bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a Modified Warpinski Method for In-Situ Horizontal Stress Prediction Coupled with Thermal Effects
Authors: Duarte M. C. , Fernandes F. B. , Gildin E. , Braga A. M. B.
Published: August 2024

Understanding the effect of in-situ stresses on geological formations has been modeled over the years aiming to evaluate their behavior in zones of interest. The relationship between horizontal stress, pore pressure, and fracture gradient significantly predicts the safe range of drilling fluid weight, avoiding kick, wellbore instability, and loss of circulation material. The challenges in estimating horizontal stress include the lack of information on rock properties, which entails the need for open-hole well tests and/or coring analysis. These techniques collaborate to estimate the stresses in a specific area well but are not applicable to all scenarios. The Warpinski method proposes an approach for elastic and viscoelastic rock behavior, introducing the relationship between stress and strain when deriving horizontal stress. This research presents a case study in which the Warpinski method is applied, assuming temperature variation and its effect compared to a second scenario when the temperature is assumed to be constant. The preliminary data were derived from a prior study referenced throughout the paper, and the results were compared to previous methods that were well-known in the oil industry. The data obtained from the Warpinski method shows a good approach related to the other methods mentioned, showing results that are in accordance with what is expected.

1 INTRODUCTION

Over the years, researchers have developed models to understand how in-situ stresses affect geological formations, intending to assess their behavior in specific zones of interest. Furthermore, as the pursuit of sustainable energy solutions intensifies, it requires intricate comprehension of the in-situ stress-strain dynamics, which makes it a paramount consideration in diverse subsurface engineering applications, playing a pivotal role in the realms of oil field development, geothermal energy extraction, and Carbon Capture and Storage (CCS) initiatives.

In the oil field, accurate estimations of in-situ stress are imperative for addressing challenges associated with bore-hole stability, hydraulic fracturing optimization, and reservoir management. The interaction between rock formations and the stress conditions is integral to mitigating risks such as wellbore collapse, induced seismicity, and fluid migration. The correlation among horizontal stress, pore pressure, and fracture gradient is a crucial predictor for determining a safe range of drilling fluid weight, preventing kicks, and the loss of circulation material (Lesage et al., 1991).
Evaluating a Practical Method for Rockfall Magnitude-Cumulative Frequency Estimation
Authors: Werley K. , Sala Z. , Hille M. , Vessely M. , Walton G.
Published: August 2024

Rockfall magnitude-cumulative frequency (MCF) distributions are useful for hazard analysis in slope asset management, including evaluating risk and the potential need for mitigation measures. MCF distributions can be produced from rockfall inventories; recently, remote sensing methods such as terrestrial lidar scanning (TLS) or structure from motion (SfM) photogrammetry have become popular tools for the generation of such inventories. However, it is not feasible to monitor every cut slope in mountainous regions such as Colorado, and for slopes that are monitored, it can take multiple years to develop an inventory that provides a reliable MCF distribution. This study evaluates the performance of an alternative rapid MCF curve estimation method relative to MCF curves generated from TLS- and SfM-based rockfall inventories. The estimation method involves a field or desktop inspection, wherein the inspector assesses the annual rockfall frequency and proportions of different rockfall volumes on the slope. The resulting frequencies are then averaged with literature values for the corresponding rockmass type to adjust the generic literature MCF curve to reflect credible rockfall from the slope. This method was applied to six cut slopes in Colorado that have at least two years of remote sensing-based rockfall inventories. We find that for many (but not all) of the slopes, the method provides a reasonable approximation of the MCF curve obtained using remote sensing data, and we discuss potential reasons for observed discrepancies.

1. INTRODUCTION

Monitoring rockfall along transportation corridors is imperative for understanding rockfall frequency and estimating risk associated with cut slopes (Hungr et al., 1999). A risk value communicates both the hazard of the slope and the potential consequences to roadway users. Rockfall hazard is represented by rockfall magnitude-cumulative frequency (MCF) distributions, which describes how often a certain rockfall volume or larger will occur. Thus, the MCF curve can be used as a key input for estimating cut slope risk.
A Statistical Review of Rock Mass Classification with Some Surprising Results
Authors: Wellman E. C. , Kemeny J.
Published: August 2024

The main classification systems that estimate rock mass properties include variants of the Rock Mass Rating (RMR) System, Rock Quality Designation (RQD), the Norwegian Tunneling Index (Q) (Barton), and the Geological Strength Index (GSI). The RMR system is based on intact strength, Rock quality designation, fracture frequency, and discontinuity condition. Typical distributions for these parameters may be approximated by normal, lognormal, or Weibull distributions and discrete distributions for fracture conditions. Water and pore pressure are sometimes included but should generally be treated as a boundary condition. RQD is a single-parameter system describing the percentage of sound rock core with a length greater than 10 cm. The Barton system has three main terms to describe a relative measure of the block size, an indicator of the inter-block shear strength, and a third quotient to describe "active stresses."

