bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Reliability Analysis of the Dilution Graph Method for Open Stope Design: A Case Study
Authors: Adoko A. C. , Zhakipbayev A. 
Published: September 2023

ABSTRACT
The equivalent linear overbreak slough (ELOS) graph is a commonly used empirical design method for open stope design. Nevertheless, this method can lead to poor design performance when the geotechnical domain data lacks confidence. This is due to the inherent variability of the design input parameters, which should be considered for more reliable stope design. Hence, in this study, the First-Order Reliability Method (FORM) is used to determine the reliability index and the probability of unplanned dilution level associated with the design for each geotechnical domain. The Maleyevsky mine, located in northeast of Kazakhstan, is used as a case study. The parameters used for the analyses are the Modified Stability Number (N’), Hydraulic Radius (HR), and the actual dilution. The results indicated that the reliability indices and the probability of unplanned dilution occurrence vary between 0.1-4.63; and 0.0001% − 46.02%, respectively, depending on the rock domains. The results were in agreement with the field observations. It is concluded that the reliability-based design method could serve as a tool in the design of the open stope in connection with minimizing unplanned dilution.

INTRODUCTION
Open stope mining is characterized by large extraction rates and often with unsupported walls, which make it susceptible to unplanned dilution. Unplanned dilution is the mixture of ore with the waste material (hosting rocks, low grade mineralization, etc.) sloughed from the stope walls outside the planned excavation boundaries. This obviously leads to poor profitability of the mining operations. Serious profitability issues due to unplanned dilution have been reported (Clark and Pakalnis, 1997; Stewart et al., 2007) by many mines. Therefore, developing design tools that facilitate the reduction of unplanned dilution, is essential for the mining industry.
Several approaches to design open stopes are currently in use, for example: numerical modelling (Henning and Mitri, 2007; Sainsbury et al., 2015; Vallejos and Díaz, 2020), analytical methods (Diederichs and Kaiser, 1999), back analysis of in situ measurements of stope overbreak (Cepuritis et al., 2010), empirical dilution graphs (Potvin, 1988; Clark, 1998; Mawdesley et al., 2001), and artificial intelligence based-design (Korigov et al., 2022). Among these methods, the empirical dilution (ELOS) graph is used in practice due to its simplicity and flexibility (Clark, 1998; Capes, 2009).
Proper Weight Distribution on Bit and Reamer Enhances the ROP of the Reaming While Drilling in Deepwater Well
Authors: Chen Haodong , Wang Shiguo , Liang Jiwen , Luo Ming , Han Xu , Jin Yan , Lu Yunhu 
Published: September 2023

ABSTRACT
In the HTHP wells of the South China Sea, deepwater drilling in complex strata presents more risks and challenges. The reaming while drilling (RWD) technique is used to solve the problem of drilling minimum clearance space caused by multiple casing strings, by the synchronously drilling with both pilot bit and reamer. According to the analysis of actual drilling data from a exploration well in the South China Sea, an abnormal phenomenon is observed where the weight on bit (WOB) is increased, but the torque is lower. The reamer is in a suspended state, and the average ROP is only 6.2m/h. In this paper, a weight distribution model is established, which takes into account the compressive strength of the formation at both the reamer-rock interface and the pilot bit-rock interface. According to the model, it is suggested to adopt a structure design for the reamer with stronger aggressiveness to balance the weight distribution, or apply depth of cut control (DOCC) bits to maximize synchronization in the interbedded formation. Relatively, in a high strength homogeneous mudstone formation, a more aggressive pilot bit can be selected to enhanced the ROP.

