bluuebunny/crossref_metadata_2025_split huggingface dataset:
Detecting and Characterizing Fluid Leakage Through Wellbore Flaws Using Fiber-Optic Distributed Acoustic Sensing
Authors: Anwar Ishtiaque , Carey Bill , Johnson Paul , Donahue Carly 
Published: September 2022

ABSTRACT:
A primary concern associated with the utilization of subsurface systems is that there may be pathways for fluid leakage from the resource storage, or disposal reservoir. Leakage of any fluid can contaminate groundwater, cause geo-environmental pollution, generate hazardous surface conditions, and potentially compromise the functionality of the subsurface system. A low-cost, innovative technique to detect and characterize fracture leakage that is functional over many years is needed for applications such as geothermal reservoirs, CO2 sequestration wells, deep borehole storage of nuclear waste, and strategic petroleum reserve caverns. In this experimental study, we investigate the use of fiber-optic distributed acoustic sensing (DAS) to measure dynamic strain changes caused by acoustic signals induced by fluid flow with an eventual goal of developing instrumentation and analytical techniques to detect and characterize the movement of fluids through leaky wellbores. In the first phase of the experiments reported here, we conducted fluid flow tests in a porous medium as an analog to a fracture filled with comminuted material. The measured effective permeability is then compared with the signals generated by the fiber-optic cable. The study indicated that acoustic signals generated from fluid flow through porous media could be effectively captured by the fiber-optic cable DAS technology.

1. INTRODUCTION
Wellbores are used for gaining access to various subsurface systems such as underground fluid reserve (Miyazaki, 2009), CO2 sequestration (Watson and Bachu, 2008; Zhang and Bachu, 2011), geothermal energy development (Shadravan, Ghasemi, & Alfi, 2015), waste disposal, oil and gas exploration (Davies et al., 2014), etc. A primary concern associated with the utilization of subsurface systems is that there may be pathways for fluid leakage from the resource storage, or disposal reservoir through the wellbore flaws. Leakage of any fluid from a leaky wellbore can contaminate groundwater, cause geo-environmental pollution (Davies et al., 2014; Ingraffea, Wells, Santoro, & Shonkoff, 2014; Jackson, 2014), generate hazardous surface conditions, and potentially compromise the functionality of the subsurface system (Gasda, Celia, Wang, & Duguid, 2013). Researchers has identified different potential leakage pathways, including fractures in the cement or micro annuli from de-bonding at the cement-casing or cement-formation interface (Celia, Bachu, Nordbotten, Gasda, & Dahle, 2005; Theresa L Watson & Bachu, 2009) or the casing corrosion product (Anwar, Chojnicki, Bettin, Taha, & Stormont, 2019; Beltrán-Jiménez et al., 2021).
Microbially Induced Calcite Precipitation for Sealing Anhydrite Fractures with Gouges
Authors: Sang Guijie , Lunn Rebecca J. , Minto James M. , El Mountassir Grainne 
Published: September 2022

ABSTRACT:
Caprock formation forms a natural barrier for geological storage of CO2, nuclear wastes, and hydrocarbon resources. Fault and natural/artificial fractures that crosscut the storage systems represent potential leakage pathways. Sealing of caprock fractures/faults is of great importance to ensure its long-term sealing integrity. In this study, we conduct microbial-induced-calcite-precipitation (MICP) experiments for sealing anhydrite fractures (artificially cut) with gouges. MICP involves a bio-chemical reaction for calcite precipitation using ureolytic microorganism – Sporosarcina pasteurii. The precipitated calcite, which occurs initially from finer pores to larger pores, induces a 10.7% decrease of porosity inside the fracture after the 1st 12 cycles of MICP treatment. After 18-21 cycles of MICP treatment, the fracture permeability of the two fractured core samples effectively decreases by 2-3 orders of magnitude. Our study also indicates that the MICP sealing efficiency could be improved by lowering the injection rate, optimizing fluid chemistry for a better bacteria retention inside the fracture. The study provides a baseline for using MICP technique to seal anhydrite fractures.

