bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geometrical Controls on Thermal Short-Circuiting in Multi-Fracture Enhanced Geothermal Systems
Authors: McLean Matthew L. , Espinoza D. Nicolas 
Published: September 2022

ABSTRACT:
Thermal short-circuiting in Enhanced Geothermal Systems (EGS) is a reservoir-scale phenomenon, which arises from coupled thermal-hydraulic-mechanical feedback in response to heat drainage. Coupled feedback on the hydraulic aperture may increase fracture transmissivity drastically and decrease the production fluid temperature lowering the economically recoverable heat energy. This paper identifies the geometrical controls on short circuiting for multi-fracture enhanced geothermal systems to optimize the recoverable heat energy including: fracture spacing, number of parallel factures, wellbore diameter, injector-producer spacing, initial hydraulic aperture, hydraulic aperture distribution and thermo-hydro-mechanical fracture response. We use a combination of simple 1D hydraulic network simulations and fully coupled thermo-hydro-mechanical 3D models solved through FEM. Results show that thermal short-circuiting is more severe in formations (1) with initial or late high hydraulic apertures, in the order of tens of millimeters; (2) when fluid pressure exceeds the minimum total stress, causing large fracture re-opening; and (3) with a large number of fractures in a small rock volume, causing severe thermal and mechanical fracture interaction. Our modeling work suggests that thermal short-circuiting can be mitigated with an appropriate fracture design and operation.

1. INTRODUCTION
Heat recovery in Enhanced Geothermal Systems (EGS) requires transmissive fractures connecting injection and production wellbores to increase hydraulic diffusivity of the surrounding rock (Brown et al., 1972; MIT, 2006; US Department of Energy, 2020). High surface area is desirable for large heat recovery because heat conduction in EGS reservoirs occurs at small rates (Fu et al., 2015; Gee et al., 2021). Yet, localized thermo-elastic contraction of the surrounding rock can increase fracture permeability and localize fluid flow, causing thermal short-circuiting (Armstead and Tester, 1986; Tsang and Neretnieks, 1998; Guo et al., 2016). Furthermore, fluid flow localization in EGS reservoirs can be caused by two processes: (1) fluid localization to preferred paths within a single fracture (flow-channeling) and (2) fluid localization to a few fractures within a hydraulic network of several fractures (plane-channeling). The latter is caused by distinct initial fracture geometries and viscous pressure loss between fractures (Shiozawa and McClure, 2014; Asai et al, 2018). These processes can form a thermal-hydraulic-mechanical (THM) coupled feedback loop because permeability increase within a single fracture tends to perturb the hydraulic network such that it accepts more working fluid. Hence, a coupled solution of fluid flow through wellbores and fractures with fluid flow and deformation of the surrounding rock is required to model the full transient behavior of multi-fracture EGS.
Remarks on Linear and Nonlinear Failure Criteria
Authors: Labuz J. F. , Asem P. , Fuselier H. 
Published: September 2022

ABSTRACT:
To explore the nature of stress states at failure, published data are analyzed for three rock types – Dunnville sandstone, Red Wildmoor sandstone, and Taiwan siltstone - within the framework of three stress invariants. Data include a series of axisymmetric (conventional triaxial) compression, axisymmetric (conventional triaxial) extension, and multiaxial strength tests. The data are fitted to linear and nonlinear failure criteria: Paul-Mohr-Coulomb (PMC), a generalized linear criterion containing all three principal stresses; Hoek-Brown, a popular nonlinear criterion containing major and minor principal stresses; and a simplified version of PMC, where the friction angle in extension is assumed to be equal to the friction angle in compression. The results show that both versions of PMC provide a better approximation of the test data and successfully capture, in a piecewise-linear manner, the well-known nonlinear nature of the failure surface in the meridian and equipressure planes.

