bluuebunny/crossref_metadata_2025 huggingface dataset:
A Critical Review of the Engineering Properties of Extraterrestrial Regolith
Authors: Zou Yuan , Wu Huanyu , Zhang Chi , Yang Wei , Zhao Qi
Published: September 2023

Deep space exploration is the frontier of the development of humanity. Investigators worldwide have conducted extensive research on the engineering characteristics and mineralogical composition of surface materials on the Moon, Mars, and asteroids, which have significant implications for future large-scale spacecraft soft landings and the construction of permanent bases. This work analyzes and summarizes a volume of previous findings on the engineering properties of the regolith of the Moon, Mars, and asteroid Ryugu, including the particle size distribution, bulk density, internal friction angle, cohesion, and presence of water ice. The methods used to obtain these properties are critically reviewed. We discuss their advantages and disadvantages and identify the potential new techniques that can be used to better constrain these engineering properties. This study can help researchers to understand the research progress on extraterrestrial regolith in the engineering properties, as well as prospective research directions in deep space exploration.

INTRODUCTION

Major government space agencies and private companies around the world, such as NASA, CNSA, and SpaceX, have launched ambitious deep space exploration programs to explore the evolution of the solar system and find a potential new habitat for mankind (Wu et al., 2012). Among the extraterrestrial celestial bodies in the solar system, Mars is the focus of the scientific community's attention due to its similarities to Earth (Li et al., 2021). Some key findings concerning Mars have been revealed by a series of probes, especially the landed ones such as InSight and Tianwen-1 (Zou et al., 2021). Due to the remote distance between Mars and Earth, the Moon is considered to be a springboard for Mars exploration (Crawford & Joy, 2014). Lunar exploration is the focus of current deep space exploration programs, including the Artemis program of the United States (Smith et al., 2020), the Chang’e (CE) Project of China (Li et al., 2019), and the Luna program of Russia (Djachkova et al., 2017). In addition, many asteroids have also attracted great interest from researchers, such as Ryugu, Bennu, 2016HO3, etc. (Zhang et al., 2022), and they also have a great chance to contribute to the solution to the evolution of the solar system.
Micro-CT Characterization of Lunar Regolith Using Machine Learning-Based Segmentation
Authors: Wu Huanyu , Zou Yuan , Zhao Qi , Zhang Chi , Yang Wei
Published: September 2023

On 17 December 2020, China's Chang’e-5 mission returned about 1.73 kg of lunar regolith from one of the youngest basalt units in northern Oceanus Procellarum. The mineralogy of the lunar surface regolith provides a wealth of information on its geological history, and the characterization of lunar regolith at high spatial resolution has been a significant goal of lunar exploration. In this study, we combine high-resolution micro-CT imaging and a state-of-the-art machine learning-based image processing approach to assess morphological and physical properties of the lunar regolith sample returned by Chang’e-5 mission. The lunar regolith sample was scanned by an X-ray micro-computed tomography (micro-CT) with a spatial resolution of 2.48 μm. A pixel-wise random forest classifier was employed to segment the volume data into regolith particles considering multiple features including intensity, edge and texture. On the basis of segmented images, the particle size distribution of the lunar regolith sample was extracted. The average density of the sample is estimated to be around 1582 kg/m3 based on a calibration of the relationship between the image intensity and material density. Particles with extremely high-density mineral phases (around 4500 kg/m3) in the sample are considered rich in metal elements such as iron and titanium. In addition, we were able to extract particles with distinguished features such as isolated pores, which implies the possible melting and solidification process related to past meteorite impacts. This study provides a workflow for micro-CT imaging-based analysis of lunar regolith.

INTRODUCTION

Characterization of lunar regolith is a key element in lunar base construction and in-situ resource utilization. Lunar exploration is currently the focus of deep space exploration programs around the world, including NASA's Artemis program (Creech et al., 2022) and China National Space Administration's Chang’e (CE) Project (Li et al., 2019). These exploration programs are ultimately expected to achieve a long-term human presence on the Moon. On 17 December 2020, roughly 1.73 kg of lunar regolith samples were brought back to Earth by China's CE-5 mission, which was the first-time sample return since the Apollo era around 50 years ago (Li et al., 2022). These lunar regolith samples came from a basaltic area in the northern Oceanus Procellarum (Qian et al., 2021), which is rather away from the previous nine sampling sites accomplished by NASA's Apollo missions and USSR's Lunar missions (Li et al., 2022). These samples provide us with rare opportunities to conduct experimental analysis using more precise methods in the laboratory, which has invaluable implications for deep space exploration research, compared to methods of remote detection of orbiters and in-situ investigation of lunar rovers.
Numerical Simulation of the Underground Storage Cavern Using FDEM
Authors: Wu Huanyu , Zhao Qi , Shen Jiayi , Li Hanze
Published: September 2023

Underground storage cavern has been increasingly exploited as it has many advantages such as reducing investment, economizing land use and improving safety compared with storage above the ground surface. We employ the hydromechanical coupled FDEM to simulate the excavation and operation phases of the underground storage cavern with a water curtain system (WCS), taking into consideration the natural discrete fracture network (DFN). The simulation results captured the propagation and slipping of the pre-existing DFN during the excavation and operation process. We quantitatively evaluate the containment performance based on the water inflow and pore pressure distribution. This study provides new insights into evaluating the stability of cavern-surrounding rock masses and containment performance of underground storage caverns.