1. INTRODUCTION
Caprocks with very low permeability and ultra-fine pores, consisting of massive consolidated clay-rich sediments (shale) and evaporites such as anhydrite and halite, create natural barriers for hydrocarbon resources, CO2 sequestration, disposal of radioactive wastes, hydrogen storage, etc. However, natural fractures/faults or injection-induced fractures that crosscut subsurface storage systems (Figure 1) could provide potential leakage pathways 1,2. Seeking an efficient technique to seal caprock fractures is crucial.
Microbially induced calcite precipitation (MICP) has been considered as an environmentally sustainable grouting technology for soil improvement 3,4, fracture sealing 5-8, removal of contaminants in ground water 9,10, among others. It has several advantages over conventional cement grouting methods, including (1) the low viscosity of the bacterial solution and cementing solution (urea and calcium chloride), which allows to penetrate with relatively low pumping power; (2) micron-size microbes for sealing fine pores and fractures; and (3) potential low carbon footprint. MICP is a naturally occurring metabolic phenomenon that can be found in soil and marine environment 11. This bio-inspired grouting technique also have advantages over conventional chemical grouting method (such as acrylates, acrylamides, and polyurethanes, etc.) due to its lower cost of the raw materials and less toxicity to the environment 12.
Comparison of Measured and Modeled Casing Deformations of a Test Well in a Longwall Abutment Pillar
Authors: Zhang Peter , Su Daniel , Kim Bo Hyun , Midler Evan 
Published: September 2022

ABSTRACT:
Shale gas wells in longwall abutment pillars are subjected to longwall-induced ground movements, and their stability has been a safety concern for both the mining and gas industries. To understand the impact of longwall mining on the stability of gas wells in longwall abutment pillars, a test well was drilled in a longwall pillar between two adjacent longwall panels to measure longwall-induced deformations in the casing as the two longwall panels on either side were retreated. The longwall panels extracted the Pittsburgh coal seam under a depth of 177 m and were developed with a 3-entry system with 52-m-wide chain pillars and 366-m-wide panels. Casing deformations induced by longwall mining were measured by 60-arm caliper logging and observed with a downhole camera. A FLAC3D model was set up to predict longwall-induced stresses and deformations in the test well casing. The model was validated with measured surface subsidence and longwall-induced pillar pressure. Both measurements and numerical modeling showed that the casing deformed because of relative displacements along distinct weak rock interfaces. Casing deformations at the weak claystone interfaces were found to be confined within the claystone layers. In this case, casing deformations occurred at the same locations with both first and second panel mining. Second panel mining caused additional deformations as the relative horizontal displacements along the interfaces shifted in the opposite direction. The FLAC3D model proved to be capable of predicting the locations and magnitudes of casing deformations with reasonable accuracy.

1. INTRODUCTION
When gas wells penetrate through coal seams in the vicinity of longwall gob, they are subjected to longwall-induced subsurface movements, and casing deformations could occur at certain locations. Longwall-induced deformations in the casing could diminish casing integrity and allow high pressure gas to leak into the mine, potentially causing fires or explosions. Over the past decade, over 1,500 shale gas wells have been drilled in the coal reserves of the Pittsburgh coal seam. The influence of longwall mining on these shale gas wells will have to be evaluated as future longwall panels are mined. Therefore, it is important to understand how longwall-induced subsurface movements and stresses affect gas well casings and to develop engineering guidelines to safely mine-by these shale gas wells.
Application of Machine Learning to the Estimation of Intact Rock Strength from Core Logging Data: A Case Study at the Newcrest Cadia East Mine
Authors: Thielsen C. , Furtney J. K. , Valencia M. E. , Pierce M. , Orrego C. , Stonestreet P. , Tennant D. 
Published: September 2022

ABSTRACT:
Understanding the spatial variation in intact and defected rock strength is critical to geomechanical mine design. At the Newcrest Cadia East mine, systematic point load testing (PLT) was used to measure the strength of intact rock and individual defects (e.g., veins) at regular closely spaced intervals along several boreholes. The systematic PLT data collection covers only 1.3% of the 590 km of hole logged at Cadia East. A procedure was developed to homogenize the available geotechnical and geological logging data, infill missing values, and encode raw data into engineered features for use in a machine learning model. A random forest classifier was applied to predict point load index (Is50) from core logging data where tests were not performed. The random forest model predicts the rolling average Is50 value within 1 MPa 48% of the time. The model gives insights into which core logging quantities have the strongest controls on rock strength and provides the basis for developing more detailed geospatial models of intact and defected rock strength.

