bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Evaluation Method and Application of Wellbore Stability Based on Geomechanics
Authors: Zhai Wenbao , Wang Qian , Chen Zhixue , Chen Xuefeng , Li Bo , Hao Weiwei , Jiang Jiwei , Li Mingyin , Liu Dezhi , Rao Jiafu
Published: September 2022

Wellbore instability is one of the difficult problems restricting safe drilling. The traditional theoretical model of wellbore stability is easy to cause the actual drilling fluid density to be high and aggravate the risk of drilling lost circulation. Therefore, firstly, the rock mechanics parameter profile is quantitatively obtained according to the field multi-source data, and the single well geomechanics model is established; Then, the Monte Carlo method is used to comprehensively consider the uncertainty of geomechanical parameters, and a quantitative evaluation method of wellbore stability based on geomechanics is established to reasonably evaluate the wellbore stability probability and optimize the safe density window of drilling fluid; Finally, taking well X of an oil field in Western China as an example, the new method is used to quantitatively evaluate the wellbore stable section and unstable section, and the evaluation results are compared with the actual complex situation to dynamically optimize the density window of drilling fluid. The results show that the calculation results of the new method are consistent with the actual situation, and the probability of wellbore stability is more than 80%. This method can effectively evaluate the wellbore stability, and provide a reasonable density window of drilling fluid, reducing the drilling complexity and cost, which is of great significance to meet the requirements of safe and efficient drilling.

1. INTRODUCTION

Drilling engineering is an indispensable and important link during oil and gas energy exploration and development, but wellbore instability causes frequent drilling complex problems, which seriously restricts the drilling cycle. Therefore, a reasonable evaluation of wellbore stability is conducive to broadening the safety density window of drilling fluid and effectively reducing drilling complexity, and shortening the drilling cycle(Darvishpour et al., 2019). In recent years, many scholars have made comprehensive analysis on the factors that may affect the wellbore stability(Germanovich and Dyskin, 2000; Germanovich et al., 1994; Li et al., 2022; Mokhel et al., 1996; Moos et al., 2003; Tran and Abousleiman, 2010; Zoback et al., 1985). Traditionally, it is considered that wellbore instability is caused by far-field stress conditions or by stress acting on a natural plane with too little or no cohesion(M. Zoback et al., 1985), which is related to shear and yield. For plastic rocks, the wellbore collapse can be described by using the plastic yield criterion(Germanovich and Dyskin, 2000), but for brittle rocks, the description of wellbore collapse can not only consider the shear failure hypothesis but also consider the shape of rock fragments, i.e. tensile failure and brittle failure (Germanovich et al., 1994).
Downhole Microseismic Monitoring of Injection Stimulations at the Utah FORGE EGS Site
Authors: Rutledge J. , Dyer B. , Bethmann F. , Meier P. , Pankow K. , Wannamaker P. , Moore J.
Published: September 2022

Downhole microseismic monitoring provides the best means of detecting, mapping and characterizing the fracture systems developed during the creation and evolution of Enhanced Geothermal System (EGS) reservoirs. EGS development requires at least two wells, one for injection and the second for production. During the initial stimulation of well 16A(78)-32, the injection well at the Utah Frontier Observatory for Research in Geothermal Energy, an array of three downhole, high-temperature, eight-level digital receiver strings will be deployed to monitor the fracture system. The well has a true vertical depth of 8540 ft, a measured depth of 10,987 ft, and a maximum temperature of 220°C. Below 7260 ft, the well plunges 25° through the granite basement rock. Three zones will be stimulated near the toe of the well. The configuration of the three monitor wells and the receiver depth placements are designed to resolve the isolation or the possible interference of the stimulated volumes and guide the placement of the production well. After the initial stimulations, the multilevel strings will be replaced with dual-level strings for long-term monitoring.

1. INTRODUCTION

The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) project is a test site for demonstrating technologies for Engineered Geothermal Systems (EGS) (Moore et al., 2020). EGS involves the creation of sustainable rock permeability to extract heat for long periods of time. At Utah FORGE, hydraulic stimulation of favorably oriented fractures will be conducted to form the reservoir. Seismicity induced by these stimulations must be monitored to map the EGS reservoir growth and to mitigate possible seismic hazards (Majer et al., 2016). An overview of the guiding risk studies, as well as the history of seismicity at the site and the planning and network deployed for monitoring potential seismic hazards is presented in Pankow et al. (2017); Pankow et al. (2019a); and Pankow et al. (2019b).
Numerical Modeling of Thermo-Hydro-Mechanical Processes Related to Geothermal Heat Pump Operations in a Subarctic Climate
Authors: Norouzi E. , Li B. , Raymond J.
Published: September 2022

