bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory Procedure to Calibrate Non-Stressed Borehole Size
Authors: Lin C. , Zou D. H. S.
Published: August 2024

Measurement of the pre-excavation 3D stresses is of great importance for mining, petroleum and other underground rock engineering. An alternative method by differential-direction drilling (called D3 method) without overcoring was recently developed based on back-analysis of the measured borehole diametrical deformation. One of the key input parameters in this back-analysis method is the borehole convergence. To calculate the convergence, the initially-drilled borehole diameter before deformation is required. The rock mass in the ground is always under stress and a drilled hole size is the ultimate result after deformation. Additionally, the size of a borehole typically deviates slightly from the nominal drill bit size. Hence, the first step is to determine the actual borehole size under zero stress to provide a base for comparison in practical implementation. This paper presents the laboratory experiment setup and the procedure for drilling and measurements. Boreholes are drilled in non-stressed rock blocks using a drill press and customized drill bits. The borehole size is measured with a borehole deformation gauge and calibrated with a precisely machined aluminum tube. The relationship between the borehole size and the nominal core bit size is thus established. A calibration procedure for determining the non-stressed borehole size is ultimately established through laboratory experiments.

1. INTRODUCTION

Pre-excavation stresses refer to the stresses existing within a rock mass before the initiation of any excavation or mining activity. It influences the stability of underground structures and excavations (Hoek and Brown, 1980; Amadei and Stephansson, 1997; Brady and Brown, 2004). Incorporating the pre-excavation stress analysis into engineering practices in mining, petroleum, and underground rock engineering is essential for ensuring safety, optimizing design, maximizing resource recovery, and managing risks, ultimately contributing to the sustainable development of these industries.

The pre-existing field stresses are in three dimensions, which can be described by six independent components. It can also be represented by three orthogonal principal stresses: the maximum, the intermediate and the minimum normal stresses (Zou, 2020). Unlike one-dimensional or two-dimensional stress analyses in different directions, which oversimplifies the stress distribution, stress analysis in three dimensions provides a more comprehensive understanding of how stresses act within the rock mass. This understanding is crucial for accurate engineering design and risk assessment.
Numerical Simulation of Flow Field and Erosion Characteristics in Hydraulic Fracturing Tool
Authors: Song Xianzhi , Cui Yueqi , Zhou Mengmeng , Zhengming Xu , Zhu Zhaopeng , Li Gensheng
Published: August 2024

Hydraulic fracturing is widely used in oil and gas reservoir production enhancement due to its notable attributes: more convenience, high efficiency, simple tool structure, absence of mechanical sealing, no compaction zone, and the ability to precisely create directional seams. During the hydraulic fracturing process nozzle dislodgement, tool leakage, and other tool failure phenomena are common occurrences, which result in the waste of time and cost and threaten the safety of the construction. Therefore, this paper uses the Computational Fluid Dynamics (CFD) method coupled with the Discrete Phase Model (DPM) to study the flow field inside the tools to get the erosion law near the nozzles of common hydraulic fracturing tools. The model has verified the accuracy by comparing it with the failed tool salvaged from the oil field. The simulation results show that the erosion phenomenon is concentrated at the top of the upper nozzle and the bottom of the lower nozzle. Meanwhile, a new erosion graphical plate is established, based on the effects of flow rate on erosion, to help and guide the modification and upgrading of hydraulic fracturing tools and the prediction of tool life.

1. INTRODUCTION

Oil and gas resources are traditional non-renewable energy sources, and how to carry out reservoir transformation to improve the production of the oilfields has become the top priority for the development of the old oilfields in the future (Zou et al., 2016). Hydraulic jet fracturing technology can improve the seepage conditions of reservoir and achieve the purpose of increasing production, which is recognized as an efficient horizontal well completion technology (Huang et al., 2017,Li and Wu,2022). During the operation, a large number of high-velocity particles continuously wash and erode the wall surface of the fracturing tools, resulting in large erosion and wear, which may lead to tool failure in serious cases and affect construction safety (Tang et al., 2015). At the same time, according to the photos of the tools taken at the field-site, it is not difficult to find that the erosion problem of hydraulic fracturing tools is very serious, especially in the area near the nozzle inlet, and the nozzle often falls off and leads to tool failure, which not only affects the progress of the operation, but also results in a waste ofcosts. Erosion is commonly found on the internal and external surfaces of tools, the impact factors of erosion are numerous and the mechanism is complex.
Mechanical and Hydraulic Characterization of 3D Printed Rock Analogues of Poorly Cemented Sandstone
Authors: Cartagena-Pérez D. , Rangriz Shokri A. , Zambrano Narvaez G. , Chalaturnyk R.
Published: August 2024

This study presents a mechanical characterization of multiple 3D printed rock samples with silica sand grains that were aimed to emulate the behavior of poorly cemented sandstones. The printing process consisted of spraying a liquid binder onto a bed of sand grains, layer by layer, followed by a curing process. To assess the quality of cementation through binder distribution, we employed Computed Tomography (CT) to get high-resolution images of the printed rock specimen. Subsequently, we conducted porosity measurements using both water and canola oil. To complete the work, intact samples at low binder saturation (i.e. cementation) underwent several UCS and triaxial tests, along with permeability measurements.

