bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced Geothermal Site Characterization Using Generative Adversarial Network and Ensemble Method
Authors: Bao Jichao , Lee Jonghyun , Yoon Hongkyu 
Published: August 2024

ABSTRACT:
Characterizing the subsurface properties such as permeability and thermal conductivity is important for stimulation planning and heat production in enhanced geothermal systems (EGS). Data assimilation methods, such as the Kalman-type methods, are widely used for characterization by assimilating observed dynamic data such as pressure and temperature. However, these approaches only perform well when the parameters follow a Gaussian distribution. The geothermal sites are usually highly heterogeneous with non-Gaussian distributed complex structures such as faults and fractures, which are difficult to characterize. Over the past few years, emerging deep generative models and their impressive applications in different tasks have provided a solution to produce images with complicated features. In this work, we use the Wasserstein Generative Adversarial Network (WGAN), a deep generative model, to generate fractured images from the low-dimensional and Gaussian distributed latent space. The ensemble method, a Kalman-type data assimilation method, is then applied to the latent variables to characterize the permeability fields of a fractured geothermal site using temperature data. A synthetic two-dimensional example is presented to show the performance of our approach.

1 INTRODUCTION
Subsurface characterization is important for a geothermal system to conduct stimulation and heat production. For the subsurface inverse problem (Carrera et al., 2005; McLaughlin and Townley, 1996; Oliver et al., 2008), spatially distributed geologic parameters such as permeability are estimated from noisy and sparse data such as pressure and temperature. Due to ill-posedness in the inverse problem, it is hard to accurately characterize subsurface properties using limited measurements. Data assimilation (DA) methods can integrate dynamic data (e.g., time-series pressure and temperature) into numerical models to identify unknown model parameters and reduce the estimation uncertainty (Liu and Gupta, 2007; Liu et al., 2012). Among various DA methods, Kalman-type methods such as the ensemble method (Emerick and Reynolds, 2013) are widely used due to their optimality and efficiency. However, the traditional Kalman-type methods share a common problem, i.e., the limitation of Gaussian assumption (Ghorbanidehno et al., 2020). These Gaussian prior-based methods can provide optimal solutions if the unknown parameters follow a Gaussian distribution, but there are also many non-Gaussian situations that these methods cannot handle (Zhou et al., 2014).
A Review of Cluster Filtering Methods for Point-Cloud-Based Rockfall Monitoring
Authors: Emmons E. B. , Walton G. 
Published: August 2024

ABSTRACT:
The standard methodology for through-time rockfall analysis from slope point clouds consists of computing changes between lidar scans, followed by grouping areas of significant change using unsupervised clustering (e.g., DBSCAN). Clusters found are indicative of a potential rockfall and can be used for the construction of a comprehensive rockfall database. However, clustered change not representing true rockfalls is common, often accounting for the majority of identified objects. Identifying these erroneous clusters requires hours of manual verification; therefore, the search for an effective filtering method to reduce the need for manual verification is a highly relevant topic in the field of point-cloud-based slope monitoring research. This paper presents a review of recent literature on the filtering of rockfall databases to remove erroneous clusters and maintain an overall high quality rockfall database. The review has highlighted the lack of standards for filtering these clusters and a corresponding high degree of variability in filtering methods.