Ground Source Heat Pumps (GSHPs) are extensively used as a renewable energy technology worldwide. However, the use of GSHPs in cold regions remains challenging. Particularly, for a shallow GSHP system, the cyclic freezing and thawing conditions may cause considerable ground subsidence and have an impact on the stability of infrastructure. Very few studies were conducted to analyze the geo-risk of installation and operation of GSHPs in subarctic regions. In this paper, a fully coupled thermal-hydro-mechanical analysis is performed based on a finite element framework to investigate the geo-risk of ground subsidence due to the installation and operation of GSHPs. The modified Clausius-Clapeyron model is included in the modeling framework considering phase change of ice under freeze-thaw cycles. The nonlinear relations between ice saturation and hydro-mechanical properties of frozen soil have been implemented using experimental data from the literature. The numerical modeling tool is applied to the case study of a potential Canadian GSHP site in Umiujaq, northern Quebec, where the ground is composed of several meters of silt overlying the bedrock.

1. INRTODUCTION

Over last decades, stabilizing the permafrost regions has been an important concern for geotechnical engineers, specially in regions where cycling freezing and thawing are encountered because of the global warming affecting infrastructure. Therefore, applying different stabilizing methods may be necessary in these regions to reduce the predicable geohazards.

Recently, the development of Ground Source Heat Pump (GSHP) systems has increased. Such systems operate with a renewable source and allows for energy storage. As solar energy is insufficient during the northern winter, GSHP systems are a potential avenue in subarctic regions as an alternative to store energy during summer and provide it in winter. With 44,561 inhabitants of Nord-du-Québec in 2016 living in villages in subarctic regions, there is a good potential to utilize the GSHP systems for heating to reduce the consumption of fuel usually shipped by boat(Gunawan et al., 2020).
A Plasticity Mechanism for Hydraulic Fracture Height Containment
Authors: Papanastasiou P. , Konstantinou C.
Published: September 2022

In this paper we present a new mechanism that explains hydraulic fracture containment in the target zone. The study is based on the modelling of hydraulic fracture propagation in weak rocks and comparison of the results of propagation in the vertical direction with propagation in the horizontal direction. The modelling is based on both analytical modelling with a Mohr-Coulomb dislocation theory and on FEM modelling of hydraulic fracture propagation in weak formations described by Mohr-Coulomb elastoplastic material and a cohesive-type fracture propagation criterion. It was found that the resistance to fracturing, expressed in the dislocation model by the required force and in the FEM by an effective fracture toughness that increases with fracture extension tending to asymptotic value, depends strongly on the fracture propagation direction. A dominant parameter that quantifies these effects is a new brittleness index (BI) that depends both on rock strength and insitu stresses. This BI defines a) if a hydraulic fracture will be created and b) if the fracture will remain contained in the target zone and c) what deviation is expected from LEFM modelling of hydraulic fracturing.

1. INTRODUCTION

An important design objective in hydraulic fracturing is the fracture to remain vertically contained in order to achieve a long penetration in the pay zone. A contained fracture will eliminate the risk of mixing hydrocarbon fluids with water or natural gas with oil if the surrounding layers contain different fluids. The overarching objective is to maximize the flow of hydrocarbon in the wellbore through a long conductive path formed by a propped fracture. Clearly, the mechanical properties of reservoir and surrounding layers affect the fracture height. An obvious explanation for the often-observed fracture containment in the reservoir layer, is the higher horizontal stress, called closure stress, in the barrier layers, usually shales. In order to restrict fracture height growth, the commercial hydraulic fracturing simulators assume that the barrier shale layers are under higher closure stress or they have higher resistance to fracturing, expressed by the fracture toughness. However, though there were cases that such conditions do not exist in the barrier layer, the hydraulic fractures still remained contained. Often, hydraulic fractures do not even reach the shale-reservoir interface. Nevertheless, in practice a cased-cemented well is perforated in the lower part of the reservoir to minimize the risk of hydraulic fracturing reaching the upper barrier layer.
The Influence of Hydraulic Fluid Properties on Induced Seismicity During Underground Hydrogen Storage
Authors: Burtonshaw J. E. J. , Paluszny A. , Thomas R. N. , Zimmerman R. W.
Published: September 2022

Geological hydrogen storage is a promising technique to seasonally store surplus renewable energy at the large scale. Depleted gas reservoirs are currently being considered as potential storage sites for hydrogen. Induced seismicity is a key aspect of the sustainability and acceptance of both onshore and offshore gas storage and production. This study conducts a preliminary numerical assessesment of the deformation of a single three-dimensional fault that extends from the reservoir and into the caprock during the injection and storage of hydrogen over a period of weeks. Simulations are conducted with a three-dimensional finite element, fully coupled poroelastic code. Induced seismicity is quantified both in terms of tangential displacements on the fault surfaces, cumulative moment release, and maximum seism c event magnitudes. The reservoir is an anticlinal structure bound from above by a low permeability caprock, and below from a low permeability underburden. Mechanical properties are defined based on North Sea depleted gas reservoirs. The effect of injection fluid parameters such as density and viscosity are investigated. For hydrogen storage in depleted oil and gas reservoirs with proximate faults, some minor seismicity can be expected. According to these preliminary simulations, geological hydrogen storage appears to be operationally sustainable in terms of the magnitude of induced seismicity, at least for the injection volumes, rates and storage periods considered in this work. For the studied case, the maximal potential seismicity observed is of moment magnitude 2.1, with very few seismic events.

