influence of the system and other interference and get a smooth well trajectory. It also has high robustness and system response, helping to reduce the distance deviation between the wellbore trajectory and the designed trajectory.

INTRODUCTION

The critical task of wellbore trajectory control in oil and gas wells is to control the bit attitude to drill according to the pre-designed wellbore trajectory in the actual drilling process. Under actual working conditions, formation and drilling parameter changes make it challenging to obtain the real attributes of the formation, making it difficult to achieve accurate control of the wellbore trajectory. Given the above problems, relevant scholars have studied the control methods of wellbore trajectory, which can be divided into two categories: mechanical control and automatic control.

Currently, the commonly used mechanical control methods predict the segment to be drilled by force and deformation analysis of the steering tool and rock-bit interaction and constantly adjust variable parameters (pushing force, tool face, weight on bit, etc.) to implement the dynamic adjustment. Birades and Fenou (1998) proposed the "balanced curvature method" to predict the wellbore trajectory in the section to be drilled by changing the wellbore curvature until the lateral force decreases to zero or approaches zero. Guan et al. (2005) proposed the concept of "drilling trend Angle" considering the influence of design parameters of drill assembly on drilling trend and took it as an evaluation index of deviation building ability of guide tool. Wang et al. (2022) proposed a guidance tool trajectory prediction method based on zero lateral drilling rate criterion considering the influence of the drilling process.
Numerical Investigation of Mining-Induced, Hydromechanically-Coupled Responses for a Nevada Mine Site
Authors: Noonan G. E. , Lorig L. J. , Beale G. , Ferré P. A.
Published: September 2023

Understanding the coupled interaction of rock and water under stress is often a key factor in assessing slope stability in open pit mining. In this paper, a numerical modeling research project is presented which demonstrates the concept of hydromechanical coupling (HMC) and assesses the sensitivity of contributing parameters to pressure responses observed in a piezometer sensor due to excavation of a mine slope. Site monitoring data showing HMC effects within a mine in Nevada are analyzed and reproduced using FLAC. This research aims to promote the understanding of HMC in pit slopes and provide improved guidance on how to plan mining activity, monitoring and slope design to incorporate the benefit of HMC effects.

INTRODUCTION

Open-pit mining is a dynamic process that involves the excavation of earth materials to retrieve ore. During the mining process, changes to the physical properties of the in-situ rock mass are induced. As excavations progress, pore pressure changes occur beyond the slope face, and, while some factors such as infiltration or recharge may increase the pore pressure, others may help reduce it. Consequently, understanding the relation between pore pressure changes and rock deformation is a key factor in ensuring the stability of slopes and maintaining safe mining conditions. Pore pressure can be measured, predicted, and managed through active dewatering and depressurization programs to control stability.

In this research paper, 2D modeling using FLAC v8.1 is presented to help explain observed behaviors in piezometer monitoring data from a mine site in Nevada, and to provide a hydromechanical explanation for these behaviors using simple model illustrations. Different case scenarios using a variation of mechanical and hydrological input parameters are performed. Varied parameters are those which govern pore pressure responses caused by induced changes in total effective stress (unloading) of the rock mass, such as elastic modulus, porosity, and permeability. Results are presented and discussed for each modeling case scenario using pore pressure history at a point representing the piezometer sensor location.
The Secondary Brine Discharge Efficiency of Salt Cavern Gas Storage Was Improved by the Chemical Cementation Method
Authors: Yao Er-dong , Zhang Kun
Published: September 2023

Salt cavern gas storage has become one of the world's important natural gas strategic reserves and emergency peaking facilities. However, most salt cavern gas reservoirs in China are built in layered salt layers. After leaching, a large number of insoluble mudstones is loosely accumulated in bottom of the cavity, and occupies a large amount of storage capacity (1/3-2/3). After the first gas injection and brine discharge in the salt cavern, there is still 2-5m of water left to the bottom. Furthermore, there is still a large amount of water in the pores of insoluble mudstones, resulting in a large storage capacity loss. Therefore, it is urgent to explore the technique of secondary brine discharge to drain more brine away.