1. BACKGROUND
The risk of rockfall from slopes along transportation corridors can be characterized by both the magnitude (volume) and frequency of block detachments. Rockfall inventories are commonly used to define a magnitude-frequency curve for a given slope of interest. Using a power-law fit to such a curve, the frequency of certain sized rockfall events can be estimated (Dussauge et al., 2003; Dussauge-Peisser et al., 2002; Hungr et al., 1999).
Using terrestrial laser scanning (TLS), high-resolution point cloud data is now available for regularly monitored slopes, allowing comprehensive rockfall databases to be created. To characterize these slopes, the construction of rockfall databases typically follows a standard methodology (Abellán et al., 2010; Brodu & Lague, 2012; Schovanec et al., 2021; Tonini & Abellan, 2014; Weidner et al., 2019):
(i). Collection of multiple epochs of TLS.
(ii). Alignment of collected point clouds.
(iii). Calculation of change between subsequent scans to determine areas of apparent volume loss.
(iv). Clustering detected areas of change using a clustering algorithm (commonly Density Based Spatial Clustering of Applications with Noise – DBSCAN) (Ester et al., 1996).
(v). Classification and filtering of detected clusters, for example to discern rockfall clusters from non-rockfall clusters (vegetation, shadows, occlusion, snowfall, etc.).
Through the application of this methodology, a rockfall database can be created for a monitored slope. While the application of either manual or automated cluster filtering (step "v") can be critical to avoid inclusion of erroneous clusters in a rockfall database, the acceptance of all clusters (i.e. no filtering) is a common approach in practice (see Table 1 for a summary of approaches adopted in the literature). This paper presents a review of the current approaches and challenges associated with rockfall cluster filtering, as well as its practical importance.
Comparative Analysis of Critical Bond Strength Parameters of Neat Class G Cement and Fly Ash Enhanced Cement to Steel
Authors: Potter C. M. , Eckert A. , Jones J. , Weicheng Z. , Meng M. 
Published: August 2024

ABSTRACT:
In subsurface engineering applications, such as wellbore integrity, the interface between cement and steel is integral to expected functionality. The interface between steel and cement is often a structural weak point in many systems, however, the critical parameters for debonding evaluation are poorly understood and derived from outdated experimental procedures. Through experimental debonding tests, this study aims to analyze the tensile bond strength and fracture parameters and their sensitivity to cement composition with a pozzolanic additive (fly ash). Neat Class G cement testing resulted in an average tensile bond strength of 0.223 MPa, an average contact stiffness of 2.94x108 N/m3, and an average critical fracture energy of 163.18 J/m2. Samples treated with 40 wt.% fly ash resulted in an average maximum tensile bond strength of 0.368 MPa, an average contact stiffness of 4.07x108 N/m3, and an average critical fracture energy of 283.26 J/m2. The higher average maximum contact stiffness, maximum tensile strength, and critical fracture energy of the fly ash samples indicate a stronger bond over neat Class G cement under ambient curing conditions. The results support the capability of fly ash enhanced cement to improve bond strength, reducing the chance for delamination under ambient conditions.

1. INTRODUCTION
Portland cement is used as the basis for many modern engineering projects. From home foundations, to fluid barriers such as dams, to zonal isolation in petroleum production, its bulk strength and low fluid transmissibility lead to its pervasive use in modern construction. Despite its extensive use in modern engineering, the bonding of cement to steel, other construction materials, and rock faces is a material property that remains poorly understood. In the context of subsurface energy engineering (petroleum extraction, carbon storage, geothermal, etc.), wellbore cement failure at these interfaces requires a better understanding of interface bond strength in order to improve failure mitigation efforts (Zhang & Eckert, 2020; Kamali et al., 2022; Wise et al., 2023).
Tailoring Barrier Design Process to Assess Cement Integrity in CCS Wells
Authors: Siva Rama Krishna Jandhyala , Samuel J. Lewis 
Published: August 2024

ABSTRACT:
In CCS wells, the hydration products in the cement sheath can react with CO2 and alter the composition of the barrier. Therefore, cement sheath mechanical properties can change spatially and temporally. Designing an appropriate barrier should account for these changes when assessing the risk of isolation failure. The proposed design process comprises of four steps: (i) Predict the extent of alteration between CO2 and the cement sheath, (ii) Predict mechanical property changes in the cement sheath due to alteration, (iii) Determine stresses and temperatures in the modified cement sheath due to CCS loads, and (iv) Assess the risk of cement sheath failure. The extent of alteration and mechanical property (compressive strength, tensile strength, Young's modulus, and Poisson's ratio) models are developed using micro-CT and destructive mechanical testing data generated on CO2 exposed cement systems. The test matrix consisted of more than ten cement compositions encompassing neat cement and reduced Portland designs exposed to a wide range of temperature, pressure and CO2 state (Dry vs. Wet vs. Carbonic) for seven days to seven months. These systems used a variety of Pozzolanic materials and additives. The models in the proposed design method incorporates variables describing composition and exposure conditions. Consequently, this vital tool enables tailoring cement compositions to minimize risk of loss in cement sheath integrity.