1. INTRODUCTION
Mohr-Coulomb (MC) failure criterion considers principal stresses σI and σIII with a linear form:
(Equation)
where ϕ = friction angle, Co = uniaxial compressive strength, and σI, σIII are major, minor principal stresses. The sign convention is compression positive. Note that the friction angle is independent of axisymmetric compression (σII = σIII) or axisymmetric extension (σII = σI) stress paths, where σII is the intermediate principal stress; i.e. in the framework of MC, the friction angles in compression and extension are equal.
Conventional triaxial compression tests show that the failure envelope is nonlinear when considering a large range of mean stress (Mogi 1971; Labuz et al. 2018; Hoek and Brown 2019). Many investigators have proposed nonlinear failure criteria, one being Hoek and Brown (1980):
(Equation)
where m and Co are material constants determined through fitting.
Because the axisymmetric tests cannot simulate general stress states, multiaxial or true-triaxial devices have been developed for investigating failure. Results of true-triaxial tests suggest that failure is affected by three principal stresses or another three stress invariants (Mogi 1971; Wawersik et al. 1997; Zeng et al. 2019).
Thermal-Hydrological-Mechanical Characterization of the Ghareb Formation at Conditions of High-Level Nuclear Waste Disposal
Authors: Kibikas W. , Bauer S. , Choens C. , Shalev E. , Lyakhovsky V. 
Published: September 2022

ABSTRACT:
The Ghareb Formation in the Yasmin Plain of Israel is under investigation as a potential disposal rock for nuclear waste disposal. Triaxial deformation tests and hydrostatic water-permeability tests were conducted with samples of the Ghareb to assess relevant thermal, hydrological, and mechanical properties. Axial deformation tests were performed on dry and water-saturated samples at effective pressures ranging from 0.7 to 19.6 MPa and temperatures of 23 °C and 100 °C, while permeability tests were conducted at ambient temperatures and effective pressures ranging from 0.7 to 20 MPa. Strength and elastic moduli increase with increasing effective pressure for the triaxial tests. Dry room temperature tests are generally the strongest, while the samples deformed at 100 °C exhibit large permanent compaction even at low effective pressures. Water permeability decreases by 1-2 orders of magnitude under hydrostatic conditions while experiencing permanent volume loss of 4-5%. Permeability loss is retained after unloading, resulting from permanent compaction. A 3-D compaction model was used to demonstrate that compaction in one direction is associated with de-compaction in the orthogonal directions. The model accurately reproduces the measured axial and transverse strain components. The experimentally constrained deformational properties of the Ghareb will be used for 3-D thermal-hydrological-mechanical modelling of borehole stability.

1. INTRODUCTION
The disposal of high-level nuclear waste is a top concern worldwide (Faybishenko et al., 2017). With increasing interest in nuclear power as an alternative to carbon-based fuels, the problem of safely storing nuclear waste is expected to grow (Kim et al., 2011). One solution for disposal is geological disposal of nuclear waste, where waste is isolated within subsurface geologic formations to be contained and isolated from the surrounding environment (Birkholzer et al., 2012). Given the risks associated with nuclear waste, any potential disposal site must be demonstrably capable of isolating the material from the surface environment for large time scales (Krauskopf, 1988).
Optimization of Well Configuration for EGS Performance with Multi-Dimensional Two-Phase Flow Modelling
Authors: Zhou Dejian , Tatomir Alexandru , Sauter Martin , Tomac Ingrid 
Published: September 2022

ABSTRACT:
Geothermal energy is a type of renewable energy with significant potential of contributing to reduce greenhouse gas emissions. Utilization of geothermal energy has become more and more attractive with the developments of the Enhanced Geothermal Systems (EGS) technology. Because of its low viscosity and density and therefore lower energy requirement for circulation supercritical carbon dioxide (scCO2) can be considered as a superior working fluid for EGS, compared to thermal brine. In this study, we developed a multi-dimensional thermo-hydraulic coupled model employing the open-source software DuMuX to model brine phase displacement and heat transport in a fractured porous reservoir. This work investigates well configuration effects with respect to three criteria of EGS performance, i.e., energy performance, economic performance, and environmental performance. Results show that the two-well configuration performs better in energy performance and environmental performance, but worse in economic performance. Additionally, for the three-well configuration, the scenario with two injection wells performs better than that with only one injection well with respect to reservoir heat production rate and sequestrated scCO2 mass.