Our results indicated an average porosity of 46% for poorly consolidated 3D printed rock analogues. The average UCS was 1.45 MPa, with a Young's modulus of 175.18 MPa; our experimental data from 3D printed rock samples align closely with actual core measurements of poorly cemented sandstones, as reported in literature for locations such as Cold Lake and McMurray heavy oil reservoirs. Following UCS testing, we observed diagonal shearing failure planes in all samples. Triaxial testing indicated low cohesion (350 kPa) and frictional angle akin to dense sands (56°), leading to a loose sand structure upon shearing. Regarding their hydraulic properties, we also conducted permeability tests at an effective confining stress of 0.5 MPa which revealed an average permeability of 1.8 Darcies, again consistent with poorly cemented sandstones.

1. INTRODUCTION

Implementation of engineering solutions in geomaterials often necessitates a comprehensive hydromechanical characterization, which involves destructive tests using multiple samples, such as uniaxial compressive strength (UCS) and triaxial tests. In response to this demand, additive manufacturing (i.e. 3D printing) technology has emerged as a cost-effective means of obtaining a substantial number of identical rock samples. This capability allows researchers and engineers to carry out multiple tests (Including destructive ones – e.g. triaxial tests) without the limitation in number and price of samples that come from actual reservoirs. This advantage is useful if the 3D printed rock is partially representative of the rocks in the reservoirs.
Enhancing Intelligent Drilling Rate of Penetration PredictionModeling Through Anomalous Drilling Data Handling Methodology
Authors: Ye Shanlin , Zhu Lin , Lv Zehao , Song Xianzhi , Liu Zihao , Zhu Zhaopeng , Pan Tao
Published: August 2024

Intelligent drilling represents a future trend in petroleum drilling. Intelligent prediction and optimization of drilling rate of penetration (ROP) constitute pivotal research areas within intelligent drilling, promising enhanced drilling efficiency and cost reduction. The establishment of intelligent prediction models for ROP relies heavily on a vast amount of drilling data. However, data collection devices in oil fields exhibit instability, accompanied by significant environmental noise. Consequently, drilling data often contain numerous outliers and noise, which disrupt the training of ROP models and degrade their accuracy. In this paper, a methodology for handling anomalous data is proposed based on oilfield drilling data. Firstly, isolated forest (IF) detection is employed to identify and remove outliers, followed by the application of K-nearest neighbor (KNN) interpolation algorithm to address missing values. Finally, locally weighted scatterplot smoothing (LOWESS) is utilized to smooth the data and eliminate noise. Results indicate that the drilling speed prediction model built upon the processed data exhibits higher predictive accuracy. The proposed anomalous data handling methodology contributes to the enhancement of intelligent ROP prediction models, demonstrating practical utility.

1. INTRODUCTION

With the advancement of technology in the petroleum industry, intelligent drilling, as an efficient and intelligent drilling technique, has gradually garnered widespread attention (Lig, et al. 2022). Within this trend, intelligent prediction and optimization of drilling rate of penetration (ROP) have emerged as significant research areas in the field of intelligent drilling. Accurate prediction and optimization of mechanical drilling speed can significantly enhance drilling efficiency and reduce drilling costs, thereby injecting new vitality into the development of the petroleum industry (Barbosa, et al. 2019).

However, in reality, we face numerous challenges. The complex and dynamic nature of oilfield environments, coupled with the instability of data collection devices and the influence of environmental noise, pose significant challenges to the quality of drilling data (Geekiyanage, et al. 2021). In such circumstances, drilling data often contain various outliers and noise, which not only have the potential to misguide decisions made by drilling engineers but also interfere with the training of intelligent prediction models for mechanical drilling speed, thereby reducing the accuracy of the models.
Salt is Not a Steady-State Creep Material
Authors: Chieslar J. D.
Published: August 2024

Steady-state creep is increasingly used to model structures hosted in salt and potash. This is presumably due to the absence of representative constitutive models available in commercial geomechanics software. We consider a standard suite of tests performed on salt. These include creep, dilation and tension. These tests are fit to a simple material model and evaluated. Simulations of a solution mine are performed with varying degrees of completeness with respect to the constitutive model. Volumetric closures are calculated. This exercise quantifies the ramifications on closure (deformations) according to the various material assumptions. It is observed that both the creep transient and dilation contribute to closure. Furthermore, if a failure criterion is considered, dilation is the most appropriate candidate. It is insufficient merely to post-process a creep calculation to evaluate the potential for dilation. By it's nature, dilation is a strain-softening response. It localizes and concentrates and therefore must be included in the constitutive calculation.

