bluuebunny/crossref_metadata_2025 huggingface dataset:
Variational Interface Physics Informed Neural Networks (VI-PINNs) for Heterogeneous Subsurface Systems
Authors: Sarma A. K. , Annavarapu C. , Roy P. , Jagannathan S. , Valiveti D. M.
Published: September 2023

This study presents a novel approach to Physics Informed Neural Networks (PINNs) called Variational Interface PINNs (VI-PINNs) for modeling physical systems with material interfaces. In conventional PINNs, a loss functional obtained from the residual of the strong form of governing equations is minimized to estimate the variable of interest. By contrast, the presented approach relies on minimizing the potential energy functional of a physical system using artificial neural networks. Firstly, we present appropriate modifications to the neural network architecture so that material interfaces can be captured effectively in a variational framework using neural networks. Secondly, we incorporate the interface coupling conditions in the energy functionals to be minimized using VI-PINNs. Thirdly, we examine several numerical integration techniques and compare their accuracy and cost to evaluate the Lagrangians in the VI-PINNs framework. Finally, we discuss a variationally consistent penalty approach to enforce boundary and interface conditions better. Several benchmark 1D and 2D examples are solved using the proposed method and conventional PINNs. Their performances are then compared in terms of cost and accuracy, and their relative strengths and weaknesses are identified.

INTRODUCTION

Subsurface systems are often characterized by a high degree of heterogeneity. Heterogeneities in the subsurface may arise from the natural layering of the earth's crust or naturally occurring faults. In addition, stimulation methods such as hydraulic fracturing also contribute to its heterogeneous character. The heterogeneity of these systems can significantly impact the behavior and movement of fluids, such as water, oil, and gas, within the subsurface. As a result, the study and understanding of heterogeneous subsurface systems are critical for a wide range of industries, including petroleum engineering, geotechnical engineering, hydrology, and environmental science, where accurate predictions of fluid behavior and movement are essential.

Traditionally, several high-fidelity physics-based numerical modeling techniques, including the Finite Element Method (FEM), have been utilized for modeling subsurface systems. These methods involve using a mesh or grid to approximate the system and necessitate the proper meshing of the subsurface into non-overlapping elements. However, generating meshes that conform to the complex geometrical shapes that represent the various subsurface features of interest is non-trivial. This pre-processing step, which involves generating meshes that effectively depict subsurface features, imposes a considerable computational burden and requires frequent analyst intervention (Annavarapu (2013)).
Impact of Deformability of Karstified Features on Production Curves: A Case Study of a Typical Brazilian Pre-Salt Carbonate Reservoir
Authors: Maria A. L. M. , Machado M. V. B. , Falcão F. O. L. , da S. Carvalho M.
Published: September 2023

More than 60% of Brazilian oil production comes from carbonate reservoirs. These reservoirs have become more significant in the Brazilian energy matrix since the discovery of the Pre-Salt layer in Santos Basin, which accounts for more than half of PETROBRAS’oil production nowadays. Brazilian Pre-Salt fractured and karstified carbonate reservoir characterization is one of the primary issues when considering the Reservoir Geomechanics discipline within PETROBRAS. For instance, the compressibility estimate method for karstified media remains challenging. In this work, the (Dobrynin, 1970) approach was used to assess the compressibility of the karst features. Due to its lower computational cost, the pseudo-coupling method was used to simulate geomechanical effects in flow simulation based on these compressibilities estimated values. The results permit the estimate of its impact on production forecast and history matching curves. The general behavior of karst compressibility as a function of porosity is one of the critical findings of this study. The magnitude of karst compressibility for a typical Pre-Salt reservoir is another essential result that permits specialists in reservoir simulation and geomechanical modeling to enhance the accuracy of production forecast and deformation estimate for karstified reservoirs.

INTRODUCTION

Currently, more than 60% of Brazil's oil production is derived from carbonate reservoirs. Due to the discovery of the Pre-Salt layer, which accounts for more than half of PETROBRAS’oil production, these reservoirs have risen to prominence in Brazil's energy matrix. Fig.1 represents the exploration and prodution maps of Pre-Salt fields.

Due to the heterogeneities of this type of reservoir, exploration and production present numerous obstacles. Regarding the development and production of a typical Brazilian Pre-Salt field, one of the most challenging aspects of the Reservoir Geomechanics discipline is the characterization of fracture and karst systems.

