bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization Method of Hydraulic Fracturing Design for Horizontal Shale Gas Well Based on Artificial Neural Network and Genetic Algorithm
Authors: Luo Y. , Guo J. C. , Zeng F. H. , Lu C. , Wang R. , Guan B. , Ren Y. , Yuan C. M. , He L. , Zhou G. Q. , Wang J. G. , Liu Y. H. , Wang X. S. , Shan X.
Published: September 2022

Multistage hydraulic fracturing in horizontal well is the key means to realize efficient development of shale reservoir. Traditional fracturing optimization mainly applies single factor analysis or orthogonal test based on numerical simulation, which is time consuming and is difficult to obtain the global optimal solution. In this paper, an optimization method of hydraulic fracturing design for horizontal shale gas well based on artificial neural network (ANN) and genetic algorithm (GA) is proposed. On the basis of collecting geology, engineering, and production data of fractured horizontal wells, the main production influencing factors are obtained with recursive feature elimination and cross validation method, then a data-driven production prediction model is constructed based on ANN, and the GA is used to search the global optimal combination of fracturing parameters. With the data set of 162 fractured horizontal wells from a shale gas field in Sichuan Basin, an ANN production prediction model is trained and tested. The calculation efficiency is high, and the determination coefficient exceeds 0.8. Furthermore, an optimal fracturing parameters combination strategy is proposed for a new completed well in this area. This method can provide some guidance for production evaluation and hydraulic fracturing design of horizontal shale gas wells.

1. INTRODUCTION

Shale gas development mainly relies on horizontal well and staged fracturing, optimizing the fracturing strategy is critical to maximize well production and the ultimate recovery. The current fracturing optimization design mainly applies single factor analysis or orthogonal test methods to find the optimal horizontal well length, number of fractures, or fracture length, with the goal to maximize well production or net present value. However, limited by the search method and search interval, it is difficult to obtain the global optimal solution. What’s more, the optimization process is carried out with numerical simulator, involving complex and coupled fluid flow in matrix, natural fractures, artificial fractures and wellbore, so the calculation is time-consuming. Thanks to the increase of shale gas development efforts, data related to development and production are accumulating rapidly and continuously (Tan et al. 2017; Zhang et al. 2022). Therefore, extracting knowledge from the existing data, establishing a reliable and fast model to predict the well production, and then carrying out fracturing optimization with the combination of intelligent algorithm, is of practical interest for fracturing engineers.
Enhanced Rate of Penetration Prediction with Rock Drillability Constraints: A Machine Learning Approach
Authors: Fan Y. D. , Jin Y. , Pang H. W. , Wang S. G.
Published: September 2022

The rate of penetration (ROP) is directly related to the drilling cost. Accurate prediction of the ROP is of great significance to reduce the drilling cost. At present, there are two main types of methods for predicting ROP. One is based on physical mechanism analysis. However, due to many kinds of parameters affecting ROP, the prediction results are often very different from the actual ROP. The other is the data-driven prediction model of ROP. For the sample data with no obvious characteristics or "small sample" data, compared with the actual results, the prediction results of data-driven model have large errors. To solve the above problems, a new machine learning ROP prediction model based on physical mechanism constraints is proposed in this paper. Based on the data of 4 wells in X block of T oil field, the random forest model is selected from the three machine models including support vector regression, random forest, and regression tree, and the rock drillability constraint is added to predict the ROP. The prediction results that do not meet the rock drillability constraints are optimized to reduce the prediction error. The results show that the random forest model with constraints has the best performance, and the prediction error is reduced from 14.52% to 11.27%.

1. INTRODUCTION

ROP prediction methods can be divided into two categories: one is the physical model based on parameter relationships, and the other is the machine learning model based on big data (Gan, 2019). Maurer (1962) proposed a model for predicting the ROP of rolling cutting tooth bit based on WOB, formation drillability, rock compressive strength, and bit size. Bingham (1965) introduced the weight index based on Maurer’s model to predict the ROP. Bourgoyne and Young (1974) considered the formation strength, formation depth, compactness, bottom hole differential pressure, bit size, bit weight, bit wear, string ROP, and bit hydraulics, and established a multiple regression ROP prediction model. Warren (1987) gave the prediction model of cone bit penetration rate based on rock compressive strength, string rate of penetration, torque, and bit size. Hareland et al. (2010) established the prediction model of ROP by considering the physical number of insertions in contact with rock, the physical number of insertions through rock, the cutting angle of formation, and the ultimate strength of rock. The ROP prediction model based on the mechanism model takes into account the limited parameters affecting the ROP, and the mechanism relationship between each parameter and the ROP is mostly given through experimental assumptions. Therefore, the accuracy of predicting the ROP based on the physical model is low.
Numerical Study on the Effect of Localized Fluid Pressurization on Shear and Hydraulic Behavior of a Natural Fracture in Granite
Authors: Du M. , Zhang F. , Liu F. , Zhuang L.
Published: September 2022