One of the primary findings of the statistical study is that two parameter systems, such as blockiness and joint condition, are better differentiators between rock mass classes; however, these systems still smear parameters. For example, a GSI range of 25-55 each indicates anything from blocky to disintegrated rock mass conditions. As a result, strength estimators based on GSI are not reliable for estimating rock mass strength and, in turn, the factor of safety. RMR and GSI results result in values on a normal distribution scaled from 0-100, typically centered on 50. The models are insufficient to describe the tail end of the distribution where rock mass failure typically occurs. The Q system significantly improves when the terms are derived independently but suffers from the same normalization issue when calculated from an RMR value.

The surprising finding is that single-parameter systems, including Fracture Frequency and Volumetric joint count, are better estimators (and differentiators) or properties across the range of rock mass conditions when looked at individually. Always understand the range of the rock mass parameters used and how that can impact the design. The paper will evaluate the need to develop strength estimators based on fracture frequency and volumetric joint count. Rock mass strength estimates should be developed from the underlying input data for classification rather than from normalized sums of multiple parameters.
Study on Post-Fracturing Inter-Well Interference in Deep Shale Gas
Authors: Wang Chen , Zhu Haiyan , Tang Xuanhe , He Mingyan , Kong Fansheng , Li Danlong , He Xiao , She Chaoyi , Zheng Majia , Wu Jianfa , Zeng Bo , Huang Haoyong , Li Junfeng , Xu Ersi , Gui Junchuan
Published: August 2024

Field practices have demonstrated that inter-well interference can lead to increased annular pressure in adjacent wells, increasing the risk of casing deformation and ultimately affecting production. Inter-well interference has become a "bottleneck" issue limiting the development of shale gas, necessitating urgent research on its mechanisms. Taking the L well area in the southern region of Sichuan Basin as the research object, this article establishes a numerical simulation model for the fracturing and exploitation of deep shale gas horizontal wells. The study analyzed the mechanisms and influencing factors of inter-well interference during the post-fracturing exploitation process. Key findings include that The higher conductivity of the hydraulic fractures, the larger fracturing scale, and the smaller well spacing, the more likely it is for inter-well interference phenomena to occur. It was also found that when there is no interference from natural fracture zone, batch exploitation can lead to more pronounced inter-well interference phenomena. Natural fracture zones between wells enhance this interference, but their impact is reduced during batch exploitation due to pressure recovery in the first exploited well. The study also highlights that the flow conductivity of natural fractures significantly affects inter-well interference during batch exploitation. Overall, this research provides insights into optimizing shale gas exploitation strategies in complex geological environments.

1 INTRODUCTION

The Sichuan Basin boasts the largest shale gas resources in China, with its annual shale gas production exceeding 90% of the country's total output. It is the main battleground of shale gas development in China. Based on extensive theoretical research and field practice, the multi-cluster fracturing process of shale gas horizontal wells has made a technical breakthrough. At present, the number of wells with interference between wells accounts for 50% in W area, which directly affects the production of old and new wells with interference (Guo et al., 2022). A large number of field practices show that inter-well interference will lead to the increase of annulus pressure in adjacent wells, increase the risk of casing variation, and eventually affect production. Interference between wells has become a "stuck neck" problem restricting shale gas development, and an effective method to evaluate interference is urgently needed.
Geothermal Resource Evaluation Based on Geological Modeling in Fushan Sag, Beibuwan Basin
Authors: Yun Xiaorui , Feng Jianyun , Zhang Ying , Zeng Yan
Published: August 2024

Fushan Sag is in the south of Beibuwan Basin, with rich geothermal resources and large development potential. Based on the regional geological background, geothermal geological conditions, this paper systematically analyzes the characteristics of thermal reservoir and evaluates the amount of geothermal resources based on geological modeling. The results show that The geothermal gradient in Fushan sag ranges from 2.48 to 4.68 °C/100m, with an average value of 3.35 °C/100m, the terrestrial heat flow values is 56.05-82.54 mW/m2 and the amount of deep geothermal resources within a range of 3-6 km is 1.4⁎1013J.

1. INTRODUCTION

Deep geothermal resources, including hydrothermal resources and hot dry rock (HDR), geothermal resources are usually buried at a depth greater than 3 km, (Dai and Chen, 2008; Younger et al., 2012; Muffler and Cataldi, 1978; Pang et al., 2020; Tester et al., 2006; Wang et al., 2017, 2002; Wang et al., 2012; Williams et al., 2008; Zhang Y et al., 2020).