The evolution of the characterization process of these systems, especially when considering geomechanical effects and fluid behavior is directly proportional to the accuracy of the production forecast curves of carbonate reservoirs. Determining the parameters required by numerical simulators for reservoir studies and geomechanical analyses is part of characterizing a reservoir. Although compressibility of pores is an essential parameter for flow simulation and the unique input that effectively represents the geomechanical effects, it is kept constant during the whole reservoir flow simulation.
Phase-Field Modeling of Hydraulic Fracturing Under Heterogeneities And/Or Layering of Rock Properties and In-Situ Stress
Authors: Fei F. , Costa A. , Dolbow J. E. , Settgast R. R. , Cusini M.
Published: September 2023

Hydraulic fracturing is a process of creating artificial fractures to enhance the hydraulic conductivity of nearly impermeable rock masses, enabling an economic development of many subsurface energy systems. Due to heterogeneities and layering of rock properties and in-situ stress, hydraulic fracture propagation commonly involves highly complex patterns. To investigate the effects of material heterogeneities and layered rock structure on hydraulic fracturing, numerical modeling usually plays a central role. Most existing numerical methods, however, face a formidable challenge in handling fracture propagation with complex geometries, which can potentially occur in heterogeneous and layered rock formations. A remedy for this challenge is to use the phase-field method. Basically, the phase-field method models the fracture propagation as evolution of a diffusely distributed damage variable, so it allows ones to model hydraulic fracture propagation without explicitly tracking the crack geometries. In this study, we adopt a recently developed phase-field approach to hydraulic fracturing to numerically investigate the effects of heterogeneities and layered structure on near-wellbore hydraulic fracture propagation. Compared with existing phase-field models, this new phase-field model features its capability to capture a rock strength that is independent of the phase-field regularization length. This capability thus allows ones to simulate hydraulic fracture nucleation and propagation in a heterogeneous and layered domain with a uniform regularization length. We then perform a series of hydraulic fracturing simulations with layering of in-situ stress and heterogeneous critical fracture energy. We believe the outcome of this numerical study can improve our understanding of the mechanisms behind the hydraulic fracture propagation in heterogeneous and layered rock formations.

INTRODUCTION

For many subsurface applications, such as oil and gas production from tight reservoir and enhanced geothermal systems (EGS), it is necessary to hydraulically fracture the rock to enhance its permeability and favor fluid circulation. The fractures are generated by injecting a high-pressure fluid (e.g., water). The characteristics of the generated fractures determine the efficiency of the stimulation treatment and possible hazards associated with the fracturing process. The propagation direction, the geometry, and the extent of the hydraulically generated fractures are greatly influenced by the in-situ stress conditions and the heterogeneity of rock properties (Yang et al., 2004; Xu et al., 2019; Zoback et al., 2022). Therefore, it is crucial to develop numerical tools that can reliably and efficiently model hydraulic fracture nucleation and propagation in heterogeneous porous media.
Distinct Element Analysis of Various Structural Element Responses for Coal Rib Support Simulation
Authors: Kirmaci A. , Guner D. , Karadeniz K. , Sherizadeh T.
Published: September 2023

Understanding the bolt responses for the efficacy of bolt performance during coal rib support applications plays a key role in controlling the stability of underground coal mine openings. Conducting pull-out tests is imperative to gain a better understanding of these responses. Field conditions such as block volume and degree of cleating may significantly impact bolt performance. These field conditions can be efficiently implemented in numerical modeling approaches, and selecting a proper structural element type for these numerical studies is crucial. This study developed a pull-out test model and compared the performance of structural elements as support members in the coal rib model using 3DEC, a three-dimensional distinct element-based numerical modeling code. This study covered commonly utilized cable, pile, and hybrid structural elements in rib models with explicitly introduced face cleats. The bolt response of numerical models was calibrated with the field data showing the load-displacement response of a pull-out test. Comparing the rib models with these structural elements showed that hybrid structural elements demonstrated better agreement with the field observation as they can simulate the reaction to shearing along the discontinuities by inducing bending stresses. The impact of support density on rib stability is also presented in this study.

INTRODUCTION

The fact that injuries and fatalities linked to rib failure persist in underground coal mines, despite measures taken to ensure rib stability emphasizes the urgent need to develop and validate support systems that can effectively reduce coal rib failures. Currently, there is no standard practice for coal rib supports that can effectively address the diverse range of conditions encountered in coal mines across the United States (Guner et al., 2023). That leaves mine operators with no option but to rely on trial-and-error or industrial legacy practices. The severity of rib instabilities as a ground control hazard in underground coal mines is highlighted by the average annual fatality rate caused by coal rib failures, which remained at 1.6 between 2009 and 2022, as reported by MSHA (2022). Although coal rib failures pose a significant risk to the safety of the miners, there is limited information on these events and how rib support can mitigate them. Therefore, conducting studies to analyze the current rib support strategies and reduce injuries and fatalities resulting from rib failures in the coal mining industry is essential.
Explosion Resistance of Reinforced Concrete Refuge Alternative Wall Under Certain Abutment Loading
Authors: Karadeniz K. E. , Guner D. , Sherizadeh T.
Published: September 2023