INTRODUCTION

Underground storage caverns have better performance on safety, security, economy, and greater environmental acceptance compared with traditional storage infrastructures such as storage tanks and pipelines. Several large underground storage caverns have been constructed, for example, Jurong rock caverns in Singapore (Zhou & Zhao, 2016) and Huangdao underground oil storage caverns in China (Wang et al., 2015).

Underground storage caverns are constructed in fractured rock masses, confining the storage medium (such as oil and gas) by maintaining groundwater pressure around caverns which is also called hydraulic confinement (Aberg, 1978; Froise, 1987; Lindblom, 1997). The basic principle of underground containment the cavern is that no gas could leak as long as the water pressure increases along all possible gas leakage paths away from the cavern (Goodall et al., 1988). To enhance the sealing performance, water curtain systems (WCS) are constructed to manually control the pore pressure distribution by regulating the water curtain pressure. (Shi et al., 2018). Previous studies has evaluated the stability of excavated rock masses (Mohanty & Vandergrift, 2012; Ma et al., 2016; Zhuang et al., 2017) and containment performance (Xu et al., 2018; Liu et al., 2021) by using in-situ monitoring methods and numerical simulation.

However, the fracture propagation and slip induced by the excavation and operation of the storage cavern, as well as the resultant fluid pressure variation, have not been illustrated.
The Geotechnical Aspects of a Pillar Recovery Project in the DOZ Cave Mine
Authors: Putra F. , Meiharriko Hasan R. , Hamman J. P. E.
Published: September 2023

The Deep Ore Zone (DOZ) mine is a part of the PT Freeport Indonesia (PTFI) underground cave mining complex. It is the third lift in the Ertsberg East Skarn System (EESS). These mines are located on elevations between 3,000 to 4,500 amsl in an area with very high rainfall of approximately 5,500 mm per year.

A significant challenge in the operations of the DOZ mine is the handling and management of wetmuck. As mining progressed since the start of production in 2000, the percentage of wetmuck drawpoints increased dramatically against the dry muck drawpoints. This condition impacted the ore blending strategy in the ore pass systems to mitigate the ore spill hazard in the ore flow systems.

To overcome this dry: wet muck ratio problem, an option for pillar recovery to increase the dry muck tonnages was evaluated. Pillar recovery strategies along the major pillar apexes in inactive extraction levels was initiated. This challenging project took place in six panels between 2019 - 2021 and had to deal with a long history of abandoned areas, active wetmuck issues, closed drawpoints and panel instability concerns.

This paper aims to provide an overview on the management of the pillar recovery project, geotechnical assessment of pillars and wetmuck to ensure safety and production targets are met.

INTRODUCTION

The Deep Ore Zone (DOZ) cave mine is a part of the PTFI underground mining complex that implement the block cave mining method between 3,000 to 4,500 amsl. DOZ mine is the third lift in the Ertsberg East Skarn System (EESS) orebody after the Gunung Bijih Timur (GBT) Mine and Intermediate Ore Zone (IOZ) Mine (Figure 1). The topography around these mines is extremely rugged and typical of the Jaya Wijaya Mountain range in West Papua, Indonesia. Wet weather with very high rainfall that averages 5500 mm per year (Widijanto et al., 2012). The very high rainfall combined with the block cave mining methods, that has broken through into the open pits or to surface, is one of the main contributors to the wetmuck at PTFI. Other contributing factors include lithology, fragmentation and draw rates (See Section 4.1 for detail Wetmuck Classification).
Comparison of Geological Profiles from Borehole Data Based 3D Geological Model and Geophysical Testing
Authors: Wu Shifan , Zhang Yu , Chu Jian , Chiam Kiefer , Goh Kok Hun
Published: September 2023

Three-dimensional (3D) geological modeling has been used for design and construction works to overcome the complex nature of underground geological conditions. The accuracy and reliability of geological information reflected by the 3D model are critical for engineers to make sound judgement. The 3D model is usually established using borehole data. The data gaps between boreholes affect the accuracy of the 3D geological model. Instead of getting additional borehole data, geophysical survey is a promisingly cost-effective method to fill the data gaps and improve the assessment of the underground uncertainties. In this study, a case of using the seismic surface wave methods to determine the engineering rockhead and thus fill the data gap in the 3D geological model is presented. In relation to a subway project in Singapore, the combination of geophysical methods and 3D geological model for rockhead detection at this site was explored. Seismic geophysical survey was carried out to map the rockhead which was calibrated and verified using borehole data. This improves the accuracy of the rockhead obtained from 3D geological model. Through this study, a procedure of using geophysical methods to obtain additional data to verify and update the existing 3D geological model has been established.