1. INTRODUCTION
This paper investigates performance optimization of scCO2-H2O-combined Enhanced Geothermal Systems (EGS) reservoirs for different injection and production well configurations based on cumulatively produced energy, cost, CO2 storage, production temperature, and scCO2 breakthrough time. Geothermal energy, as a renewable energy source, has become attractive due to its constant baseload energy provision, the considerable potential to reduce greenhouse gas emissions and to decrease the reliance on fossil fuels (Jacobson et al., 2018; Teske, 2019). EGS are advanced geothermal reservoirs independent of the availability of an apriori minimal permeability field by generating/re-opening new/existing fractures through hydraulic or supercritical carbon dioxide (scCO2) fracturing at depths between 3 km and 10 km below the ground surface (Huang et al., 2020).
With scCO2 as working fluid circulation, well operation yields a considerably larger production rate for a given pressure gradient than the traditional EGS working fluid, i.e., H2O-brine, because of the lower energy consumption to upkeep circulation due to lower viscosity and density of scCO2 (Lu, 2018). Pruess et al. (2006, 2008) first investigated the performance of scCO2 as a working fluid for EGS with increased interest in employing scCO2-based EGS during recent years. Many researchers have contributed to the development of numerical models for the simulation of long-period (decades) phase migration, heat transport, and chemical reaction in EGS reservoirs with the aim of economic optimization and energy output maximization (Borgia et al., 2013; Cui et al., 2018; Guo et al., 2019; Norouzi et al., 2021).
Simulation of Proppant Placement Efficiency at the Intersection of Induced and Natural Fractures
Authors: Merzoug A. , Mouedden N. , Rasouli V. , Damjanac B. 
Published: September 2022

ABSTRACT:
The intersection of the pre-existing natural fractures (NF) with the hydraulic fractures (HF) forms a complex fracture network, which allows for increased well productivity. However, the complex fracture geometry may adversely affect the proppant placement and its transportation inside the fractures. The study reports the results of the Lattice numerical simulations of proppant placement at the intersection of fractures. Sensitivity analysis was performed to investigate the effect of pre-existing fracture friction angle, angle of approach as well as differential horizontal stress on HF-NF interaction mechanisms and proppant transport and placement. The results present the effect of these parameters on proppant transport and placement in NF.

1. INTRODUCTION
Hydraulic fracturing (HF) is a commonly used stimulation technique that essentially consists of generating fluid-driven fractures in the reservoir to allow the flow of oil and gas into the wellbore with the goal of increasing reservoir conductivity (Michael J. Economides, 2000). However, this process can be more complex in naturally fractured formations (Boualam et al., 2019; Alexeyev et al., 2017; Djezzar et al., 2019, 2020; Djezzar et al., 2019; Djezzar et al., 2019b, 2019a) due to the possibility of intersection of induced fractures with the natural fractures. Crossing, arresting and opening are the three interaction mechanisms when HF intersects a natural interface (Kolawole & Ispas, 2020). The fracture network development leads to increased fracture conductivity (Djezzar & Boualam, 2020, 2021; Djezzar & Boualam, 2020), with NFs contributing to well productivity. However, intersection of HF with NF may negatively affect the propagation of the HF and the proppant placement, making pressure analysis and prediction of fracture morphology very difficult. Moreover, proppant may accumulate in the near region of the intersection by forming a proppant bridge(Kou et al., 2019), or that it is a continuous transport behavior of proppant in the natural fracture(Kou et al., 2018). Therefore, it is important to anticipate and understand intersection mechanisms when designing and executing HF treatment.
Application of Seismic Attributes on Digital Elevation Model: Fractures Detection and Reservoir Implication
Authors: Djezzar Sofiane , Boualam Aldjia , Merzoug Ahmed , Chemmakh Abderraouf , Laalam Aimen , Ouadi Habib 
Published: September 2022