Build-in-place (BIP) refuge alternatives (RAs) are used to provide safe havens for miners unable to escape their working area after an accident like an explosion. These underground infrastructures are built over time in various locations and might expose to mining-induced stresses. The convergences related to these stress redistributions around the mine openings might change their structural integrity and, subsequently, the explosion resistivity. Studying the effect of increasing vertical load like abutment stress on such underground mine stopping for the explosion resistance is difficult because repetitive explosion experiments on these structures are perilous and challenging. This study uses two case studies to simulate the real-time monitored abutment loading condition and the explosion testing on such steel-reinforced underground structures. A BIP RA design's performance and failure analysis were evaluated under these two conditions using 3DEC, a three-dimensional distinct element solver. This study aims to reveal the effects of vertical convergence due to panel extraction on the explosion resistance of such reinforced concrete walls. The model results demonstrate that the abutment loaded stopping shows higher deformation during and after the explosion than the models without excessive vertical loads. The stopping has high displacement levels at the top of the structure, resulting in the highest deformation zones being extremely distinctive.

INTRODUCTION

Mine explosions are among the most concerning hazards associated with underground coal mining, as a single gas explosion can result in injuries and fatalities among miners. In 2006, three separate disasters - the Sago Mine Explosion in West Virginia, the Aracoma Alma Mine Fire in West Virginia, and the Darby No.1 Mine Explosion in Kentucky - claimed a total of 47 lives in the United States (Yantek and Schall, 2017). This tragic outcome led to the Mine Safety and Health Administration (MSHA) introducing more rigorous regulations and served as the catalyst for the creation of the Miner Act of 2006 (Fasouletos, 2007; Mitchell, 2008; Zipf et al., 2009; Karadeniz et al., 2022). The regulations stipulate certain requirements, some of which concern the construction of underground structures to isolate areas from active workings, such as the provision of refuge alternatives. The primary purpose of a refuge alternative (RA), whether mobile or BIP (built-in-place), is to provide a safe haven for miners who are unable to leave their working location due to hazardous gases or a blocked escape path immediately following an explosion.
Creep and Lateral Stress Behavior of Gulf of Guinea Miocene Mudrock Specimens
Authors: Bhandari A. R. , Flemings P. B. , Ewy R. T. , Germaine J. T.
Published: September 2023

We measured axial creep and lateral stress behavior in drained uniaxial strain experiments on intact and resedimented Gulf of Guinea Miocene kaolinite-rich mudrock specimens. At axial effective stress of ∼10 MPa (close to the in situ vertical effective stress of 7.9 MPa), the uniaxial lateral stress ratio (K0) is 0.75 for the resedimented material and 0.62 for the intact material. The intact material behaves over-consolidated because its in situ state (7.9 MPa) is less than the yield stress (∼20 MPa). The compressibility of the resedimented specimen is an order of magnitude higher than that of the intact specimen. The in situ void ratio is ∼0.15 void ratio units less than the void ratio of the resedimented specimen at the in situ vertical effective stress; this suggests that creep deformation has occurred over geological time. In addition, the creep rate of the resedimented material is an order of magnitude higher than the intact material. Overall, this paper illuminates the role of creep in the compression process.

INTRODUCTION

Intact specimens of in-situ clay deposits are usually impacted by sample disturbance (Lunne et al., 2006), especially for deep or offshore samples. The resedimentation technique has been used to prepare uniform test specimens that do not have sampling disturbance, and thereby study sediments for over half a century. It allows for control over stress history and produces specimens of desired porosity with complete saturation. It is commonly assumed that the laboratory resedimented material closely reproduces the mechanical behavior of intact specimens (Casey et al., 2016; Casey et al., 2019). However, recent studies have found that the resedimented specimens are usually less dense than the intact specimen at the in-situ vertical stress level (Finnegan, 2020), and the intact material (with no apparent geological unloading) shows measured yield stress markedly greater than the maximum past stress (Ewy et al., 2020; Finnegan, 2020). Such behaviors suggest that creep may have played a role in-situ. We systematically study intact and resedimented specimens to explore their behavior and understand mudrocks’ in-situ properties.
Using Low-Field Nuclear Magnetic Resonance and X-Ray Computed Microtomography Imaging to Explore Potential of Microbially-Induced Calcium Carbonate Precipitation Treatment to Seal Shale Fractures
Authors: Willett M. R. , Seymour J. D. , Bedey K. , Kirkland C. M. , Phillips A. J. , Cunningham A. B. , Dobeck L. , Crandall D. , Rutqvist J.
Published: September 2023