Beibuwan Basin located in the northern part of South China Sea has been a key area for oil and gas exploration and development in recent years, and a large number of researches have been carried out on the basin structure, rocks, sedimentation, oil and gas reservoirs, etc. It is found in the process of oil and gas exploration that the overall geothermal temperature gradient in Beibuwan Basin is relatively high, and the geothermal temperature gradient of the Cenozoic stratum of the Sag area is generally in the range of 3.1-3.8°C/100m, and that the uplift area can reach 4-7°C/100m, indicating that the basin has the potential for geothermal resource development. Fushan Sag is in the south of Beibuwan Basin, with rich geothermal resources and large development potential, but the research degree is low and has not yet been exploited on a large scale (Zhu and Jiang, 1998; Li et al., 2012; Huang et al., 2012; Liu et al., 2008; Meng et al., 2009; Ma et al., 2012; Wu and Liu, 2021; Zheng et al., 2022; Gao et al., 2020; Dai et al., 2009; Li et al., 2007; Xu et al., 2021). Strengthening the research on the structure of the geothermal field, geothermal geologic conditions, amount of geothermal resources, and exploitation potential of the region is of great strategic significance to improve the energy structure of Hainan Island.
Engineering Geological Hazards Along Doroud-KhorramAbad Railway Rock NATM Tunnels
Authors: Azali Sadegh Tarigh , Samadi Hanan , Hassanpour Jafar , Rostami Jamal , Hamidishad Mohammad Hossein
Published: August 2024

The characterization of geological hazards holds significant importance in the context of underground spaces, specifically in tunnelling projects. This importance stems from its crucial role in determining the tunnel route, excavation techniques, and adopted risk management technologies. Tunnelling projects frequently encounter various engineering geological hazards, including issues related to ground conditions, groundwater levels, and in-situ stress regimes. Challenges such as encountering fault and crushed zones, mixed face formations, geological and structural instabilities such as wedge-failures and plan-failures, squeezing phenomena, karst formations, water inrush in the tunnel, hard and abrasive rock, landslides, and convergence are considered as primary causes of geotechnical risks in hard rock tunnelling. The primary objective of this study is to identify potential engineering geological hazards along the Doroud-KhorramAbad railway tunnels in Iran. The project spans 121 km, with 30 km comprising tunnels (13 tunnels) that have been excavated using the new Austrian tunnelling method (NATM). Detailed descriptions are provided regarding geotechnical considerations specific to tunneling. Based on the results of laboratory and field investigations, it has been determined that encountering crushed zone, structural instabilities and collapse as well as water inrush and rock fall, are the most significant hazards in this project.

Introduction

Railway tunnels used for underground transportation purposes have been widely constructed in recent years. Despite facing challenging geological conditions during construction, there remains a pressing need to effectively manage construction risks in complex and variable geological environments (Ren et al. 2016, Iegupov et al. 2018). Both highways and railways are recognized as efficient modes of transportation that play a crucial role in supporting the economic advancement of Iran. Consequently, the construction of tunnels has experienced a surge, positioning Iran as a country with the highest number of mountain tunnels.
Experimental Study on Interaction Behavior Between Caves and Fractures in Fractured-Vuggy Carbonate Rock
Authors: Zheng Zhenquan , Hou Bing , Zhao Zhiqiang
Published: August 2024

Deep fractured-vuggy carbonate rock oil reservoir storage spaces are complex, and natural reservoir structures develop randomly. The natural fractures and caves are the primary oil-containing zones within carbonate rock reservoirs. Conventional acid fracturing methods often encounter challenges in effectively communicating with these natural caves. Therefore, in order to reveal the interaction dynamics between acid fracturing and these caves, clarify the dominant factors affecting communication between natural caves and acid fractures, and improve the effect of acid fracturing, this study involves the preparation of 70mm×70mm×5mm thin rock plate samples from carbonate rock outcrops. Subsequently, indoor true triaxial acid fracturing experiments are conducted. For a model specimen of fractured-vuggy carbonate rock, the results show that: (1) Under the condition of the same in-situ stress field and fracturing construction conditions, the acid fluid will erode the nearby holes and disturb the large-scale holes at close range after the acid fracturing fractures connect the small-scale holes; (2) Under the conditions of the same hole structure and fracturing construction conditions, the expansion process of acid fracture is mainly influenced by the stress difference factor; (3) In high stress difference conditions, the expansion path of acid fractures in fractured-vuggy carbonate reservoirs becomes more complex, and it is highly likely to activate nearby natural fractures in the vicinity of the hole group, leading to the formation of a short and dense fractured-vuggy network structure.

1. INTRODUCTION

Acid fracturing is one of the most commonly used methods for reservoir modification in carbonate reservoirs[1,2], and the complex distribution of hole clusters and highly developed natural fractures are the most representative geological qualities of carbonate reservoirs[3-5], which not only affect the expansion path of acid fracture, but also lead to changes in the geostress near the body of the holes[6-9], so that the connectivity effect of the hole clusters often determines the oil and gas recovery rate[10-13]. In this paper, we adopt a visualized experimental method for real-time observation of acid fracture initiation and extension[14-15].
SOSAT: Geohazard Risk Assessment in Carbon Sequestration Operations
Authors: Haagenson R. , Burghardt J. , Wang W. , Saxena S. , Appriou D.
Published: August 2024

