bluuebunny/crossref_metadata_2025_split huggingface dataset:
Failure Surface Identification and Structural Domain Segregation Using Drone-Based Structure from Motion Photogrammetry
Authors: Benfield S. , Gutierrez M. , Zhou W. 
Published: September 2023

ABSTRACT
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

ABSTRACT
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.
Need and Design of a Field Test to Improve the Knowledge on Strength and Behavior of Massive Hard-Rock Pillars in Deep Mines
Authors: Ladinig T. , Wagner H. , Grynienko M. 
Published: September 2023

ABSTRACT
Pillars have a central role in an active stress management approach, which has been proposed for the extraction of thick tabular and massive hard-rock mineral deposits. A mining method making use of this approach, is the novel raise caving mining method. Initially, the pillars have width-to-height ratios of 5 to 10. In the course of stope extraction, the dimensions of the pillars are altered, namely the height of pillars is increased and the width of pillars may be decreased. Consequently, the pillar strength is reduced and pillar crushing is triggered. A stable crushing process must be ensured. Knowledge on the complete stress-strain behavior of massive hard-rock pillars is paramount for the design of these pillars. However, a review shows that there is insufficient knowledge available. An in-situ pillar test is found to be best suited to improve the knowledge. The need for, objective of and design of such a full-scale in-situ pillar test are discussed. An in-situ pillar test is planned in one of LKAB's underground operations in connection with the development of the raise caving mining method. The layout and sequence of the test and the current progress of design and open points in the design are outlined.

INTRODUCTION
Pillars are used in underground mining for several, different purposes. The tasks for pillars comprise regional support of the overburden strata (panel pillars), local support of the immediate roof strata (crush pillars), the separation of adjacent extraction areas (inter-panel pillars), the control of regional convergence and the associated limit of mining-induced seismicity and abutment stresses (stabilizing pillars) and the protection of critical infrastructure, such as shaft systems (protection pillars). This paper addresses massive hard-rock pillars, which take over a central function in an active stress management strategy in massive deposits or in thick tabular deposits. Due to the shape and dimensions of the deposits and the considered purpose, the pillars are massive and they have a width and height in the range of several tens of meters and a length of up to and more than hundred meters.
3D Geomechanical Model Construction and Application of Deep Shale Gas in the Luzhou Block, Sichuan Basin
Authors: Wang Yuan , Yang Henglin , Fu Li , Chen Gang , Yuan Guangjie , Zhang Heng , Wang Zixin 
Published: September 2023

ABSTRACT
Deep shale gas with a burial depth of 3500–5000m became an important area for shale gas development in China. The characteristics of the rock's mechanics and the in situ stress have a significant impact on the drilling and fracturing effects of horizontal wells. Finite element simulation is used to build an accurate in situ stress model from the data of acoustic logging, diagnostic fracturing injection test, FMI imaging logging, and stress measurement. The results show that Young's modulus and Poisson's ratio in the Luzhou block change vertically with the deposition time. The Longmaxi reservoir has an abnormally high pore pressure gradient which ranges from 16.7 kPa/m to 21.7 kPa/m. The stress regime of the Luzhou block is primarily strike-slip type, with an overburden pressure gradient of 25.5kPa/m, and a minimum horizontal stress gradient range of 18.8 to 24.5kPa/m. According to wellbore breakouts and acoustic emission experiments of cores, the ratio between σhmax and σhmin is 1.165. The horizontal principal stress of the reservoir increases with the increase of Young's modulus and pore pressure. The conclusion is that high-precision geomechanical models can effectively serve to improve the efficiency of drilling operations, improve the production of single wells and benefit development.