Microbially-induced calcium carbonate precipitation (MICP) is a biological process in which microbially produced urease enzymes convert urea and calcium into solid calcium carbonate (CaCO3) deposits. Studies have shown that MICP can be used to seal fractures in shale, raising the possibility of applying this technology to restimulate fracking wells by plugging underperforming fractures. For this and other applications to become a reality, non-invasive tools are needed to determine how effectively MICP seals shale fractures under subsurface conditions. In this study, a 2.54 cm wide and 5.08 cm long Marcellus shale core with a single, ∼1 mm wide fracture held open by sand "proppant" underwent MICP-treatment at 60°C until reaching three orders of magnitude permeability reduction. Low-field nuclear magnetic resonance (LF-NMR) and X-Ray computed microtomography (μ-CT) techniques were used to assess the extent of biomineralization within the fracture. These tools revealed that while CaCO3 precipitation occurred throughout the fracture, there was preferential precipitation around proppant, and the core sealed at the effluent end before filling most of the fracture. Both tools were able to independently calculate of the amount of solid biomineral formed inside the fracture. This study found that the distribution of proppant within the shale fracture was an important parameter controlling the degree of biomineralization.

INTRODUCTION

Background

Shale is a fine-grained, sedimentary rock often found adjacent to layers of sandstone and limestone up to thousands of feet below ground surface (bgs). The unique characteristics of this formation have led it to play multiple roles in the ever-changing energy landscape of the 21st century. Possessing relatively high porosity but extremely low permeability, shale has been targeted for geologic carbon sequestration and nuclear waste disposal (Washburn, 2014). Many shale deposits also contain rich quantities of hydrocarbon fuels, which can be extracted from very tight pore spaces with hydraulic fracturing, also known as fracking. All of these applications highlight a need for methods to control permeability to ensure the long-term safety and utility of these reservoirs. For example, there may be a need for a method to plug fractures that arise in shale used for storage purposes to mitigate leakage. There is also motivation to seal fractures created in fracking wells to prevent contamination of aquifers by fracking fluids or potentially restimulate the well to enhance natural gas recovery (i.e. "frack/re-frack").
Quantifying the Variability in Interpretation of Shear Testing of a Natural Fracture
Authors: Franco M. A. , Potter J. , Ross B. J.
Published: September 2023

The shear strength of discontinuities (e.g., joints, bedding planes, faults) plays an important role in the mechanical behavior of a rock mass and is crucial to the analysis and design of rock slopes. The shear strength of natural discontinuities is typically determined by performing a series of direct shear tests. Several sources of variability in direct shear test results are recognized by the geotechnical community (e.g., the inherent variability of shear strength in a rock mass, joint roughness), but the effect of variations in testing equipment, testing methods, and in the interpretation and application of test results has been little studied. The focus of this paper is the potential variance introduced by the interpretation of direct shear test results. The authors explore potential variation in a single direct shear test by examining test results from a natural joint with four different approaches. Potential future research paths are also discussed.

BACKGROUND

The direct shear test (DST) is widely used to determine the shear strength of natural discontinuities in rock and soil. This determination is of particular importance when designing rock-based engineering structures and assessing failures. Direct shear tests are performed using a shear box apparatus that maintains a constant force normal to the discontinuity while applying an increasing shear force parallel to the discontinuity (ASTM, 2016). The information recorded includes the applied normal force, displacement of the top of the specimen in relation to the bottom, the shear force applied to achieve that displacement, and fracture roughness. The test is generally performed three to four times with increasing applied normal loads, resulting in a set of traces corresponding to the applied normal forces. Figure 1 illustrates an idealized trace resulting from a direct shear test. Recorded forces are then converted to stresses by dividing by the surface contact area measured at the time of the test.

Two parameters are calculated based on the trace data described above (ASTM, 2016):

• Peak shear strength is associated with the maximum shear stress value along a sheared surface attained during a test.

• Residual shear strength is associated with the point at which the shear stress remains essentially constant with increasing shear displacement.
Investigation of Natural Fracture Orientation and Clustering Impact on Fracture Propagation Using the Semi-Circular Bend (SCB) Test
Authors: Bhadariya Vishesh , Somishetty Varun K. , Lee Hunjoo P.
Published: September 2023

Sedimentary rocks contain abundant pre-existing discontinuities that directly impact the trajectory of the fracture propagation. In this study, the Semi-Circular Bend (SCB) test was employed to investigate the interaction of opening mode fracture with multiple pre-existing discontinuities. In the first set of SCB specimens embedded with homogenous parallel inclusions, mechanical properties analogous to the host rock, demonstrated that fracture diversion is more likely to occur for smaller approach angle and wider spacing. The second set of samples were designed to contain heterogeneous inclusions to simulate clusters of mineral-filled natural fractures, which have different mechanical properties compared to the host rock. The stiffness, strength, and thickness of the inclusions were varied by adjusting the mixing ratio of gypsum powder and water. The results indicated a similar trend for approach angles as in the first set, while the samples with weaker and softer inclusions showed longer fracture diversion distance than the samples with stiffer and stronger inclusions. As the thickness increased, the fracture diversion distance became longer. The findings of this study will help to evaluate the Stimulated Rock Volume (SRV) in naturally fractured formations, which is directly related to the hydrocarbon production volume.