Like all operations in which fluids are injected into the subsurface, geologic carbon storage (GCS) presents inherit risks that must be assessed and mitigated to successfully deploy such technology in the field. For example, alterations to pore pressure and the stress state due to fluid injection may trigger certain geohazards, such as potential fault activation and induced seismicity or unintentional hydraulic fracturing. Here we present capabilities for assessing these potential risks using the State of Stress Analysis Tool (SOSAT): a Python library and web-based application capable of probabilistically estimating the subsurface state of stress informed by various field observations. Using posterior distributions of principal stress components, SOSAT can assess the risk of fault activation within the injection formation for either a critically oriented fault or a fault with a user-prescribed orientation. Additionally, SOSAT can estimate the probability of unintentional hydraulic fracturing of the intact reservoir rock. Here, we demonstrate these SOSAT capabilities using a hypothetical GCS site. This type of risk assessment can assist with the effective deployment of GCS technology in the field by informing safe design and management practices.

1. INTRODUCTION

One potential approach to lowering carbon emissions is to capture produced carbon at the source and inject it into a safe, subsurface storage site for permanent sequestration (Alivisatos & Buchanan, 2010; Fahs et al., 2023; IPCC, 2005). This process, called geologic carbon sequestration (GCS), has been a prevalent topic of recent research, from reservoir simulation studies (Tang et al., 2022; Lyu & Voskov, 2023) to field testing (Pawar et al., 2006). Numerous GCS projects are currently operational, with many more in the planning stages (Greenberg, 2021). Successful deployment of GCS, though, relies on the appropriate assessment of the associated geomechanical risk.

As with any subsurface operation, GCS contains certain risks that must be carefully considered and mitigated to safely deploy the technology in the field. For example, geohazards – such a fault activation and induced seismicity or unintentional hydraulic fracturing potentially leading to upward fluid migration – might arise during GCS operations if not carefully designed and managed. A systematic method for assessing geomechanical risk, therefore, would provide critical insights into the sensitivity of a given injection site to GCS operations and what mitigation strategies might be employed to ensure project safety. When planned and managed with care and appropriate risk mitigation strategies, GCS can be effectively deployed in the field, ensuring both operational safety and a reduction in carbon emissions.
A Discussion of Traditional Rock Slope Stability Analysis Methods with a Technical Evaluation of a Former Quarry Site in Jessup, Pennsylvania
Authors: Fleischer N. A. , Thomas R. D.
Published: August 2024

Rock slope stability is generally controlled by the orientations of the discontinuities present in a rock mass. Depending upon the orientations of these features and the orientation of the slope in question, slope failures may be possible. In this analysis, common analytical methods are discussed and presented for a site in Pennsylvania. An analysis first begins with discontinuity mapping. In this study, quarry walls were mapped, and observations of active slope failures were made. The data collected were plotted on stereonets for cluster and kinematic analyses, which identified several potential failures. Field and laboratory data were used to calculate the Factor of Safety for each predicted failure mode for each slope. Several slopes had elevated failure risks and mitigation recommendations were provided to the client. Rock slope stability analysis is a crucial step when considering development in proximity to rock slopes. It is necessary to understand the continuity of the rock mass and failure risks, and to mitigate those risks which can have devastating impacts on human lives and infrastructure. This technical paper aims to present a basic example of a complete analysis in the hope of providing a guide for fundamental rock slope stability analysis methods.

1. INTRODUCTION

Rock slope stability at a site is generally controlled by the orientations and conditions of the discontinuities (bedding planes, fractures, faults, and joints) that are present in the rock mass. These roughly planar features often form the edges of the individual blocks of rock that constitute the overall rock mass. Depending upon the orientations of these features and the orientation and dip of the slope in question, planar, wedge, and/or toppling failures may be indicated. Other factors such as the presence of groundwater, vegetation, ice, surcharge loads, seismicity, along with the geomechanical properties of the rock can also greatly affect the stability of rock slopes.

2. BASIC FIELD METHODS

To understand the fabric of the rock mass and determine the orientations of the discontinuities present throughout, a geologist or geotechnical engineer should visit the site of the proposed or existing rock slope to complete a thorough reconnaissance of the slope(s) in question. The reconnaissance should involve a systematic evaluation of rock slope conditions including detailed rock discontinuity mapping, observation, examinations of the presence of groundwater and photo-documentation of key rock slope features.
Deep Learning for S-Wave Arrival Time Picking in Acoustic Emission Source Location Analysis
Authors: Xiong Q. , Johnson E. K. , Wu C. S. , Hampton J. C.
Published: August 2024

Traditional laboratory acoustic emission (AE) source location analysis predominantly relies on P-wave arrival times, limiting the number of locatable sources due to the requirement of four signals for solving four unknowns. This paper explores the feasibility of incorporating S-wave arrival times, which are often otherwise discarded, into source location analysis to reduce the fundamental requirement from four to two signals. We employ a U-Net deep learning model to pick S-wave arrival times on AE signals, trained using theoretical calculations based on P-wave and S-wave velocities. Despite only achieving an accuracy of 29.6% on the testing dataset, the model shows promising improvement towards the desired shape after only 100 epochs of training. Potential approaches for improvement, such as integrating error distributions into the analysis and employing a training→prediction→and manual picking cycle, are discussed. These findings suggest pathways for future work to enhance AE source location analysis through deep learning techniques, potentially unlocking new insights into rock fracture processes in laboratory settings.