INTRODUCTION

Three-dimensional (3D) geological modeling has been widely used for underground design and construction works to overcome the complex nature of underground geological conditions (Dong et al., 2015; Pan et al., 2018; Pan et al., 2020; He et al., 2020; Zhu et al., 2021). The accuracy and reliability of the geological information indicated by the 3D model are critical for engineering practitioners to comprehend and visualize the subsurface conditions and make a sound judgement (Wu et al., 2022; Qi et al., 2021). It is considerably significant and valuable in practice to locate the top surface of moderately weathered rock (Weathering Grade III or better) in the 3D geological map since the geo-materials and mechanical behaviors start to vary apparently from this interface. The engineering rockhead is conventionally identified via the traditional geotechnical investigation which involves drilling boreholes and the subsequent interpretation of the borehole logs and coring samples. The accuracy of the interpreted rockhead or geological profile largely depends on the borehole quantity, location and spacing, as well as the interpretation of geologist. When the boreholes are sparse, the uncertainties become large and thus additional boreholes are required to reduce them. Unfortunately, getting more borehole data is expensive. It is also challenging to carry out drilling works within restricted areas such as urbanized cities or inaccessible terrains such as natural reserve or lakes.
Effect of Water Saturation on Failure Behaviour of Mudstones Under High Pressures
Authors: Iyare U. C. , Frash L. P. , Carey J. W. , Blake O. O. , Ramsook R.
Published: September 2023

Water as pore fluid is an important factor that influence rock deformation and failure behaviour. This paper presents an experimental study on the effects of water saturation on the failure behaviour of mudstones at high confining pressures. Triaxial compression experiments were performed at confining pressures up to 130 MPa, on dry and water-saturated mudstone samples. Results including stress-strain curves, failure strength, and failure modes, showed that the mudstones experienced brittle, brittle-ductile transition, and ductile failure behaviour as the confining pressure increases. The results also revealed that water significantly weakened the rock, thereby reducing the failure strength and causing the rock to become ductile at lower confining pressure compare to dry conditions. Furthermore, in water-saturated conditions, the brittle-ductile transition behaviour is accompanied by shear band fractures and ductile flow, as opposed to shear fractures to shear band fractures in dry conditions. The findings of this study could provide valuable information for optimizing hydraulic fracturing techniques and improving production efficiency in unconventional oil and gas reservoirs by identifying the conditions and depths of the transition from brittle to ductile failure behavior.

INTRODUCTION

Crustal rocks typically contain some form of pore fluid, and most of these fluids are water (Price, 1975). Understanding how pore fluids affect the mechanical properties of rocks is crucial in solving a range of problems in geotechnical and geological applications. For example, water's significant impact on the strength and deformability of rocks has been linked to many rock engineering hazards like landslides (Iverson, 2000). Water has been shown in numerous studies to weaken the mechanical strength of various types of rock, including mudstone, sandstone, granitic rocks, and quartzite. (Cai et al., 2019; Lu et al., 2017; Wasantha and Ranjith, 2014). When rocks are saturated with water, they become weaker and more prone to failure. This is because water can act as a lubricant between the individual particles, reducing the frictional forces that hold the particles together. As a result, the rock may experience reduced strength, stiffness, and cohesion, as well as an increased risk of creep, plastic deformation, and failure rates (Brantut et al., 2013; Chen et al., 2019; Wong et al., 2016).
A Rock Physics Feasibility Study of the Geothermal Lodgepole Reservoir, North Dakota
Authors: Alamooti M. , Namie S.
Published: September 2023

Geothermal energy extraction from the Earth's crust requires a thorough understanding of the mechanisms that enhance fluid flow in rocks. Geoscientists must evaluate the elements that regulate the development of permeability networks and the parameters that control rocks’ responses to stimulation procedures across various spatial and time scales. The Williston Basin is a major geological depression with complex stratigraphic sequences, and its rocks’ complex microstructures and mineral compositions make it challenging to assess effective moduli accurately. In addition, the Lodgepole Formation in the Williston Basin is a primary geothermal aquifer with low-salinity waters co-produced with oil and gas, which are often discarded as waste. This study aimed to develop a rock physics model of the Lodgepole formation, emphasizing its geomechanics and petrophysical features, and explore the connections to locate additional geothermal energy sources in the future. The study used several methods to estimate rock physics characteristics, including elastic modulus of minerals and rock pore shape and found that the intra-particle model matches the available data.

INTRODUCTION

The Lodgepole Formation, is the second deepest (Fig. 1) of the Williston Basin's four principal geothermal aquifers. The Formation has been identified as a potential source of low-salinity geothermal fluids co-produced with oil and gas. These fluids are often considered waste and are discarded by reinjection into the ground. However, North Dakota is now exploring harnessing geothermal waters to produce power. To evaluate the geothermal potential of the Lodgepole Formation, it is essential to understand the geomechanical and petrophysical features of the rocks in the Formation. Non-typical reservoir rocks, such as tight sandstones and shales, are known for their complex microstructures and mineral compositions, making it challenging to assess their effective moduli. Additionally, data from the literature may only sometimes be accurate since XRD data is only continuous at some levels, and the elastic modulus information for minerals can vary based on the study location.
Data-Driven Models for Predicting Rate of Penetration Based on Machine Learning Algorithms
Authors: Liu Yang , Xi Yang , Xiang Xingyun , Ma Tianshou , Chen Sitong
Published: September 2023