INTRODUCTION
As an important unconventional energy source, shale gas has become a global hotspot for resource development. Shale gas deposits are abundant in China and are predominantly concentrated in the southern Sichuan Basin (Zou, et al. 2022; Ma, et al. 2021; Zhao, et al. 2020). Currently, deep shale gas deposits with a burial depth of 3500–5000 m have recently achieved a strategic breakthrough and have become an important area for shale gas development in China. However, deep shale gas development still faces numerous geological and engineering problems, though, as a result of the short exploration period, complex geological conditions, and inadequate engineering technology adaptability (He, et al. 2021).
Shale is a typical "artificial gas reservoir" with nanoscale pore space and Nadasi grade permeability, and has no natural production capacity, therefore, commercial development of shale gas needs the use of horizontal wells drilling and large-scale volume fracturing technologies (Jiang, et al. 2017). The effectiveness of horizontal well drilling and large-scale volume fracturing is significantly influenced by reservoir characteristics and in situ stress conditions. During the drilling stage, high shear stress and pore pressure can lead to wellbore stability problems. Loss of circulation and sticking caused by the unreasonable design of drilling fluid density will negatively impact the drilling cycle (Mehrabian, et al. 2017). At the completion stage, casing deformation is a significant obstacle to shale gas production (Chen, et al. 2016).
An Intelligent Prediction Method of Horizontal Well ROP Based on Di-GRU
Authors: Pan Tao , Song Xianzhi , Wang Zheng , Yin Zhiyong , Ji Yong , Zhu Lin , Pei Zhijun , Ye Shanlin , Liu Muchen , Li Zhen , Zhu Zhaopeng 
Published: September 2023

ABSTRACT
At present, with the continuous development of unconventional oil and gas exploration and development, horizontal wells, as an important means of unconventional oil and gas exploitation, have attracted much attention from drilling teams and oil field companies. However, the cost of horizontal well drilling is relatively high, so more targeted construction should be carried out according to the characteristics of horizontal well drilling. Therefore, rate of penetration (ROP) prediction of horizontal wells is extremely important. The current ROP prediction models of horizontal wells mainly rely on manual experience and some mechanism models, and do not take field data and actual construction conditions into account, so the field application effect is difficult to be ideal. To solve this problem, an intelligent algorithm based ROP prediction model for horizontal Wells is proposed and a novel dual-input neural network structure is designed. Sequential data such as hook load and rotary torque are input into Gated recurrent unit’ (GRU) network, and non-sequential data such as bit type are input into back-propagation neural network(BP), which is called Dual Input GRU(Di-GRU) ROP prediction model. The results show that mean absolute percentage error and R-squared of this model are 11.8% and 0.923 respectively. The prediction model based on Di-GRU proposed in this paper has higher accuracy and better mobility, which is of guiding significance for improving the drilling efficiency of horizontal wells.

INTRODUTION
With the deepening of oilfield exploration and development, the development of deep and complex oil and gas reservoirs has become the focus of stabilizing oil and increasing production, which has important strategic significance. At present, horizontal wells have become the main well type for developing complex oil and gas reservoirs(Yassie et al.,2020). Compared with vertical wells, horizontal wells usually have more complex geological conditions and greater drill string friction, resulting in poor formation drill ability and difficulty in drilling the drill string. The low rate of penetration(ROP) and the small footage of a single bit bring severe challenges to drilling engineering and seriously affect the progress of exploration and development(Soares et al.,2019). Accurate ROP prediction of horizontal wells can assist the scientific allocation of resources before drilling and the accurate formulation of operation plans, which is of great significance for improving drilling efficiency and reducing costs. Horizontal well drilling engineering operation is a complex process. Formation, tools and operating parameters all play an important role in the rock breaking of the drill bit, such as formation drill ability, drill bit wear, rotary speed, mud performance, drill bit pressure, build-up rate, etc. Therefore, it is difficult toaccurately predict the ROP of horizontal wells.
Numerical Simulation, Parametric Analysis, and Equipment Design for Backfilling of Waste Rock Cavities with Oil-Based Rock Cuttings
Authors: Luo Yuyang , Hu Naikun , Wei Yaoran , Yang Heng , Deng Jingen , Feng Yongcun 
Published: September 2023