1. INTRODUCTION

Numerous material models have been considered for describing salt and potash. Among these are MatMod (Miller, 1976), the WIPP creep law (Senseny, 1985) and more recently, the much researched and enhanced Munson-Dawson model (Reedlum, 2018). The principal shortcoming of these models is that each geological site is typically unique and has to be characterized anew, that is, there is not a universal constitutive model for salt nor for potash, as is typical for various metal alloys. The large suite of tests required to calibrate these models is impractical. These models typically have several tens of parameters. Tests must be diverse enough to span the basis represented by all of these parameters/freedoms and furthermore be consistent. For industrial operations, this becomes infeasible due to the expense of the expanded test regime and also the limited amount of core available, layered media, for example. Characteristic of the aforementioned models is the lack of attention to dilation. Salt and potash are complex materials, exhibiting a crystalline creep response much like metals, and also a dilational response (expansion as grains shear against one another) characteristic of granular materials, i.e., rock. Only the Munson-Dawson model addresses dilation but the corresponding state variable is a scalar. Anisotropy requires, at a minimum, a second-order tensor state variable.
Enhancing Cluster Efficiency by Modeling Swelling Diverter Particles in PKN-Type Fractures
Authors: Luo Bo , Wong George K.
Published: August 2024

Uneven fracture propagation stemming from reservoir heterogeneity, nonoptimal design, and stress interference significantly affects cluster efficiency in unconventional reservoirs. While the use of diverter agents in field to mitigate overgrown or less stimulated fractures holds promise, a thorough comprehension of the underlying mechanisms remains crucial. This work presents a coupled simulator that integrates a PKN-type fracturing model with a particle transport model to address the challenges of uneven fracture propagation in unconventional reservoirs. By combining nonlocal elasticity for stress interaction, a global tip asymptotic solution for multiscale tip behavior, and Eulerian-Eulerian method for particle transport and bridging, the simulator provides a robust framework for modeling field-scale particle diversion. The model includes particle swelling and dissolution characteristics to enhance fluid diversion effectiveness. The simulator replicates field treatment procedures, incorporating sequential additions of a fluid pad, diverter particle slug, and proppant-laden slurry. Numerical examples demonstrate its capability to achieve uniform non-propped lengths in viscosity-dominated propagation regimes and equal propped lengths in transition propagation regions. This tool optimizes pumping schedules and applies particle diversion technology to improve cluster efficiency during stage fracturing, enabling the design of optimal procedures for enhanced field performance.

1. INTRODUCTION

The heterogeneous nature of formations, coupled with nonoptimal well completions and stress interference, often results in unequal stimulation among clusters during stage fracturing (Rafieepour et al., 2020; Soliman et al., 2008; K. Wu & Olson, 2015; Zheng et al., 2019). This disparity in fracture growth leads to production variability substantiated by production logs (Cipolla et al., 2011; Miller et al., 2011). To counter this, fluid diversion techniques have emerged as a mitigation strategy by modifying or redirecting fluids toward less stimulated fractures. Field-tested applications have demonstrated the effectiveness of this approach (Evans et al., 2016; Fragachán et al., 2016; Gomaa et al., 2016; McCartney & Kennedy, 2016; Ugueto et al., 2020). Diverter agents, strategically placed at various locations such as perforation inlets, perforation tunnels, fracture entrances, and fracture tips, serve this purpose (Daneshy, 2019).
Modification of the Rock Mechanical Design of Salt Caverns on the Basis of Recent Research
Authors: Zapf Dirk , Körner Feline , Leuger Bastian , Baumgärtel Lukas
Published: August 2024

For some years now, the world has been facing the challenge of achieving an energy turnaround in the coming years. In this context, renewable energies are increasingly coming into focus, also with regard to the construction and operation of storage caverns in rock salt. In order to be ready for these challenges from an engineering point of view, a lot of research work has been carried out in recent years in the sector of dimensioning salt caverns for the storage of renewable energies. At the Institute of Geotechnical Engineering at Leibniz University in Hanover, Germany, a test apparatus was created that allows fracturing processes to be induced in rock salt test specimens. Various rock salt locations were investigated in the process. Research work on this aspect will be completed in the near future. The results of the research project will be presented and their consequences for the future storage of renewable energies in salt caverns will be discussed from an engineering point of view. In addition to the maximum and minimum operating pressures of a storage cavern, the thermodynamic stress during operation and the resulting stress and fracture conditions on a cavern wall will be discussed. The results of the research project are used to explain the modified dimensioning approaches.

1. INTRODUCTION

Energy in the form of gas, oil or petrol has been stored in salt caverns around the world for decades (Bays 1963, Thoms 2000). Some cavern structures already exist for storing renewable energies such as compressed air and hydrogen. The storage capacities of these media will be greatly expanded in the future and thus contribute to the global energy transition.