Data-driven models are used extensively for predicting rate of penetration (ROP). However, what data-driven algorithm is best suited to ROP prediction is currently undecided. In this paper, the data-driven model based on back propagation neural network (BP-ANN) and random forest (RF) algorithms are proposed respectively to predict ROP. The features that include both the engineering and formation parameters are selected as the model inputs by combining physical drilling laws and correlation analysis. The optimal hyperparameter combinations of the model are found by cross-validation. The MAE, MSE and R2 are adopted as the indicators to evaluate the model performance. The case study illustrates how accurately and rapidly the data-driven model can be used to predict the ROP. The results indicate that the RF model can track the data-based ROPs more accurate even if hyperparameters optimization is ignored. The MAE, MSE and R2 of the optimized model are 0.243m/h, 1.599m2/h2, 0.989, respectively. While for the BP-ANN model, the predicted ROPs can achieve a more desired result after hyperparameters optimization, but it still cannot come close to the result of RF model. The present model provides some methodological bases for the further study on optimizing drilling parameters.

INTRODUCTION

Rate of penetration (ROP) is one of the key factors affecting drilling period and operating cost. Over the past few decades, researchers in drilling engineering field have been devoted to accurately predict and obtain an optimal value of ROP. Several physics-based models, e.g. the Maurer model (Maurer, 1962), the Warren model (Warren, 1987), the B-Y model (Bourgoyne and Young, 1974), the Hareland model (Hareland and Rampersad, 1994), the Detournay model (Detournay et al., 2008), the Motahhari model (Motahhari et al., 2010), are therefore proposed to predict ROP. All of these models take into account the engineering and geological factors to various extent, however, it still exists a great many limits in itself, especially in the extremely complex downhole environments. The primary reason is that the strong nonlinear relations between the ROP and the governing factors are not thoroughly understood (Zhang et al., 2022).
High-Resolution Fluid Flow Simulation in X-Crossing Rough Fractures
Authors: Ifrene Ghoulem E. H. , Egenhoff Sven , Pothana Prasad , Nagel Neal , Li Bo
Published: September 2023

Modeling of fluid flow in rock fractures is a key issue in answering numerous geoengineering problems in the fields of geophysics, reservoir engineering, rock mechanics, to geothermal processes. Although fluid flow in single fractures has been extensively studied in the last 7 decades, fractures commonly seen in fractured reservoir systems intersect each other forming complex geometric structures. Such fracture networks likely affect fluid flow behavior and solute transport. To investigate the impact of geometric characteristics of connected rough-walled fractures with an X junction shape on linear and nonlinear fluid flow behaviors, a sensitivity analysis was carried out by conducting a series of numerical fluid flow simulations on X shape fractures, generated by scanning real rock fractures with distinct roughness (low, medium, and high), intersecting angles, and apertures. The fluid flow through these fractures at different flow rates was simulated by solving Naiver-Stokes equations. The results show that tortures paths and the formation of eddies are more accentuated on the rough fracture than the smoother ones, and the tortuosity of the streamlines is related to the roughness and the geometric characteristics of the intersection. Simulation results of the different models were compared, which show that the intersection significantly impacts the relationship between the hydraulic gradient and the flow. Therefore, the pressure gradient increases with the decrease of the intersection angle especially for low aperture and rough cases.

INTRODUCTION

Understanding fluid flow through a fractured rock mass has great importance to numerous underground industrial activities, such as geothermal extraction (Zhao, 2016), CO2 storage (Catherine Noiriel et al., 2013), oil and gas exploration (Bo Li et al., 2016), underground oil storage (Qiao et al., 2017; Wang et al., 2015), and hydraulic fracturing (Blanton TL,1982).

It is important to measure the impact of roughness to improve the performance of large-scale models since most existing large-scale models still rely heavily on simplified smooth parallel-plate models and related models for natural rock fractures with rough walls (Zimmerman et al., 1992; Zimmerman and Bodvarsson, 1996; Ge 1997; Bodin et al., 2007; Zhao et al., 2013; Wang et al., 2015).
Assessment of Empirical Methods-Based Pillar Strength Estimation Through Numerical Modelling
Authors: Cammarata G. , Elmo D. , Brasile S.
Published: September 2023

Over the past decades, many pillar strength relationships have been formulated from empirical observation of stable and failed case histories. These empirically derived equations are still widely adopted as a general technique for estimating pillar strength and simplified methods for evaluating the pillar stress (i.e., tributary area method). These generally accepted assessment methods might result in non-fully optimized solutions in terms of safe and, at the same time, economical designs. Numerical methods provide a better alternative to evaluate the mechanical behaviour of pillars in the context of progressive failure and, in turn, for a proper definition of the safety margins. In this paper, we propose using numerical modelling to determine the pillar strength through 3D analyses. An advanced constitutive model (Hoek-Brown with softening) is adopted to predict brittle mechanisms in rock masses. The results are compared with those obtained through empirical methods, providing insights about the implications of adopting empirical pillar design methods.