ABSTRACT
Oil-based rock cuttings present a significant technical challenge in terms of the economic, environmental, and efficient processing in the engineering field. This paper employs fluid finite element theory, particle discrete element theory, and particle multiphase flow calculation model to couple the particle domain and fluid domain bi-directionally through the udf compilation interface. By employing the particle segmentation volume fraction model and CFD-DEM multiphase flow equation with particles, the study simulates the process of filling salt caverns with oil-based rock cuttings mixed mud, and analyzes the impact of multi-factors on the overall back-filling effect of the cavities. The results demonstrate that under the conditions of particle size of 4 mm, initial velocity of 5 m/s, and fluid viscosity of 40 m·Pas, the overall trajectory of particle movement aligns with actual working conditions and conforms to the fluid phase velocity distribution. In practical engineering, besides the control of the parameters of parcels, real-time monitoring and adjustment should also be attached according to specific conditions and requirements. Additionally, a sufficient understanding and study of the physical properties of the filling particles and the fluid's properties are required to optimize the parameters and back-filling schemes, ultimately leading to improved backfilling efficiency.

INTRODUCTION
Due to the characteristic of salt minerals being soluble in water, the exploitation of salt deposits commonly uses the method of water-soluble mining (Liang et al., 2004). If the salt mine is stopped exploitation or abandoned, a large amount of abandoned salt cavities will be generated underground. If the cavity is not backfilled and sealed in time, the continued dissolution of cavities will lead to further problems such as roof collapse, forming severe geological disasters.
Salt cavities have the characteristics of deep burial, good sealing, and high safety. It is suggested to consider using salt cavities to treat nuclear waste and establish salt cavity gas storage facilities (Ding et al., 2015). It is also recommended to strengthen the research on automation control systems, reduce the convergence of dissolved cavities, and enhance stability assessment standards (Xiao, 2012).
Fracture Propagation Behaviors of High-Temperature Granites During Liquid Nitrogen Fracturing with Multi-Branch Wells
Authors: Sun Yaoyao , Wu Xiaoguang , Zou Wenchao , Huang Zhongwei , Xie Zixiao , Li Jingbin , Long Tengda 
Published: September 2023

ABSTRACT
We propose a low temperature medium fracturing mode in combination with a multi-branch well to overcome the challenges of difficult initiation, communication, and control in the traditional hot dry rock (HDR) fracturing. Fracturing experiments on multi-branch wells subjected to various fluid conditions were conducted to analyze and compare fracture behavior. The method of pressure curve fitting analysis and the method of permeability test by re-injection fracturing fluid were used to quantitatively characterize the rock fracture morphology and evaluate the effect of liquid nitrogen (LN2) fracturing. The characteristic of injection pressure of HDR with different numbers of branch wells under LN2 fracturing are compared, and the characteristics of fracture morphology of HDR are evaluated. The experimental results show that: ① compared with hydraulic fracturing, multi-branch well can reduce the breakdown pressure in a certain range (About 25 to 61 %), and breakdown pressure can be further decreased under LN2 stimulation; ② with the increase of the number of branched boreholes, the extension of fractures is longer and fracture interconnection is better; ③ The HDR after multi-branch well fracturing has better conductivity than that of hydraulic fracturing. According to the experimental results, the multi-branch wells can enhance the thermal shock areas of LN2 in HDR, and has a great potential in creating complex fracture network. This technique is expected to provide a new insight into better developing HDR geothermal.

INTRODUCTION
Geothermal energy is an important part of the world's energy plan for the 21 centuries. It has many benefits over traditional energy sources, including being clean, efficient, and having large reserves (Lu et al,2018). The type of geothermal energy we’re talking about is found deep underground in certain rocks, like granite and gneiss. There are many ways to get this energy out of the ground, but the most common one is called an enhanced geothermal system. This involves creating fractures in the rock using a special fluid, so that hot water can be pumped through the rock and used to make electricity. Scientists are working to find ways to make this process more effective and cheaper.
Evaluating the Geothermal Potential of Hot Sedimentary Aquifers Using a Hybrid Approach
Authors: Cottrell Mark , Lacazette Alfred , Chmela Bill , Karimi Saman , Marsh B. D. 
Published: September 2023