Mechanical and hydraulic properties of fractures are strongly affected by the exploitation of enhanced geothermal system (EGS) and unconventional reservoirs. This study attempts to reveal the evolution of shearing properties and fluid pressure heterogeneity of natural fractures, possibly caused by mud loss during drilling and hydraulic stimulation. A series of triaxial shear-flow and injection-driven shear numerical simulations were carried out using a coupled hydro-mechanical pore network method (PNM) in DEM. Fracture surface profiles were generated according to the X-ray computed tomography scanning data of open and closed joints of rock cores retrieved from a 4.2-km-deep well at the Pohang EGS site. We developed an algorithm to update the orientations of joint contacts automatically and overcome the mismatch between joint roughness and contact direction especially at large shear displacement. A refreshing fluid grids approach based on the PNM is modified by Delaunay triangulation and Kriging interpolation. The results indicate that injection has caused pressure heterogeneity in the pressurized area. Localized shear rupture could occur in the area with highly concentrated pore pressure. These characteristics also emphasize the significant cause of fluid pressure heterogeneity in rupture propagation in a fracture, likely resulting in unstable slip of critically stressed preexisting faults after small fluid pressure perturbations.

1. INTRODUCTION

Mechanical and hydraulic properties of fractures are strongly affected by the exploitation of enhanced geothermal system when hydraulic stimulation is utilized to enhance the permeability of hot dry rock (Rathnaweera et al., 2020). Anthropogenic fluid injections into rock crust can generate seismicity (Guglielmi et al., 2015; An et al., 2020), which brings more challenges to exploit this clean energy. For instance, an Mw 5.5 earthquake, one of the most damaging events in South Korea, was induced by hydraulic stimulation in 4.2-km-deep granodiorite. After 2 years’ hydraulic stimulation, highly localized fluid pressurization and perturbation induced by hydraulic stimulation destabilized and activated the fault where the main shock happened (Kim et al., 2018; Gorigli et al., 2018). Many injection-driven shear tests experiments and numerical computation have been carried out to investigate injection-induced fracture instability. Ji et al. (2020, 2021) carried out triaxial shear-flow experimental tests and COMSOL numerical simulations to recover fluid pressure heterogeneity on rock fractures. Fluid pressure heterogeneity on a rock fracture may induce localized shear rupture and propagates to activate the entire fracture. Analytical models that could describe the decrease of frictional strength of a rock fracture and predict potential seismic events have been proposed (Wei et al., 2021; Ji et al., 2021).
Contribution of the Water Weakening Effect to Plastic Strain: Case Studies from Danish North Sea Chalk Fields
Authors: Amour F. , Hajiabadi M. R. , Nick H. M.
Published: September 2022

The experimental studies highlighting the strength weakening of chalk when water replaces oil in pore space have incited geomodellers to systematically solve for the effect of water saturation on chalk strength at each simulation step to estimate reservoir compaction. The present study demonstrates quantitatively for the first time the important role played by the water weakening effect on the deformation of several producing fields in the Danish North Sea. Although non-negligible, the water weakening effect in the studied fields is caused by the initial water saturation of chalk rather than by its changes through time. Representative of numerous Danish North Sea reservoirs, the outcome of this study suggests that a preliminary assessment of the potential magnitude of the water weakening effect during production should be first performed prior to compaction simulation. If considered negligible, the adjustment of the rock strength according to the saturation conditions at each simulation step can be ignored, thereby reducing the computing time required to perform coupled geomechanical and fluid flow modelling.

1. INTRODUCTION

Waterflooding of reservoir is a common stimulation technique to enhance the recovery factor of hydrocarbon fields within chalk intervals of the North Sea. The resulting increase in water saturation in pore space leads to a softening of the mechanical properties of the rock, such as the pore collapse stress, a process referred to as the water weakening effect. This process has been extensively studied in laboratory during the last three decades and the underlying mechanisms are still under debate. Nevertheless, the adsorption of ions and water molecules from the aqueous phase at the surface of calcite particles that involves an additional repulsive force between grains favouring grain -to-grain slippage is commonly pointed out as the main mechanisms. Laboratory studies have shown that the pore collapse stress of oil-saturated outcrop samples is consistently reduced by 50-60% when saturated with water, thereby causing additional strain. Triaxial tests conducted on core samples from the North Sea have also demonstrated the dependency of the pore collapse stress to water saturation.
A Case Study on Longwall-Induced Rockmass Permeability Under Medium Cover: Potential Gas Inflow Implications
Authors: Khademian Z. , Ajayi K. M. , Kim B. H.
Published: September 2022

In the Northern Appalachian Basin of the United States, most of the production wells in shale gas reservoirs intersect with a bedded sequence of minable coal layers. The gas wells are often positioned in the coal mine abutment pillars for protection, but longwall-induced stresses may lead to excessive deformation in the gas well casing and potentially leak high-pressure gas to the mining area. Quantitative analyses of the potential gas inflow need an understanding of the rockmass permeability evolution during longwall mining. For this study, a medium-cover (198-m deep) mining site in eastern West Virginia was selected to calculate longwall mining-induced permeability changes. A model in 3DEC numerical modeling code was constructed using the Discrete Fracture Network (DFN) technique to explicitly create fracture systems in the model and calculate fracture apertures under longwall-induced stress and deformations. The calculated fracture apertures are used in a fracture flow code (FFC) to predict the volumetric gas inflow to the mine in the case of a hypothetical breach in a gas well casing. The potential breach location was identified using a 60-arm caliper survey in a test well in abutment pillar, showing that the maximum horizontal displacement occurs 51 m below the surface. The results of FFC simulation for the breach in this location shows that in 100 different DFN realizations, there is no sign of gas reaching the mine workings.