ABSTRACT:
The Ordovician formation in the Mouydir basin is characterized by low reservoir properties where the natural fractures play a critical role in its production. The study of the Ordovician analog enhances the natural fractures that affect the area of study to lead the future exploration and drilling of potential wells in the Mouydir basin. The study of outcrop analog can be easier and more accessible compared to the subsurface study which needs specific data like 3D seismic and well logs data such as borehole imagery. The reservoir analog study can be used to model fractures at different scales, from mega-scale to microscale. The ending could be used to understand the fractures’ distribution, fractures’ connectivity, and fractures’ kinematics. The aim of this work is the proposition of an integrated workflow to characterize and model the natural fractures by using seismic curvature and illumination attributes applied on a Digital Elevation Model. The Ordovician reservoir analog in the southern edge of the Mouydir basin was chosen as a case study.

1. INTRODUCTION
The unconventional reservoirs have rapidly evolved over the last years and a significant increase in hydrocarbon discoveries where natural fractures play a significant role in the production. This has helped to enhance the understanding of the effect of fracturing on fluid flow mechanisms. During the development of the fields, the wells of the implementation strategy are determined by the spatial distribution of fractures across the field or reservoir. The geoscientists seek to intersect areas with a high density of fractures and good connectivity, where the drainage of the matrix is more effective. The orientation of the wells should be in accord with the geometrical and geomechanical parameters such as the orientation of fracture planes and the maximum horizontal stress. The study of the naturally fractured reservoirs is very challenging with the main difficulty being how to model and predict the fracture networks at different scales extending from outcrops and shallow depths to the reservoir and basin depths. Advanced 3D seismic and well data are needed to characterize and model the fractures. This process requires great effort in terms of time, data collection, and analysis. The study of the reservoir analog can be a substitute approach with more readily accessible data (Djezzar et al, 2022).
Comparative Study of Anionic and Cationic High Viscosity Friction Reducers in High-TDS Marcellus Shale Formation Water
Authors: Ge Xiaojing , Biheri Ghith , Imqam Abdulmohsin 
Published: September 2022

ABSTRACT:
High viscosity friction reducers (HVFRs) have been recently gaining more attention and increasing in use, not only as friction-reducing agents but also as proppant carriers. Reusing of produced water has also been driven by both environmental and economic benefits. Currently, most of friction reducers on the market are anionic friction reducers, which are fully compatible with most of produced water with low to medium level of Total Dissolved Solids (TDS) but show significant decreasing at high TDS conditions in term of their friction reduction performance for most cases. On the contrary, cationic friction reducers are believed to have better TDS tolerant and performance under high TDS conditions. However, concerns are remained about performance of using anionic and cationic HVFRs with produced water to transport proppant. The ultimate objective of this experimental study is to comparably analyze the proppant transport capabilities of HVFRs in high TDS environments. The effects of TDS, temperature, wall retardation, and particle hindering on the performance of both anionic and cationic HVFRs are investigated.

1. INTRODUCTION
During the last few years, the industry has been accelerating the adoption of HVFRs to replace traditional fracturing fluids, such as slickwater and guar, in hydraulic fracturing (Hu et al. 2018; Johnson et al. 2018). This is mainly due to several operational and economic advantages of HVFRs including significantly cutting operational cost with less process and equipment required, exhibiting a higher retained conductivity in the fractured formation, and yielding ideal production improvements in fields (Johnson et al. 2018; Ba Geri et al. 2019; Biheri and Imqam 2020, 2021). Besides these benefits listed above, the most critical consideration behind using HVFRs in place of traditional fracturing fluids is their proppant-carrying and transporting capability. For traditional fracturing fluids treatment, because the viscosity is too low to suspend the proppant for a sufficient time, the dominant proppant transporting mechanism occurs at a high injection rate. However, even with a significantly high pumping rate, only small and light proppant (40/70 sand, resin coated sand [RCS], and 40/80 lightweight ceramic [LWC] are the most popular) are pumped with slickwater in the early stages (Palisch et al. 2008). Then, larger and heavier proppant is typically pumped with linear or crosslinked gels, which can better carry and transport this proppant deep into the fractured formation.
A Screening Methodology Using Fuzzy Logic to Improve the Well Stimulation Candidate Selection
Authors: Mouedden N. , Laalam A. , Rabiei M. , Merzoug A. , Ouadi H. , Boualam A. , Djezzar S. , Mahmoud M. 
Published: September 2022

