bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experiment Study of Stress and Pore Pressure in Setting Cement Paste
Authors: Hu Zhao , Yonglin Shan , Jiadi Ding , Ligang Shi , Dayang Wen , Wenke Cao , Wei Liu 
Published: September 2022

ABSTRACT:
Cement sheath integrity plays an important role in ensuring the wellbore safety. Shear failure, tensile crack or debonding may happen in the cement sheath during the cement sheath setting, later pressure test or production period. The failure condition is up to the effective stress state and strength criterion. However, how to determine effective stress in the cement sheath is difficult. In this paper, a device is designed to test the lateral and pore pressures evolution of a cement column when a constant pressure is applied on the top of the column. Meanwhile, the cement paste volume change could be monitored. It is found that the lateral and pore pressures show a three-stage feature of stable-decrease-stable when the cement paste is hardening. The lateral and pore pressures are nearly equal at the early time and then separate without water charging, both the ultimate pressures are pretty low. The lateral pressure and pore pressure are nearly same too when suppling water to cement. However, the ultimate pressures are slightly higher than the former case. The experiment study could provide an inspect to research cement behavior, which contributes to developing and verifying the cement sheath stress evolution model.

1. INTRODUCTION
Cement sheath integrity is important to the wellbore safety. In order to study the cement integrity condition, the stress state is needed to know first. However, it is not easy to determine the cement sheath stress state. Since cement sheath is originally slurry, the cement solidification process changes its material physical and mechanical properties. The stress state of cement sheath may be different from its initial hydraulic pressure.
The casing-cement-formation is normally regarded as an entire system, the cement sheath stress state could be obtained based on the thick wall cylinder theory. The methods include theoretical solution (Li et al., 2015; Liu et al., 2017; Thiercelin et al., 1998; Yuan et al., 2013) and numerical simulation (Nabipour et al., 2010; Wong and Yeung, 2005). Both of them could provide an exact cement stress distribution. However, these models usually assume the system is a one-part structure, it means that the stress or displacement boundaries are applied on the model at one time. Actually, such treatment disagrees the fact, the well construction, the hole drilling, casing running and cement pumping are done separately and step by step (Gray et al., 2009). Therefore, the cement stress state should consider the procedure and the cement setting process (Agofack et al., 2019; Amziane and Andriamanantsilavo, 2004; Zuo and Bennett, 2019).
Improvement of Lost Circulation Control While Drilling by Using Managed Pressure Drilling System
Authors: Zhang Pei , Ma Tianshou , Liu Yang , Li Zhilin , Zhong Chengxu 
Published: September 2022

ABSTRACT:
Due to the complex lithology and geological conditions of deep and ultra-deep formations, fractured formations with narrow safety mud weight window are often encountered during drilling, which is easy to cause lost circulation and gas kick. In order to enhance the pressure bearing capacity of fractured formations, lost circulation material (LCM) is usually employed as an effective measure. However, the wellbore pressure fluctuation in conventional drilling can affect the fracture width, which makes LCM difficult to enter into the fracture, consequently, lost circulation occurs frequently. In this paper, we aim to explore the improvement of lost circulation control while drilling by adjusting the fracture width using managed pressure drilling (MPD) system. Firstly, the range of wellbore pressure fluctuations in the process of drilling operation was investigated. Then, the changes of fracture width with dynamic wellbore pressure were calculated and analyzed. Finally, the relationship between fracture width and choke pressure of the MPD system was analyzed, and the proper choke pressure was optimized to enhance the effect of lost circulation control while drilling. The results indicated that with the increase of wellbore pressure, the fracture width gradually increases, and the stronger the nonlinearity of fracture width distribution. The fracture width is highly dependent on the wellbore pressure, and the dynamic wellbore pressure will cause dynamic fracture width. The improper particle size distribution of LCM is difficult to match the dynamic fracture width in the process of lost circulation control while drilling. An appropriate stable wellbore pressure is a useful way to adjust the fracture width, which can make the LCM enter into the fracture to bridge, consequently, the lost circulation control while drilling can be improved by adjusting the fracture width using the MPD system.