INTRODUCTION

In mining excavations, rock pillars are commonly adopted in most underground mining methods to support adjacent underground openings and thus guarantee the stability of the rooms for extracting the ore in a safe working environment. A system of pillars is designed to provide a suitable factor of safety that relates the pillar strength, defined as the maximum resistance to the axial compression, to the pillar stress.

Over the past decades, stone mine pillars have been the subject of many studies that have led to the formulation of empirical strength equations (e.g., Hedley and Grant 1972; Von Kimmelmann et al. 1984; Krauland and Soder 1987; Potvin et al. 1989; Sjoberg 1992; Lunder and Pakalnis 1997; Walton and Sinha 2021), which generally refer to square pillars. However, several equations have been developed to predict the increase in strength from a square to a rectangular pillar (e.g., Mark and Chase 1997; Esterhuizen et al. 2011), which also include the effect of pillar length. Although all these empirically derived equations should only apply to design conditions consistent with the database supporting their development, they are still widely adopted as a general technique. Due to the complexity of the engineering problem, which is usually associated with rock fracturing and spalling failure process as the mine depth increases, it is difficult to consider which empirical method is the most appropriate. For such a reason, the significant limitations of the empirical methods have received the attention of several authors (e.g., Sinha and Walton 2019; Wang and Cai 2021; Wessels and Malan 2023) and should be carefully considered when pillar design is carried out.
Workflow for Discontinuity Set Characterization in Rock Masses Using 3D Digital Outcrop Models Derived from UAV Survey in an Iron Ore Mine Slope
Authors: Ribas G. P. , Gontijo A. A. , Matos A. R. , Gomes L. , Silva J. , Barros M. , Cacciari P. P.
Published: September 2023

The rapid development of unmanned aerial vehicle (UAV) technology has enabled numerous open pit and underground mining companies to leverage this tool for slope stability assessment and the construction of geotechnical models. The use of aerophotogrammetry techniques with UAVs enables geotechnical and geological engineers to work in a safe and agile manner, maintaining a safe distance from hazardous areas. These techniques can identify the orientation of discontinuities in the rock mass, which is vital in evaluating slope stability. Moreover, new semi-automatic extraction techniques for discontinuities in rock masses allow aerophotogrammetric models to be utilized in geomechanical characterization in a more accessible and efficient way. With the use of 3D point cloud analysis software, the primary sets of discontinuities in a rock mass outcrop can be identified, measured, and utilized in various applications. This study presents a methodology for constructing three-dimensional models of a mine slope and utilizing them to determine the primary orientations of discontinuity sets using images captured through UAV survey. The method comprises four primary steps: (i) UAV flight and image capture, (ii) 3D point cloud construction using SfM technique, (iii) detection and measurement of discontinuities, and (iv) statistical data analysis.

INTRODUCTION AND OBJECTIVES

The collection of structural data is a critical task in characterizing rock masses and evaluating slope stability in mining. Traditionally, this task is carried out manually using a geologist's compass, exposing the technical team to various risks. Additionally, many areas are inaccessible to the team, resulting in data gaps.

With the advancement of aerial surveys using unmanned aerial vehicles (UAV) and the structure from motion (SfM) image processing technique, 3D point clouds (3DPC) can be generated from RGB images taken by UAVs, as described by Francioni et al. (2019). This 3DPC can be used in various applications, such as terrain analysis, slope stability, and hazard monitoring, which can reduce risk exposure and provide crucial information to the technical team, as discussed by Papathanassiou et al. (2020).
Effects of Fractures on Seismic Wave Propagation Path: Laboratory Studies
Authors: Madenova Y. , Suorineni F. T. , Mukhamedyarova Z.
Published: September 2023

In this study, discrete physical models using different blocks and hole sizes, and backfill characteristics are used to simulate changing underground mine conditions due to mining activities. In addition to voids and various backfills, this study includes fractures to investigate their effect on seismic wave propagation. The fracture systems in concrete blocks with sizes of 150 mm, 225 mm, 300 mm, 375 mm, and 450 mm were created by filling holes of various diameters in the concrete cubes with a static cracking agent (SCA). This process mimicked blast and stress-induced fracturing in the underground mine environment. AE measurements indicate that AE signal attenuation from fractures is more severe than due to backfill and in presence of fractures, backfill did not create a favorable environment for AE wave propagation toward receivers. AE signal arrival time to receivers mainly depends on the direction of AE wave propagation rather than the geometrical arrangement of the sensors in the presence of the voids, backfills, and fractures. AE signal arrivals to receivers are governed by the subsurface variability, Snell's law, and AE wave propagation direction. These factors should be considered to enhance the current source location approaches in microseismic monitoring systems.