1. INTRODUCTION

Traditional laboratory acoustic emission (AE) source location analysis uses primarily P-wave arrival times for solving source locations [1-7] with a limited number of studies using S-wave arrival times. In the mathematical inverse process, the P-wave arrival times of AE signals and the coordinates of the sensor array are inputs to an optimization function. This optimization function is based on the time delay of wave propagation from source to sensor (Fig. 1(a)) and has four unknowns, i.e., three spatial coordinates and one source onset time. The source locations produced by the mathematical inverse process are also refined based on the physical principle [8] or mathematical (i.e., error or residual) features [9-11]. Upon this conventionally practiced procedure, at least four signals must be involved to solve the four unknowns [12]. Because energy releases of rock fractures are scale-invariant [13, 14], i.e., its frequency-magnitude distribution obeys the power law, sources with low magnitude that only trigger a few signal recordings are exponentially more prominent than those of greater magnitude. This leads to the number of locatable sources being one to three orders of magnitude lower than the total signals [15] with only a small percentage being used for source location [12, 16]. A majority of recorded signals will be discarded from the catalog and will not be considered in the subsequent advanced AE data analyses [17-21].
A Novel Evaluation Method of Double Sweet Spots in Shale Oil Reservoirs: A Case Study
Authors: Ji Pengcheng , Zhu Haiyan , Zhang Zhaopeng , He Xiao , She Chaoyi , Zheng Majia , Song Junbei , Wang Dajiang , Li Yuanzhao
Published: August 2024

This paper mainly studied the effects of eight parameters including Young's modulus, formation brittleness, internal friction angle, fracture energy, fracture toughness, porosity, permeability, and clay content on the double sweet spots of shale oil reservoirs. We calculated the double sweet spot indexes comprehensively. Further, the double sweet spot index profiles were imported into the Petrel software to obtain the correlation diagram of the double sweet spot index versus the well depth for a single-well and the three-dimensional model of the double sweet spots in the target block. Double sweet spot evaluation was conducted on shale oil reservoirs in Jiyang Depression. The results show that the double sweet spot layers of FY1-X well are located at the depth of 4034∼4160m and 4556∼4686m. The double sweet spot layers of well FY1-Y are located at 4883∼5043m, 5121∼5280m, and 5394∼5717m depth. The double sweet spot index of this block is between 0 and 1.41. In the middle of the block, the double sweet spot index is almost 0, while in the southwest and northeast of the block, the double sweet spot index is greater than 1, which is considered as a double sweet spot area.

1. INTRODUCION

Shale oil refers to thermogenic petroleum resources occurring in shale formation mainly in free state, supplemented by adsorbed state and dissolved state. It includes the oil in the pores and fractures of shale, as well as the oil resources in the adjacent layers and interlayers of tight carbonate rocks or clastic rocks in shale formations. (Zhang et al., 2012) The technical recoverable resources of continental shale oil in China are 4.352 billion tons, ranking third in the world. Shale oil resources have become the focus and hot spot in current petroleum exploration and development research. Shale oil sweet spot refers to the relatively rich area of shale oil that can be extracted under current technical conditions. The evaluation of shale oil double sweet spots is of great help to the exploitation of shale oil resources. The efficient development of paleogene shale oil in Jiyang Depression of Bohai Bay is a major strategic measure to ensure national energy security. However, the high reservoir heterogeneity of shale oil in Jiyang Depression and complex distribution of favorable properties results in low recovery efficiency and reservoir productivity without design optimization of fracturing and construction parameters. Therefore, a dual-sweet spot evaluation model suitable for shale oil reservoir is established to provide strong support for efficient development of shale oil and optimization of fracturing construction parameters.
Numerical Modeling to Investigate the Influence of Jointing on Production Blast Fragmentation
Authors: Dare-Bryan P. C.
Published: August 2024

Blasthole pattern selection is often decided without any evaluation of the structure of the rock mass to be blasted. This is in part due to production constraints that can determine the position of a given blast in the pit, thereby making it difficult to correctly accommodate the rock structure in the pattern orientation. An improved understanding of the influence of blasthole pattern in relation to the jointing in the bench could aid blast design selection to achieve the required fragmentation. Numerical modelling using a hybrid finite/discrete element program coupled with a non-ideal detonation model was conducted to evaluate different orientations of a single joint set, and the influence of the blasthole spacing-to-burden (SB) ratio within different configurations of two joint sets. A comparison of the particle size distribution curves for the range of blast deigns and rock masses modelled highlighted the general trends that: wide jointing produces finer fragmentation than tighter jointing; wider SB ratios produce finer fragmentation in square jointing; and an equilateral SB ratio produces finer fragmentation in angled jointing.