INTRODUCTION
The Lingshui 25-1 block is located in the Qiongdongnan Basin with an average water depth of 980 meters, which is characterized by deep-water, high-temperature and high-pressure (Liu et al., 2022). In deep-water gas fields, there is an abnormal high pressure, which leads to a narrower drilling mud pressure window and increases the risks of drilling and cementing. Reaming while drilling (RWD) technology can realize enlarging the borehole as the same time as the bit drills the pilot hole by the concentric expandable reamers placed at the top of the bottom hole assembly (BHA). Using a reamer in deepwater operations can save an additional drilling trip, reduce the time that problematic formations are exposed, and result in significant cost savings in rig time. Underreaming can create a wellbore larger than the inner diameter of the upper casing at the lower part of the casing, optimizing casing sizes and providing a good safety window (Chen et al., 2022, Ho et al., 2013, Li et al., 2016).
Application of Artificial Intelligence in Prediction of Wellbore Stability Using Well Logging and Drilling Data
Authors: Wu Juntao , Liu Wei , Lin Hai , Liu Hailong , Peng Chengyong 
Published: September 2023

ABSTRACT
Wellbore instability is one of the most critical challenges during drilling, often manifested as wellbore collapse, shrinkage, falling rocks, and formation fracturing, which may result in complex problems such as pipe sticking, high torque, mud loss, thus impeding the drilling progress and increasing the cost of the drilling operation. Conventional wellbore stability prediction relies on some deterministic physical models, involving some empirical coefficients which are difficult to determine and often dependent on field experience. In addition, some complex factors, such as natural fractures, cannot be explicitly and quantitatively characterized in existing wellbore stability prediction models. Artificial intelligence technique has shown unique advantages in nonlinear issues. The artificial intelligence technique is used to predict wellbore stability in this study, including artificial neural networks (ANNs) and support vector machine (SVM). The logging data and drilling data were collected from the field. According to the correlation analysis between influencing factors and wellbore enlargement rate, 16 parameters were extracted, such as mud density, formation density porosity, acoustic interval transit time, weight on bit as the input data of the models, and wellbore enlargement rate as output. Both SVM and ANNs models have exceptional performance in predicting wellbore stability. When the kernel of the SVM model is Linear, predictions perform optimally. In the ANNs model prediction results, the result performs optimally when the total number of neurons is 1024 in the hidden layer. Overall, ANNs model performs better than SVM model with a coefficient of determination (R2) of 0.991, therefore it is recommended to apply ANNs to predict wellbore stability. The present analysis supplies knowledge that can be used to predict wellbore stability problems before drilling, optimize drilling parameters, and reduce drilling accidents and costs.

INTRODUCTION
Wellbore instability refer to a series of responses resulting from mechanical, chemical and other effects of the rock around the wellbore. Wellbore instability is one of the most critical challenges during drilling, often manifested as wellbore collapse, shrinkage, falling rocks, and formation fracturing, which may result in complex problems such as pipe sticking, high torque, mud loss, thus impeding the drilling progress and increasing the cost of the drilling operation.
Study on the Mechanical Characteristics and Optimization of Composite Lining Structure Under High Geostress
Authors: Deng J. Q. , Cui W. , Zhu Y. B. , Liu Y. , Du S. L. 
Published: September 2023

ABSTRACT
Aiming at the problem of high geostress faced by deep buried tunnel, the mechanical characteristics and optimization of composite lining structure are studied. The influence of consolidation grouting ring and backfill grouting measures on the mechanical characteristics of composite lining structure are studied based on the three-dimensional finite element calculation theory, so as to determine the optimal thickness of concrete lining. The maximum tensile stress of 20cm lining during operation is about 8.73MPa, and that of 120cm lining during operation is about 4.68MPa. The maximum pressure stress during the construction period of 20cm lining is about −13.47MPa, and the maximum pressure stress during the construction period of 120cm lining is about −4.95MPa. After the pre-consolidation grouting of class IV surrounding rock, the maximum tensile stress during the operation period decreases. If backfill grouting is not carried out within 120° of the top arch of the lining, the maximum tensile stress during the operation period and the maximum compressive stress during the maintenance period are significantly increased, so the backfill grouting of the lining and its grouting quality have a significant role in improving the bearing capacity of the composite lining structure.