1. INTRODUCTION

In an energy future dominated by conventional renewable energies such as wind and solar power, periods of energy surplus and deficit will be commonplace due to seasonal and annual variations in climatic conditions (Heinemann et al., 2021). During periods of energy excess, wind and solar derived electricity can be diverted to electrolyzers for green hydrogen production (Elberry et al., 2021). This hydrogen must then be stored for production and subsequent utilization during the periods of energy deficit, reducing reliance on coal, natural gas, and oil as emergency seasonal fuels. Depleted reservoirs are a potential candidate for storage at the large scale.
Interference Analysis of Shale Gas Horizontal Wells Considering Magnetic Azimuth Correction
Authors: Yu Ruifeng , Diao Binbin , Gao Deli
Published: September 2022

In order to analyze the interference risk of shale gas horizontal wells, a model is established to analyze the interference domain in shale gas horizontal wells. With this model, the borehole uncertainty and the fracturing interference domain can be coupled reasonably. To reduce borehole uncertainty and further reduce the interference domain, the multi-station analysis (MSA) is employed to correct the magnetic azimuth of the shale gas horizontal wells. The interference domain of a shale gas horizontal well was studied. With magnetic azimuth correction, the semimajor axis of ellipse of borehole uncertainty (EOU) decreases from 23.10 m to 19.48 m (lateral) at the measure depth of 5671.60 m. And the edge length of the interference domain decreases from 206.20 m to 198.96 m. The results show that, magnetic azimuth correction based on MSA can reduce the interference domain and interference risk. And this analysis method can provide a theoretical reference for avoiding interference in shale gas horizontal wells.

1. INTRODUCTION

In order to achieve long-term stable production of shale gas fields, infill and adjustment wells are deployed to reduce the well spacing in shale gas fields. With the well spacing reduced, the overall benefit is improved. But it also leads to earlier well to well interference. Interference will result in many drillings technical problems, such as complex and frequent overflows and leakages. Therefore, interference analysis has always been the focus and hot issue in shale gas development.

The interference domain is determined by fracturing interference domain and the borehole uncertainty. Numerical simulation method is usually employed to calculate the fracturing interference distance. A discrete fracture model is proposed for multi-scale flow in large-scale fractured tight oil reservoirs (Fang et al., 2017). On the basis of this model, a method for analyzing the well spacing of shale gas horizontal wells based on the integration of geology, engineering and economy is established (Yong et al., 2020). Numerical simulation shows that the cross section of the fracturing interference field in the direction of wellbore extension can be approximated as an ellipse ( Liu et al., 2018; Zhou et al., 2021). Actual drilling data of Fuling shale gas field in the Sichuan shows that the semi-major axes of the ellipse can be approximated to 80m and 50m (Gu et al., 2020; Liu, 2020).
Study on Heat Extraction Performance of 3D Enhanced Geothermal System with Faults Connected
Authors: Tang Yijia , Ma Tianshou , Guo Jianhua , Hu Xihui , Liu Bo
Published: September 2022

Enhanced geothermal system (EGS) is the major way to extract heat from impermeable hot dry rocks. As heat mining process in EGS is complex, effective numerical simulation method is required. Lots of EGS simulation models are proposed with different kinds of fracture system using discrete fracture network method or equivalent porous media method. However, the situation that EGS with faults connected have seldom investigated. Thus, a 3D geothermal heat extraction model connected with faults is established, and solved by the finite element method. The proposed numerical model is validated with single fracture heat extraction analytical model. The largest error between two models is 5.63%, which shows the efficiency of the proposed model. The effect of faults on heat extraction in EGS is studied. The results demonstrate that compared with the EGS disconnected with the fault, the EGS with fault get higher production temperature and poor production flow rate. The more faults there are, the more injected fluid is lost, resulting in lowest heat extraction performance. Thus, in hot dry rock heat mining engineering practice, hydraulic fracturing operations should avoid connect with faults to ensure much more injection fluid can be extracted.

1. INTRODUCTION

With the energy crisis and environmental pollution problems more and more serious, increasing attention has been paid to the development of clean energy, especial for the hot dry rock (HDR) (Lund and Boyd, 2016). HDR is a kind of dense, high-thermal geothermal resource buried 3,000 meters underground. In China, the geothermal resource of HDR rock is about 7×1015 MWh, 2% of which can meet the requirement of energy consumption for 3,400 years (Zhu et al. 2015; Huang, 2014).

