bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Elliptical-Geometry Wellbore on Zonal Isolation
Authors: Zheng D. , Miska Z. , Ozbayoglu E. , Zhang Y. 
Published: September 2022

ABSTRACT:
Zonal isolation is key to the safety of drilling, injection, and production. If zonal isolation fails, significant financial losses or environmental damage can occur. Cement integrity is critical to maintain zonal isolation. The objective of this paper is to study the influence of wellbore shape on cement sheath integrity and zonal isolation. To diagnose cement sheath integrity, cylindrical wellbore models which contain circular-shape casing, cement, and formation layers have been built. However, the wellbore geometry in real drilling process is elliptical instead of circular. In this study, we built an elliptical-geometry Casing-Cement -Formation System (CCFS) analytical model by applying complex variable method. Two case studies were performed with the elliptical-geometry CCFS model and circular-shape CCFS model that does not consider the wellbore shape factor.

1. INTRODUCTION
Quality of cement is an integral part of well integrity. The change of downhole condition and post well site operation may lead to change of the stress-strain state of casingcement- formation system (CCFS) [1]. Cement sheath failure is manifested by inter zonal annular fluid movement and abnormally high annular pressure at some point behind casing up to and at the surface [2]. The detrimental effects of cement sheath failure are numerous and may cause lost revenue from lost production, potentially hazardous rig operations and producing operations. Losing zonal isolation may lead to contamination of freshwater table [3]. To understand the failure behavior of cement is significant for maintaining zonal isolation.
Previous research has built analytical/numerical models for predicting the stress distribution around the circular wellbore [4] [5]. However, wellbore geometry in real drilling process is elliptical instead of circular. The geometrical irregularities can result from a combination of geology and/or drilling/completion operations [6]. Two reasons that may cause elliptical geometry were listed here: 1) Tilt angle is the angle between the centerline of the hole and the centerline of the bit. Figure 1 is a simple sketch of tilt angle. The red line shows the plane that is perpendicular to the hole axis. The geometry for this plane is elliptical because of tilt angle.
Influence of Grain Structure Representation on Bonded Block Models of a High Porosity Rock
Authors: Chaurasia A. , Walton G. 
Published: September 2022

ABSTRACT:
With the increased adoption of numerical modeling in the last two decades, it is now possible to study rock mass deformation and failure using tools such as FEM (Finite Element Method), DEM (Discrete Element Method), and FDEM (Finite Difference Element Method). Bonded Block Models (BBMs) are a type of DEM that can be used to simulate rock at both the laboratory and field scales. However, limited studies have been performed on high porosity rocks (porosity &gt; 15%) using BBMs. This research focuses on the generation of a 2-Dimensional 27% porosity BBM model for a large-scale Texas Cream Limestone specimen using two different approaches. The first approach uses the software Neper, which uses the block size distribution, distribution type, and circularity to generate a convex polygonal block structure; to achieve 27% porosity, some blocks are removed from the structure ensuring that each block has at least one contact. The second approach uses PFC to generate circular balls with a bimodal size distribution to achieve an initial 12-15% intrinsic porosity; an algorithm in MATLAB is then utilized to convert this into a polygonal structure, and the removal of additional small blocks increases the porosity to 27%. Following initial model calibration, model results are used to understand the effects of different block and pore structures on the emergent behaviors of the BBMs.

1. INTRODUCTION
Underground mine pillars provide natural stability to the mine area allowing for safe operations. If the load on a pillar exceeds its strength, it will fail and can increase the risk of subsidence, roadway blockage, worker injuries, air blast, etc. Therefore, a sound knowledge of pillar failure mechanisms is necessary to design stable pillars under different loading and geologic conditions. Empirical pillar design approaches provide a reliable and straightforward option for the preliminary design of hard and soft rock pillars. However, these empirical approaches have some limitations that need to be addressed, such as their inability to explicitly account for post-peak behavior and rock-support interaction. Large-scale laboratory tests offer a potential alternative approach to study pillar behavior, but such tests are expensive, time consuming, and difficult to conduct in practice (Bieniawski, 1968; van Heerden, 1975). With the advent of high performance computational software, it is now possible to use numerical modeling tools to study rockmass deformation and mechanical behavior in various geological conditions. This study considers a scenario where limited large-scale laboratory testing results can be used to constrain numerical models, which in turn can be used to study rock pillar failure mechanisms and rock-support interaction.
Experimental Study on the Causes and Protective Measures of Hydrogen Sulfide in Formation and Wellbore
Authors: Qi He , Guangsheng Cao , Daye Wang , Yongcun Feng , Jingen Deng , Zhiyi Zhou 
Published: September 2022