1. INTRODUCTION
Well construction and operation will invariably cause changes in the near wellbore (NWB) temperatures, pore pressures and three-dimensional stress state. These changes govern the risk of cement sheath failure after successful placement. For many years, the oil and gas industry has successfully relied on design tools (Bosma et al. (1999), Thiercelin et al. (1997), Onaisi et al. (2017), Bois et al. (2015)) to quantify and mitigate the cement sheath failure risk posed by well construction and operation loads. Risk mitigation is attained through the process of tailoring cement composition in the laboratory until its thermo-mechanical properties meet the recommendations from the design tool. These design tools generally model the cement sheath as a material with constant thermo-mechanical properties. In case of carbon capture and sequestration (CCS) wells, the injected CO2 undergoes a time and space dependent reaction with the hydration products in Portland cement. These reactions cause time and space dependent changes to cement's thermo-mechanical properties. Tools that do not account for these changes can mislead a design engineer trying to tailor cement composition for the purpose of NWB integrity.
Tunnel Interaction in Low-Permeability, Squeezing Ground
Authors: Nordas A. N. , Leone T. , Anagnostou G. 
Published: August 2024

ABSTRACT:
Tunnelling through squeezing ground may induce deformations and stress redistributions in a large area, thereby affecting the later construction of neighbouring underground structures. In general, the tunnelling-induced stress redistributions cause the surrounding ground to experience plastic yielding, which may be unfavourable for a later constructed tunnel. In low-permeability, water-bearing ground, however, tunnel excavation additionally induces pore pressure relief over an extensive area, wherein the effective stresses and the undrained shear strength increase, thereby generating more favourable conditions for later works – an effect analogous to advance drainage. Considering the example of two parallel tunnels, constructed consecutively with a shielded tunnel boring machine (TBM), the present paper numerically evaluates the effect of the first on the later excavated, second tunnel in the cases of dry and water-bearing, squeezing ground. The investigations demonstrate radically different effects. In dry ground, the interaction between the two tunnels is minor. Conversely, in low-permeability water-bearing ground, the consolidation preceding the second tunnel excavation leads to a remarkable reduction (even up to 90%) in the rock pressure developing on the TBM shield, and thus also in the required thrust force to overcome shield skin friction.

1. INTRODUCTION
The term "squeezing" in tunnelling refers to the phenomenon of large rock deformations or, equivalently, the development of large rock pressures on the tunnel support that hinders said deformations. Although squeezing may manifest itself rapidly upon tunnel excavation, in most cases it is markedly time-dependent due to rheological processes (creep) or consolidation processes in the case of saturated, low-permeability ground (Barla 2001; Anagnostou and Kovári 2005; Anagnostou 2007).
The tunnelling-induced deformations and stress redistributions in squeezing ground may be substantial and affect an extensive area, and thus also other existing or planned underground structures within it. In the case of a twin tunnel, for example, the excavation of the 1st tube may affect the stress field at the location of the subsequently excavated 2nd tube, and hence the rock deformations during its construction and the rock pressure on its support. And vice versa, the later construction of the 2nd tube may affect the rock pressure acting upon the lining of the 1st tube.
Experimental Investigation of CO2-Brine Simultaneous and Alternate Injection: Implications for Geomechanics and CO2 Storage Capacity
Authors: Eyitayo S. , Watson M. , Ispas I. , Kolawole O. , Moronkeji D. 
Published: August 2024