INTRODUCTION
With the continuous construction of water conservancy and hydropower projects in China, a number of deep-buried, long and large diversion tunnels crossing high altitude and high mountain areas have emerged, which are significantly different from the diversion tunnels of conventional power stations. The lining structure of deep-buried, long and large diversion tunnel is affected by many adverse factors, such as large burial depth, long tunnel line, large section, rich groundwater, high water head and high geostress level. The design and construction of lining structure is very difficult. The geological conditions in the western mountainous areas are complex, and the construction of deep-buried large-section tunnels is very easy to cause engineering accidents such as landslides, water inrush, mud inrush, etc. The main reason is the lack of understanding of the stress of such tunnel lining structures.
Effects of Supercritical CO2-Brine/shale Interaction on Fracturing Behavior
Authors: Qiu Renyi , Zhang Guangqing , Anhai Zhong , Mingjing Lu , Feng Yang , Zhou Dawei 
Published: September 2023

ABSTRACT
As a caprock for CO2 geological sequestration, the mechanical properties of shale may change significantly from the long-term CO2-fluid interaction. To study the long-term effects of supercritical CO2-brine interaction on the mechanical properties of shale, the marine LMX shale was treated with supercritical CO2-brine at temperature of 110 °C and pressure of 30 MPa for 15, 30, and 60 days, respectively. The Brazilian tests combined with Acoustic Emission (AE) monitoring were conducted on shale before and after the treatments. The results show that: (1) Compared with the dry shale, the tensile strength of shale saturated with supercritical CO2-brine for 15, 30, and 60 days decreases by 40%, 48.6%, and 68.8%, respectively. The fracture morphology changes from a straightly single fracture to a fracture band consisting of two to four curved fractures; (2) The effects of supercritical CO2-brine interaction on the initiation and damage stresses are quantitatively analyzed. Taking the initiation and damage stresses of dry shale as the reference, the initiation stresses of shale saturated with supercritical CO2-brine for 15, 30, and 60 days decrease by 17.7%, 37.8%, and 48.4%; the damage stresses decrease by 35.5%, 58.3%, and 75.8%; (3) The AE characteristics of shale are closely related to fracture modes. The tensile fracturing of shale is sudden, manifested as an obvious step in the cumulative AE energy, while the shear fracturing of shale is gradual. With the supercritical CO2-brine treatment time, the fracture mode gradually changes from tensile-dominated to tensile-shear mixed failure mode, which can be inferred from that the slight step increases significantly and the ratio of tensile to shear events decreases from 10.7:1 to 0.8:1. The mechanical properties of shale weaken with the increase of supercritical CO2-brine treatment time.

INTRODUCTION
As one of major greenhouse gases, excessive CO2 exacerbates global climate change. CO2 geological sequestration is one of the important means to mitigate the greenhouse effect by injecting large amounts of CO2 into deep formation (Bachu et al., 2007; Wood, 2015; Jia et al., 2019; Nie et al., 2022). The deep shale formation has low porosity, low permeability, with beddings, which can effectively prevent and isolate the upward migration and leakage of CO2, which is suitable for the target formation of CO2 geological sequestration (Kalantari-Dahaghi, 2010; Lyu et al., 2021; Xie and Economides, 2009; Liu et al., 2013; Chen et al., 2015; Chen et al., 2023; Zhang et al., 2021). CO2-shale-fluid interaction will significantly affect the mechanical properties of shale under the condition of high temperature and high pressure for long-term CO2 geological sequestration (Zou et al., 2018; Al-Ameri et al., 2016; Choi and Song, 2012; Zhou et al., 2022).
Effects of Rapid Cooling and CO2 Depressurization on the Compressive Strength of Limestone
Authors: Verberne B. A. , van der Linden A. J. , El Azouzi K. , Wolterbeek T. K. T. , van Schalm R. , Coorn A. 
Published: September 2023