ABSTRACT:
The generation of H2S (hydrogen sulfide) in formation and wellbore is a significant cause that results in natural disasters, wellbore corrosion, and personal safety. It is essential to study the generation causes and precautions of H2S to avoid harmful gas damage. BSR (bacterial sulfate reduction) and TSR (thermochemical sulfate reduction) experiments have been discussed based on different reaction environments and conditions of H2S. It has been demonstrated that BSR is the primary cause and TSR is the secondary cause of the H2S generation in the studied fractured wells. The existence of SRB provides a premise for the occurrence of BSR. The pH value of solutions will affect SRB activity and H2S generation quantity. The reaction temperature will affect whether TSR occurs and the amount of H2S generation. The reaction pressure only affects the occurrence time of H2S in TSR, but hardly affects the generation quantity. Furthermore, the replacement of fracturing fluid formula, NaOH, bactericides and high temperature steam can be used to inhibit the generation of H2S in the formation and wellbore. This study has a certain reference value and suggestions on the causes, influencing factors, laws and prevention methods of H2S in oil reservoir.

1. INTRODUCTION
Hydraulic fracturing is one of the most significant technical issues to improve underground flow environment and increase the well production in petroleum engineering. It has made great achievements in the field of rock mechanics in recent decades(Atkinson, 2015; Hubbert & Willis, 1957). In the process of hydraulic fracturing, fracturing fluid needs to be injected to extend fractures and transport proppant into the fractures, so that more fluid channels can be kept open for a long time(Gandossi & Von Estorff, 2013). However, use of fracturing fluid with certain composition in some oil and gas fields may generate toxic gas and endanger personal safety(Michalski & Ficek, 2016). Taking Daqing Oilfield in China as an example, hydrogen sulfide (H2S) has been detected from some fractured wells, and the value has greatly exceeded the allowable safety range (150 mg/m3 for H2S). Furthermore, the presence of H2S will also corrode wellbore and bring environmental risk because of its sour corrosivity(Hedges, Chen, Bieri, & Sprague, 2006; Holubnyak et al., 2011). Hence, the generation source, influencing factors and elimination measures of H2S generated from the formation or the wellbore ought to be found out immediately.
A Comparison Between Field-Measured and Empirically Estimated Rock Mass Modulus Values
Authors: Lindenbach E. J. , Dalton S. C. , Bearce R. G. , Arany G. D. 
Published: September 2022

ABSTRACT:
Rock mass modulus, also referred to as the deformation modulus, is an important input variable for any load-deformation analysis of a foundation, such as a finite-element analysis for a dam. As the representative volume of rock is increased the rock mass will appear weaker and more deformable due to the inclusion of more discontinuities. The rock mass modulus can be measured directly downhole with a variety of devices, such as a uniaxial or radial jacking rig, a flat jack, or more commonly, a dilatometer. Modulus values can be estimated indirectly using site-specific empirical relationships.
This paper provides a comparison of field- and laboratory-derived rock mass modulus values in an effort to develop a range of likely parameters and evaluate data quality/confidence levels. The in-situ values were compared to values developed from eight commonly used empirical relationships. Results indicate that the dilatometer-measured and empirically estimated values are similar where the rock is massive and relatively intact but vary significantly where the rock is fractured or weathered. These significant variations appear to be related to how the rock deforms in unconfined/semi-confined conditions (i.e., failure occurs into open space).