In Germany, the dimensioning of salt caverns is the responsibility of civil engineers specializing in geotechnical engineering. There is a strict mining law, and the approval authorities have high demands on the tightness and stability of the caverns. For this reason, dimensioning concepts have been developed by companies and universities in recent years, which differ in detail but all pursue the same goal: Safe storage of energy sources in salt caverns.
Experimental Study of the Effect of Porosity on EICP Biomineralization in Dolostone and Shales Under Uniaxial Compressive Stress Condition
Authors: Ngoma M. C. , Kolawole O. , Olorode O. , Kwon T.-H.
Published: August 2024

Biogeochemical-induced rock alteration is an evolving process that focuses on harnessing biologically induced chemical activities to change the mechanical properties and behavior of rocks. It often relies on enzyme-induced carbonate precipitation (EICP) which utilizes biomineralization by promoting the formation of calcium carbonate (CaCO3) in the rock pores and fractures. However, there is still a lack of knowledge on the effect of porosity on biomineralization in rocks from a mechanistic view. This study uses an experimental method to investigate the core-scale thermo-biogeomechanical alterations in low-permeability clay-rich rock (shale) and in high permeability dolomitic rock using the EICP treatment method. We first conducted EICP treatment of shale and dolostone samples using jack bean urease enzyme over a 3-day period at a distinct temperature. Subsequently, the mechanical properties were measured using uniaxial compression test. Finally, we analyzed the pre- and post-treatment changes in the dolomite-rich and shale rock samples to better understand the effect of enzyme-induced calcite precipitates on mechanical response of the rock samples. The results suggest that in dolostones with higher porosity, carbonate precipitation will have a greater impact on the mechanical properties than in shales with ultra-low porosity, when treated with EICP.

1 INTRODUCTION

Biogeochemical processes can enhance mechanical and flow (porosity and permeability) properties of rocks (Phillips et al., 2015; Kirkland et al., 2020; Kolawole et al., 2021). Prior research has provided insights into the impact of such complex processes for various geotechnical and energy engineering applications (Kolawole et al., 2021, 2022; Whiffin et al., 2007; Gao et al., 2019; Kolawole et al., 2023; Kolawole, 2023). For instance, Kolawole et al. (2022) evaluated the effect of bio-induced precipitation on tight carbonates for long-term storage integrity. To investigate this, biological media was injected into low-porosity carbonate samples for 30 days and the mechanical strength of the treated samples was measured using the uniaxial compression test. The results of the study showed an increase (>100%) in Uniaxial Compressive Strength (UCS) of the carbonate samples. This increase in rock strength suggests that biogeomechanical alterations can enhance the strength of rocks and facilitate security of low-porosity carbonate caprocks.
An Efficient Coupled Hydro-Geomechanical Model for Determination of Open Hole Extended Limit of Drilling Horizontal Wells in the Permian Basin by Using Developed Environmentally Friendly High Performance Water-Based Mud
Authors: Metwally Mohamed , Gyimah Emmanuel , Koray Abdul-Muaizz
Published: August 2024

Drilling horizontal and extended reach wells (ERW) has played critical role in enhancing well productivity, efficient reservoir drainage, and minimizing environmental impact. Despite the benefits, technical challenges like high torque, shale instability, and managing equivalent circulation density pose limitations to extending lateral sections. To address these issues, the paper proposes a high performance environmentally friendly water-based mud (WBM) with a friction reducer (FR) for ERW drilling in the shaly Wolfcamp and Spraberry formations within the Permian Basin. Objectives include developing a thermally stable WBM, inhibiting shale instability problems, mitigating barite sagging, being environmentally friendly and determining the maximum open hole extension limit for ERW using the hydraulic Herschel-Bulkley rheological model coupled with geomechanics. The laboratory analysis showcases the WBM's thermal stability, improved capability to inhibit shale, effectiveness in preventing bit balling, reduction in barite sagging, and mitigated adverse effects on the ecosystem. The hydraulic model utilizing the Herschel-Bulkley rheological model exhibits high accuracy in determining equivalent circulation density and annular pressure losses. The study introduces an innovative environmentally friendly WBM that not only minimizes pressure loss but also effectively addresses shale-related challenges, serving as a viable substitute for oil-based mud. It provides a reliable hydro-geomechanically model for predicting the increase in open hole extension limit within a safe mud weight window, thereby enhancing wellbore stability in the Permian Basin.

1. INTRODUCTION

In the context of oil and gas exploration, the stability of wellbores plays a pivotal role in determining the success and safety of drilling operations. The subsurface environment introduces formidable challenges, with diverse geological conditions that can significantly impact the structural integrity of a wellbore (Amanullah et al., 2018). Geomechanics analysis emerges as a crucial tool in this scenario, providing a systematic framework for comprehending and addressing the intricate interactions between the wellbore and the surrounding rock formations (Gyimah et al., 2023). This analysis integrates geological, geophysical, and engineering data to construct predictive models, offering insights into potential instabilities and guiding drilling operations. Key parameters such as in-situ stress conditions, rock strength, pore pressure, and the effects of drilling fluid circulation are carefully considered in geomechanics analysis for wellbore stability (Bagheri et al., 2021).
The Role of Thick Competent Strata in Face Bursting in Underground Longwall Mines
Authors: Chambers D. , Boltz M. S. , Khademian Z. , Walton G. , Shragge J.
Published: August 2024