In this study, a lab simulated brine discharge device was set up. If conventional sand control screen is used, the brine discharge efficiency was quite low and a mass of mudstones plugged the pipeline. The permeability of the pipeline can be reduced to 0.1mD. The reason for the blockage of the pipeline is that the mudstone particles are loosely accumulated and can migrate into the pipeline with the fluid. To solve this problem, we propose to use the chemical cementation method to improve the efficiency of secondary brine discharge. In order to improve the mudstone porosity after cementation, a foam resin system with bisphenol A epoxy resin and corresponding curing agent was prepared. It can cure sand at room temperature and 80 °C in 4 days to form a porous solid with high conductivity. This solid formed by foam resin and sands has good sand control performance. Under a constant gas injection pressure (0.1MPa), the pipeline flow and sand production were tested, and the temperature resistance and salt resistance were also tested. The experimental results show that the measured permeability of the foam sand system can reach more than 15mD, the sand production can be controlled within 0.5% in the secondary brine discharge process and is greatly reduced. The foam resin system has good temperature resistance and salt resistance, and can still have good sand control and conductivity under the temperature of 20°C-80°C and brine concentration of 0-26%. This study provides a new idea for the secondary brine drainage and sand fixation of salt cavern gas storage.
An Improved P-Wave Velocity-Stress Model for Rocks in Triaxial Compression Experiments
Authors: Wang X. Y. , Jin Y. , Li K. C. , Zhou J.
Published: September 2023

The acoustic velocity-stress equation of rocks is important to underground stress or pore pressure prediction. The P-wave velocity has different dependencies on stresses in different directions. An improved model between P-wave velocity and stress was established. P-wave velocity was measured for sandstone at both hydrostatic and differential stress up to 60MPa in the laboratory. P-wave velocity increases with increasing confining pressure and differential stress, at different rates. The proposed model can fit the P-wave velocity measurement results very well. It provides an approach to model the stress dependency of P-wave velocity for rocks under differential stress.

INTRODUCTION

The stress dependency of elastic wave velocity of rocks is important for many geophysical applications such as pore pressure prediction and hydrocarbon detection. However, uncertainty still exists and the need to overcome it has become more critical. In the past few years, the relationships between elastic wave velocity and the effective stress in rocks has been studied by many researchers and several analytical models have been put forward. Generally, elastic wave velocity increases with increasing effective stress (Katsuki et al., 2014). In previous studies, most laboratorial measurements of P-wave velocity were made at hydrostatic pressure (Vinciguerra et al., 2005). Accordingly, most of the empirical models only focused on the dependency of elastic wave velocity on the mean effective stress, which assumes that the stresses in different directions have the same effect on the elastic wave velocities. The most popular empirical relationship originally has the following form (Zimmerman et al., 1986):

(Equation)

where VP is the wave velocities, Pe is the mean effective stress, A, B, C, D are empirical parameters determined from velocity-stress data set. Greenfield et al. (1996) proposed another wave velocity-stress model:

(Equation)

Both models are founded on the classical elastic velocity equation, in which the square of wave velocity is proportional to the elastic moduli, and the assumption that the matrix second order elastic moduli are linear functions of stress over the range of interest, and use an inverse exponential relationship to fit the effect of crack closure. (Greenfield et al., 1996) In the next few years, Zimmerman's model was developed by many researchers (Eberhart-Phillips et al., 1989; Freund, 1992; Jones, 1995; Prasad & Manghnani, 1997; Khaksar et al., 1999; Carcione & Tinivella, 2001; Pervukhina et al., 2010) to fit elastic wave velocities for different types of rocks over a wide range of effective stress levels.
Development of an Expert System for Unplanned Fall of Ground Assessment in Coal Mine Excavation Intersections
Authors: Adoko A. C. , Kaisa N. B.
Published: September 2023