1. INTRODUCTION
The deformation modulus of the underlying rock mass is an important input variable for any load-deformation analysis of a foundation, such as a finite-element analysis for a dam. The deformation modulus of a rock mass is subject to the scale effects typically found in any rock mechanics analysis. An in-situ rock mass may have a modulus that is a fraction of the intact modulus of specimens tested in a laboratory due to the heterogeneous nature of the mass and presence of discontinuities (fractures, joints, faults, etc.) that serve as planes of weakness. Variability of these rock mass properties can result in wide ranging modulus values for discrete test intervals (in-situ and laboratory). In general, as the scale of the rock mass being analyzed is increased, the number of weaknesses increases and the rock mass will appear weaker and more deformable (Wyllie and Mah, 2004). Both deformation modulus and rock mass modulus terms imply load deformations in the elastic and inelastic ranges (Ulusay and Hudson, 2006).
Developing a range of values for model inputs is important as a lower foundation modulus is not necessarily more conservative; the "softer" foundation may allow more transfer of dam load to the abutments and can also lead to increased damping during an analysis of seismic stability. Performing the load-deformation analysis with a variety of rock mass modulus inputs allows a reduction in uncertainty regarding a dam’s reaction under static or seismic loads. The sensitivity of any design to changes in the inputs is likely more critical than any discrete calculation of anticipated deformation or stability (Hoek and Diedrichs, 2006).
Analysis of Concentration Field in Underground-Storage Salt Cavern Using Two-Well-Vertical Solution Mining
Authors: Guan Yueyang , Ban Fansheng , Wang Xiaoyang , Chen Chunyu 
Published: September 2022

ABSTRACT:
The well spacing and the brine concentration are crucial for the volume and morphology of the two-well salt cavern gas storage by affecting dissolution rate of the cavity. However, it is hard to directly monitor the brine concentration inside the cavity. This study uses the classical method of Navier-Stokes, based on which the three-dimensional mathematical model of Two-Well-Vertical solution mining is established. Using Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm to solve the concentration distribution, while using Volume of Fluent (VOF) algorithm to solve the movement of boundary, so as to research the variation of cavity shape. According to the simulation results, it can be concluded that the region with the brine concentration of 210 g/L – 270 g/L is the key to enlarge the cavity volume in the connectivity stage. Compared with single-well salt cavern gas storage, two-well salt cavern gas storage mainly expands along the connection direction of two wells. The well spacing of 50 m can increase the maximum cavity diameter by nearly 78% compared to that of 10 m. With the increase of well spacing, the final cavity shape will change from cone shape to hump shape, however, the large well spacing may affect the cavity forming efficiency.

1. INTRODUCTION
There are more than 800 underground gas storage facilities in the world, and the total capacity is close to 450 billion cubic meters (Caineng Zou et al. 2020). Among them, salt cavern gas storage is the main technology for natural gas storage due to its lower permeability, higher gas injection efficiency and less gas consumption of cushion. However, Considering the number of salt cavern gas storage, the storage volume of salt cavern gas storage is much smaller than other underground gas storages. Therefore, accelerating the construction and increasing the volume of salt cavern gas storage are the most dominant approach to improve the competitiveness and economy. The construction of salt cavern gas storage mainly uses the salt layer of certain depth to dissolve. When the string reaches a predetermined depth, fresh water is injected to dissolve the salt layer, forming a storage space for natural gas.
Up to now, a series of experiments and theoretical studies have been carried out about salt cavern underground gas storage. Menezes, J. D. et al. applied mixed boundary and finite element methods to numerical simulations of salt caverns, in order to study the state of natural gas in underground rock salt (Menezes, J. D. and Nguyenminh, D. 1996). The ground subsidence and cavity dissolution were analyzed by comparing the numerical simulation results with actual data.
A Conventional Neural Network Lithology Classification Method Based on Vibration Data
Authors: Chen Gang , Tan Peng , Li Jiran , Jiang Hailong , Fu Li , Yang Henglin 
Published: September 2022

