bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Photogrammetric Rockfall Database and Analysis of Trends at a Rock Slope Along I-70W, West of Idaho Springs, CO
Authors: Hollander J. A. , Walton G. , Kromer R.
Published: August 2024

Rockfall along roads can cause significant hazards to human health and infrastructure or interrupt transportation. A section of rock slope on Interstate 70 west, west of Idaho Springs, has been monitored at a daily frequency since March 2018 using a 5-camera photogrammetric system that collects high-definition photos to establish the rockfall MCF trends. An established semi-automated workflow was utilized to produce raw 3D point clouds and locate areas of potential rockfall using change detection. The high frequency of monitoring at this site allows for precise determination of timing and volume of rockfalls and creation of a high temporal resolution database. This database can then be leveraged to analyze trends in rockfall volume and frequency on an annual or seasonal basis. We provide an overview of the workflow applied for database development as well as preliminary results regarding interpretations of variations in rockfall activity.

1. INTRODUCTION

According to the US Census Bureau (2023) the US population has expanded from 151 million in 1950 to 331 million in 2020. This growth in population has led to an increased demand for previously undeveloped land, including in relatively hazardous mountainous regions (Thornton et al., 2022). Mountainous regions are prone to rockfall and other geohazards that can have serious repercussions on human infrastructure and health (Abellán et al., 2010; Copons and Vilaplana, 2008; Dussauge et al., 2002). The Colorado Department of Transportation (CDOT) is particularly interested in understanding rockfall trends along critical transportation routes in the mountains.

Rockfall can be described as a type of mass wasting event where an individual rock or multiple rock fragments detach from a slope and travel downhill (Cruden and Varnes, 1996; Varnes, 1978). Rockfall generally occurs when blocks detach along existing discontinuities or by sliding and toppling (Hungr et al., 2014). Rockfall can be further subdivided into two categories: primary and secondary. Primary falls occur when a block detaches from the host bedrock, and secondary falls occur when previously detached blocks are moved further downslope (Luckman, 2013).

A commonly investigated aspect of rockfall is the mechanism of its triggering and any seasonal trends a site might exhibit. Numerous studies have shown rockfall frequency to follow seasonal trends, likely controlled by weather conditions (Delonca et al., 2014; Matsuoka and Sakai, 1999). The importance of certain conditioning and triggering mechanisms that might be more prevalent in certain seasons can greatly influence these relationships (Krautblatter and Dikau, 2007).
Enhanced Geothermal Site Characterization Using Generative Adversarial Network and Ensemble Method
Authors: Bao Jichao , Lee Jonghyun , Yoon Hongkyu
Published: August 2024

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

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

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

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

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

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

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 >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

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.
Coupled Wellbore-Reservoir-Geomechanics Modeling of Parent Well Depletion-Induced Stress Evolutions and Their Potential Impact on Infill Well Fracturing
Authors: Guo Xuyang , Jin Yan , Chen Mian , Song Hongwei
Published: August 2024

Parent well depletion in shale oil reservoirs leads to in-situ stress changes, consequently altering infill well fracturing quality. Parent well depletion-induced responses are often modeled by coupled flow and geomechanics where the effect of wellbore flow is not thoroughly considered. This study introduces a coupled wellbore-reservoir-geomechanics model considering the wellbore flow. Both system responses in the reservoir and in the wellbore are quantified. Results show that considering the wellbore flow can improve the comprehensiveness of the modeling scheme. The non-uniform productivity distribution among perforations and its relationship with the coupled flow and geomechanical response are documented. The effect of wellbore flow becomes greater as the scale of the problem increases, and the synthetic field scenario has a more significant wellbore flow impact on geomechanics. This work proposes a coupled wellbore-reservoir-geomechanics model that considers the mass conservation and fluid flow in both the wellbore and the reservoir. It specifically quantifies the effect of the oil rate competition between parent well fracture clusters.