INTRODUCTION

Pre-existing discontinuities in tight and low permeability formations act as weak planes that influence the propagation of hydraulic fractures and the ultimate fracture network, which is directly related to the overall hydrocarbon recovery. Micro-seismic interpretations (Fisher et al., 2002), core observations (Anders et al., 2014) and logging activities (Khoshbakht et al., 2009) provide an insight into the orientation and distribution of these discontinuities in fine-grained layered structures (Lai et al., 2022). Previous studies have experimentally and numerically investigated the impact of orientation, stress anisotropy and mechanical properties of natural fractures on fracture propagation (Fatahi et al., 2017). The interaction of an opening mode fracture with pre-existing discontinuities could lead to fracture arresting, crossing or diversion depending on the approach angle, stress anisotropy as well as strength of the natural fracture (Warpinski and Teufel, 1987; Dahi-Taleghani and Olson, 2009; Lee at al., 2015; Wang et al., 2018). Bahorich et al. (2012) performed an experimental study on hydro-stone block samples containing inclusions representing cemented natural fractures to characterize the interaction behavior between the hydraulic fracture and the inclusions. To conduct systematic tests for sensitivity analysis, other studies utilized the Semi-Circular Bend (SCB) test to investigate the impact of approach angle, thickness, stiffness, and strength of the natural fracture on interaction with the opening mode fracture (Lee at al., 2015; Wang et al., 2018; Huang et al., 2020).
Similarity Solutions for Shallow Hydraulic Fracture in Impermeable Rock
Authors: Wang Z. Q. , Detournay E.
Published: September 2023

The paper deals with the plane strain problem ofa shallow fluid-driven fracture propagating parallel to a free surface in an impermeable elastic rock. For a shallow fracture, the aperture corresponds essentially to the deflection of the layer defined by the free-surface and the crack. This problem is thus governed by the Euler-Bernoulli beam equation and by the lubrication theory. We show that the solution generally depends on two independent time scales and that there exist 4 similarity solutions denoted as (Equation), (Equation), (Equation) and (Equation). Furthermore, we demonstrate that the parametric space of solution is a rectangle with the vertices corresponding to the similarity solutions. The (Equation) and (Equation)-solutions are two different early time solutions characterized by a small length of the fluid-infiltrated region compared to the fracture length (i.e., the fluid lag occupies nearly the whole fracture), while the (Equation) and (Equation) solutions are two large-time solutions characterized by a vanishingly small lag. The (Equation) and the (Equation) vertices are similarity solutions for the particular case when Gc = 0, while (Equation) and (Equation) are similarity solutions for the case σo = 0. Thus the (Equation)-edge and the (Equation)-edge represent two particular fracture evolutions, the first one when Gc = 0 and the second one when σo = 0. However, the large time solution for the general case Gc > 0 and σo > 0 has not yet been identified, as the numerical solutions conflict with the large time matched asymptotic solution.

INTRODUCTION

Various instances of fluid-driven fracture near a free surface can be found in nature and in geo-engineering. They include excavation of hard rocks (Young, 1999), cave in-ducement in mining (Jeffrey et al., 2000), contaminant spill remediation (Murdoch, 2002), and the formation of sills by magma rising from deep underground chambers (Bunger and Cruden, 2011; Michaut, 2011).

Models of hydraulic fractures propagating near the surface of a homogeneous elastic semi-infinite domain can be formulated mathematically using elastic integral equations that relate the displacement discontinuity across the fracture to the net traction acting on the fracture faces, in combination with the nonlinear lubrication equation that governs the flow of viscous fluid inside the fracture (Zhang et al., 2002, 2005; Gordeliy and Detournay, 2011). The resulting system of integro-differential equations together with the boundary conditions at the injection point (typically a constant injection rate) and at the fracture tip (including the propagation criterion) is closed in regard to predicting the evolution of fracture geometry, fluid pressure, and aperture from given initial conditions.
Modeling Frac-Hits Using Reservoir Geomechanics and Phase Field Finite Element
Authors: Almetwally A. G. , Wheeler M.
Published: September 2023

Frac-hits can have a significant negative impact on hydrocarbon production by reducing mobility efficiency and modifying pressure profiles around wells, particularly with increased infill drilling. However, the relationship between operational fracturing parameters and frac-hit events is still not well defined. To address this issue, this study presents an integrated simulation model that combines reservoir geomechanics and phase field finite element methods to simulate frac-hits events. This model considers reservoir and fracturing parameters for multiple horizontal wells in a drilling spacing unit. It was cross-validated with Molina's (2019) analytical model and Morales’ (2020) mechanical testing apparatus, enabling the evaluation of hydraulic and mechanical interactions, such as pressure communication, fracture merging while propagation, and stress shadowing (Molina, 2019; Morales, 2020). This approach provides valuable insights into optimal well and fracture placement, fracture behavior in relation to pre-existing fractures, and the impact of operational parameters on frac-hits. Ultimately, this research represents an effective tool for improving fracture designs and mitigating frac-hits, thereby enhancing field performance.