1. INTRODUCTION

Due to the specific geologic conditions in the Northern Appalachian Basin of the United States, many minable coal seams are located above shale gas reservoirs. Shale gas operation wells can intersect with future or active longwall mines, but guidelines must be followed to ensure the safety of both operations (PADEP 2018). If the longwall-induced deformation of rockmass surrounding the gas wells leads to excessive deformation and stress in well casings, the high-pressure, explosive gas may reach mine workings and overwhelm the mine ventilation systems. In order to protect gas wells from longwall-induced deformations, the wells are usually designed to be installed within the abutment pillars between longwall panels. However, for developing safety guidelines, it is important to quantify the amount of gas that would travel to the mine workings in case of well damage.
Research of Casing Deformation Problem Based on U-Tube Effect During Cementing Injection Stage
Authors: Liu Jinlu , Li Jun , Li Hui , Liu Gonghui , Li Yizheng , Wang Shiguo , Yang Hongwei
Published: September 2022

During the cementing injection stage, due to the existence of U-tube effect, the casing deformation and even fracture occur, which seriously threatens the wellbore safety. In this paper, according to the critical moment, the cementing injection stage is divided into the different process. Based on the equations of friction resistance, a calculation method of vacuum section is proposed. Through the analysis of the casing force, a mathematical model for simulating casing deformation and calculating parameters such as displacement is established. The model is validated with data from Well X in the South China Sea, and the simulated results have high reliability, within 10% of the measured values. The results were analyzed and the following conclusions were drawn: when the U-tube effect occurs in the wellbore, the outflow displacement is not equal to the injection displacement; when the vacuum sect ion is generated, the pump pressure is 0; the injection displacement is the most influential factor on casing deformation, and the suitable displacement is 12-14L/s, where the casing deformation is small and fatigue failure does not occur.

1. INTRODUCTION

During past few decades, drilling gradually to the deep well, ultra-deep well development. In the process of development, scholars have encountered many problems, one of which is casing deformation during cementing. Casing deformation is a problem throughout the cementing process, from the beginning of the cementing injection stage to several decades after the waiting setting (Ping et al., 2021; Gqha et al., 2021; Xi et al., 2020). At present, the problem of wellbore integrity after the waiting setting stage has become increasingly mature (Jiang et al., 2020; Yan et al., 2019; Li et al., 2019), but the problem of casing force and deformation during injection stage have not been unified

In cementing injection stage, a U-tube effect occurs in the wellbore because the cement slurry is denser than the drilling fluid. The U-tube effect will redistribute the wellbore pressure field and velocity field, and then affect the force and deformation of casing. At present, scholars have formed a certain understanding of the U-tube effect. A mathematical model and simulation simulator have been established (Beirute et al., 1984; Sauer et al., 1987) to predict the flow rate, bottomhole pressure and other parameters during the U-tube effect in vertical Wells. For directional wells, a computational analysis model has been proposed (Liu et al., 1995) that takes into account the difference between vertical and deviated sections. Corresponding computer software has also been developed (Li et al., 2006), which can be used to analyze the velocity field and pressure field of fluid under different conditions.
Stress Interference Between Fractures of Alternating Fracturing of Horizontal Wells
Authors: Wang Wenrui , Zhang Guangqing , Zhao Chunyang , Shen Liji , Chen Houze , Zhang Tongwu
Published: September 2022

The fracturing sequence could affect the stress disturbance, which is main factor of the formation of a complex fracture network. The characteristics of inter-fracture interference under different fracturing sequences needs to be studied. We carried out the hydraulic fracturing experiment with multiple fracture points under three-dimensional stress conditions. A numerical model of hydraulic fracturing was constructed based on the extended finite element method, which was used to study the effect of fracturing methods under the conditions of different fracture spacing and initial horizontal stress. The results show that :(1) A lot of branch fractures are generated near the main fracture due to subsequent fracture cyclic compression, being perpendicular to the primary fracture. Meanwhile, the stress interference could lead to the activation and coalescence of natural micro-fractures. (2) When the fracture spacing exceeds 25m, and the original horizontal stress difference exceeds 6 MPa, the complex fracture network is more easily formed by alternate fracturing. (3) The average interference pressure will increase with the initial horizontal stress difference, while its rate is less than the increase of initial horizontal stress difference. The higher original horizontal stress would activate less natural micro-fractures. (4) The average interference stress generated by alternating fracturing is higher than that generated by sequential fracturing, ranging from 0.70 MPa to 1.90 MPa. The alternating fracturing is more benefit to form complex network of fractures, with the increase of the initial horizontal stress difference and fracture spacing, comparing with sequential fracturing. This research could guild the optimization of hydraulic fracturing in field application.