INTRODUCTION

A major concern in deep underground mines is seismicity and rockburst of which frequency increases with mining depth. These phenomena significantly influence mine safety, productivity, and operating costs. Considering the undesirable impacts and consequences of seismic activities and rockbursts, their forecasting and control play a critical role in deep underground mines. Seismically active mines rely on microseismic monitoring systems to predict microseismic events and to minimize the exposure of personnel and equipment to seismic hazards. The microseismic monitoring system is able to identify, locate and quantify the mine seismicity enabling a better understanding of the rockburst mechanism.
Brittle-Ductile Transition and Correction to Brittleness Index of Deep Shale Gas Formation
Authors: Kong L. , Jiang S. , Li Y. , Song G.
Published: September 2023

The brittle to ductile transition phenomenon in deep shale gas formations is a challenge for hydraulic fracturing and is of interest from both a geological and an engineering perspective. A series of uniaxial and triaxial compressive experiments at increasing confining pressures was conducted on Longmaxi shale core plug samples from a deep gas reservoir (>3500m). The stress-strain curves at confining pressure <45MPa show the shale samples experience linear elastic response and brittle failure. The peak strength increases greatly as confining pressure increases. At 100MPa confining pressure, approximately the in-situ horizontal stress of the shale samples, the test demonstrates the existence of an elastic-plastic response and high residual strength after peak failure, indicating ductile property. The brittleness index was calculated from elastic properties and strength properties, respectively, and the correlation model was established with respect to the confining pressure. The correlation model is used to modify the log-based brittleness index from elastic response. This model reflects the ductile property of a deep shale gas formation subjected to brittle-ductile transition. This method can be applied to the nearby wells that have no drilling cores and improve the accuracy of the brittleness index evaluation.

INTRODUCTION

Deep shale reservoirs will be a source of oil and gas resources in the upcoming decades as shallow reservoirs are steadily depleted (Ma et al., 2021). On the other hand, developing and utilizing natural gas is an important step towards the carbon-neutral goal as the world is transferring from conventional oil to clean energy (Wang et al., 2022). Fuling Area is the one of the most commercialized shale gas fields in China and the Longmaxi shale formation has been studied extensively in the past decade (Nie et al., 2020). Yet, studying geological features in deep formation (deeper than 3500 meters depths) bring up more challenges in tectonics, sedimentology, and diagenesis. Particularly, stimulation by hydraulic fracturing didn't provide detail to the level of expectation which impacted gas production (Zhao et al., 2022). The critical problem lies in the geomechanical properties and brittleness evaluation.
Investigation to Integrated Geomechanics of Casing Deformation and a New Technique: A Case in Deep Gas Shale of Sichuan Basin, China
Authors: Zhu Haiyan , He Xinru , Li Yang , Tang Xuanhe , Huang Chuhao , Zeng Bo , Song Yi
Published: September 2023

To investigate the mechanism of casing deformation and failure during volumetric fracturing of deep gas shale in Sichuan Basin, we put forward targeted comprehensive prevention and control measures. Based on the idea of geological-engineering integration, a three-dimensional geo-mechanical model is established, which coupled the formation - cementing sheath - casing during hydraulic fracturing of deep shale reservoir. Taking TB01 well as an example, the correlation between induced stress, cementing quality, fault or natural fracture dislocation and other factors in the process of hydraulic fracturing was analyzed. The main cause of fault or natural fracture dislocation under the influence of multiple factors is determined firstly. Then, the effectiveness of fracturing scale controlling, casing and cementing quality improvement and other process measures are investigated. Finally, based on the above study, a novel process and supporting tools for fault pre-slip are proposed in this paper. The feasibility of the process is demonstrated, and the structural parameters of the supporting tools are optimized. Taking Luzhou as an example, it provides theoretical and technical support of deep shale gas in safety and high efficiency.

INTRODUCTION

China has abundant reserves of shale gas with great development potential. Speeding up the development of shale gas is of great significance for relieving the pressure on natural gas supplies and adjusting energy structure. Shale gas is developed according to the causes of casing deformation, many of those who learn to conduct the research, puts forward the effect of thermal stress[1-3], asymmetric fracturing[4-9], the cementing quality [10-15] and fault slip[16-30], etc.

At present, most scholars have recognized that fault activation in the process of hydraulic fracturing may be the main controlling factor leading to casing deformation[17-29], which has been verified by more and more field data. These research understandings provide theoretical guidance for the field, however, casing deformation still occurs from time to time, and there is still a lack of specific measures to solve the problem, which needs further research.
Study on the Collapse Behaviors of a Single Cavitation Bubble Near a Concave Wall
Authors: Wu Xiaoya , Zhang Yiqun , Hui Chengyu , Huang Haochen , Tan Yawen , Li Gensheng
Published: September 2023

The enormous power emitted from cavitation bubbles has been positively utilized in drilling rate improvement and increasingly comes into prominence in oceanic hydrate recovery. Previous studies mentioned that the collapse process of a cavitation bubble near a wall is seriously affected by the wall shape. In present study, the dynamics of a single cavitation bubble near a concave wall with hydrate properties are numerically investigated. The evolutions of the bubble profile varying with the defined parameter θ have been computed. Then, the effect of θ on the bubble volume and collapse time was discussed. Moreover, the cavitation damage towards the concave wall was preliminarily revealed. The simulated results show that the shrinkage process of a cavitation bubble near a concave wall mainly includes a jet penetration stage and a collapse stage. Increasing θ leads to the reduction of bubble shrinkage rate and the extension of collapse time. With the θ varying from 0° to 180°, the pressure at wall center emitted by shock wave increases gradually, while the impinging pressure induced by micro-jet reaches its maximum when θ = 90°. The thermal effect is greatest when θ = 90° due to its higher generated temperature and micro-jet velocity.