INTRODUCTION

Infill well development has become a widely used strategy for hydrocarbon production in unconventional reservoirs, with an increasing number of "infill" wells being drilled offset to one or more existing producers. However, the proximity of these new wells ("child" wells) to existing producers ("parent" wells) often leads to negative impacts on production due to "fracture driven interactions" (FDI's) or "frac-hits" (Daneshy et al., 2019; King, 2012). The severity of the impact depends on factors such as well spacing and the age of the parent well (Gupta et al., 2020; Lindsay et al., 2018; McDowell et al., 2019), and impacts are highly variable between different shale plays (Esquivel et al., 2017; Gupta et al., 2020; Miller et al., 2016). Various techniques have been applied to mitigate impacts from parent/child well interaction, such as preloading the parent well by injecting into it prior to the offset frac, varying well spacing, varying fracture sequencing, cube (or tank) development, chemical treatments, refracturing, and far-field diverter (Bommer et al., 2018; Haustveit et al., 2020; McDowell et al., 2019; Miller et al., 2016; Nieto et al., 2018; Patel et al., 2016; Sani et al., 2015; Swanson et al., 2018; Vidma et al., 2018; Whitfield et al., 2018; Zhang et al., 2019). Although these strategies have been successful, there is no universal solution, as each technique comes with different costs and benefits.
Investigations on Cement Thermal Properties with Direct Application to Underground Energy Storage
Authors: Abid Khizar , Velazco Alberto Toledo , Teodoriu Catalin , Amani Mahmood
Published: September 2023

The current energy storage wave that looks at low temperature and heat storage in shallow reservoirs as well as the intensification of Hydrogen storage (especially as by product to methane) have reopened the quest for accurate and precise well temperature prediction and modeling. This prediction plays a critical role in the determination of wellbore storage capabilities, well integrity and overall energy storage efficiency. This paper shows experimental results on measuring thermal properties of various cement properties as well as selected rock which are used as comparison. Our data will show that small amount of additive products in cement may dramatically change cement thermal properties that could become important for the overall well heat transfer and thus will enhance the energy storage efficiency.

INTRODUCTION

With the focus of the world going toward the net zero goal with respect to carbon emission, the storage of hydrogen in the subsurface will play an important role to achieve that target. It is reported by Tarowskia and Uliasz-Misiak, (2022) that due to the ease of hydrogen availability around the world and increasing global acceptance, hydrogen has the potential to replace fossil fuel by 2050. At the moment the main source of hydrogen storage at the surface consists of the cryogenic and high-pressure tank. However, with further expansion of hydrogen gas as a source of renewable energy the storage capacity has to be increased. In this respect, underground hydrogen storage (UHS) gives an alternate solution in which hydrogen is injected into a suitable geological formation such as a depleted oil and gas reservoir, aquafer, and salt cavern, and can be reproduced when needed (Sambo, et al., 2022). As the only connection to the UHS is the well so it is of utmost importance that the integrity of the well is maintained. Hence, well cement plays an important role in the well integrity as it provides zonal isolation, give support to the casing, and seals of the problem some subsurface formation (Rincon, et al., 2022). Like any other subsurface gas storage, well cement will be exposed to different temperature cycles due to the process of injection and reproduction that can lead to thermal loading and degradation of the cement matrix. Therefore, it is necessary to know the thermal properties of the cement placed in the UHS so that the integrity of the well can be assured.
Characterization of a Tight Gas Reservoir Using the Integration of Electrofacies and Fracture Aperture, Ahnet, Algeria
Authors: Irofti Doina , Ifrene Ghoulem E. H. , Aihar Aimene , Bouabdallah Nassim , Khouissat Abdelhakim , Djemai Safouane
Published: September 2023

The integration of this heterogeneity analysis with the interpreted fractures of the four wells in the area shows that the lithology has a major influence on the number and type of fractures. The well logs that are most impacted by composition were used to perform cluster analysis in four wells. Cluster analysis generates more representative scaled input parameters for reservoir characterization, which may be compared to the fractures obtained from borehole imaging result. On the basis of their measurable features, these approaches group like things and identify them from dissimilar objects. Because the procedure is neither driven by an external model or specified by a reference training set of previously known items, this clustering is known as unsupervised classification. We employed cluster analysis to classify rocks based on their core compositional characteristics. We utilized well logs that were impacted by composition in this investigation (NPOR, RHOB, GR and PEF). The cluster analysis was carried out using the Techlog software module Heterogeneous Rock Analysis (HRA).