1. INTRODUCTION

Horizontal well-staged fracturing technology is crucial for shale reservoirs’ stimulation. However, the fracturing process deflected the hydraulic fractures, and the shape is uncontrollable(Wu and Olson 2015; Wu et al. 2012). Research shows that this phenomenon is that the original fractures will produce stress interference, resulting in uncontrollable subsequent fracture shapes. The shorter the fracture spacing is, the more significant this phenomenon is. However, if a larger fracture spacing is set, the fracturing blind zone will lead to the fracturing effect being unsatisfactory(Wenrui et al. 2018; Gang et al. 2020). Alternate fracturing achieves the result of using stress interference by changing the fracturing sequence, producing a complex and morphologically controllable fracture network. Studying the effect of alternating fracturing stress interference can provide a theoretical basis for better utilization of stress interference.
Dry and Fluid Permeated Hydraulic Fractures and Their Geophysical Signatures in Granitic Rocks
Authors: Butt Awais , Hedayat Ahmadreza , Moradian Omid
Published: September 2022

Passive seismic monitoring can assist in mapping the generated hydraulic fracture network and determining the fracture source mechanisms during fluid stimulation operations. While this is the most applied technique that provides critical information, it has certain limitations which can influence its capability to estimate the efficiency of the stimulation operation. This study involved the HF of true-triaxially loaded low permeability Barre granite cubes with combined real-time active (ultrasonic) and passive (acoustic emission) monitoring using high viscosity gear oil with the injection rate of 0.1 ml/min. After data filtering, acoustic emission (AE) monitoring successfully mapped the fluid induced damage and its evolution in the brittle rocks mass. Different attributes of the continuous ultrasonic signals (velocity and energy) were analyzed in combination with the detected micro-seismic events which highlighted the difference between fluid permeated and non-fluid permeated fracturing along with various fracturing processes induced due to pressurized fluid injection. These results indicate that utilizing different acoustic techniques together has the potential to better characterize the fluid induced damage in brittle rocks.

1. INTRODUCTION

While hydraulic fracturing (HF) is a widely employed technique, it is difficult to predict the HF growth and the underlying mechanisms (Zhuang and Zang, 2021). AE or seismic monitoring at the laboratory or field scales, respectively, is a passive acoustic monitoring technique that has been the most effective and robust technique available for monitoring the fluid induced damage in brittle rocks (Stanchits et al., 2015). This method can record real-time micro-seismic data, which can be utilized not only to map the generated HF but can also be processed to determine the underlying source mechanisms in both field and laboratory scales (Hampton et al., 2018). This detailed analysis of the detected micro-seismicity can greatly assist in determining the efficiency of the stimulation operation (Maxwell, 2014). However, detected micro-seismicity only represents one component of the geo-mechanical response to HF. Micro-seismicity can occur both due to the localized fluid pressure and stress perturbations causing inelastic micro-damage surrounding the propagating fracture (Maxwell et al., 2015). Micro-seismicity will be generated surrounding the injection borehole, even if the fluid is prohibited from entering the surrounding rock, for example through sleeve fracturing (Ishida et al, 2004). Therefore, it may be difficult to distinguish between the fluid permeated fracturing, and non-fluid permeated fracturing. This is a crucial piece of information required for an accurate estimation of stimulated reservoir volume and efficient design of the deep underground stimulation operation.
Influence of Plastic Dissipation on the Behaviour of Hydraulic Fracturing in a Saturated Porous Elasto-Plastic Media Based on the Assumed Enhanced Strain (AES) Method
Authors: Zhang Jianfeng , Hong Yi , Liu Fushen , Wang Lizhong
Published: September 2022

Despite the extensive numerical investigations into hydraulic fracturing with various methods, the constitutive behaviour of the host materials in most of these studies is assumed to be linearly elastic. Under many circumstances, hydraulic fracturing has to take place in geo-materials that exhibit strong plasticity, e.g., geologically stored CO2 fracturing through the overlain clayey caprock. The effect of plastic dissipation accompanying hydro-fracturing on the fracture geometry (e.g., length and aperture) and the near-tip stress field in an elasto-plastic material remains unclear. Meanwhile, there is a lack of numerical tool that enables simulation of discontinuity while taking incremental elasto-plastic constitutive behaviour of the host material into account. In this study, a coupled hydro-elasto-plastic model for investigating and quantifying the effect of plastic dissipation in hydraulic fracturing process is proposed. This is achieved by implementing an incremental hardening/softening elasto-plastic model (i.e., Modified Camclay model, or MCC) into the assumed enhanced strain (AES) method, in conjunction with a coupled flow-deformation approach. The role of plastic dissipation on fracture geometry and the near-tip stress field are interpreted, and discussed with their practical implications.