1. INTRODUCTION

The aim of this study was to use numerical modelling to undertake an analysis of the influence of rock structure on fragmentation. While rock structure includes, folding, faulting, bedding planes and joint sets, for this study only jointing is investigated. However, even within jointing there can be a significant variation in how they present in the rock mass, for example in the top image of Figure 1, there are consistently spaced joint sets, while in the bottom image there are abrupt changes in the joint spacing and resulting in-situ block sizes.

Previous studies into the influence of rock structure and discontinuities have tended to be conducted in the laboratory. The detailed work by Fornery et al., (1983) investigated the influence of discontinuities on the transmission of blast induce stress waves, highlighting the resulting complex wave patterns. A considerable amount of work has been undertaken by researchers in India, constructing laboratory scaled benches from slabs of limestone bonded together with plaster of paris. Bhandari (1983) conducted a series of single blasthole tests with vertical and sub-vertical joint sets orientated parallel and perpendicular to the free face (Figure 2) and found that jointing perpendicular to the face produced excessive backbreak, while parallel jointing caused poor toe breakage.
Automation of Underground Void and Support Deformation Monitoring – Effective Decision-Making Data and Tools Without the Penalty in Time and Effort
Authors: Franke J. , Gonzalez C.
Published: August 2024

Despite the potential of Light Detection and Ranging (LiDAR) technology for tracking underground mining voids, its adoption has been slow because associated conventional data processing is excessively time consuming, and requires training, upskilling, and devotion by geotechnical engineers. This often becomes a bottleneck to bringing this otherwise highly advantageous method into use.

Our paper introduces a new solution of fully automated LiDAR point cloud data processing dedicated to void deformation tracking that not only enables geotechnical engineers to avoid having to learn unrelated skills, but also provides immediate output of sophisticated reporting deliverables not available elsewhere. This opens up the opportunity to monitor many more excavation volumes at a higher frequency and gain much better insights than is possible with conventional manual processing tools and methodology.

Critically, automatically generated 3D files for localized deformation assessment as well as automatically generated summary reports presenting key deformation tracking analysis outcomes to decision makers facilitate the detection and understanding of

• In situ support system capacity and capacity degradation

• Ground support behavior for dynamic conditions and squeezing ground

• Cost efficiency of ground support

1. INTRODUCTION

The introduction of LiDAR technology allows a quantitative assessment across the entire excavation volume and its rock surface by collecting a full three-dimensional (3D) image of the entirety of an excavation such as an underground drive, decline, stope or more generally a tunnel as also a core feature for civil engineering. Comparisons between epochs of complete 3D data coverage allows for change detection over time that doesn't feature otherwise typical omissions.

Such omissions are a fundamental flaw of single-point measurement systems including bolt-mounted laser sensors, extensometers, or wall-mounted prisms surveyed using total stations. Point-wise systems are functional mature technologies and accurate if used correctly, but they will never provide a representative measure of underground drive or tunnel deformation. This is because depending on how many single-point sensors are in use, which will never match the density of a LiDAR point cloud, they inevitably miss at least the worst, if not all deformations actually occurring in-situ. Fig. 1 illustrates this issue.
Mechanical Stability Analysis of Fracture-Cavity Carbonate Gas Storage
Authors: Tang Huiying , Zheng Xin , Wang Xiaoping , Zhao Zihan , Chen Yuye , Zhao Yulong , Zhang Liehui
Published: August 2024

The Chinese Laoweng Chang gas storage is developed from a typical depleted fractured-cavity carbonate gas reservoir. Due to the fast injection and production rates in gas storage period, the reservoir rocks, the caprock, the faults and the base may all suffer the ricks of failure. In this paper, the importance of cavities on stress distribution and failure in reservoir rock is emphasized. First, the influence of cavities on stress and failure risks is analyzed with numerical models. The analytical solutions for stress distribution around cavity is derived to be used for reservoir scale problems. The practical geological and geomechanical models of Laoweng Chang gas storage are used to analyze the mechanical risks of different regions. The stress evolution of each grid during production and injection processes is calculated with finite element method by one-way fluid-solid coupling. The calculated stresses of each grid in reservoir rock are considered as boundary conditions to obtain the stress distribution around cavities. Mohr-Coulomb criterion and tensile failure criterion are then used to judge the shearing and tensile failures. The results indicate that the low permeable caprock and base are less susceptible to failure. The existence of cavities increases the risks of both tensile and shearing failure in the reservoir rock. However, the failure of fault is the still dominate the mechanical stability of the gas storage. This work provides an effective method for considering the influence of cavities on reservoir rock failure in practical analysis.