ABSTRACT:
Drilling string vibration data is a high-density ancillary data and it has the advantages of low-latency and low-cost which can be acquired in real time. In this study, vibration dataset is used as signal source, and the original vibration signal is filtered by Butterworth (BHPF). vibration time-frequency characteristics are extracted into time frequency images with the application of short-time Fourier transform (STFT). This paper develops lithology classification models using new data sources based on convolutional neural network (CNN) combining with Mobilenet and ResNet. This model is used for complex formation lithology including fine gravel sandstone, fine sandstone and mudstone. In order to improve the trustworthiness of decision-making results, the gradient-weighted class-activated thermal localization map is applied to interpret the results of the model. The final vertification test shows that the single-sample decision time of the model is 10ms, the test macro precision rate is 90.0%, and the macro recall rate is 89.3%. The lithology classification model is more efficiency and accessible. In conclusion, The CNN model using drill string vibration supplies a superior method of lithology classification. This study provides low-latency and low-cost lithology judgment methods to ensure safe and rapid drilling.

1. INTRODUCTION
Lithology classification of underground formation is of great importance in the field of oil & gas exploration engineering as lithology represents the reservoir petrophysical characterization.(Buryakovsky et al. 2012). Vibration data of drill string can also be used to make real time lithology classification considering different formation characteristics. (Esmaeili et al. 2012b)
Some researchers made logging-based lithology prediction by using artificial neural networks. It is demonstrated that lithofacies information from images could be used for lithology classification based on ANN.(Ivchenko et al. 2018) Random Forest is always applied to make underground formation lithology compared with other machine learning algorithms such as GTB, GBM and AdaBoost.(J. Sun et al. 2019) Baraboshkin applied convolutional neural networks on rock description based on color distribution and feature extraction by using different neural network architectures. GoogleNet make a better performance than other algorithms.(Baraboshkin et al. 2020) Ahemd used three machined learning models to predict the lithology changes and formation tops in real-time while drilling including ANN, ANNFIS and FNN, the results shows ANN model shows better performance.
Laboratory Imaging of 2D Hydraulic Fracture Propagation in Laminated Shale
Authors: M. Gu , G. Li , S. Cheng , M. Sheng , S. You , S. Tian 
Published: September 2022

ABSTRACT:
Man-made fracture systems caused by hydraulic fracturing is an essential way to improve the success of reservoir stimulation for hydrocarbon production. However, direct observation of reservoir stimulated regions including induced fractures has been difficult. This paper proposed a 2D high-speed imaging scheme for hydraulic fracturing test in the plane strain and in-situ stress conditions. Five bedding angles were taken account to understand the effects of shale anisotropy on hydraulic fracture propagation. The dynamic propagation behaviors and their trajectories were recorded by high-speed camera in 240 Hz. Results indicate the fracture initiation angle is correlated to the shale bedding angle. The fracture initiated along the prefabricated fracture line when β= 30° and 90°. On the contrary, when β= 45°, 60° and 75°, the fracture deviated from the original fracture line and propagated along the bedding direction after initiation of the prefabricated fracture tip, and the induced fracture becomes more likely to divert into the shale bedding direction as the bedding angle becomes larger.

1. INTRODUCTION
Understanding man-made fracture systems caused by hydraulic fracturing is essential to improve the success of reservoir stimulation for hydrocarbon production (Miller, Paneitz, Yakeley, & Evans, 2008). The initiation and propagation of hydraulic fractures are more complex due to the large differences in mechanical properties between shale and sandstone(Dahi-Taleghani & Olson, 2011; Kan & Olson, 2015; Mehrabi, Pei, Haddad, Javadpour, & Sepehrnoori, 2021). As shown in Fig. 1, the interaction of hydraulic fractures with shale bedding structures is the primary cause of complex fracture morphology(Fisher & Warpinski, 2012). The actual fracture height is recognized to be lower than desired value since the shale bedding is activated by hydraulic fracturing(Gao & Ghassemi, 2020; Miskimins & Barree, 2003; Yue, Olson, & Schultz, 2019). It is significant to understand the initiation and propagation behaviors of hydraulic fractures in height by considering the activation of shale bedding structures.
Design and Field Application of Large-Size PDC Bit in Gravel Layer in Tarim Basin
Authors: Bo Zhou , Ning Li , Shenglei Wang , Bao Zhou , Hongjun Liang , Bin Tang , Jinlong Liu , Xueqing Liu 
Published: September 2022