Enhanced geothermal system (EGS) is developed to extract HDR geothermal resources. Typical EGS is composed of injection well, production well, and fracture network. The wells are connected through fracture network (Olasolo, 2016; Tang et al. 2020). The injected fluid extracts the heat though the fracture network and produces high thermal fluid from production well. The Fenton Hill EGS project in the United States was the world’s first EGS site trial, proving the concept of EGS. France built the world’s first EGS site for commercial application, namely the Soultz EGS site. The generation power reached 1.5MWe. Australia built the world’s first EGS site from private company in Cooper Basin (Lu 2017). Other countries built EGS power stations after another. Unfortunately, most of them eventually shut down, because the fluid loss in the fracture network is dramatic, which is hard for commercial use (Kelkar et al. 2016). Therefore, it is very important to study the heat extraction mechanism of fluid in fracture network.
Effects of Partially Cemented Annulus on Casing Integrity in Salt Formations
Authors: Melo D. D. E. F. , Fontoura S. A. B. , Inoue N. , Zhou C. , Marcou S. R. , Soares C. R. W. , Carneiro G.
Published: September 2022

The time-dependent behavior of salt rocks poses challenges to well design. Salt mobility is associated with critical wellbore closure and excessive casing loads. In the presence of cement imperfections, non-uniform loads on casing strings can lead to failure. A parametric finite-element analysis considers an uncemented annulus, a fully cemented annulus, and a partially cemented annulus with a channel covering 20%, 50% and 80% of the pipe circumference. No pressure build-up was considered. Commonly applied to Brazilian salts, a double-mechanism creep law is adopted, and strain rate uncertainties are accounted for. The stress distribution is less severe when uniform loads act on the casing surface. A partially cemented annulus results in non-uniform loads and deformation of the casing cross-section. A small volume of cement channels leads to localized regions of critical stress within the casing. As the channel size increases, the higher moment arm results in higher casing stresses, especially when two-point bending occurs at the salt-casing contact. Analysis of casing yield and failure when cement channels are present along salt sections allows for more accurate evaluation of casing integrity.

1. INTRODUCTION

Well design in salt formations faces many challenges due to the time-dependent behavior of these rocks. Wellbore closure due to salt creep may lead to drill string sticking or aborted casing runs, and the correct drilling mud weight must be applied. After casing is set, salt creep can increase casing loads and compromise well integrity.

When submitted to a deviatoric stress, salt exhibits a time-dependent strain response according to Figure 1. During the first stage of loading (primary creep) salt undergoes a high rate of deformation, that gradually slows down until it reaches steady state (Secondary) creep. Finally, during tertiary creep the strain rate increases until rupture (Jaeger et al, 2007; Goodman, 1989). The strain rate is influenced by many factors, such as mineralogical composition, impurities, formation temperature and the imposed differential stress (Liu et al., 2013, Fjaer et al., 2008).
A New Method for Evaluating Radionuclide Migration in Groundwater
Authors: Feng Shengyang , Chen Xiaojie , Jiang Yourui , Tang Hao
Published: September 2022

The purpose of this study is to propose a new method for evaluating the migration of nuclides of uranium tailings paste backfill in groundwater. Uranium tailings reservoir is a significant threat to the nearby environment and the health of residents. Filling the uranium tailings paste backfill into the mine goaf can effectively reduce the impact of uranium tailings on the surrounding environment. However, there is still a lack of effective methods to evaluate the effect of radionuclides in uranium tailings paste backfill on groundwater. Uranium tailings paste backfill was made from the samples collected from a uranium tailings reservoir, and leaching experiments were carried out to obtain a variation curve of uranium concentration. The fractal parameters of rock fractures are obtained from the goaf of a gypsum mine exploration. The discrete fracture network model (DFN) of underground rock mass in the goaf is established according to the fractal parameters. When the results of leaching experiments are introduced into the numerical simulation model, it is found that when the local water is in the flow state, the flow direction of uranium is consistent with that of groundwater and is related to fractures.