1. INTRODUCTION

Hydraulic fracture is an important issue encountered in multiple natural processes and engineering applications, such as in the case of CO2 storage, induced cracking under hydraulic structures or stimulation of oil or gas exploitation. Fracturing deformation can significantly influence the permeability and strength of the host materials. Thus, accurately predicting the hydraulic fracturing process is vital to many engineering applications. During the past several decades, numerous research works have been conducted to develop the hydraulic fracture modeling techniques, including the analytical solutions and numerical simulators (Adachi et al., 2007). Notably, most of the existing studies are based on the linear elastic fracture mechanics (LEFM). This may not be suitable for the purpose of predicting fracture characteristics in geo-materials that exhibit strong plasticity, such as the ductile shales and mudstones.
Automated Extraction of Borehole Breakout Properties from Acoustic Televiewer (ATV) Data
Authors: Yang J. , Goodfellow S. D. , Harrison J. P.
Published: September 2022

Analysis of borehole breakouts is a widely used indirect method to estimate in situ stress and assess borehole instability. The Acoustic Televiewer (ATV) is commonly used to log borehole breakouts, but noise inherent to ATV data affects the interpretation of the breakouts. ATV data are usually interpreted manually with associated low efficiency and high cost, and to overcome these deficiencies here we propose a high performance combined de-noising procedure based on the median filter and deep learning techniques. We investigate the use of a convolutional neural network (CNN) method to automate the process of breakout identification, by extracting the underlying relationship between the ATV data and the borehole breakouts. We show that the CNN method can capture breakouts with reasonable accuracy, and when compared to manual procedures the new technique offers both procedural efficiency and reduced interpretation costs.

1. INTRODUCTION

Breakouts occur in borehole walls when the induced stress exceeds the local rock strength. Their presence is thus indicative of high in situ stress conditions, and it is therefore valuable to interpret and analyze them in order to assess borehole stability.

Two kinds of borehole imaging devices are in wide use: optical imaging tools and acoustic imaging tools. The Acoustic Televiewer (ATV), a popular acoustic imaging tool, is the source of the data used in this work. The ATV transmits ultrasonic waves out to the borehole wall, and records the travel time and the amplitude of the echo. The locations and sizes of breakouts can be obtained from interpretation of ATV data.

Currently the process of breakout interpretation is conducted manually, with associated low procedural efficiency and high costs. As a means of avoiding these shortcomings, we set out to investigate whether modern deep learning methods can provide efficient tools for automatic detection and interpretation of breakouts in ATV data. Deep learning segmentation methods are widely used in many different fields, such as identifying tumor boundaries in MRI images (Ranjbarzadeh et al., 2021), delineating infected regions or lesions of lung lobes due to COVID-19 infection in X-ray and CT images (Shi et al., 2021), and detection of cars, traffic signals and pedestrians for self-driving motor vehicles (Song et al., 2018).
Comparative Analysis of Synthetic and Steel Mesh Performance
Authors: Benton D. J. , Sweet D. J. , Emery T. M.
Published: September 2022

The Spokane Mining Research Division (SMRD), of the U.S. National Institute for Occupational Safety and Health (NIOSH) is continuing research on the mechanical behavior of primary surface support components in mining ground support systems. Mining ground control safety often depends on supporting, or at least containing, the ground between rockbolts using what is referred to as local, surface, or areal ground support. Steel mesh, in various combinations and with other components, is often used to accomplish this, as well as to retain loose rock. Local ground support is an integral part of maintaining a safe underground operation. However, as underground hard rock mining continues moving towards automation, increased challenges regarding support installation and maintenance will create a need for a new generation of mesh support systems. Advanced materials engineering has created various synthetic meshes to meet this need. This study begins a process of compiling technical information on multiple types of mesh performance, leading to an eventual comprehensive index for industry use. Using SMRD’s high-energy high-deformation (HEHD) testing machine, a program was developed to assess the behavior of a variety of steel and synthetic mesh products in quasistatic loading conditions. The data from these tests were used for comparative analyses of the force-displacement and energy-displacement characteristics of conventional steel meshes to synthetic meshes. Considerations were also given to several additional operational and performance factors, including corrosivity, flammability, durability, and handling. This work was completed as part of the SMRD mission of improving the health and safety of underground metal mine workers, and this paper presents the findings of these tests.