1. INTRODUCTION

Infill well drilling and hydraulic fracturing have become a key strategy in the development of shale oil reservoirs since the combination of parent and infill wells can help to improve the estimated ultimate recovery (Lindsay et al. 2018). Infill wells are often drilled and completed later than parent wells, and the pressure and in-situ stress fields for infill wells fracturing can be rather different from parent wells. Since the hydraulic fracturing quality is often governed by the pressure and stress states, the reliable and accurate prediction and modeling of the stress state changes in infill zones and at candidate infill well drilling locations become very relevant (Kurtoglu and Salman 2015; Zhi et al. 2021 Chen et al. 2021). Pressure drops, stress magnitude changes, and stress orientation changes in infill zones should all be evaluated before infill well completion designs are made. If infill well fracturing parameters are not carefully determined, negative outcomes such as productivity decrease, well control problems, casing damage, and loss of wells can be obtained (Morales et al. 2016; Jacobs 2017; Rainbolt and Esco 2018).
Geomechanical Practices in Developing Open-Pit Slopes at Kinross Gold
Authors: Ran Jerry J.
Published: August 2024

Open-pit slope instabilities may lead to personnel injuries and/or equipment damages in some cases. However, in most cases, these events require mitigation measures like step-outs, unloading, buttressing and local slope flattening with potential impact on mine production in short or long term.

Noncompliance with slope design criteria, which may be a contributing factor in slope instability, potentially creates an unsafe working environment and has a negative impact on mine performance.

Achieving an optimized balance between open-pit slope performance and financial objectives is the goal of many corporate risk management systems in the mining industry. The basis for a practical and achievable slope design is a reliable geomechanical model. Application of this model and slope design acceptance criteria leads to selection of slope design parameters that derive from various geomechanical analyses and numerical modeling, and this process reflects the risk tolerance level of the project or operation owner. In the mine production stage, i.e., implementation of the slope design, operational controls in drilling and blasting, bench face cleaning and visual and instrumentation monitoring play a key role in achieving the recommended slope design.

Building the geomechanical model and subsequent slope design normally start with data collection by launching a drilling and testing program with or without outcrop or exposed bench mapping. As mining progresses, the initial slope design is updated based on actual slope performance and data collected through ongoing programs, for instance, physical and image mapping.

Hydrogeological input to slope stability analysis is critical in many cases particularly in weak rock masses. Input data normally come from non-mining functional groups in early stages of a project or mine operation. This practice may create slope performance issues in the design implementation phase.

This presentation discusses topics described above with examples from Kinross mines. The intention is to draw discussions from peers, initiate ideas in research and development, and help practitioners learn from industry cases.
Evolution of Proppant Embedment and its Impact on Shale Permeability
Authors: Qian Sijin , Lu Mingyuan , Li Jimmy Xuekai , Huang Yixiao , Chen Zhongwei , Shen Luming
Published: August 2024

Hydraulic fracturing is important for modern gas extraction. However, the proppant embedment affects gas recovery significantly. This study investigates the impact of proppant embedment on permeability over time in shale reservoirs. The study utilized a series of experiments to determine the impact of proppant embedment on permeability over time and designed new methods to induce long-term proppant embedment in proppant-supported fractures. The results showed that the permeability loss after 8 weeks of compression ranges from 4.38 to 6.44 mD, and the percentage ranges from 6.74 to 8.89%. The study also found that the average proppant embedment depth reaches 87.96 μm after 8 weeks compression. The correlation between embedment depth and compression day can be suitably modeled with a logarithmic function. These findings can help optimize production in shale reservoirs by providing a better understanding of proppant embedment and its impact on gas recovery.

1. INTRODUCTION

Hydraulic fracturing is a vital technique to increase the gas production from unconventional reservoirs, which are characterized by low permeability and porosity such as shale and coal seam. This technique creates a network of fractures in the formation, which increases the production rate of natural gas. Due to the high closing stress underground, proppants, typically sands and ceramic grains, are also mixed with the fracking fluid and pumped into the fracture to prevent the fracture from closing and allow gas to pass through the fracture continually. However, the fracture still trends to close over time due to some behaviors in the formation such as proppant flow back (Chuprakov et al., 2020; Hu et al., 2014; Murphey et al., 1989; Parker et al., 1999), proppant fines generation and migration (Kong et al., 2023; Pan et al., 2018; Wang et al., 2020), proppant crush resistance (Liang et al., 2015; Liang et al., 2016; Stephens et al., 2006; Zheng et al., 2018) and proppant embedment (Ghanizadeh et al., 2016; Huang et al., 2019; Liu et al., 2021).
Solids Production Geomechanical Evaluation in a Fractured/Vuggy Carbonate Reservoir from Abu Dhabi Offshore Field: Postmortem Analysis and Advanced Finite Element Simulations
Authors: Pourpak Hamid , Su Kun , Bikong Christian , Rammal Hadi , Bigno Yann , Xi Guifen , Kheidri Hamza , Bere Adam , Kato Jun
Published: August 2024