1. INTRODUCTION

Mining is extracting underground resources and can be divided into open-pit and underground mining depending on the mining method. The mining process generates a large volume of tailings and void areas and releases hazardous substances into the surrounding environment. The threat to the surrounding environment from tailings and voids does not end with mining (Yilmaz and Yumlu, 2017). The pollution of the surrounding environment by tailings, especially uranium tailings, is obvious. Although uranium in uranium tailings has been extracted, there are still a lot of harmful substances in the tailings. These harmful substances can be carried into the environment by dust and groundwater and enriched into the human body through the food chain, posing a threat to human health. What’s more, the dams of uranium tailing reservoirs may be destabilized by extreme weather or seismic activity, and a large volume of tailings in the ponds may break through the constraints of the tailings dams under gravity, with disastrous consequences for the lives of the surrounding residents and the environment.
Numerical Mesh Sensitivity Works Performed to Analyze Advective Gas Flow in a Compact Clay
Authors: Damians I. P. , Noghretab B. S. , Olivella S. , Gens A.
Published: September 2022

In this work, the suitability of several meshing strategies to optimize the CPU time consumption is investigated. The mesh sensitivity strategy is established by applying the basic framework of a coupled hydro-gas-mechanical 3D FEM numerical model to simulate the tests in terms of types of the elements, number of elements and nodes to quantify the influence of different meshes on the accuracy of the test results with regard to optimization of the CPU time consumption. In this study, the problem is represented and the performance and calculation time of both element types and mesh size in the utilized 3D FEM model are checked. To achieve this, both tetrahedral and hexahedral meshes and their refinement/coarsening are generated. Then the performance of the element types and sizes on the test results are compared. This is a main issue for modelling gas injection through clay-based engineered isolation barriers that requires clear up-scaled tests due to full-scale experiments.

1. INTRODUCTION

To quantify the physical properties of a phenomenon such as fluid flow, heat transfer, mass transport, and wave propagation, mathematical equations must be utilized. The finite element method (FEM) is a general numerical method that is the most widely used approach for numerically solving engineering problems (partial differential equations) in 2 or 3-dimensional variable space. In order to calculate the solution in the FEM method, the domain must be divided into a discrete number of elements which is referred to as mesh generation. Striking a balance between accuracy and speed is challenging. A large continuous medium can have infinite degrees of freedom (DoF), as a result, to do the FEM modelling, the meshing approach (mesh size and type of element) is the key component to acquire the most accurate and reliable outcomes in the finite element modelling (Cavin et al., 2005). Accuracy depends on both mesh size (the total number of elements) and element type (the shape of individual elements). Mesh size typically refers to the CPU time consumption. The smaller the mesh size becomes the more accurate the result achieves, hence in larger simulations required solving time of the model extends. To achieve the best balance of accuracy and solving time, mesh coarsening (refining) is required.
Horizontal Well Orientation Optimization Based on the Integration of Hydraulic Fracturing Network Simulation and Productivity Prediction
Authors: Qian Wang , Shengxian Zhao , Chenxi Ye , Wenbao Zhai , Chao Fang , Peng Tan
Published: September 2022

Horizontal drilling and large-scale hydraulic fracturing are currently used to increase artificial fracture networks and per well production in unconventional reservoirs. Due to the differences of regional geological characteristics, natural fracture characteristics and geomechanical characteristics, different wellbore directions may lead to different hydraulic fracturing effects and post-frac productivity. If the well orientation is not correct, it can result in poor hydraulic fracturing propagation and inefficient production. The high precision geological model and geomechanical model of platform of typical shale gas blocks in Sichuan were established. First, considering the interaction of hydraulic fracture and natural fracture, interaction of hydraulic fracture each other, hydraulic fracturing network distribution in different in-situ stress orientation, natural fracture azimuth, wellbore azimuth combination cases were simulated. Second, high-precision unstructured grid numerical model was established on the basis of hydraulic fracturing fractures to accurately characterize fracture network morphology and fracture conductivity. The flow characteristics of hydraulic fracturing network was simulated, and post-frac productivity were predicted. Finally, the optimal wellbore orientation under various in-situ stresses and natural fracture combination cases was obtained by combining the fracturing effect and post-frac productivity. The research results show that, under the typical fracturing construction and production conditions in Sichuan shale gas block, the optimal well orientation is not affected by the natural fracture orientation. The fracturing effect and production within the range of 0-30 degrees of horizontal minimum in-situ stress are better. When the angle between natural fracture orientation and horizontal minimum in-situ stress is more than 50°, the overall production becomes better in various well directions.

1. INTRODUCTION

Hydraulic fracturing in horizontal well can greatly improve the production capacity of a single well in unconventional oil and gas resources. Due to regional differences in geological characteristics, natural fracture characteristics and geomechanical characteristics of unconventional reservoirs, variability in in-situ stress directions, natural fracture directions and wellbore directions may lead to different fracturing effects and post-frac productivity under the same fracturing construction and production conditions. Therefore, it is very important for horizontal well orientation optimization.
Stress Relaxation Tests on an Outcrop Shale
Authors: Fjær E. , Stenebråten J. F. , Larsen I. , Lozovyi M. , Holt R. M.
Published: September 2022

Numerous observations have shown that shale formations may creep in and close the annulus between rock and casing in deep wells, thus effectively sealing off the well sections in a natural way. This movement of the rock is partly controlled by strain and partly by stress, and parts of the rock may be in a post-peak state while other parts are in a pre-peak state. The effect of pre-peak versus post-peak conditions on creep characteristics was studied in a set of stress relaxation tests on Pierre II shale. It was found that the stress relaxation process can be described with great precision both by a logarithmic function and a power-law function. However, only the power-law function fulfills the expected asymptotic behavior for infinite time. Temperature fluctuations can be accurately accounted for by an Arrhenius-type factor. The shear stress relaxation appears to be insensitive to pore pressure alterations. There is an indication that the relaxation rate is slightly higher when the rock is in a strain hardening state than in a strain softening state. No significant effect of exposure to NaOH was seen on the relaxation process.