INTRODUCTION

Cavitation demonstrates that the vapor bubbles occur in liquid as the local pressure decreases below the saturated pressure value (Brennen, 2014; Franc & Michel, 2006; Zhang et al., 2017). The source of severe erosion on warship propellers, hydraulic pumps and turbines originates from the collapse of cavitation bubble clouds, in which process the instantaneous high pressure and high temperature are generated (Choi & Chahine, 2016; Franc et al., 2011). Generally, when the bubbles collapse in the vicinity of a wall, they will release shock waves and micro-jets with high velocity. Once its aggressiveness exceeds the threshold determined by the material properties, it will cause deformation, pits and craters on the surface of the material (Choi et al., 2014; Hsiao et al., 2014; Pöhl et al., 2015). Although the cavitation phenomenon is undesirable in many hydraulic engineering situations, the extreme energy generated by cavitation bubbles has been positively used in some technologies. For example, the cavitation jet producing cavitation bubble in flows, has been adopted for pipes cleaning (Bukharin et al., 2020; Peng et al., 2018), drilling rate improvement (Li et al., 2002; Li et al., 2005; Li et al., 2007), and metal peening (Soyama, 2020; Soyama et al., 2011; Soyama et al., 2020).
Peak Particle Velocity for Blasting Rock Modeling
Authors: Yang R. , Green S.
Published: September 2023

Blasting mechanisms are a complex coupling of the rock mass properties and the explosive detonation performance as well as the blast design parameters. Both rock mass and explosive properties have parameters that are inherently not well defined. Thus, blast modeling is greatly challenging to predict rock fragmentation, blast vibration, and the broken-rock mass movement. For blast modeling, previous work has shown that near-field signature-hole blast vibration monitoring is an effective method to obtain critical blast model input. In a blast field, multiple charges create nonlinear additive strains at a given point in the rock and time, which further complicates blast modeling. This paper shows how the measured peak particle velocity ("PPV") from the signature-hole blast vibration serves as a key controlling parameter for modelling. Using PPV as the controlling parameter, pressures and strains can be approximated at a point of interest. Rock breakage is then related by simplified approximations to the pressures and strains. The modelling method described in the paper relates all blast design parameters to the PPV induced by multiple charges at a point in the rock. Therefore, using PPV as a key parameter allows blasting models to simulate all blast design parameters and significantly simplifies blast modeling.

INTRODUCTION

Predicting the results of rock blasting has been a long-standing challenge since its inception. However, the complex and dynamic mechanisms of rock blasting remain unclear (Fourney, 2015). The variables affecting the blast results are numerous, including rock mass properties, explosive properties, and blast design parameters. These variables interact in a nonlinear manner, making rock blast modeling more difficult than static or quasi-static rock mechanics modeling.

If a blasting model is built purely based on the first principles of physics, it must involve many parameters related to rock properties and explosives. However, these parameters are often difficult to impossible to measure, which makes it challenging to obtain relevant blast modelling input. Moreover, most of these blast models cannot simulate full blasts and design parameters. Even a single modeling prediction requires a large amount of computing time and can only simulate a small number of blastholes. This forms a major impediment to the engineering applications of blast modelling.
Geothermal Energy Storage: A Conceptual Assessment of Geologic Thermal Storage Systems in North Dakota
Authors: Gyimah E. , Metwally M. , Tomomewo O. S. , Hurtado J. P. , Alamooti M. , Gosnold W.
Published: September 2023

Geothermal energy and Aquifer thermal energy storage can provide beneficial ways of storing energy in excess and providing energy when needed. North Dakota's renewable energy system is impacted by its harsh winters. Geologic aquifer thermal aquifer storage system is a large scale geothermal system that can act as energy storage media. Aquifer thermal storage systems are dependent on heat conductivity of rocks, storage capacity of aquifer, fluid flow, geochemistry and geo-mechanics. The goals of the project are to 1) evaluate the amount of energy that can be stored in deep aquifers; 2) access the amount of energy that is thermally recoverable; 3) monitor changes in geo-mechanical parameters. CMG STARS, a three-phase multi-component thermal and steam additive simulator, was used for the thermal numerical simulation which takes into account the geo-mechanics (thermal dilation and re-compaction). A conventional reservoir with representative porosity and permeability is modelled in CMG and Semi Analytical Model (SAM) was used to calculate the wellbore dynamics involved with geothermal operations. This is used to calculate heat transfer to the surrounding formation and determine our heat loss. Our preliminary results show us the reservoir pore volume dilation re-compaction model changes from cold water injection. The grid block void porosity dilation re-compaction model changes are greatly influenced by grid block pressure.