1. INTRODUCTION

Mining in ground that may fail from the combination of in situ and mining induced stress is commonplace. Ground support elements are installed to reinforce such ground and preserve personnel and mine safety. Typically, the strength of support is considered key, and is used to prevent or halt ground failure. In stiff rock masses, confining stresses generated by the ground support system are very small compared with the stresses associated with rock fracture, and the support pressure will have no direct effect on fracture initiation (Ortlepp, 1969). However, ground movements driven by creep of weak ground or seismic loading may be somewhat effectively managed by support that is able to yield with the ground in a safe manner while maintaining confining pressure on the rock in the immediate perimeter of the opening. In addition, it is usually desirable to contain ground between rockbolts to protect miners from loose rock that might fall or be ejected (Potvin and Hadjigeorgiou, 2020).
Laboratory Investigation Fracture Penetration in Multi-Interlayers with the Cyclic Hydraulic Fracturing
Authors: Tang M. R. , Zhang G. Q. , Lyu Y. J.
Published: September 2022

In the tight reservoirs of Ordos Basin, shale interlayers are abundant. The mechanical properties of interlayers are different greatly from the adjacent sandstones, affecting the vertical propagation of hydraulic fractures, and resulting in a poor reservoir simulation with conventional hydraulic fracturing. The cyclic fracturing is an effective method to improve the efficiency of stimulation in such reservoirs. To verify the penetrating feasibility of hydraulic fractures with the cyclic fracturing and the conventional hydraulic fracturing, stimulation tests with true triaxial stresses are used to simulate the cyclic hydraulic fracturing in outcrop blocks of 300 × 300 × 600 mm. Hydraulic fractures form in the shale interlayer and penetrates both neighboring layers of sandstones. From visual observations and 3D scanning of the fractures, hydraulic fracture penetrations shows that: (1) Hydraulic fractures in the shale interlayer are complex, and a series of horizontal fractures along the bedding exist, which makes it difficult for fractures penetrate into the adjacent sandstones with conventional hydraulic fracturing; (2) Different from conventional hydraulic fracturing, hydraulic fractures can penetrate the neighboring sandstones from shale interlayer with the cyclic fracturing.

1. INTRODUCTION

In recent years, the production of unconventional oil and gas has increased rapidly (EIA, 2021). The Ordos Basin has tremendous reserves of unconventional oil and gas resources. Shale oil in the Ordos basin are over 10 billion tons (Zhou et al., 2020). The production of shale oil in Chang 7 is of great significance for alleviating China’s overly dependence on importing oil and gas and guaranteeing national energy security (Fu et al., 2019).

The shale oil in Chang 7 formation can be divided into three types (Yang et al., 2016) according to lithology, the thickness of sand body and other factors. Type I shale oil has been developed a lot (Fu et al., 2020), and the Qingcheng Shale oil field with an annual output of one million tons of crude oil has been built. However, for Types II and III shale oil, with many interlayers, the thickness of sand body is generally less than 5 m. The reservoir changes rapidly laterally and is strongly heterogeneous. In horizontal well drilling, it is easy to drill into interlayers, resulting in frequent encountering interlayers (Jiao, 2020). As a result, many sections are abandoned with conventional hydraulic fracturing.
Time-Series Event Prediction for the Uranium Production Wells Using Machine Learning Algorithms
Authors: Merembayev Timur , Amanbek Yerlan
Published: September 2022

The efficient estimation of the production rate in the uranium reservoir plays a vital role in the evaluation of operational performance. This paper presents the data-driven production model in the uranium field using LightGBM for the data from the Kazakhstan deposits. We focus on predicting the fault events of the well production solution. Numerical results of this investigation show that LightGBM achieves an accurate prediction with wavelet transformation. The evaluation of the model score is conducted by using metrics such as Recall and F1. With feature engineering by wavelet transformation, we obtained the recall of 0.84 and f1 of 0.89. The LightGBM model with the Morlet wavelet transformation can be useful to solve the issue of prediction maintenance of production well.

1 INTRODUCTION

Uranium production has been gaining importance in recent years since it can be utilized for sustainable nuclear energy, which is also a low-carbon energy source. Due to the Covid-19 pandemic in the world, the optimization of uranium production is required to meet limited demands. In situ leaching (ISL) or in situ recovery (ISR) technology is widely used for uranium production in many countries, including the US, Canada, Russia, China, Kazakhstan. Kazakhstan has a large portion of the world’s uranium production. The main deposits utilized the ISL technology for the production places such as Inkai, Mynkuduk, Moinkum, Kanzhugan, and others (Grancea et al., 2020). ISL method is one of the key recovery technology for uranium in the Kazakhstan fields. In this method, the sulphuric acid is injected into the subsurface to extract pregnant uranium solutions to the surface (Grancea et al., 2020). Next stages, the pregnant solutions go through several chemical processes and refinement steps to recover a uranium concentration.