1. INTRODUCTION

The underground gas storage, as a type of "artificial gas reservoir," serves as an effective means to ensure gas supply security and balance natural gas supply and demand. These storage facilities operate through multi-cycle high-speed injection and production processes, featuring injection and production rates that surpass those of natural gas reservoirs by 20-30 times, thereby exacerbating the risks associated with gas leakage and water intrusion. The occurrence of a leakage accident could result in irreversible economic losses. Therefore, studying the changes in in-situ stress during the operation of gas storage and conducting mechanical integrity assessments are particularly important (Jia et al., 2020; Verdon et al., 2013; Li et al., 2023). The Laoweng Chang gas storage in southwest China is a typical fracture-cavity carbonate gas storage. The stress distributions are significantly influenced by cavities and other medium spaces (natural fractures and rock matrix), posing greater challenges in characterization compared to conventional porous gas storage (Zhang et al., 2019).
Numerical Study on Mode I Fracture Characteristics of Rock Under Confining Pressure
Authors: Luo Senlin , Zhang Guangqing , Sun Bin , Qiu Renyi , Ling Yansen
Published: August 2024

Hydraulic fracturing is a key technology for the efficient exploitation of deep oil and gas resources. Mode I fracture is the main fracture type of hydraulic fracturing. However, it is difficult to consider the process of mode I fracture under confining pressure in laboratory experiments. Based on numerical methods, this study aims to reveal the influence of confining pressure on mode I fracture of rock. A three-point bending numerical model was established by discrete particle method to monitor the tensile stress concentration zone at the fracture tip and analyze the fracture morphology and fracture parameters under different confining pressures. The results show that the tensile stress concentration zone changes from a horizontal narrow band to a semi-ellipse as confining pressure increases, and its distribution range becomes smaller. Confining pressure enhances the actual tensile strength and actual fracture toughness of the rock. The mode I fracture of rock under confining pressure needs to overcome the confining pressure and rock cohesion resistance. The compaction effect of confining pressure on the rock will strengthen the fracture performance of the rock itself. This strengthening mechanism is affected by the critical confining pressure. This work provides a theoretical basis for studying the mode I fracture of hydraulic fracturing.

1. INTRODUCTION

Hydraulic fracturing is a widely stimulation method to increase oil and gas production (Detournay, 2016). Fracture mechanics has proven to be a useful tool for the investigation of brittle failure of rocks during hydraulic fracturing (Janiszewski et al., 2019; Yue et al., 2020). Generally, the fracture can be divided into three fundamental modes, tensile (mode I), in-plane shear (mode II), anti-plane shear (mode III), and mixed mode. The fracture is constrained by the in-situ stress state in the process of hydraulic fracturing and mode I fracture is the main fracture mode. However, it is difficult to conduct traditional fracture mechanics experiments under confining pressure, such as three-point bending, four-point bending and semi-circular three-point bending (Kuruppu et al., 2014; Wang and Hu, 2017; Zhu and Deng, 2023). It is of great significance to reveal mode I fracture rule of rock under confining pressure for further understanding of hydraulic fracturing mechanism.
In-Situ Horizontal Stress Inversion and Error Analysis Based on Borehole Deformation Monitoring
Authors: Chen Jie , Ma Tianshou , Liu Yang , Xu Wen
Published: August 2024

In-situ measurement is one of the most accurate and effective methods, but it is challenging to measure directly in the deep well. Therefore, a new horizontal in-situ stress inversion method was proposed based on the relationship between the borehole deformation and the in-situ stress state under nonuniform horizontal in-situ stress. The accuracy of the inversion model is validated by finite element simulation. The sources of measurement errors and their control method were discussed. The results indicated that the inversion error for the maximum and minimum horizontal principal stress is 0.001% and 0.052%, respectively. The results and errors of the horizontal principal stress inversion are significantly influenced by the measurement deviation of the borehole diameter, the borehole deformation, the wellbore pressure, and the elastic parameters of the rock. If the deviation from the borehole diameter measurement is less than 0.5 cm or the percentage deviation from the borehole deformation, the wellbore pressure and the elastic parameters of the rock is within ±5%, the horizontal stress inversion error is less than 4%, and thus the horizontal principal stress inversion results are deemed acceptable. This study can provide new ideas for in-situ stress measurement in the petroleum industry.

1. INTRODUCTION

In-situ stress is a natural stress that exists in formation without engineering disturbance. Accurate measurement of the magnitude and direction of in-situ stress is a prerequisite for determining the mechanical properties of engineering rock, for analyzing the stability of the surrounding rock, and for the scientific design and decision-making of rock engineering excavations (Cai, 1993; Wang et al., 1991; He et al., 2000).