1. INTRODUCTION

Completion of oil and gas wells often implies that the annulus between rock and casing is left open in long sections. Such sections are potential pathways for leakage from the reservoir to the surface and needs to be sealed off at selected spots prior to plugging and abandonment. It is however a frequent and highly welcome observation that shale formations creep in, closes the annulus, and thus form a natural barrier that seals the well (Williams et al., 2009; Kristiansen et al., 2018). There are limited possibilities to monitor this process in the field as it goes on behind the casing, but the terminal state is nevertheless of great importance since it governs the long-term sealing efficiency of the barrier. It is therefore interesting to study long-term shale creep under controllable laboratory conditions.
3D Hydro-Mechanical Modeling of Shaly Caprock Response to CO2 Long-Term Periodic Injection Experiment (CO2LPIE)
Authors: Sciandra D. , Rahimzadeh Kivi I. , Vilarrasa V. , Makhnenko R. , Jaeggi D. , Rebscher D.
Published: September 2022

Carbon capture and storage in deep geological formations is necessary to achieve a meaningful reduction of anthropogenic CO2 emissions into the atmosphere. Given the buoyancy of the injected CO2, it is essential to adequately characterize the sealing caprocks commonly comprised of clay-rich formations, including shales. If the inherent anisotropy of shales is not considered, model prediction errors will propagate with time and space. To limit errors, the accurate experimental laboratory measurements should be scaled up and the in-situ behavior of the caprock should be studied in detail. Underground rock laboratories (URLs) offer a unique opportunity to investigate the caprock sealing capacity at a few meters scale in a well-defined and well-monitored environment. This perspective applies to the CO2 Long-term Periodic Injection Experiment (CO2LPIE) at the Swiss Mont Terri URL. In the experiment, it is planned to inject gaseous CO2 into Opalinus Clay, which is considered as a representative caprock for underground storage. Opalinus Clay shows large-scale anisotropic behavior due to the presence of bedding planes and heteorogeneities. We numerically simulate the CO2LPIE experiment using a 3D hydro-mechanical model and assuming linear poroelastic transverse isotropic behavior of the rock. We find that the CO2 is unlikely to penetrate the rock in free phase, while the diffusive front of dissolved CO2 in resident brine hardly propagates half a meter after two years of injection. The overpressure and induced deformation and stress changes preferentially develop along the bedding planes, although not sufficiently to lead to shear failure.

1. INTRODUCTION

To limit global warming to 1.5 °C, net carbon removal after 2050 should be targeted (IPCC, 2014). To reach this goal, it is critical to develop novel technologies and a promising approach is Carbon Capture and Storage (CCS). CCS is generally understood as the set of CO2 capture from a large stationary source, transport to an injection site, and permanent storage in the subsurface (Benson and Cook, 2005). CO2 density at the pressure and temperature of typical underground storage formations in sedimentary basins is approximately 65 % of the in-situ brine density. As a result, the plume of the injected CO2 will not only migrate outwards from the injection well, but also upwards until it finds a sealing layer called caprock (Tsang and Niemi, 2017). To assure long-term CO2 trapping, it is of fundamental importance to properly characterize the caprock sealing capacity, commonly presented in terms of permeability, porosity, capillary entry pressure and relative permeability curves, and their evolution with time (Kaldi et al., 2011).
Inertia Dominant and Transient Flow in Fractures - Beyond the Cubic Law
Authors: Gee B. , Gracie R.
Published: September 2022

There are many applications which require a fracture flow model that accounts for variations in aperture beyond surface roughness. Large-scale models and simulations of fluid flow through fractures are almost exclusively based on the cubic law (Poiseuille flow) for steady-state flow through rigid parallel plates. When the fracture aperture is time and/or spatially varying, flow is transient, and/or flow rates are modest (Re≥1), cubic law predictions can deviate substantially from true fluid behaviour. In this paper, we present a new Reduced Dimension Fracture Flow (RDFF) model which more accurately predicts transient flow for incompressible fluids with modest Reynolds numbers through fractures with time and/or spatially varying aperture. The RDFF model is derived from the two-dimensional Navier-Stokes equations and yields a two-field model (fluid flux and pressure) governed by the conservation of mass and momentum. The RDFF model is shown to conserve energy in spatially varying fractures where the cubic law does not. We demonstrate that the RDFF model captures complex transient and inertial behaviours not previously captured for flows with modest Reynolds numbers (1≤Re≤100) and demonstrates up to 400% improvements in error over the cubic law in steady-state flow conditions through fractures with sinusoidally varying aperture.