INTRODUCTION

Geothermal Energy and Aquifer Thermal Energy Storage (ATES)

Geothermal energy refers to the earth's thermal energy that can be converted into electrical energy. Emissions from the geothermal energy industry are substantially low, which is an excellent asset to reaching a low-carbon economy. Hot dry rocks and hydrothermal resources are the primary geothermal energy sources. Water from surface seeps through faults and cracks of earth and is warmed by hot rocks or water is trapped by impermeable layers to create geothermal reservoirs. Sedimentary basins have great geologic and reservoir properties for low-cost energy generation for geothermal energy. Hot water moves from deep sources to shallow reservoirs for hot water geothermal reservoirs. Hydrothermal systems use steam or water for electricity generation. Enhanced geothermal systems extract thermal energy from geothermal resources with lower permeability and fluid saturation. (Grant & Bixley, 2011)(Barbier, 2002)
Failure Surface Identification and Structural Domain Segregation Using Drone-Based Structure from Motion Photogrammetry
Authors: Benfield S. , Gutierrez M. , Zhou W.
Published: September 2023

An emerging topic in the geotechnical site characterization is the use of drones for rock mass characterization through Structure from Motion (SfM) photogrammetry. This study highlights a series of surveys utilizing a DJI Mavic II drone performed between July and August 2022 at an abandoned quarry in Clear Creek Canyon Park, located 0.25 miles west of Golden, Colorado. The purpose of these surveys was for failure surface identification of a historic wedge failure and structural domain segregation of the remaining rock slope. The study site is composed of a heavily jointed interlayered gneiss rock mass with distinct planar discontinuities. However, structural discontinuity orientations may only be homogenous across some sections of the rock mass. This research highlights an improved contour density-based methodology drawing upon existing methods of structural domain identification to locally divide the rock mass into domains of similar structural orientation. Stereographic comparisons between domains are considered utilizing an exponential Kamb density method. The results of this study reveal that both blasting effects and tectonic features likely induced the historic wedge failure. This study also reveals that the remaining rock mass may have profound spatial differences in structural orientations, requiring appropriate domaining for rock mass characterization.

INTRODUCTION

Most all rock masses have discontinuities in the form of joints, bedding planes, faults, lamination planes, foliation planes, and lithological contact surfaces whose quantity and orientations govern the rock mass strength (de Vallejo et al., 2011). Drone technology, in tandem with Structure from Motion (SfM) photogrammetry, is increasingly being used to characterize the discontinuities of slopes, particularly for steep and hard-to-access locations (Bar et al., 2021; Krajnovich et al., 2020; Papathanassiou et al., 2020; Salvini et al., 2017). Furthermore, data acquired from SfM photogrammetry can also be used in conjunction with previously established semi-automatic discontinuity identification methods (Buyer et al., 2020; Buyer & Schubert, 2016; Buyer & Schubert, 2017; García-Luna et al., 2019; Krajnovich et al., 2020). In addition, drone-based remote sensing can be safer than traditional methods (Battulwar et al., 2021; Deliry & Avdan, 2021).
Numerical Analysis of Fracture Propagation Behavior in Hot Dry Rock During Radial Borehole Fracturing
Authors: Zou Wenchao , Huang Zhongwei , Sun Yaoyao , Wu Xiaoguang , Long Tengda , Huang Pengpeng , Yu Huiyong
Published: September 2023

Radial well fracturing is a promising stimulation method, which shows great potential in addressing the issues suffered in enhanced geothermal system (EGS), such as poor connectivity and difficulty in controlling the fracturing paths. To determine the applicability of radial borehole fracturing in HDR, a THM-FDEM coupling model for studying the fracture propagation behavior of radial borehole fracturing is established. Firstly, the reliability of the coupled THM model is validated by radial borehole fracturing experiments. Then, the effects of azimuth, number, length and spatial distribution of radial boreholes on fracture propagation behavior are analyzed. The results show that implementing radial borehole fracturing in HDR can overcome the adverse effects of in-situ stress, allowing fractures to expand in the desired direction. Increasing the number and azimuth of radial borehole while decreasing their length can increase the angle of fractures deviating from the direction of maximum horizontal principal stress. In the case of double-branch, a branch angle of 60° can result in stress interference between radial boreholes, inhibiting fracture propagation from the toe of the radial borehole. The research findings of this study are expected to provide valuable guidance for the field application of radial borehole fracturing in HDR geothermal reservoirs.

INTRODUCTION

Geothermal energy, as a clean and renewable energy resource, can promote the development of electricity generation, heating, tourism, and other industries (Mock et al., 1997; Fridleifsson et al., 2001; Armstrong et al., 2016). HDR geothermal formations have the characteristics of high temperature, dense lithology, low permeability, and poor crushability. The building of an enhanced geothermal system (EGS) by hydraulic fracturing is the major means of extracting deep-subsurface heat energy (Anderson et al., 2019; McClure et al., 2014). However, there are some technical issues in the practical application of EGS technology, such as poor connectivity between injection and production wells, and difficulty in controlling the fracturing paths.