ABSTRACT:
It is one of the key difficulties that extremely thick gravel layer distributed in the shallow and middle layers in the Tarim Oilfield. The maximum thickness of the gravel layer is more than 5000m, which seriously restricts the efficient exploration and development of Piedmont tight sandstone oil and gas reservoir. According to the characteristics of gravel layer in Bozi block, this paper selects the appropriate outcrop, studies the parameters such as conglomerate composition, hardness and compressive strength through rock mechanics experiments, and summarizes the diagenetic characteristics of gravel layer in Bozi block. The experimental results show that there are great differences in mineral composition in the plane of rock samples and a wide range of spatial strength variation, so the impact load on the bit during drilling is large. According to the results of experiments, a new large-size PDC bit is designed from optimization of cutters, tooth arrangement and force balance design. The designed large-size PDC bit has obvious effect of speed-up, which achieves the footage of a single bit is 510m, and the ROP(rate of penetration) is 1.89m/h. Compared with adjacent wells with the same lithology in the same well section, the footage and average ROP of a single bit are doubled, which achieves a good speed-up effect, and provides technical reference and support for efficient exploration and development of oil and gas reservoir in the Tarim Basin.

1. INTRODUCTION
Huge thick gravel layer is developed in the upper part of Kelasu structural belt in Kuqa depression, Tarim, especially in Bozi block. The average thickness of gravel layer is 3000m and the maximum thickness is more than 5000m(Teng et al., 2015; Zhong et al., 2012). Multiple sets of strata contain gravels with different compositions, which are poor sorting, strong heterogeneity and poor drillability. During the drilling process, cutting teeth of conventional PDC bits are easy damaged due to the positive impact of gravel. The damage of PDC teeth leads to slow ROP(rate of penetration), less bit footage and more bit consumption(Pei, Yan, & Hongbo, 2020; Zhang, Dang, Chen, & Zhang, 2017), that seriously restricts the efficient exploration and development of oil and gas reservoir.
Damage Character and Fracture Propagation Study of Longmaxi Shale in Southern Sichuan Basin During Hydraulic Fracturing
Authors: Fu Li , Yang Henglin , Xi Yunlong , Chen Gang , Zhang Guangqing , Lv Yanjun 
Published: September 2022

ABSTRACT:
Longmaxi S1l11 layer is main shale gas reservoir formation in southern Sichuan Basin, the difference of sublayer post-fracture response is significant. In this paper, we make triaxial tests with Longmaxi shale samples from southern Sichuan Basin layers to study damage character during hydraulic fracturing. Cohesive unit numerical simulation method is used to study the characteristics of hydraulic fracture (HF) propagation considering shale damage. The results show that in Longmaxi shale compression damage is divided into three stages: compaction, linear damage and rock failure. Reservoir shale damage due to HF concentrated in the linear damage stage. The degree of S1I13, S1I14 shale damage is greater than that of S1I11, S1I12 shale with the same strain. Fracture propagate straight into S1I12 layer after S1I11 layer fracture initiation, most fractures propagate into S1I11 layer, and few fractures propagate into S1I13 layer after S1I12 layer fracture initiation, which is the similar HF in S1I13 layer. The fracture propagation of S1I11 and S1I12 layers is highly sensitive to the liquid injection displacement. With the increase of liquid injection displacement, the total length of the fracture increases significantly and the number of damage and failure units increases significantly. During HF propagation, more plane bedding and natural weak surfaces can be better connected and opened to form more branch fractures; The fracture propagations of S1I13 and S1I14 sublayers are highly sensitive to the liquid injection displacement. With the increase of liquid injection displacement, the total length of fractures and the number of damage and failure units are significantly reduced. During the fracture propagation of S1I13 and S1I14 sublayers, the fracture shape is relatively straight, and only a small amount of plane bedding and natural weak surfaces in the formation are connected and opened, forming a small number of inconspicuous branch fractures.