Solids production can happen in carbonate rocks even with high strength matrix, because of presence of natural fractures and vuggy or weak zones. Solids production is known to be a common factor in many oil and gas producing wells in carbonate reservoirs both at the early production period but also in later life of a reservoir under depleted conditions. In this paper, we present a real case study performed on a carbonate reservoir located in Abu Dhabi Offshore Field. The production of carbonate debris was observed in a 900m horizontal well completed as barefoot in Arab limestone formation which is a gas bearing reservoir on the area of study and is characterized by natural fractures and weak zones. Anomalous well head flowing pressure (WHFP) behavior and progressive reduce of gas rate were observed with choke fully open and the choke was found partially plugged by debris of centimetric size. The study goal was to investigate whether the solids production experienced was a result of the geomechanical behavior of the rock and fractures during production and to propose mitigations for future wells in terms of completion option and critical drawdown pressure (CDP). This solids production modeling study gave helpful insights regarding the mechanisms of solid production in open hole and cased/perforated wells for the studied carbonate formation. It could also guide the choice of completion and help the solid management decisions for the development of such carbonate reservoirs.

1. INTRODUCTION

Solids production can happen from poorly consolidated carbonate rocks or even in high strength but naturally fractured vuggy carbonates including weak zones. The risk of solids production from carbonate rocks or mitigations of the risks have been discussed in recent literatures (Asadi et al, 2017, AL-Aamri et al, 2020, Ghazali et al, 2020). Solid production is a common factor in many wells in carbonates rocks (oil and gas) during production stages and especially in the later life of a reservoir under depletion conditions (Asadi et al, 2017). Clusters of cemented grains of the formation can be produced together with oil, gas, and water and these could have highly damaging effects on completion equipment, tubing, pipes, valves, and other facilities. Solids production is generally caused by mechanical failure of near wellbore formations due to effective stresses acting on borehole walls, and perforations under drawdown and well flowing conditions exceeding the mechanical strength of reservoir rocks (Asadi et al, 2017).
Seismic Risk Management Practices at Vale's Sudbury Operations
Authors: Yao M. , Landry D.
Published: August 2024

Vale Base Metals has been operating many underground mines in the Sudbury Basin for over a century and all mines have experienced a significant increase in the number of major seismic events over the last decade. Various mitigation strategies have been developed at Vale's North Atlantic Operations in Ontario to manage and control the risks associated with seismicity and rockbursts. The mines have seen a significant increase in the number of large seismic events, but the overall trend of rockbursts is decreasing. This paper will focus on Seismic Risk Management Strategies developed over the last decade, including both strategic and tactical control measures. Examples will be given in the paper to demonstrate the effectiveness of control measures over the last decade. Recent developments in Seismic Hazard Assessment for burst prone ground conditions are also presented in this paper. Although the strategies presented in this paper can be applied to other deep hard rock underground mine operations that face similar challenges with burst-prone ground conditions, they should be applied with caution and tailored for site specific conditions.

1. INTRODUCTION

Vale Base Metals has operated several underground mines in Sudbury for over a century, and currently five mines are active (Coleman, Creighton, Copper Cliff, Garson, and Totten Mines). Numerous mining methods have been employed including cut and fill, post pillar cut and fill, and sub-level caving, however, currently the primary mining method employed is open stoping.

The primary rock mechanics challenge at these operations is seismicity and rock bursting. Figure 1 shows a recent rockburst at one of the mines which was associated with a large seismic event.

Seismicity has been observed to be primarily linked with:

• Late stage of extraction: sill and diminishing pillars

• Brittle and high strength rocks (UCShost > 200 MPa)

• Mining depths between 1.5 and 2.5 km below surface

• Lack of confinement due to higher extraction ratio

• Presence of seismically active geological structures

A Seismic Risk Management Plan is an important element at any seismically active mine and is also a legal requirement in some mining jurisdictions. The following main items are key requirements:

• Responsibilities

• Microseismic Monitoring & Data Analysis

• Seismic Hazard Assessments

• Hazard Mitigation Plans/Strategies

• Training

This paper will focus on two key requirements described above: Hazard Mitigation Strategies and Seismic Hazard Assessments.
3DEC Modelling Exploration of Residual Stress Mechanisms
Authors: Trzop M. , Corkum A. G.
Published: August 2024