The literature on the modeling of well production shows a variety of approaches, particularly the flow and transport simulations in the oil and gas industry. In (Regnault et al., 2015), the reactive transport model in 3D was proposed to predict the production of uranium solution. In this model, the accuracy of the result can be achieved by using detailed information on the geometrical properties. To improve computational time of the reactive transport model, parallelization with GPU was developed for the streamline-based simulation in (Tungatarova et al., 2020). Asymptotic analytical solution of the 1D flow with chemical reaction was developed by (Panfilov et al., 2016). This model was verified qualitatively by the result of laboratory experiments for the uranyl sulfate.
A Numerical Comparison of Linear Elastic and Cohesive Fracture Models for Hydraulic Fracturing Based on Assumed Enhanced Strain (AES) Method
Authors: Liu Fushen , Zhang Jianfeng , Cheng Zhang , Hong Yi
Published: September 2022

Geomaterials are porous, and there are air, water and other liquids inside the pore space. Pore pressure fluctuation may result in the change of contact forces between the solid grains. The deformation of solid skeleton changes the size of pore and therefore the fluid flows inside the pore space. The coupled process is often described with the mixture theory in continuum mechanics. Localized deformation may lead to the displacement discontinuity or the fracture, increasing the complexity of the whole fluid-solid coupled process. Numerical simulations of the complex processes in the subsurface are essential in understanding many geoengineering systems, such as hydraulic fracturing, geological fault reactivation, waste water management, geothermal energy extraction and CO2 sequestration and so on. This paper presents an assumed enhanced strain (AES) finite element method to model the fracture evolution in porous media, where the discontinuous function enrichments are introduced into the displacement approximation to simulate fracture deformation. The enriched degrees of freedom can be removed by the standard static condensation method, which means the method does not introduce additional global system of equations. The mass and stress coupling is described by the standard Biot’s poro-elasticity theory. The numerical method is verified by the mesh sensitivity studies and comparisons with analytical solutions. Particularly, with the AES framework, we have numerically compared the cohesive fracture model and linear elastic fracture mechanics model for simulating hydraulic fracture propagation in porous media.

1 INTRODUCTION

Predicting the mechanical behavior of subsurface fractures is crucial to many engineering practices, especially in the industry of energy resources. Subsurface processes, such as hydraulic fracturing and induced seismicity, pertains to the fracture deformation and propagation driven by fluid flows in subsurface porous media. Hydraulic fracturing is dominated by the opening mode, while induced seismicity may be dominated by the shear modes. Fracture deformation and propagation can also significantly impact subsurface fluid flows, by providing additional flow conduits or barriers to the subsurface. Therefore, understanding the interaction between fractures and fluid flows in porous media is key for the comprehension of those subsurface processes. The motivation of this work is to provide a convenient finite element framework to simulate fracture propagation coupled with fluid flows in the complex subsurface environment.
Composition and Structure of the EGS Collab Test Bed 1 Based Upon Electrical Resistivity Tomography, Core Compositions, and Wireline Logging
Authors: Roggenthen W. M. , Johnson T. C. , Crandall D. M. , Paronish T. J. , Ulrich C.
Published: September 2022

The EGS Collab project drilled eight 60 m long boreholes at the Sanford Underground Research Facility (SURF) at a depth of 1.5 km to support rock fracturing and stimulation investigations. The test bed was in a complexly folded metasedimentary carbonate mica phyllite with a NW-SE structural grain. Monitoring included electrical resistivity tomography (ERT) that shows the presence of a well-defined electrical conductivity high that defines a fold structure occupying much of the test bed with an orientation similar to the local structure. The nature of this folded conductive unit was evaluated using a range of methods characterizing the rock and geophysical properties. These included core examination, high resolution XRF analyses on selected core intervals, and wireline geophysical logs. Electrical resistivity profiles from the wireline geophysical surveys are consistent with the electrical resistivity tomographic three-dimensional images, and the XRF profiles show elevated levels of sulfur in the vicinity of the interpreted conductivity anomalies. The compositional and wireline logging data are consistent with interpretations from the ERT data. Based upon these observations the best candidate for the source of the high electrical conductivities is the presence of significant amounts of sulfides within the unit making up the folds.

1. INTRODUCTION

The EGS Collab Project has developed two test beds within the underground of the Sanford Underground Research Facility (SURF) located in Lead, SD, USA. The test beds support investigations of fracturing, stimulation, and modeling of these processes at the 10-meter scale in crystalline rocks (Kneafsey et al., 2018). The experiments support the implementation of geothermal utilization by improving the ability to predict and control fractures created and stimulated during the experiments (Kneafsey et al., 2019; Kneafsey et al., 2020). The first test bed (E-1) is located on the 4850 Level of SURF (1.5 km below the surface), and the second (E-2) is located on the 4100 Level. Of these experimental areas, only results from Test Bed E-1 will be discussed here. A major part of the monitoring of the test bed experiments consisted of the application of a range of geophysical techniques that were active as the fracturing and stimulation of regions in the test bed were conducted. These techniques were also employed to characterize the state of the test bed prior to the experiment initiation.
Comparison of Sand Onset and Sand Mass Models in a Field Case
Authors: Papamichos E. , Furui K. , Berntsen A. N. , Rolli O. A. , Morita M. , Koch C. , Li G. , Morgan S. , Nes O.-M. , Yao Z.
Published: September 2022

Sand production onset and mass/rate predictions are difficult to validate in the field because the field sand production data are often unreliable. To overcome this difficulty recent research has concentrated in representing as realistically as possible the field conditions in laboratory experiments and focused on the effects of fluid saturation of the test specimens and the effects of stress anisotropy. The laboratory results were used to calibrate a semi-analytical model and a numerical nonlinear finite element model for developed for sand onset and sand mass/rate prediction studies. The correlations pertain to sand production functions that depend on the fluid saturation and stress anisotropy and account for the observed physical behavior in the laboratory. The models are compared for field case analyses including parametric studies of various completion and operational parameters. They show the importance of anisotropy and fluid saturation during the upscaling from laboratory data to the field.