ABSTRACT
Flow through geothermal reservoirs is highly complex, and often includes contributions from both fracture networks and the porous rock matrix. Discrete Fracture Network (DFN) models are proven, effective tools for the characterization of rock masses especially where fracture dominated fluid flow is encountered; whereas more conventional tools, such as Finite Volume (FV) methods, are more numerically favorable for simulating problems where detailed multiphysics is required.
This paper presents a workflow that combines discrete and continuum descriptions that captures the salient features of the geological materials whilst also remaining numerically tractable. DFN models of fractured rock masses are typically developed using statistical distributions to generate realistic three-dimensional (3D) descriptions of the natural fracture network. Superimposed with this fracture description, is a matrix-orientated description based on an intact rock property model. Integration of these two descriptions into a single continuum rock mass description is achieved through a novel discrete-continuum upscaling process which combines fractures and intact properties into a unified form, providing effective mass permeability and geomechanical descriptions.
The composite rock mass description is then carried forward into a numerically efficient multiphysics solver that provides effective simulation of both temperature and flow in a fully coupled manner to evaluate the performance potential of geothermal reservoir units. In addition, it will be demonstrated how the presented work can naturally embed within the stochastic framework of DFN and permit a probabilistic based evaluation.
This paper presents application of the hybrid DFN-FV workflow for a hot sedimentary aquifer. The application is presented in terms of the characterization steps and a description of the input used, which is then supplemented with the dual fracture and matrix description. The demonstration will also touch on the efficient gridding of geological domains and provide example simulation results of multi-well injector and producer fluid flow and heat transfer. The work in this paper shows how the DFN-FV approach can be systematically employed to help with the success of geothermal well placement and completion studies in hot sedimentary aquifers.
An Analytical Solution for Linear Elastic Geomechanical Responses in a Layered Vertical Transversely Isotropic Medium
Authors: Yan H. , Park J. , Holt R. M. , Bakk A. 
Published: September 2023

ABSTRACT
The isotropic homogenous assumption in the conventional Geertsma model is often contradicted by reality because the rock properties in the overburden are typically anisotropic and often can be quite different from the reservoir. Thus, we present an analytical solution that extends Geertsma's solution and can consider layered subsurface, including anisotropic elasticity. Namely, five independent parameters are assigned in each anisotropic layer in this analytical model. The derived functions are expressed in terms of both displacements and stress fields accounting for any number of layers. Different from the original Geertsma model, this model also describes horizontal stress changes inside the reservoir. We assess the analytical solution's performance, advantages, but also limitations by comparing it to finite-element numerical modelling results in three cases. The results of the analytical solution agree well with those of the numerical solution for both fully anisotropic and isotropic cases. It is also learned that side-burden has a minor impact on stress and displacements for the case with anisotropic surrounding around a depleted isotropic reservoir. The analytical solution enables us to achieve sufficiently accurate results with low computational cost and be focused on the essential features of the Geertsma-type geomechanical problems.

INTRODUCTION
Pore pressure changes due to fluid injection for underground carbon storage or depletion for hydrocarbon production can cause stress redistribution in the subsurface. Therefore, a quantitative understanding of the geomechanical changes in the subsurface is essential for safe drilling and carbon storage processes. ‘Stress path’ is commonly used to help understand the changes in the stress state within the rocks around or inside an injected or depleted reservoir. For the overburden, the stress path coefficient κov is defined as the ratio between total horizontal stress change ΔSr and total vertical stress change ΔSz for an axisymmetric model:
(Equation)
The value of κov corresponds to different stress change scenarios. For example, three values of κov −0.5, 0, and 1 correspond to constant mean stress (CMS) change, uniaxial stress change, and isotropic stress change, respectively. Studying the stress path is crucial for safe reservoir operation and can help design monitoring strategies to prevent geomechanical instability and other risks.