Residual stress exists as a natural phenomenon found in situ and as a by-product of creation for certain man-made materials. An early implication for residual stresses was illustrated with Prince Rupert's drops where, due to induced compressive residual stress magnitudes the material strength is effectively increased. Residual stress exists in a state of equilibrium with their own internal forces, and as a result are often omitted from stress considerations for design but we believe that these stresses may impact the mechanical behaviour. The purpose of this study was to include residual stresses in modelled specimens of rock to investigate the potential for damage to be present as a result of their redistribution. Residual stresses were formed under load, and once present the specimen was unloaded and damage was quantified through the number of broken subcontacts within the model. Compression tests were then performed on the damaged specimens to investigate the presence of crack closure strains as a result of the produced damage. It was shown that residual stresses can produce damage, and such damage also can produce crack closure strains.

1. INTRODUCTION

Residual stresses exist as a natural phenomenon found in situ and as a byproduct of formation for certain man-made materials. The state of residual stress contains both compressive and tensile stress magnitudes which allows for the residual stress field to reach a state of equilibrium independently from external pressures. As a result of this self-equilibrating nature, residual stresses are often overlooked as they exist separately from both in situ stress and excavation-induced stresses. However, if a residual stress field is disturbed (e.g., fracture formation), the stresses will mobilize in an attempt to reach a new state of equilibrium and will accompany a measurable strain. Although these stresses exist separately from other common stresses, it is important to understand their existence as they may have consequential impacts if not properly understood. An example of this in steel is the case of the split I-beam (Nau, 2015) where due to casting, residual stresses were created within the beam. Once fully hardened the beam was cut at an angle on both ends which disturbed the state of equilibrium and caused a redistribution of the residual stresses. As a result of their redistribution, the I-beam fully split through the web which then destroyed the beam.
A Play-Agnostic Thermo-Poro-Hydro-Mechanical Approximation for Hydraulic Fracture Initiation: Insights on Stress Distortions Between the Wellbore and a Perforation Tunnel
Authors: Bouabdallah Nassim , Michael Andreas
Published: August 2024

Predicting near-wellbore hydraulic fracture (HF) orientation is crucial for designing stimulation treatments. This work proposes a physics-based approach to determine the orientation of HF initiation considering formation breakdown pressure (FBP) and key geomechanical parameters. A novel closed-form pseudo three-dimensional (3D) approximation captures thermal, poroelastic, hydraulic, and mechanical effects (TPHM), visualizing the stress distortion at the intersection between the wellbore and a perforation tunnel. While specific formations like the Bakken Shale may present unique challenges, the proposed approach transcends such limitations. The play-agnostic TPHM model allows the identification of favorable conditions for transverse HFs across diverse geological settings and wellbore pressure regimes. This empowers engineers to manipulate controllable parameters, such as wellbore pressure and perforation design, to optimize stimulation treatments in various formations, ultimately maximizing well productivity. By promoting favorable HF initiation and early propagation, this approach has the potential to reduce completion issues, enhance well performance, and contribute to a more efficient and sustainable approach to the development of unconventional reservoirs.

1. INTRODUCTION

A number of analytical attempts were made to describe HF initiation from perforated wells. Common to all are two-dimensional (2D) analytical expressions of elasticity relationships, solving the stresses on the wellbore walls. While these models are elegant closed-form expressions of the HF initiation and are particularly useful in practical HF design, they do not consider the presence of perforation tunnels intersecting the wellbore.

Economides et al. (1989) described the stimulation of horizontal wells and the criteria for the decision between longitudinal (axial to the wellbore) and transverse (orthogonal to the wellbore) HFs, as displayed on Fig. 1. Multiple transverse-HF initiations from horizontal wells is the desired outcome of modern-day reservoir stimulation operations. This is despite that in a transverse HF, the flow regime from the reservoir into the HF is linear, while the flow inside the HF is radial, resulting in a pressure drop that contributes to the well's skin. Being able to "stack" multiple transverse HFs near each other in shales will outperform a gigantic longitudinal HF, which is the inadvertent outcome of multiple longitudinal-HF initiations from a horizontal well's lateral.
Correlation of Static and Dynamic Mechanical Properties of Australian Sedimentary Rocks
Authors: Li Jimmy Xuekai , Chen Shuai , Qin Sijin , Flottmann Thomas , Huang Yixiao , Saber Erfan , Chen Zhongwei
Published: August 2024