ABSTRACT:
Stimulation techniques are performed to improve the well productivity in fields where a large number of wells is present. However, the selection of candidate wells for stimulation treatments, in particular acidizing and hydraulic fracturing, is a challenging task. The conventional candidate selection technique that is based on analyzing manually a large volume of data is not efficient and cannot capture the impact of all parameters correctly. This study was carried out with the aim of developing a decision-making tool (FIScreT tool) based on Fuzzy logic that would allow the selection of candidate wells for stimulation to be automated rather than manually examining the performance of each well. The FIScreT tool uses a simple and efficient workflow that initially consists of eliminating problems related to completion status, reservoir characteristics and well integrity. Subsequently, a selection is made through two fuzzy interference systems using accessible production and reservoir data. Finally, the production gain is estimated in order to assess the wells’ productivity after treatment.

1. INTRODUCTION
Well stimulation refers to any treatment carried out to restore or improve the productivity of an oil/gas well. Its main objective is to improve the economics of oil fields through faster and greater deliverability of hydrocarbons without major investment (Michael J. Economides, 2000). In addition to reservoir performance and the quality of completion, the effectiveness of the treatment depends on three essential, interrelated elements: the selection of the candidate well, the treatment design, and the execution of the field operation (Zoveidavianpoor et al., 2012)(See Fig. 1.)
Applying the best treatment design and effective field operation to the wrong well will result in the failure of the entire operation. This implies that selecting the most appropriate wells for stimulation is one of the greatest challenges affecting reservoir production and field economic development.
Numerical Implementation of a Cohesive Zone Element Coupled with Continuum Damage Mechanics Volume Elements
Authors: He Haozhou , Arson Chloé 
Published: September 2022

ABSTRACT:
The objective of this paper is to develop a two-dimensional Cohesive Element Model (CZM) coupled with a Continuum Damage Mechanics (CDM) model. The novel cohesive element model allows expressing the separation criterion in terms of the damage tensor used in the CDM model implemented in the neighboring volume elements. Above a critical damage value, debonding triggers. The residual tensile and shearing strength of the CZM follow a linear softening law. The proposed model was calibrated against published triaxial compression tests conducted on shale. Single-cohesive zone tests highlight that the proposed approach allows simulation of hardening during damage propagation followed by softening and failure. The model predicts different strengths in tension and compression and different stiffnesses and strengths for different confinements. A boundary-value problem was solved by using a mesh with embedded cohesive zones at all interfaces. It is shown that the 2D model can predict realistic stress/strain curves, stress and strain fields, and fracture patterns for biaxial compression tests. The advantage of the proposed approach is that it can be used to simulate diffuse damage followed by localized fracture with a smooth transfer of field variables between the finite and cohesive elements.

1 INTRODUCTION
Simulating fracture propagation from the inception of microscopic cracks to the localization of macroscopic fractures remains a challenge. To date, finite element modeling approaches based on Continuum Damage Mechanics (CDM) and Cohesive Zone Models (CZM) emerge as the most widely used approaches. The goal of this study is to couple both, in order to take advantage of the benefits that each technique can bring.
In CDM, sets micro-cracks are represented by a damage tensor, which is modeled as an internal variable within the framework of thermodynamic irreversible processes. Stiffness and strength decrease as damage accumulates. CDM models can be formulated based on phenomenological principles (Xu and Arson, 2014) or micromechanics principles (Jin and Arson, 2017). Exhaustive reviews of damage rock mechanics are available in (Arson and Gatmiri, 2008; Arson, 2020).