1 INTRODUCTION

Large-scale simulations of flow through fractures rely almost exclusively on the Poiseuille flow model, also known as "the cubic law". The cubic law is the analytical solution to the Navier-Stokes equations for steady flow of an incompressible fluid through parallel plates. It provides a constitutive equation linking the pressure gradient to the fluid flux according to the relationship

(Equation)

in which p is the pressure, μ is the kinematic fluid viscosity, w is the fracture aperture, and q is the fluid flux. In hydro-mechanical models with deformable fractures, such as hydraulic fracturing or enhanced geothermal energy, the cubic law is often combined with the conservation of mass derived from a fracture-scale control volume:

(Equation)

in which q is the flux from the cubic law. Despite the assumption that the cubic law applies for rigid parallel plate geometries, the conservation of mass allows both time and spatially varying apertures.
Experimental Investigation of Desiccation Behavior in Inorganic Microfiber-Reinforced Engineered Barrier Materials (IMEBM) for Geological Repository of Nuclear Spent Fuel
Authors: Grasley Julia , Rahmani Mohammad , Azzam Abdullah , Nsengiyumva Gabriel , Kim Yong-Rak , Eun Jongwan , Kim Seunghee
Published: September 2022

Secure storage of nuclear spent fuel is of great concern for protecting public health and safety. The standard long-term solution for nuclear waste disposal is containment in geological repositories. Nuclear spent fuel, stored in canisters, is placed deep underground with one or more Engineered Barrier Materials (EBM) forming a buffer between the waste containers and the natural rock. Bentonite clay is commonly used as an EBM for its low cost, long-term stability, low hydraulic permeability in a saturated state, high thermal resistance, high radionuclide retardation capacity, high swelling pressure, and "self-healing" capability. However, bentonite clay subjected to heating from nuclear waste decay may undergo desiccation cracking. In this study, inorganic microfiber reinforcement was evaluated as a method of reducing desiccation cracking in EBM. A restrained ring test method for soils coupled with digital image correlation (DIC) was employed to capture free shrinkage and desiccation cracking. Reinforcement of bentonite clay with 1.0 % wt. basalt fibers was shown to be effective in reducing crack propagation and separation.

1. INTRODUCTION

1.1 Research Significance

Each nuclear power reactor generates 20-30 tons of highly radioactive waste, annually. Secure long-term storage of nuclear waste is a great concern for public health and safety. A preferred long-term solution for highly radioactive waste disposal is containment in geological repositories. Canisters filled with radioactive waste are placed in tunnels, with one or more Engineered Barrier Systems (EBS) encapsulating them.

A material like bentonite clay, which is physio-chemically compatible with both natural rock and nuclear waste, can be used in EBS. In fact, bentonite is preferred as an Engineered Barrier Material (EBM) for its advantageous properties including low cost, long-term stability, low hydraulic permeability and conductivity in a saturated state, high thermal resistance, high radionuclide retardation capacity, high swelling pressure, and good "self-healing" capability. However, heat-induced desiccation cracking of bentonite can cause transmission of radiation in EBS (Allen & Wood, 1988; Bharat et al., 2017; Hirose & Matsubara, 2018; Mohammad, 2020; Soujanya & Thyagaraj, 2017).
Salt Cavern Dissolution Mining: Lessons Learned from Simulations
Authors: Li Li , Gracie Robert , Dusseault Maurice
Published: September 2022

Salt caverns are usually developed by circulating fresh water through a well in a salt formation and extracting brine. Due to the difference in density (buoyancy), fresh water quickly rises to the top of the cavern and promotes dissolution, so the shape of the cavern can be controlled in part by an air pad at the top of the cavern. Relatively high fluid velocities and buoyancy lead to the creation of vortices that are shown to play a critical role in cavern development. Vortices induce higher localized rates of dissolution, leading to complexity which has traditionally been thought to be exclusively due to heterogeneity of the salt formation. Using a combination of simulation based on a novel method involving full CFD and physical-driven dissolution front evolution, we demonstrate how flow complexities combined with the non-reversible nature of salt dissolution drive cavern shape complexity. We discuss and compare mechanisms observed in terms of concentration distributions, brine flow patterns, dissolution rates, and the non-linear impact of injection rate and insoluble interlayer on cavern shape and size.