This paper presents a comprehensive analysis of the correlation between static and dynamic mechanical properties of sedimentary rocks from Australian basins. By leveraging both empirical and machine learning techniques, we provide valuable insights into the predictive capabilities of different methodologies and identify the most effective approaches for capturing the intricate relationships within the dataset. The results of our study reveal that several machine learning methods consistently outperform empirical approaches, yielding lower error values and providing more accurate predictions of the correlation between static and dynamic properties. Furthermore, we rank these machine learning methods based on their respective error values, offering insights into the relative performance of each algorithm. Our findings not only advance our understanding of sedimentary rock mechanics but also offer practical recommendations for improving reservoir characterization, enhancing geotechnical assessments, and optimizing engineering design.

1. INTRODUCTION

Sedimentary rocks are integral components of the Earth's crust, encompassing a vast array of lithological compositions, depositional environments, and geologic histories (Miall, 2013; Milliken, 2014). Their mechanical properties play a critical role in various engineering and geotechnical applications, including reservoir characterization, wellbore stability assessment, and underground mining design (Abdollahipour et al., 2019; Ghassemi, 2012; Li et al., 2022; Li et al., 2023; Zhong et al., 2021). Understanding the relationship between the static and dynamic mechanical properties of sedimentary rocks is fundamental for accurately predicting their behavior under different loading conditions and is also crucial for interpreting subsurface geology, predicting reservoir behavior, and designing resilient infrastructure (Chang et al., 2006; Sone & Zoback, 2013; Wang et al., 2016).

The Australian continent hosts a diverse range of sedimentary basins, each with unique depositional settings and rock types (Huston et al., 2016; Jaireth et al., 2014; Jaques et al., 2002). These basins offer an excellent opportunity to investigate the correlation between static and dynamic mechanical properties across different geological contexts. Despite the significance of such correlations, comprehensive studies addressing this relationship in the Australian sedimentary basins are limited.
Generation of Micro-Fracture Clouds in Rocks: Mechanisms and Applications
Authors: Mutlu U. , Boitnott G. , Lisjak A. , Mahabadi O. , Sherizadeh T. , Guner D. , Nowak S. , Ghassemi A.
Published: August 2024

Volume increasing or decreasing processes in rocks can lead to inter or intragranular fractures in subsurface formations. The volume change can be caused by chemical reactions involving fluid, reactive transport, and coupling with the mechanical deformation of the grains. Depending on stress, material properties and coupled thermo-hydro-mechanical-chemical (THMC) conditions, grain scale fractures may propagate and coalesce, forming a cloud of well-connected fracture networks. The mechanisms responsible for propagation, coalescence and inhibition of cloud fractures are not well known. In this study, we review coupled micro-fracture network generation mechanisms as published in the literature and observed in field, experiments, and models. We then introduce simple (decoupled or weakly coupled) models within the framework of analytical and hybrid finite-discrete element models (FDEM). We discuss key parameters that promote (or limit) the generation of micro-fracture clouds under in-situ conditions. Based on the review of literature and preliminary model results, we discuss the implications of micro-fracture generation mechanisms on subsurface storage, hydrogen exploration/production and super-hot supercritical geothermal technologies.

1. INTRODUCTION

Rock deformation and fracturing characteristics under high temperature and pressure (HTHP) conditions are of fundamental significance to emerging subsurface engineering technologies such as super-hot supercritical thermal resources, hydrogen and CO2 storage, and geologic hydrogen production. To unlock the full potential of these applications, it is important to fundamentally understand the fracture initiation, propagation, coalescence and resulting permeability alteration processes and be able to model them at different scales (grain to wellbore to reservoir scale) within the framework of Thermo-Hydro-Mechanical-Chemical (THMC) coupled HTHP systems.

For example, serpentinization is a THMC coupled process that occurs when mafic and ultra-mafic rocks come in to contact with water at specific pressure-temperature conditions to produce hydrogen. This reaction can lead to a significant volume increase, swelling pressures and associated micro-fracture clouds: which in turn can generate additional permeability pathways for flow. Continuous flow of water and mineralization can lead to favorable conditions for a self-driven micro-fracture network, as this process can repeat in a loop: creating a progressive change in host rock permeability.