INTRODUCTION

Serra & Abbott, 1980 coined the word "electro facies," which they define as "the set of log responses that distinguishes a bed and allows it to be recognized from others" (Kumar et al.,2006). Because log responses are measures of the physical qualities of rocks, electro facies may typically be ascribed to one or more lithofacies. Petroleum prospecting and reservoir characterization require the identification of facies. Facies were previously determined manually using graphical approaches such as cross-plotting from wire-line recordings and linking their behavior to cores. Several mathematical methods have recently been devised to automate the job of identifying facies.

The quality of the distribution of petrophysical characteristics is driven by reservoir rock type, which is critical for reservoir characterization (Cherana et al., 2022; Doghmane et al., 2022). It improves knowledge of fluid flow, rock storage capacity, and pore size distribution. Many different criteria may be used to classify rock types. Rock typing divides reservoir rocks into discrete units that were formed under comparable geological settings and have undergone similar diagenetic changes (Guo et al., 2005). Fracture aperture characteristics in a reservoir rock are the crucial parameters that control the quality of tight reservoir rock (Mahmood & Guo, 2019) and need to be considered in reservoir rock typing. This research combines rock classification with knowledge of fracture parameters such as aperture.
Thermal Effect on Long-Term Shale Behavior in Nuclear Waste Storage
Authors: Makhnenko R. Y. , Kim H. , Kim K.
Published: September 2023

Shale-like formations can serve as barriers for geologic disposal of high-level nuclear waste. Adopting these tight materials has an advantage that any radionuclides emitted from the canisters would stay with hardly mobile pore water within the rock. However, there are a few issues associated with the sealing capacity of shales as high temperatures experienced in nuclear waste disposal can strongly affect their geomechanical and flow properties. In this study, we investigate how the continuous heating and hydromechanical loading are affecting the flow properties of a shale with the clay content above 50% and the dominant pore size on the order of tens of nanometers. Both intact and fractured specimens are considered, and parameters associated with a coupled hydromechanical model are measured in high-pressure laboratory experiments, including the time-dependent deformation introduced to the model through bulk viscosity. It appears that even a small increase in temperature from 24°C to 40°C significantly impacts long-term (viscoelastic) response of shale, while the effect on the short-term (poroelastic) behavior is less pronounced. At the same time, the thermal effect on the fluid flow is ambiguous: the permeability increases with temperature but is predicted to eventually decrease due to the accelerated rock compaction at elevated temperatures.

INTRODUCTION

Argillite geological formations have been considered worldwide as potential host rocks for geological disposal of high-level radioactive waste (HLW) because of their low permeability, high retention capacity for radionuclides, and capability to self-seal fractures (Sassani et al., 2021). Other favorable characteristics of argillites (often times represented by shales) are the strong sorptive behavior for many radionuclides reducing conditions because of the lack of oxygen transport from the surface, and chemical buffering of the effects caused by materials introduced during repository construction and operation (Tournassat et al., 2015; Urpi et al., 2019). One unfavorable feature of argillites compared to other potential host rock types is a relatively low thermal conductivity that would lead to higher host rock temperatures (potentially above 100 °C). This means that it will be crucial to gain reliable data for being able to confidently predict long-term, high-temperature responses of shaly host rock. This is exacerbated by the recent interest of disposal in large-sized canister of high decay heat that may lead to higher host rock temperature (Rutqvist, 2020). Moreover, with almost a hundred nuclear power plants across the US waiting for the permanent storage solutions, it is necessary to establish a procedure for obtaining properties of a wider range of typical argillites, from the more ductile materials with high clay content to more brittle rock that could respond vastly different when exposed to high temperature.
Wellbore Stability Analysis Based on Poro-Elastic Dynamics
Authors: Yang Shuai , Zhang Yanru , Pang Huiwen , Chen Ang , Li Yuan
Published: September 2023

The poro-elastic dynamics method was adopted to analyze the near-wellbore stress field and shear failure response. Different from the traditional method, this proposed model includes the time-dependent characteristics of stress field, the fluid-solid coupling and the effects of fluid and solid inertia. A set of deep well parameters were taken as the examples to calculate the near-borehole stress field and failure response compared with the poro-elastic static model. The influences of poro-elastic parameters, in-situ stress and wellbore pressure on the shear failure responses were also analyzed in a detailed parametric study. The results show the importance of the inertial effects of the solid-fluid system, which produces a wave-diffusion behavior in the early times. Potential failure area calculated by the dynamic model is larger than that calculated by the static model, implying that the static solution underestimates the risk of wellbore collapse. Thus, the present model can help us understand the dynamic instability mechanism and it can also provide the theoretical basis for predicting collapse pressure accurately, optimizing drilling mud density and maintaining wellbore stability.