1. INTRODUCTION
Understanding the spatial variation in intact and defected rock strength is critical to many aspects of geotechnical mine design, including predicting caveability, and excavation and ground support design. At the Newcrest Cadia East mine, there are 590 kilometers of logged core. Having measurements or estimates of point load index at every meter along each core enables the production of geospatial models of rock strength for use in predictive models. While point load testing is relatively quick and inexpensive, performing point load tests at a tight spacing along 590 km of core would be costly and impractical (see ASTM, 2016 and Franklin, 1985).
Systematic point load testing (PLT) was used to measure rock strength based on guidelines provided by Pierce Engineering (Pierce, 2019; Pierce, 2020). It offers a means to quantify the variability in both intact and structural tensile strength over the largest possible volume with a minimum of bias. It involves performing diametral point load tests at strict 1-2m intervals along core from multiple boreholes and taking care to recognize both structure (which requires careful alignment of the test platens in order to test the strength of the structure itself) and pre-disturbed sections of core (which should be registered as having zero tensile strength, unless marked as an induced break). Axial tests are also conducted periodically to check for anisotropy. The testing is carried out in accordance with ISRM standards (ISRM, 1989), with careful attention paid to the maintenance of the radius of curvature on testing points to ensure a high proportion of valid tests.
Transient Inverse Analyses of Overcoring Data for Improved Stress Estimation
Authors: Valley B. 
Published: September 2022

ABSTRACT:
Overcoring is a common technique for measuring stresses in mining projects. Knowledge of the in-situ stress state is essential to ensure the stability of underground infrastructures as well as to assess the induced microseismic risk associated with deep mining operations. There are different types of overcoring probes. Some are bonded in the pilot hole with an epoxy resin and allow for 3D stress measurement (e.g. CSIRO-HI), and others are based solely on a mechanical coupling of the probe, but are limited to biaxial stress measurement (e.g. USBM). The need to glue the probe to obtain a 3D measurement limits the applicability of this technique to short boreholes because it is technically difficult to glue probes in deep boreholes. In any case, traditionally the data analysis is done only based on the final deformation obtained after overcoring. In this paper we propose to use the transient deformation response during overcoring to: (1) allow to evaluate the 3D stress field from a single biaxial overcoring measurement, and (2) add a quality control component by reproducing the entire overcoring response. The general principle of our approach is to simulate the transient response of overcoring by numerical elastic simulation. The principle of superposition is used to derive the responses for any set of parameters from a limited number of basic models and thus allows to limit the total number of model runs. Such approach allows for a systematic inversion procedure to be applied for determining the optimal parameter sets that best capture the transient response of the overcoring. This allows the estimation of a 3D stress tensor from biaxial measurements. It also allows to have a quality control on the measurements evaluating the quality of the fit between the model and the data. In this paper, we evaluate the robustness of the proposed approach by performing a systematic sensitivity analysis on the stress estimation from the inversion of transient overcoring data. We demonstrate the advantages of the approach but also its limitations. The preliminary results obtained in this study suggest that the transient overcoring response contains sufficient information for constraining efficiently the 3D stress tensor. The inversion must be performed using multiple starting point, and the mode of the obtained calibrated parameters is in close adequacy with expected values, while some outliers can be present in the calibrated set. Further work is required for confirming these encouraging results by testing of broader range of stress configurations and applying the method to actual field measurements.
Results from Benchmark Testing of Zonal Isolation Borehole Completions for Multi-Stage EGS Stimulation in the Bedretto Underground Rock Laboratory in Switzerland
Authors: Meier P. M. , Serbeto F. , Christe F. , Alcolea A. , Castilla R. , Bethmann F. , Dyer B. 
Published: September 2022