Coal bursts are violent dynamic failures that occur in underground coal mines and can injure workers and disrupt mining operations. The coal bursting phenomenon is complex and many factors contribute to a mine's propensity to experience bursting. Among these is the presence of thick competent strata (TCS) in the immediate roof or floor, but how the TCS contribute to bursting is not fully understood. In this work, we created a suite of simple 2D models of a longwall cross section whose stratigraphy is dominated by sandstone. We used these models to explore which TCS parameters influence burst severity and to define a likely failure mechanism. We found that the undermined length of un-caved TCS and properties of the coal-sandstone interface have the greatest effects on a model's burst severity. Interface slip initiated by coal yielding and driven by stored strain energy is the primary failure mechanism. Although real coal bursts are certainly more complex, this work provides insight into a plausible burst mechanism and contributing TCS factors that can guide future research.

1 INTRODUCTION

Coal bursts are violent dynamic failures that occur in underground coal mines. Much like earthquakes, coal bursts are notoriously difficult to predict and can be highly destructive. For example, in the past 40 years, coal bursts have resulted in more than 240 injuries and 20 fatalities in the United States (Iannacchione and Tadolini, 2016). In China, over 300 coal burst related fatalities have occurred since 2006 (Zhang et al., 2017). Many other countries have also experienced coal bursts including Japan, Australia, India, South Africa, Czech Republic, Canada, Germany, and Russia.

Coal bursts are driven mainly by stored strain energy in the coal or nearby strata, or triggered by a pressure wave from a remote source (Gale, 2018). Coal bursts continue to injure workers and disrupt mining operations and, despite research dating back nearly a century (e.g., Rice, 1935), many questions remain about the associated mechanisms and causative factors. For longwall mines, the most productive underground coal mining method, Mark (2016) identified significant seam depth (> 600 m), mining proximity to faults or intrusions, dipping coal beds, multiple seam interaction, and the presence of thick competent strata (TCS) in the immediate (< 15 m) roof or floor as risk factors. Face bursts (coal bursts occurring on the longwall face) have been particularly problematic for many deep mines in the Western United States. For example, between 1983 and 2017 the majority of the 149 bursts reported to the Mine Safety and Health Administration (MSHA) from mines in the state of Utah occurred on the longwall face (Mark, 2018). Severe face bursting has resulted in fatal injuries and even mine closures (Mark, 2016).
A Review of the Anelastic Strain Recovery (ASR) Technique for In-Situ Stress Measurements: A Suggested Test Protocol and Further Challenges
Authors: Lin W. , Sakai Y. , Kamiya N. , Cao Y. , Ishitsuka K. , Sun D. , Zhang C. , Nagano Y.
Published: August 2024

Determination of in situ stress states is one of the most important issues for rock mechanics, rock engineering, and geomechanics, but difficult challenges in its measurement technique remain. In the past two decades, we have conducted more than ten case studies related in-situ stress measurements by a core-based method called anelastic strain recovery (ASR) technique in both oceanic and continental deep drilling projects. The case studies covered a wide range in terms of rock types, retrieved depths of core samples, and research backgrounds. Through learning by trial and error of the applications of the ASR technique, we have established a practical test protocol and data processing procedure for determining three-dimensional in-situ stresses from the ASR measurement data. In this paper, we review previous case studies of stress measurements using the ASR technique and summarize the detailed test procedures, and suggest a standard test protocol for both oceanic and continental deep drilling project. In addition, we will also address challenges for the future.

1. INTRODUCTION

Stress state is a key parameter to understand plate tectonics, structural geological setting of subduction zones and to ensure safe and efficient developments of underground energy resources in great depths. Therefore, determination of in-situ stress states is one of the most important issues for rock mechanics, rock engineering, and geomechanics, but difficult challenges in its measurement technique remain. Stress measurements are carried out both in tunnels with large overburdens in civil and mining engineering and in deep boreholes for natural underground resources developments and for scientific investigations. Here, we focus on the in-situ stress measurements in both deep ocean drilling and continental (onshore) drilling in this paper.

In deep boreholes, methods of stress determination can be divided as downhole measurements such as hydraulic fracturing / extended leak off test, stress analysis using borehole breakouts and drilling induced tensile fractures, and core-based techniques. As the core-based techniques, Anelastic Strain Recovery (ASR), Diametrical Core Deformation Analysis (DCDA), Acoustic Emission (AE), Differential Strain Curve Analysis (DSCA), Deformation Rate Analysis (DRA) have been proposed (Amadei and Stephansson, 1997; Zoback et al., 2003; Zoback, 2007; Zang and Stephansson, 2010; Ito et al., 2013). In the past two decades, we have successfully conducted more than ten case studies of in-situ stress measurements by the core-based method called anelastic strain recovery (ASR) technique in both oceanic and continental deep drilling projects in geoscience and/or geoengineering areas. In this paper, we review previous case studies of stress measurements using the ASR technique, summarize the detailed test procedure, and suggest a standard test protocol mainly for deep boreholes.
Granite Rock Mass Identification and Geothermal Well Location Deployment Based on the Wide Field Electromagnetic Method: A Case Study of Sanshui Basin
Authors: Zhang Q. X. , Zhang Y. , Feng J. Y. , Luo J.
Published: August 2024