ABSTRACT
CO2-injection into depleted reservoirs can lead to rapid cooling and a CO2 phase change in the near-wellbore region, potentially affecting rock mechanical integrity. We report unconfined compressive strength (UCS) and thick-walled cylinder (TWC) collapse strength tests on dry and brine-saturated limestones subjected to cooling (ΔT) or CO2 depressurization (ΔP). Plug samples were prepared from Indiana limestone and a limestone from the Green River Formation, outcropping in Sanpete Valley, Utah, USA. The ΔT-treatment consisted of a thermal shock from 60°C to −78°C, while the ΔP-treatment consisted of three cycles of rapid depressurization from ∼9 MPa CO2 pressure to atmosphere. The ΔP-treatment was performed at room temperature and at 60°C. The results show that dry samples are generally stronger than their brine-saturated counterparts, while effects from ΔT- or ΔP-treatment on rock strength or stiffness are indiscernible. Based on our findings on the Indiana and Green River Formation limestones, we suggest that CO2-injection-induced cooling or depressurization in limestone reservoirs can lead to strengthening of desiccated regions with negligible negative impact on rock mechanical integrity.

INTRODUCTION
Carbon capture and storage (CCS) is a key strategy on the way to a net-zero CO2-emissions industry, including in carbonate reservoirs, which constitute vast potential storage volumes (e.g., Bonto et al., 2021). However, large-scale implementation of CCS will only be viable if operational risks are understood and mitigated. One of the important geomechanical concerns for geological CO2 sequestration are thermal stress effects due to injection of relatively cold CO2 (Rutqvist, 2012; Roy et al., 2018). Especially in cases where the reservoir (residual) pore pressure is substantially lower than the intended CO2 supply pressure (typically &gt;7 MPa), adiabatic, isenthalpic expansion of CO2 in the near-wellbore region can lead to sharp temperature drops, possibly even reaching below freezing conditions (Oldenburg, 2007; Mathias et al., 2010). Rapid temperature changes can result in thermal strains, fracturing, and, potentially, loss of containment (Pašić et al., 2007; Wang et al., 2022).
Long-Term Development of Shale Barrier Efficiency: Laboratory Tests on an Outcrop Shale
Authors: Fjær E. , Bakheim S. , Stenebråten J. F. 
Published: September 2023

ABSTRACT
The annulus outside the casing of a deep well is often left open after completion, however it is observed in numerous shale formations that the shale creeps in and closes the annulus, thus forming a "shale barrier". This is a gradual process which implies that the sealing efficiency of the barrier is also developing gradually. This paper describes small scale laboratory tests on an outcrop shale, where long-term development of shale barrier efficiency is studied. The test conditions are such that creep is likely to be the dominating process during the tests. The results show that the sealing efficiency of the shale barrier improves with time. The magnitude of the improvement depends on the stress conditions and the conditions prior to the initiation of the barrier. The final value of the sealing efficiency appears to depend primarily on the net stress which corresponds to the in-situ stress minus the in-situ pore pressure. Impacts of rock properties and annulus gap size were not investigated in this study. Theoretical considerations suggest that the seal improvement process can be significantly faster even at moderately higher formation temperatures.

INTRODUCTION
"Shale barrier" is a commonly used term for a natural barrier against uncontrollable flow outside the casing of a deep well through a shale formation. A shale barrier is formed as the shale creeps in and fills the initially open annulus between rock and casing, usually without dedicated interference by the operator (Williams et al., 2009; Kristiansen et al, 2018). Such barriers represent huge cost savings for the operator, as it may reduce or even eliminate the need for time-consuming cement jobs. It is essential however that the long-term sealing efficiency of the barriers can be trusted.
The presence of barriers outside the casing is usually detected by indirect, acoustic methods which may reveal whether the casing is in contact with a solid material or only fluid (Williams et al., 2009). The sealing efficiency of such barriers can only be tested by leak-off or pressure communication tests, however such tests are either very time consuming or rather inaccurate (Raaen and Fjær, 2020). The long-term sealing efficiency of shale barriers is therefore rarely studied in the field.
Modeling Material Fracturing with a Phase-Field Method Taking into Account Hydro-Mechanics Coupling and Material Heterogeneity
Authors: Wang Meng , Yu Zhan , Vu Minh-Ngoc , Shao Jian-Fu 
Published: September 2023