1. INTRODUCTION

Sand management of sand producing field requires accurate predictions of sand onset and sand mass to optimize the well completion method and the drawdown and depletion during the life of the well. Research in sand production has addressed various issues in this topic by e.g., classifying sandstones according to their sand production potential, by looking at multiphase flow conditions and the effect of water breakthrough and gas flow in gas reservoirs.

Recent research has concentrated in representing as realistically as possible the field conditions in laboratory experiments and focused on the effects of fluid saturation of the test specimens and the effects of stress anisotropy. The laboratory results are used to calibrate both a semi analytical model for sand onset and sand mass prediction and a numerical model with empirical correlations based on field data. Both models are used in the industry for field case analyses and sand onset and mass predictions.
Thermal Imaging for Rockfall Detection
Authors: Wellman E. C. , Schafer K. W. , Williams C. P. , Ross B. J.
Published: September 2022

Under a NIOSH research grant, the Geotechnical Center of Excellence (GCE) evaluated the capability and limitations of thermal cameras to detect rockfall events and the conditions that can lead to rockfall. This two-year study tested four different thermal imaging cameras in controlled rockfall experiments and long-term surveillance tests in various mines and conditions. The cameras can detect rockfall events at less than their resolution as rockfall creates larger craters, impacts, and dust trails visible in the thermal IR. The surveillance test determined that the cameras work in both day and night conditions under a wide range of conditions. However, fog, heavy precipitation (rain, snow, hail), and dust limited visibility in the thermal IR.

Four thermal infrared cameras were acquired for the project. The cameras were installed on a mobile mine monitoring platform. The project tested thermal imaging cameras’ effectiveness to detect and record rockfall events and rockfall hazards in surface mining operations as a method to protect mine workers from the risks of rockfalls. One of the primary findings of the project is that off-the-shelf cameras can be used to increase situational awareness at the mines in low-light conditions. This presentation will document camera selection, resolution, and results from the project.

1. INTRODUCTION

The Thermal Imaging project for Rockfall Detection Mobile Monitoring Platform (MMP) has been deployed at seven different open-pit mines for over one year. Since April 7, 2021, the MMP has been deployed with all four thermal cameras installed and operational at seven Western US and Canada mine sites. The system was initially deployed at two different mine sites in Arizona starting in January 2021 with three cameras.

The research project has tested thermal imaging cameras’ effectiveness in detecting and recording rockfall events and rockfall hazards in surface mining operations as a method to protect mine workers from the risks of rockfalls. One of the primary goals is to identify cost-effective, off-the-shelf systems that can be integrated with existing slope monitoring systems or installed separately as a part of routine mine observations.
Groundwater Drainage-Induced Rock Mass Deformation During the Gotthard Base Tunnel Excavation in the Swiss Alps: 3D Modelling and Comparison to Field Measurements
Authors: Zhao C. , Lei Q. , Zhang Z. , Loew S.
Published: September 2022

The Gotthard Base Tunnel (GBT), constructed between 2000 and 2011, is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Swiss Alps. Significant ground surface displacements up to 10 cm were observed during and after the tunnel construction. To gain a better understanding of the physical mechanisms underpinning such conspicuous ground deformations, we develop a 3D fully-coupled hydro-mechanical model to simulate the excavation-induced groundwater drainage, stress perturbation, and poroelastic response in faulted rock masses over both space and time. First, we construct a geological model with topographical features, lithological units, and natural faults realistically represented. We constrain the material properties of faults and rock masses based on extensive laboratory testing results and site characterisation datasets. We then simulate the tunnelling process with the resulting coupled hydro-mechanical responses of the faulted rock captured and ground surface displacements analysed. The simulation results show a good agreement with the field monitoring data of both ground surface displacement and tunnel settlement. The research findings from our work have important implications for many groundwater drainage-related geoengineering activities such as underground excavation in alpine mountains and fluid withdrawal in subsurface reservoirs.

1 INTRODUCTION

The Gotthard Base Tunnel (GBT) is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Central Alps of Switzerland (Fig. 1). The excavation work of the two tunnel tubes started in 2000 and successfully completed in 2011. The Sedrun and Faido sections of the GBT are located in crystalline basement rocks of the Gotthard Massif, where three arch dams are located on the ground surface at the Nalps, Curnera and St. Maria hydropower lakes. Due to the significant concern regarding the safety of these nearby hydropower infrastructures during and after the GBT excavation, a comprehensive in-situ monitoring system was installed to closely monitor the surface displacement and tunnel inflow/settlement. According to the monitoring data, up to 10 cm surface displacements and 50L/s tunnel inflow took place during the construction period (Loew et al., 2015).