Due to the special geological environment, two sets of geothermal reservoirs of Buxin Formation with lithology of sandstone and deep volcanic rocks have been formed in Sanshui Basin. Although a lot of research progress has been made in the geological conditions such as heat source, channel, reservoir and cover layer in this area, the depth and range of deep dry hot rock mass are not clear. Therefore, effective exploration methods are needed to provide technical support for geothermal well deployment and resource assessment. In this paper, based on the principle of wide field electromagnetic method (WFEM), four survey lines are laid to explore the geothermal resources in the study area. Secondly, the underground resistivity data are obtained by the location information of the field source and measurement points on the surface and the observed electric field signals. Finally, the electrical cross-section is interpreted with geological data. The results show that the longitudinal section can be roughly divided into four electrical layers of "low-high-low-high", which are Paleogene, Cretaceous, Permian-Carboniferous, and granite basement. According to the distribution of granite, the range of deep granite body with high resistance has been delineated, which provides a prerequisite for the geothermal well deployment.

1. INTRODUCTION

The special geological environment of Sanshui Basin leads to the formation and enrichment of CO2 gas, which indicates that there may be deep geothermal resource potential in this area. At present, oil and gas drilling is mainly concentrated in the depth range of 700∼1300 m (Chen, et al., 2008). The drilling temperature is not high, but the geothermal gradient is about 3.1 °C/100m. Based on the geothermal gradient, it is inferred that there may be carbonate or igneous bedrock reservoirs in the bedrock uplift structure of the deep concave area to form the accumulation of medium-high temperature geothermal resources.

From the perspective of sedimentary evolution, there are two sets of geothermal reservoirs in the Sanshui Basin. The first set of reservoirs are limestone and dolomite deposited in Carboniferous-Permian-Triassic period, and the second set of reservoirs are sandstone deposited in Buxin Formation and rhyolite and trachyte formed by volcanic eruption. (Chen, 2018). At the same time, the mudstone of Buxin Formation provides good capping conditions for the sandstone reservoir, volcanic rock reservoir and limestone reservoir Triassic-Carboniferous. The development of faults in this area provides a good migration channel for deep geothermal fluid and heat flow, so the sedimentary evolution and fault development characteristics determine the vertical development of two sets of deep geothermal reservoir-cap assemblage systems.
Geological Analysis of Typical Geothermal Systems in East of China
Authors: Feng Jianyun , Zhang Ying , Luo Jun , Zeng Yan , Yun Xiaorui , Liao Dawei , He Zhiliang , Zhang Ying , Luo Jun , Zeng Yan , Yun Xiaorui , Liao Dawei
Published: August 2024

Eastern China, which lies to the east of the Hu Huanyong Line that connects the Heihe and Tengchong areas, has a high population density, a developed economy, and a huge demand for energy. To determine the geothermal resources in eastern China, this study analyzed the typical geothermal systems in this region based on disciplines of structural geology, and petrology. As a result, this study determined the distribution patterns of medium and deep geothermal resources in this region. Eastern China is a superimposed region of three major global tectonic domains, namely Paleo-Asia, Circum-Pacific, and Tethyan. Its crust-mantle structure presents a special flyover pattern, while its shallow surface has alternating basins and mountains and well-spaced uplifts and depressions. Studies have shown that medium-high-temperature geothermal resources in China are mainly distributed in the Mesozoic-Cenozoic basins in eastern China. However, they are dominated by medium-temperature geothermal resources with low abundance. The geothermal reservoir types mainly include porous sandstone reservoirs, karstified fractured-vuggy carbonate reservoirs, and fissured granite reservoirs.

1. INTRODUCTION

Eastern China, which lies to the east of the Hu Huanyong Line that connects the Heihe and Tengchong areas, consists of Northeast China, North China, the middle and lower reaches of the Yangtze River, Southwest China, and South China from north to south, has a high population density, hosting 96% of the total population of China, as well as a developed economy and a huge demand for energy (Fig. 1).