Unplanned roof falls in tunnel intersections are commonly associated with casualties, accidents, economical loss and therefore pose a serious threat for coal mine profitability. Despite the technological advance in ground control, fall of ground (FoG) in tunnel intersection often occur. Subjective data and information are inevitably used in the design of coal mine development excavations which contribute to unplanned ground instabilities. These aspects are not considered in conventional design tools. Hence, the aim of this paper is to propose expert systems capable of adequately quantify the relationship between the unplanned roof falls, support methods and the geology. Fuzzy inference system (FIS) which uses fuzzy logic to discern relationships between data is implemented in this study. FoG in tunnel intersection data were compiled from several coal mines. Expert knowledge approach was used to construct the FIS. The system parameters include the FoG size, geology, types of support and groundwater conditions. Overall, the results indicated quite good agreement with the field observations. The correct classification rate varied between 67 and 80%. It is concluded that FIS could be used to assess FoG in tunnel intersection in coal mines.

INTRODUCTION

Despite greater awareness of the environmental implication of the coal business, there is still a considerable demand for it globally. The industrial development in China, India, and Southeast Asia countries were recently reported to be the main drivers of the 0.7% rise in worldwide coal consumption (Zhironkin and Cehlár, 2021). Meanwhile, there are a wide ranges of safety issues associated with coal mining. One of them is fall of ground (FoG) which is a generic term used to describe loose rocks falling from excavation faces (roofs and side walls). Unplanned FoG in roadway intersections in coal mines present a serious threat to mine safety, as intersections are by far the most common area for FoG to happen (Mueller, 2010; Mark and Gauna, 2017). It can occur in many geological and operational situations; even with primary and secondary support structures. There are several reasons for it to happen which include over-spanned intersections, non-sufficient support, excess horizontal stress, and weak geology with low strength of rock intersection.
Effect of Alternate Fracturing on Rock Porosity and Permeability Near Hydraulic Fractures
Authors: Li Shuai , Zhang Guangqing , Zhang Liye , Wang Wenrui , Zhao Chunyang
Published: September 2023

Stimulated Reservoir Volume (SRV) fracturing of horizontal wells significantly increases oil and gas production by generating a large amount of high-permeability main and branch fractures. This study attempts to explores the effect of fracturing sequences on smaller-scale fractures (micro-fractures, pore scales). We carried out multi-stage sequential and alternate hydraulic fracturing experiments, respectively. The effect of fracturing sequence on porosity and permeability characteristics was quantitatively analyzed from the microscopic perspective through Nuclear Magnetic Resonance (NMR) technology. The results show that: (1) the fracture deflection angle of alternating fracturing is about 50% of that of sequential fracturing, and alternate fracturing can reduce inter-fracture interference and effectively control crack propagation morphology; (2) alternate fracturing can reduce horizontal stress difference, which is more conducive to the formation of complex microcracks than sequential fracturing; (3) compared with sequential fracturing, the porosity and permeability near the fracture of alternate fracturing increased by 14.2% and 126.7%, respectively. In conclusion, alternate fracturing has more advantages in increasing the production performance of horizontal wells than sequential fracturing.

INTRODUCTION

The volume fracture formed by multi-stage fracturing of horizontal wells has significantly increased oil and gas production. It is one of the key technologies for the efficient development of unconventional oil and gas reservoirs (Shelley et al., 2012; Shelley et al., 2010). The stimulated reservoir volume (SRV) fracturing system is generally considered to be formed by main fractures and branch fractures. Multiple hydraulic fractures formed by multi-stage fracturing of horizontal wells will interact with each other. The hydraulic pressure in the formed hydraulic fractures will change the stress field distribution around the hydraulic fractures, thus affecting the initiation, extension, and development of new hydraulic fractures formed around them, thus affecting the recovery and fracturing efficiency of horizontal wells. This phenomenon is usually called the "stress shadow effect" (Bunger et al., 2012; Daneshy et al., 2012; El Rabaa, 1989; Nagel and Sanchez-Nagel, 2011).