ABSTRACT:
Multi-stage stimulation concepts are considered the most promising approach for a breakthrough in EGS technology. Multi-stage stimulation enables a reduction of seismic risks and an increase of circulation flow rates through the reservoir and thus an increase of energy production. However, there is a debate about the best technology for zonal isolation. Some experts favor cementing a liner in the borehole and fracturing through perforations or sliding sleeves in order to obtain a hydraulic connection to the reservoir rock whilst others prefer open-hole packer solutions in order to avoid the possibility that cement could block access to fractures that are favorably oriented for shear stimulation. We have performed a benchmark in-situ test in the Bedretto underground rock laboratory in the Swiss Alps in granite at a depth below surface of 1100 m. The results show that multi-stage stimulation works well with both zonal isolation methods. Both methods were able to hydraulically connect the reservoir well to the borehole. This is good news for reservoir and drilling engineers as the choice between the two methods can now focus on drilling and completion aspects such as wellbore stability, completion deployment, reservoir temperature and completion system costs.

1. INTRODUCTION
Multi-stage stimulation concepts are considered the most promising approach for a breakthrough in EGS technology. Multi-stage stimulation enables a reduction of seismic risks and an increase of circulation flow rates through the reservoir and thus an increase of energy production (Meier et al., 2015). Therefore, a number of innovative projects throughout the world aim to demonstrate the multi-stage stimulation concept (e.g. FORGE, Utah; Haute-Sorne in Switzerland).
However, there is a debate about which is the best technology for zonal isolation (e.g. Walters et al. 2012; Guinot and Meier, 2019; Glauser et al., 2013; Gradl, 2018). Some experts favor cementing a liner in the borehole and fracturing through perforations or sliding sleeves in order to obtain a hydraulic connection to the reservoir rock. In contrast others prefer open-hole packer solutions in order to avoid the possibility that cement could block access to fractures that are favorably oriented for shear stimulation.
Characterization of Natural Discontinuities in Tight Sandstone and Gas Shale Unconventional Reservoir Rocks of Thrace Region in Turkey with DFN Method
Authors: Celen F. , Develi K. 
Published: September 2022

ABSTRACT:
The gas shales of the Mezardere formation and the tight sandstones of the Teslimköy unit in this formation in Thrace region have been considered for many years to be some of the remarkable sources of hydrocarbon production from unconventional reservoir rocks in Turkey. Design of a hydraulic fracturing (HF) operation is the only way for oil and gas recovery from such unconventional reservoirs. As hydraulic fractures induced by HF operations are likely to interact with natural ones, geometrical characterization of natural discontinuities gains importance to be able to build a more realistic reservoir model including structural geological components before an operation. This may reduce operational costs as well as increase production efficiency. Discrete fracture network (DFN) modeling of natural discontinuities (e.g., fractures, joints, faults, bedding, planes etc.) is quite a strong tool for this kind of purpose. In this study, preliminary results of an ongoing study on the development of DFN models in FracMan from outcrop data of natural discontinuities of tight sandstone and gas shale unconventional reservoir rocks of Thrace region are presented. These models can serve as unique database in reservoir modeling prior to potential HF operations probable to be performed in Thrace region in the future.

1. INTRODUCTION
Unconventional reservoirs are becoming more important in natural gas and petroleum industry in Turkey as well as in the world. Especially, Thrace Region, in NW Turkey, has a big potential to produce oil-gas from unconventional reservoirs. While Hamitabat Formation and Ceylan Formation have been defined as host rock for natural gas and limited oil (Soylu et al., 1992), Mezardere Formation is defined as good host rock for gas and oil (Bürkan, 1992 and Soylu et al., 1992). A DFN model is essential for the reservoirs to run processes. Traditional data in structural geology from natural discontinuities, which are location, orientation and position, are used to create a DFN model. The originality of this study is that it is the first DFN modelling attempt being carried out on aforementioned unconventional reservoir rocks of Thrace region in Turkey. The DFN models defined through this study can serve as valuable database in terms of reservoir modelling studies prior to potential HF operations probable to be performed in the study area in the future.
Development, Creation and Application of a Reinforcement Systems Database
Authors: Thompson A. G. , Villaescusa E. 
Published: September 2022