As an earth-derived energy source, geothermal resources are clean, renewable, and highly competitive and can be used for indoor heating, industrial and agricultural utilization, and power generation. The successive launch of national projects in China, such as the Deep Resource Exploration and Exploitation Program, began the exploration of the deep earth in China, and important achievements have been increasingly achieved in basic geology and geothermal geology. Moreover, research on deep-crust temperature and crust-mantle dynamic mechanisms has been gradually intensified (Shi 1990; Xu et al., 1995; He et al., 2001; An et al., 2007; Wang et al., 2012; Qiu et al., 2015). Remarkable progress has been made in research on terrestrial heat flow (Jiang et al., 2016, 2019), geothermal system types (Chen et al., 1996; Zhang et al., 2017), the division of geotectonic units and geothermal units (Pan et al., 2009; He et al., 2017), the selection and evaluation of optimal exploration areas (He et al., 2020; Zhang et al., 2020; Ke et al., 2022), hot dry rock development experiments (Wang et al., 2022), and geothermal applications (Wang et al., 2014), laying a solid foundation for the study of deep geothermal resources.
Modeling Erosion in Hollow Cylinder Tests: The Case of Low Pressure Under Variable Confining Stress
Authors: Kakonitis Panos , Papaloizou Loizos , Gravanis Elias , Sarris Ernestos
Published: August 2024

Modelling the erosional behavior of rock cores in hollow cylinder tests is a formidable task because it involves coupled hydro-mechanical processes. In a recent work of the authors, we proposed semi-analytical hydro-mechanical framework for modelling erosion at laboratory scale through the hollow cylinder test. The model was based on the kinematic formulation of classic hydro-mechanical models also known as volumetric sand production models. The original formulation was constructed to include variable confining stress and flow rate conditions. In this new formulation, a power law dependency of the erosion coefficient λ with stress is incorporated to investigate its dependency on the variable external radial stress boundary condition reflected on the sand production curve. This is a significant update with respect to the previous formulation that assumed a constant sand production coefficient. Results show an improved performance with respect to experimental results. This model can be used to systematically calibrate sand production coefficients for different types of rocks.

1. INTRODUCTION

Sand production is a phenomenon where solid (predominantly sand) particles are produced together with hydrocarbons during production operations. This sand influx to the wellbore is responsible for causing various operational and mechanical issues within the wellbore and surface facilities. To avoid such issues, an appropriate design of bottom hole completion technique remains a formidable task especially when the reservoir rock is an unconsolidated sandstone. Completion engineers are requested to choose between open hole or cased, cemented and perforated completions but when opting for communication between the well and the formation may cause further formation stability issues albeit manageable if gravel packed. The main reason for this dilemma is the mechanically weak behavior of sandstones especially if they are unconsolidated. Actually, significant percentage of the world' s hydrocarbon reservoirs are hosted in unconsolidated sandstone rocks which might present high risk of sand production. Once sand production onsets, cleaning operations cause time delays and costly investments due to time consuming and expensive workovers. To avoid these delays, operators are forced to restrict production rates, hence reducing the drawdown to cut-down formation stresses which are now believed to be one of the root-causes of sand production after reaching rock failure. Kakonitis et al. (2023a), Fattahpour et al. (2012), Deng et al. (2019), Nouri et al. (2007).
Insights into Fracture Dynamics Through Advanced Coupled Flow and Geomechanics Modeling
Authors: Pei Yanli , Sepehrnoori Kamy
Published: August 2024

This work develops an advanced coupled flow and geomechanics model, integrating the Embedded Discrete Fracture Model (EDFM) and the Extended Finite Element Method (XFEM), to enhance unconventional reservoir exploration. The model, now refined for multiple fracture scenarios, uniquely simulates multiphase compositional flow and matrix-fracture deformations, overcoming the limitations of simplified empirical models in capturing dynamic fracture behaviors during the reservoir injection-production process. Benchmarked against established standards like Sneddon and Elliot's problem, the model through an iterative coupling accurately predicts fracture property changes under various reservoir and operational conditions. Key findings underscore the influence of matrix permeability and rock stiffness on fracture apertures and reservoir pressure as well as stress fields throughout development cycles. The study demonstrates that reduced fracture angles relative to the flow path lead to elevated reservoir pressures and more uniform fracture property changes, while higher pressure differentials intensify stress around fractures, correlating positively with fracture aperture variations. This model contributes to a better understanding of well productivity optimization and effective reservoir management, particularly in addressing the challenges posed by the dynamic properties of multiple fractures during the reservoir injection-production process.

1. INTRODUCTION

The application of hydraulic fracturing has transformed tight formations into viable resources for the oil and gas industry, presenting both opportunities and challenges in reservoir management and production optimization (Gaurav et al., 2012; Wang et al., 2020; Mehrabi et al., 2021; Pei and Xiong, 2023; Wang and Olson, 2023). Despite the initial high production rates, the rapid decline in output due to fracture closure and conductivity loss remains a critical concern (Yu and Sepehrnoori, 2014; Fan et al., 2017; Xu et al., 2019). Additionally, the slip and opening of fractures induced by fluid injection are common in reservoirs rich in fractures and faults (Zoback and Gorelick, 2012; Kumar and Ghassemi, 2018; Ren et al., 2018; Kamali and Ghassemi, 2020). Such changes, driven by variations in pore pressure and the consequent response in local in-situ stresses (Marongiu-Porcu et al., 2016; Safari et al., 2017; Pei and Sepehrnoori, 2022; Pei et al., 2022), necessitate a precise understanding of fracture dynamics to sustain reservoir productivity.
Maximizing Geothermal Energy Recovery from Enhanced Geothermal Systems Through Huff-And-Puff: A Comprehensive Simulation Study
Authors: Sekar Lokesh Kumar , Okoroafor Esuru. R.
Published: August 2024