INTRODUCTION

Wellbore instability can cause many substantial problems during drilling, such as stuck pipe and lost circulation. Overall, problems related to wellbore collapse account for 5–10% of drilling costs in exploration and production, which are hundreds of million dollars per year, when considering time loss and the rental of drilling equipment (Fjar et al., 2008). When a wellbore is drilled, the concentration of stress around the borehole will occur which may damage the rocks if the concentrated stress exceeds the rock strength (Zoback et al., 1985). If the failed rock exceeds the cleaning capacity of the mud circulation, the excessive failed rock can cause stuck drill pipe or bottom-hole assembly. Sometimes, wellbore collapse can result in sidetracked holes and abandoned wells, which means a great loss in oil and gas industry. Therefore, wellbore stability analysis is vital to safe and effective drilling and production.
Comparative Study of Machine Learning Vs. BIS Approach for Landslide Hazard Zonation in Kashmir Himalayas, India
Authors: Singh Ankit , Singh Tarun , Rao K. S.
Published: September 2023

Presently slope stability analysis and landslide hazard monitoring are the most challenging tasks in mountainous regions like the Himalayas. These events which were earlier considered as a process of attaining equilibrium in the topographic surface of the earth by nature, with the increase in population and onset of industrial revolution in the past few decades, changed the scenario of this natural phenomenon and transformed it into a disaster. The main reason for this is the utilization of inaccessible terrains for engineering mega projects and urbanization. Today, landslides are considered as the worst natural disasters and have become the objects of mass destruction and thereby new approaches for landslide study are being constantly developed with time to understand this natural phenomenon as much as possible. Witnessing the severity of this disaster in India and globally; this study is aimed to study landslide hazard in the domain of landslide susceptibility mapping and hazard zonation. This approach makes use of different instability causing parameters prevalent in the area to demarcate the region into different probable hazard zones. The resulting maps thus prepared are called Landslide Hazard Zonation (LHZ). For the study, a sub-part of Karewa Basin is selected as an area of study in Anantnag district, Jammu and Kashmir, India. Two different methods, the established Bureau of Indian Standards (BIS) method and the new machine learning based classification method using decision tree classification algorithm, are selected for the study of landslide hazard in the area. The resulting maps from both methods are analyzed and validated using the landslide inventory data. The results from both the methods are also used to perform a comparative analysis to examine which method yields better results. It is concluded that machine learning based methods, provided accurate training dataset can yield better results than the traditional methods which require a makeover to incorporate more data, made available with the advancement of technology.
Geomechanical Characterization of the Mount Simon Sandstone and Eau Claire Formation of Northern Illinois Basin
Authors: Camargo J. T. , Appriou D. , Burghardt J.
Published: September 2023

The purpose of this paper is to analyze publicly available geomechanical data from two carbon storage sites in the Illinois Basin: the Illinois Basin-Decatur Project (IBDP) in Macon County, IL and the FutureGen2.0 project in Morgan County, IL, which was cancelled before injection began. This study estimates the magnitudes and directions of the least compressive principal stress gradient using hydraulic fracture-based stress measurement tests, borehole breakouts, and sonic logs in the Eau Claire Formation (primary confining zone) and the Mount Simon Sandstone (targeted reservoir). The range of stresses expected in the underlying Precambrian basement is also investigated. The evaluation of the state of stress is carried out in a probabilistic manner using the State of Stress Analysis Tool (SOSAT) developed under the National Risk Assessment Partnership (NRAP) program. Finally, the paper also provides a discussion on distinctions between fracture initiation pressure, propagation pressure, and fracture closure pressure, given that hydraulic fracture testing results show a significant difference between these three values. The discussion also addresses why the fracture closure pressure should be preferred in injection pressure determinations, a critical point in geological carbon storage projects.

INTRODUCTION

In this paper, geomechanical data from two geological carbon storage (GCS) sites in the northern Illinois basin are analyzed and compared to each other. The GCS projects are the Illinois Basin-Decatur Project (IBDP) in Macon County, IL, and the FutureGen2.0 project in Morgan County, IL. While operations in IBDP were fully completed, the FutureGen2.0 project was interrupted before injection began. Both sites underwent extensive subsurface characterization and made their geomechanical data publicly available.

The geomechanical datasets have been analyzed separately. For example, Appriou (2019) assesses the geomechanical risks associated with CO2 injection at the FutureGen2.0 site and Gilmore et al. (2016) describe and analyze the comprehensive characterization program at the FutureGen 2.0 site and refer the readers to essential publications regarding further characterization efforts, modeling of carbon dioxide (CO2) injection and transport, monitoring, verification, and accounting plan. For IBDP, Bauer et al. (2016) and references therein provide an overview of the geologic characterization of the site and analyze the microseismic response to CO2 injection at the IBDP site.