1 INTRODUCTION

The increases in renewable energy generation promote a high demand for large energy storage facilities. Compressed Air Energy Storage (CAES) is considered one of the best options because it has the advantage of possessing a large storage capacity, small energy loss rate, relatively high cycle efficiency, and is environmentally friendly (Li et al., 2018). A large compressed air storage reservoir is key to ensure the CAES system performs large-scale energy storage, and cavern stability is needed for storage security. Salt formations provide favourable conditions for large-scale cavities because the salt rock has low permeability and excellent self-healing characteristics (Chen et al., 2013; Ozarslan, 2012), ensuring air tightness. However, during the construction of the salt cavern by dissolution mining, overhanging blocks will develop, and the failure of these blocks can threaten the utility of the cavern (Wang et al., 2017). Although different technologies, such as blanket application with sonar monitoring, are used to control roof dissolution and help optimize cavern shape, caverns with high irregularity, as sketched in Fig. 1 are still commonly constructed. So, the key factors that affect the dissolution of solid minerals should be investigated in order to guide and execute effective cavern shape control. Numerical simulation is an efficient way to investigate the factors, especially for large cavern dissolution, which is challenging to explore through laboratory or field experiments.
Experimental Investigation to Fabricate Synthetic Laminated Rock with Different Bedding Plane Cohesive Strengths
Authors: Shi Qingwen , Mishra Brijes
Published: September 2022

Bedding plane properties influence the failure behavior of laminated rocks such as slate and shale. For safe and stable underground coal mine design it is imperative to understand the relationship between the bedding plane strength and the failure of laminated rock. However, it is difficult to obtain in situ laminated rocks with various bedding plane properties while keeping other properties constant. In the present research, we experimentally investigated various approaches to vary the weak plane cohesive strength (Cp). Concrete block incorporating a weak plane was casted and the Cp of the weak plane was varied experimentally using two methods. Direct shear tests along the planes validated that applying normal stress on the concrete block successfully varied the Cp. The verified method was then used to cast synthetic laminated rock (SLR) with various Cp. We then conducted Brazilian splitting tests on SLR with different orientations of bedding planes and compared the failure strength and failure modes with that of shale specimen. The results validated the second method as both failure strength and failure modes of SLR specimens matched the behavior of shale specimens. This research provided a validated method to fabricate SLR with different Cp in the laboratory.

1. INTRODUCTION

Bedding planes cause anisotropy and strength reduction of laminated rocks such as slate and shale. Laminated rock-caused roof failure has caused numerous fatalities in the underground mining industry 1-6. Shi and Mishra summarized historical research on laminated roof failure in underground coal mines 5. Bedding plane properties influence the stability and mechanical behavior of laminated roof. In practical engineering applications, especially in underground coal mining, it is imperative to understand the relationship between the bedding plane properties and the laminated rock failure. For example, a laminated shale roof exposed in underground entries at two longwall coal mines in the eastern US extracting the lower Kittanning coal bed. Although geological conditions such as in situ stress, longwall panel layout, and uniaxial compressive strength of shale roof are similar, the stability of the laminated roof at these two mines differs significantly due to the distinct bedding plane properties7.
Comparison of Different Approaches of 1D Mechanical Earth Model Used in Geomechanics
Authors: Su K. , Onaisi A. , Vidal-Gilbert S.
Published: September 2022

1D Mechanical Earth Model (1DMEM) is the base of many petroleum related works: drilling, completion, prediction of subsidence and cap rock integrity study etc. It provides the profiles of in situ stresses and mechanical properties of geological formations crossed through by a well. The requirement of 1DMEM becomes almost systematic from exploration to development and later to plugging and abandon phases, for both conventional and unconventional fields. There are three types of 1DMEM model based on three distinct assumptions to compute the profile of in situ horizontal stresses: (a) the fault stability model, (b) the poro-elastic model, c) the poro-elasto-plastic compaction model using the Modified Cam-Clay or Mohr-Coulomb model. This paper presents a comparison of the above three types 1DMEM. The assumptions used by each model are examined and their limits of applicability are discussed. The key parameters controlling the in-situ stress contrast regarding to the vertical stress are discussed. Although all these models need well data to calibrate the stress profiles, the stress contrast and the vertical variability of the horizontal stress profiles could be very different between the models. The poro-elasto-plastic approach with eventual consideration of thermal and tectonic stress has high capacity to provide the horizontal stresses profiles consistent with well data in many geological contexts.

1. INTRODUCTION

Mechanical Earth Model (MEM) refers to the numerical representation of the magnitude of in-situ stress in geological formations and their thermo-poro-mechanical properties. It can be elaborated at various scales, 3D or 2D at field scale, or 1D at wellbore scale. Today in the petroleum industry, the request of 1DMEM at wellbore scale is almost systematic over the life of a well, from well preparation, drilling & completion, production phase, infill wells, to plugging-abandon works. Such systematic request of geomechanical model comes from the need to guarantee the well integrity and subsurface integrity of the operations, a need accentuated after the accident of Deepwater Horizon happened in 20th April 2010.