The huff-and-puff technique, originally developed for cyclic single well operations in low-permeability sedimentary reservoirs, has shown promise for improving oil recovery. This approach is particularly relevant in tight reservoirs where conventional multi-well patterns face challenges due to extremely poor permeability. The technique involves cyclic injection of various fluids like steam, solvents, surfactants, or their combinations to enhance the recovery process. This study extends the application of the huff-and-puff technique to deep, tight Enhanced Geothermal Systems (EGS) with the aim of harnessing geothermal energy. Leveraging a sophisticated thermohydromechanical model, a key scenario is investigated: which is optimizing huff-and-puff cycle durations. The results demonstrate that substantial enhancements in geothermal system performance can be achieved by fine-tuning the heat farming strategy through strategic adjustments in injection and soak times. While this method may not provide continuous geothermal energy, it presents a viable option for heat storage and direct utilization. These insights represent a significant step towards the more efficient exploitation of geothermal resources, ultimately enhancing the overall energy recovery process in tight EGS reservoirs. This research opens avenues for broader applications of the huff-and-puff technique in geothermal energy production and promotes sustainable energy solutions in challenging subsurface environments.

1. INTRODUCTION

Geothermal Energy involves harnessing heat beneath the Earth's surface to generate electricity. The process involves drilling wells to access geothermal reservoirs and using steam or hot water to drive turbines and produce electricity (Bagher et al., 2014). Flexible energy resources are key for a reliable power supply in a decarbonized grid with a significant fraction of variable power sources (Cruz et al., 2018). Geothermal energy has always been an economic resource for baseload power and district heating (Kyriakis & Younger, 2016). Recently, geothermal facilities have been expanding beyond baseload to supply flexible heat and electricity (Aljubran & Horne, 2024). The major challenge associated with geothermal energy tapping is its reduced thermal performance over time (Abbas et al., 2014). To reduce dependency on naturally occurring geothermal reservoirs and to increase the contact area in low permeability reservoirs, Enhanced Geothermal Systems (EGS) are introduced. EGS involves creating an artificial reservoir by stimulating the natural permeability of hot rock formations beneath the Earth's surface (Lu, 2020). The technology delineates the establishment of a meticulously engineered geothermal reservoir within hot, often crystalline rock through the utilization of reservoir stimulation methodologies. Subsequently, water circulation is employed within this engineered reservoir to harness thermal energy from the heated rock (Duchane & Brown, 2000).
Insights from Thermohydromechanical Simulations for Real-Time Monitoring of UHS in Saline Aquifers
Authors: Okoroafor E. R.
Published: August 2024

Real-time continuous monitoring provides high-resolution spatial and temporal data for tracking fluid migration. In this study, we numerically investigate the temperature, pressure, strain and displacement responses in potential monitoring wells locations during cyclic hydrogen injection into saline aquifers. A coupled thermohydromechanical flow model was used to mimic the injection and withdrawal of hydrogen. Potential locations for injection and monitoring wells are mapped. The primary focus of the analysis was to determine the temperature, pressure, strain and displacement responses and what they could inform about hydrogen distribution.

The study shows that pressure, temperature, displacement and seismicity are key parameters to track the cyclic behavior of hydrogen in the subsurface. The recommended locations for such measurements include for Pressure, Temperature, and Displacement, monitoring tools are best placed at the above-storage reservoir. For Strain, and induced seismicity – in or near the storage reservoir. These insights have practical implications for the design of monitoring wells equipped with monitoring sensors and for enhancing data interpretation practices.

1. INTRODUCTION

Underground hydrogen storage in porous media has the potential to complement renewable energy resources by storing excess energy from these resources during low demand and releasing the energy during peak demand. Hydrogen can be produced via electrolysis. Excess energy can be stored as hydrogen in geological media like salt caverns or porous media. However, there are few experiences with hydrogen storage in porous media (summarized in Zivar et al., 2021), and the few cases are not hydrogen stored with 100% purity.

There have been instances of the application of numerical modeling to understand the behavior of hydrogen in porous media (summarized in Okoroafor et al., 2023), but few of these works discuss or capture the geomechanical implications of hydrogen storage in porous media. The storage integrity of underground hydrogen storage in porous media remains a critical concern, especially regarding potential losses during the cyclical processes of hydrogen injection and withdrawal. Current understanding lacks insights into the geomechanical implications of hydrogen storage in porous media, making it imperative to address this gap. Thus, the primary objective of this study is to investigate and enhance storage integrity during hydrogen storage within porous media. Specifically, the study aims to anticipate and mitigate potential integrity issues by analyzing various parameters, including pressure, temperature, displacement, strain, stress, and fluid composition, throughout different hydrogen storage and withdrawal phases.