ABSTRACT:
To enhance carbon management, the study investigates water-alternating gas (WAG) injection for carbon dioxide (CO2) sequestration in saline aquifers, focusing on its impact on storage capacity. Utilizing core flooding experiments with Gray Berea sandstone and Indiana Limestones at 2500psia confining pressure and CO2 injection at 1100 psi and 100°F to maintain CO2 in a supercritical state, the research compared Continuous CO2 Injection (CCI) and Simultaneous or Alternate Injection of CO2 and Brine (SAI). Findings indicate that CCI and SAI are more favorable regarding increasing storage capacity with SAI, showing a 7.8% porosity increase in sandstone and 11.3% in limestone. However, there is a higher increase in permeability in the case of CCI, which could lead to a higher risk of leakages. SAI demonstrated lower overpressure, suggesting more CO2 can be stored relative to CCI, efficient plume management and enhanced fluid displacement through residual and mineral trapping. This study shows SAI's potential in CO2 sequestration projects, offering insights into brine-assisted strategies for improved storage capacities.

1. INTRODUCTION
The escalating levels of atmospheric carbon dioxide (CO2), primarily attributed to fossil fuel combustion and industrial processes, are a significant driver of global climate change (Mouli-Castillo et al., 2021; Tang et al., 2021). This phenomenon poses unprecedented challenges, including extreme weather events, rising sea levels, and detrimental impacts on biodiversity (Hanaoka and Masui, 2020; Napp et al., 2019; United Nations, 2015). In response, CO2 sequestration—capturing and storing atmospheric CO2—has emerged as a pivotal strategy in the global effort to mitigate climate change (Hepburn et al., 2019; Mac Dowell et al., 2017; Zhang et al., 2017). Among the various sequestration techniques, the injection of CO2 into deep geological formations holds promise due to its potential for large-scale storage and the additional benefit of enhancing oil recovery in depleted reservoirs (Global CCS Institute, 2016).
Water-alternating gas (WAG) injection is a mature technology developed to improve hydrocarbon reservoirs' oil recovery rates (Afzali et al., 2018; Christensen et al., 2001; Khoshsima et al., 2023). This technique involves the sequential injection of water and gas to maintain reservoir pressure and improve sweep efficiency, thereby maximizing oil extraction production (Aleidan, 2010; AlRassas et al., 2022; Caudle and Dyes, 1958; Rogers and Grigg, 2001; Stephenson et al., 1993; Walker and Turner, 1967; Wang et al., 2023). Given its success in the oil and gas industry, applying WAG injection principles to CO2 storage presents an intriguing opportunity. By alternating between CO2 and water injections, WAG could optimize CO2 storage efficiency, minimize environmental risks, and potentially enhance the integrity of the storage formation.
Characterization of Non-Uniform Propped Fractures and Critical Aperture Strain Caused by the Stresses in Conglomerate Reservoir
Authors: Du Buge , Zhang Guangqing , Wang Xiaohan , Xu Changzhuo , Liu Kaixin 
Published: August 2024

ABSTRACT:
The conglomerate reservoir is strongly heterogeneous, causing the hydraulic fracture to be tortuous and complex; there are many factors controlling the closure behavior of propped fractures caused by in-situ stress. However, the API conductivity cell can merely measure the average fracture aperture, the closure behavior of actual propped fractures is incompatible and non-uniform. In this study, three modes of propped fracture aperture variation are proposed, and a definition of "critical aperture strain" is given to analyze the mechanism further. The non-uniform propped fracture aperture strain was confirmed by monitoring a large-size fracture (length &gt;20 cm) aperture using Digital Image Correlation (DIC), caused by the fact that local lithofacies composition and undulation angle affect proppant embedment, deformation, and crushing. Moreover, the lithofacies composition plays a significant role, and local propped fractures propagating around large gravels will be closed more seriously. The maximum aperture stain calculated by the elastic contact model is the critical aperture strain, and the local aperture strain higher than it will significantly reduce the overall permeability of hydraulic fractures. Results show that the fracturing design in conglomerate reservoirs should include lithofacies characteristics, and increasing proppant strength may inhibit the decline of the fracture conductivity. It is also necessary to predict the fracture geometry to evaluate the prop procedure.