In petroleum exploration and development, in-situ stress plays a very important role (Ma et al., 2022a, 2022b). In-situ measurement is one of the most accurate and effective methods (Wu, 2012). Currently, the hydraulic fracturing method has been widely used in petroleum, mining, and underground engineering. However, it can only directly measure the minimum horizontal principal stress (Duan et al., 2023). In mining and underground engineering, some in-situ measurement methods can directly measure both the minimum and maximum horizontal principal stresses, but it is very difficult to measure them directly in the deep well.
Coupled Numerical Simulation of Coal Failure Caused by Thermal Impacting in Underground Coal Gasification Zone
Authors: Zhao Yufeng , Zhang Mengyuan , Chen Yanpeng , Dong Zhen , Chen Hao , Chen Shanshan , Xue Junjie , Konietzky Heinz
Published: August 2024

Underground Coal Gasification (UCG) is an environmentally friendly way to utilize coal resources. The cavity evolution process, especially the thermal impact on coal rock, is an important topic of UCG. The thermally induced coal rock failure processes in gasification environment are rarely investigated, but they are important to the gas production space and the flow from the injection well to the production well. In this study, a coupled numerical simulation program based on PFC3D and FLAC3D was established to realize multi-field coupled thermal impact conditions. The numerical model of burning-induced coal surface failure was established, and the basic cavity evolution mechanism was revealed. The main results show that (1) the redistributed temperature field in the coal rock is the most important parameter for the coupling model. The mechanical properties of the model element are assigned in accordance with its temperature state. (2) Taking into account the effects of heating, microscopic fracture and deformation are generated through PFC3D model, inhomogeneous temperature distribution is simultaneously achieved through FLAC3D model. (3) The evolution law of the expansion of the gasification cavity has been obtained by the coupled numerical simulation. (4) Eventually, the height of the gasification cavity increases, and the upper coal seams expand to an approximate equilibrium, the height affected by the temperature field becomes stable, and the vertical expansion rate of the gasification cavity gradually decreases.

1. INTRODUCTION

Underground Coal Gasification (UCG) is a revolutionary technology for clean coal utilization that integrates the three key processes of well construction, coal mining and gasification for efficient gas production. This technology allows coal to undergo controlled in-situ combustion, pyrolysis and gasification reactions to produce syngas with methane, hydrogen, carbon monoxide, carbon dioxide and other components for surface recovery by injecting air, oxygen-enriched air, oxygen/water and other gasification agents into underground coal seams[1–4].

Currently, the underground gasification of middle-deep coal seams has no practical experience, especially for the dynamic study of the deforming and destroying process of the surrounding stone (coal) in the gasification cavity under high temperature and high pressure. The numerical simulation technology of gasification cavity development dynamics is still in the initial stage. The simulation technology of gasification cavity controllable development control is not deep enough, and the analysis of the effect of dynamic process parameters in the process of cavity formation is still insufficient.
Simulation of Elastic Waves Transmission and Attenuation Considering Fluids Properties Change and Radiator of Branches Well
Authors: Tan Yawen , Tian Shouceng , Zhang Yiqun , Wang Tianyu , Wang Fei
Published: August 2024

Crude oil production is promoted by means of physical vibration, such as the use of high-power acoustic waves, ultrasonic waves, electro-hydraulic pulse waves, and high-pressure shock waves of explosive gases to stimulate the reservoir. And the propagation speed, distance, and attenuation of the elastic waves generated by physical vibration are the main factors affecting the effect of production enhanced by physical vibration. In this paper, the Biot model is improved. Firstly, the influence of elastic wave on reservoir physical properties is considered, and the change of viscosity and permeability field under the elastic wave is obtained by numerical superposition method. Then, the branch of horizontal wellbore is equivalent to a finite linear radiator, the wave field constructed as a superposition of fields generated by branches in all. And we simulated for different branches cases, the propagation and attenuation of pressure wave in oil reservoirs are obtained. When the lateral level is used as the vibration source, the fast attenuation area and the slow attenuation area of the pressure fluctuation can be formed in the reservoir. The size and range of slowly decreasing pressure wave can be controlled by optimizing the structure of branch horizontal well pattern.

1. INTRODUTION

Improving the recovery rate of oil and gas resources is a crucial subject in the petroleum industry. Stimulating reservoirs through pulse injection is one of the important methods. The elastic waves generated during the pulse injection process can facilitate the flow of oil and gas, thus increasing the production yield of oil and gas.

Heavy oil is an important fossil energy source(Zheng, Li, Sun, & Yang, 2016; Zhou, Yuan, Peng, Zeng, & Zhang, 2018). Due to its high viscosity and poor flowability, the cost of extracting heavy oil is higher than conventional oil and gas resources. Heavy oil extraction typically requires methods such as steam injection or chemical viscosity reduction. Supplementing existing techniques with physical vibrations can further reduce crude oil viscosity and increase production yields.

During pulse injection, elastic waves primarily propagate in the form of pressure waves (longitudinal waves). This study simulates the propagation velocity and attenuation of waves in heavy oil reservoirs, considering the coupled effects of fluid and solid phases in the reservoir, particularly the influence of liquid phase viscosity. The wave field is simulated using staggered-grid finite difference method. Ultimately, the transmission characteristics of elastic waves are obtained.