ABSTRACT:
Reinforcement systems are used widely for the stabilisation of excavation surfaces associated with surface and underground excavations in mines and civil engineering projects. To be effective the reinforcement must be of sufficient length to pass beyond the boundary between the unstable and stable rock regions and transfer the loads imposed by the unstable zone to the stable zone. The behaviour of the reinforcement in the unstable zone is quite different as it involves a direction of loading away from the excavation surface towards the stable rock. In order to attempt reinforcement design it is necessary to take into account the differences between the behaviours of both the toe and collar zones. A generic reinforcement system configuration specification has been developed which clearly defines the geometric differences between these zones. In order to create a database of reinforcement system force-displacement responses to loading it was found necessary to combine mechanical testing and model simulations. Details are provided as to how the database has been developed for many different reinforcement systems. In addition, it is shown how the database is applied to the stability assessment of a reinforced block for the purposes of design.

1. INTRODUCTION
Rock reinforcement systems are used widely to improve the stability of both open pit and underground excavations in both civil and mining projects. These reinforcement systems have a wide range of materials and configurations. Consequently, the performance of these reinforcement systems measured in terms of force and displacement responses to loading vary considerably. Whilst the reinforcement systems may be subjected to formal proof and suitability testing according to codes (e.g. BS8081 1989, AS5100.3:2017), many reinforcement systems are not subjected to formal evaluations, even for a limited number of configurations and small range of rock mass conditions.
When it comes to design of reinforcement systems, it soon becomes apparent that for many reinforcement systems the yield and ultimate force capacities of the "element" may be the only reliable parameters that are available from the manufacturer. Note that the term "element" was developed by Windsor and Thompson (1993) to describe the manufactured item of a rock reinforcement system. Consequently, it then becomes necessary for a potential client to perform testing for a single configuration in local ground conditions, often without the necessary understanding of what tests are needed and how the results may be analysed and interpreted for the purposes of design.
Development and Application of a Novel Dynamic Loading Simulation for Reinforced Blocks of Rock
Authors: Thompson A. G. , Villaescusa E. 
Published: September 2022

ABSTRACT:
Ground support consisting of integrated internal rock reinforcement systems and surface restraint systems are used widely for the stabilisation of excavations associated with underground excavations in mines. As mines have developed at ever increasing depths below the earth’s surface, so have the stability problems associated with stresses exceeding the rock strength with resulting violent failures and high energy demands imposed on the ground support. In order for excavations to remain open, ground support schemes have to dissipate the energy being imposed on them. A previous static analysis technique using a force equilibrium approach was modified to enable dynamic loading simulated by an initial vector of block velocity followed by small increments of displacement in the direction of the velocity vector. The dynamic loading technique is described in detail and demonstrated by an example using the SAFEX software package developed by the writers and their colleagues. An importance observation from the analysis results is that the total energy dissipation capacity of the reinforcement systems may need to be significantly greater than the ejection energy imposed at the start of the analysis due to the additional energy associated with the vertical loss of height when ejection is from the roof or the wall of an excavation.

1. INTRODUCTION
Reinforcement systems are used widely to maintain the stability of excavations formed in rock. The shapes and sizes of potential instabilities are usually defined by combinations of discontinuities within the rock mass and the free faces of the excavation. The discontinuities may exist prior to the creation of the excavation or may initiate and propagate due to stress redistribution subsequent to the formation of the excavation.
The forces causing detachment of potential instabilities may be classified as being imposed statically or dynamically. Consequently, the responses from reinforcement systems are required to be resistant to these different imposed forces. Also, the methods of analysis for reinforced blocks need to be different.