ABSTRACT
We introduce a novel numerical approach for modeling cracking in heterogeneous materials by considering hydromechanical coupling. The proposed approach addresses the need for more accurate models to study cracking processes in materials with mineral heterogeneity, which are frequently encountered in geomechanics and civil engineering applications. A new phase field model is developed to describe the transition from diffuse damage to localized cracks, including both tensile and shear cracks. The model incorporates an elastic-plastic constitutive law to describe the basic mechanical behavior of the material. We account for mineral heterogeneity by considering the mineral compositions of rock-like materials, such as inclusion content, which affect the macroscopic elastic properties of the material. The proposed model is applied to analyze desiccation and mechanical tests performed on mortar. We compare the numerical results with experimental measurements to demonstrate the accuracy of the proposed model.

INTRODUCTION
Based on laboratory tests and in-situ monitoring, it has been observed that rock-like materials commonly experience failure as a result of the initiation and propagation of fractures and cracks. These materials are subjected not only to mechanical loading, but also to changes in water saturation, temperature, and chemical degradation. Hence, it is imperative to conduct an analysis of the damage mechanics of these materials by accounting for the multi-physical coupling phenomena.
Over the past few decades, numerous phenomenological damage models have been proposed for various engineering materials, including rocks and concrete. Many of these models were developed within the framework of thermodynamics and employed a scalar internal variable for isotropic damage (Jefferson and Mihai, 2015; Chen et al., 2015; He et al., 2015) or tensorial variables for anisotropic damage (Voyiadjis et al., 2008; Desmorat, 2016; Zafati and Richard, 2019). In these models, the connection between macroscopic behavior and microscopic crack evolution is not explicitly established. More recently, the phase field method has emerged as a powerful tool for modeling the transition from diffuse damage to localized cracks (Bourdin et al., 2000; Miehe et al., 2010a,b; Borden et al., 2012; Ambati et al., 2014), by approximating sharp cracks with regularized smeared cracks. Various formulations have been proposed for modeling tensile, shear, and mixed cracks in elastic materials. Additionally, several phase-field models have incorporated the coupling between plastic deformation and damage evolution (Miehe et al., 2015a; Borden et al., 2016; Areias et al., 2016; Samaniego et al., 2021; Khalil et al., 2022).
Study on Reducing Casing Shear Deformation by Using Composite Cement Slurry Column Structure
Authors: Xi Y. , Yao Y. , Chen J. , Jiang H. L. , Ren Z. K. , Liu P. L. , Wang H. T. 
Published: September 2023

ABSTRACT
Shale reservoirs are usually developed by horizontal wells and staged fracturing, and severe casing deformation occurs during development. The main deformation form is shear deformation. The main reason for casing shear deformation is that during hydraulic fracturing, when the fracturing fluid enters the natural fracture or weak cementation surface, the normal stress between the fracture surface or bedding surface will be significantly reduced, and the friction coefficient between the two will also be substantially reduced, which will lead to relative sliding of the rock mass on both sides of the fracture or bedding. Once the rock mass slips, it will lead to shear deformation of the casing. Given this, a method of reducing casing shear deformation using composite cement slurry column structure is proposed: inject conventional cement slurry, elastic and ductile cement slurry, and cement slurry containing hollow glass beads into the wellbore in sections. The high porosity cement sheath formed by cement slurry containing hollow glass beads can effectively reduce the degree of casing shear deformation during formation slip, and the elastic and ductile cement slurry can effectively seal the possible gas channeling problem. During the research, the optimal rheological model of the composite cement slurry column was optimized, the change of the annulus pressure loss caused by the mixing was calculated, and the influence of the cement sheath formed by the structure solidification of the composite cement slurry column on the reduction of the shear deformation of the casing was analyzed. The research results show that the established rheological composite cement slurry column model can be well applied to the project site. Still, the influence of the cement slurry system on friction should be considered in the use process. The cement sheath formed by cement slurry containing hollow glass beads can effectively reduce the shear deformation of the casing. With the continuous increase of the content of hollow glass beads, the ability to reduce the shear deformation of the casing is continuously improved. The research results provide a new way to solve the problem of casing deformation caused by interlayer slip and shear during hydraulic fracturing.