1. INTRODUCTION
Hydraulic fracturing is an important stimulation for enhancing oil and gas production. Fractures induced improve effectively flow conductivity of hydrocarbon from the reservoir to the wellbore (Tang et al., 2018 & Maziar et al., 2018). To avoid fractures from being completely closed caused by in-situ stress, proppants (sand, ceramic particles) are added to prop fractures (Bandara et al., 2019 & Wu et al., 2022). Propped fractures will be compressed under stress conditions, resulting in reduced aperture and conductivity, which is one of the main factors contributing to production decline (Bandara et al., 2021). Therefore, it is necessary to research and effectively predict the fracture aperture to guide fracturing in fields (Voltolini eta al., 2020).
Numerical Study on Influencing Factors of Breakdown Pressure in Perforated Horizontal Wells in the Mahu Tight Reservoir
Authors: Jia Wenting , Mou Jianye , Li Xiaowei , Zhang Shicheng , Wang Lifeng , Xu Yajun 
Published: August 2024

ABSTRACT:
In this paper, a numerical method was used to study how breakdown pressure varies with different factors and how to lower the breakdown pressure in hydraulic fracturing of perforated horizontal wells in the Mahu tight reservoir. The research shows that the breakdown pressure is the lowest with a perforation angle of 0° relative to the maximum horizontal principal stress. When the perforation depth varies between 5 cm and 33 cm, the breakdown pressure decreases remarkably with depth increase. The diameter beyond 12 mm of the perforation hole has a small impact. The acid pretreatment has a significant influence on the breakdown pressure. The acid-rock reaction dissolves the minerals, significantly increasing the porosity and permeability of the rock and reducing the tensile strength of the formation so it can effectively reduce the breakdown pressure. The quality of cementing also has an impact on the breakdown pressure. High cementing quality increases the difficulty of initiation. The breakdown pressure can be lowered by reasonably optimizing parameters up to 11 MPa.

1. INTRODUCTION
The Mahu Oilfield in Xinjiang, China, was discovered in 2017. It has one billion tons of reserves and contains rich oil and gas resources (Qin et al., 2023). The tight reservoirs in the Mahu depression have low porosity and permeability, with poor physical properties and undeveloped natural fractures (Zhuo et al., 2023). Due to the high breakdown pressure in hydraulic fracturing of perforated horizontal wells in the Mahu tight reservoir, significant difficulties are increased in the fracturing treatment (Zhang et al., 2023). Many scholars have investigated the influencing factors of formation breakdown pressure through theoretical, physical experiments and numerical simulation.
Regarding theoretical research, Li conducted a theoretical analysis to calculate breakdown pressure for horizontal wells based on elastic mechanics and tensile strength theory (Li, 2009). Recent years have witnessed a spurt of progress in computational mechanics; numerical simulation techniques have gradually been implemented in the investigation of fracture initiation mechanisms and breakdown pressure. Li et al. used finite element numerical simulation technology to analyze the influence of perforation parameters on breakdown pressure (Li et al., 2009). Zhu et al. analyzed and predicted the factors that affect the breakdown pressure under oriented perforation conditions (Zhu et al., 2014). Jia et al. studied the effects of different perforation and acid pretreatment parameters on breakdown pressure using natural outcrops excavated from the Mahu sag through an experimental method (Jia et al., 2023). However, what are the main factors affecting the breakdown pressure and the technology that lowers the breakdown pressure under perforation conditions against the Mahu tight reservoir is still a current research hot spot and aporia.