1. INTRODUCTION
With the development of oil and gas resources of deep and ultra-deep formations, more and more deep and ultra-deep formations with complex lithology and geological conditions will be encountered during drilling (Ma et al. 2016). Due to the deep and ultra-deep formation is generally featured by well-developed fractures, so as to the pressure bearing capacity are significantly reduced by the existing of weak fractures (Liu et al. 2020a). Consequently, the deep and ultra-deep formations usually have a narrow safety mud weight window, and even the caving pressure or pore pressure is much higher than the fracturing pressure (Chen and Ma 2014; Ma et al. 2018, 2019; Liu et al. 2019, 2020b; Zhang et al. 2021). For the drilling operation in such a fractured formation, the conventional drilling operations are prone to a series of downhole conditions and drilling problems, such as lost circulation and gas kick.
Temporal Variation in CT Values of Pore Water in Granite Fracture Subjected to Long-Term Confining Pressure and Temperature
Authors: Nakashima S. , Isumi Y. , Song C. , Kishida K. 
Published: September 2022

ABSTRACT:
The groundwater flow in rock fractures and the chemical dissolution of rock minerals, which are greatly affected by the confining pressure and temperature, are important issues in the geological disposal of radioactive waste and geothermal studies. In order to investigate the long-term deformation and permeability of rock fractures, the authors conducted long-term permeability tests using a granite specimen with a single split fracture, with parameters of confining pressure and temperature. The saturated specimen was subjected to confining pressure of 3 MPa at 20°C for more than six months, and then the temperature was raised to 60°C. Microfocus X-ray computed tomography (CT) images were taken at predetermined times. The results showed that the CT values inside the fracture rapidly increased with time for 60 days at 20°C and 3 MPa, and then became stable. However, after the temperature was raised to 60°C, the CT values started to increase again. This evolution in the CT values implies pressure solution at the fracture interface due to the long-term confining pressure and temperature.

1. INTRODUCTION
The groundwater flow in rock fractures and the chemical dissolution of rock minerals, which are greatly affected by the confining pressure and temperature, are important issues in studies on the geological disposal of radioactive waste (Tsang et al. 2012; Watson et al. 2018), enhanced geothermal systems (EGS) (Pruess 2006; Gerber and Marechal 2012), and petroleum extraction (Chen and Spiro 1994; Gan et al., 2009).
In order to investigate the long-term deformation and permeability of rock fractures, the authors conducted long-term permeability tests using a granite specimen with a single split fracture, with parameters of confining pressure and temperature (Song et al. 2021). The saturated specimen was subjected to confining pressure of 3 MPa at 20°C for more than six months, and then the temperature was raised to 60°C. The results revealed that the permeability measured in the short-term tests showed reversible behavior and a dependence on the applied confining pressure and temperature. In contrast, the permeability measured in the long-term tests displayed irreversible behavior and an irregular change under constant confining pressure. In the experiment, microfocus X-ray computed tomography (CT) images were taken at predetermined times to observe the changes in the internal fracture structure.
Numerical Investigation of Shock Wave Stimulation and Comparison to Experimental Work
Authors: Khalaf Mina S. , Gordon Peter , Rezaei Ali , Soliman Mohamed Y. , House Waylon 
Published: September 2022

ABSTRACT:
Efficient production from tight and unconventional reservoirs requires drilling horizontal wells with an extensive network of high-quality (i.e., long, and conductive) fractures. However, the hydraulic fracturing process may be costly and may not be economically the best option when the oil and gas prices are low. The shock wave (pulsed loading) stimulation is a potential complement to traditional stimulation (e.g., hydraulic fracturing), that can add additional permeability enhancement to rock (via dynamic fracture processes) and bypass the skin region. The shock wave technique generates multiple fractures propagating in different directions around the wellbore, and is waterless, and less impacted by stress shadowing.
This work presents a numerical study on the effects of rock properties (e.g., rock density, Young’s modulus, and Poisson’s ratio) on the shock wave fractures quality (e.g., length, type, and number). In addition, repetitive application of shock waves in wellbore is investigated. Pulsed fracturing in the cased and perforated wellbore is compared with open-hole situation. This work examines the effect of confining stresses and stress anisotropy. The shock wave propagation in rock along with the developed fracture types (shear and tensile) are discussed. Furthermore, the numerical results are compared with previous experimental observations. The main objective of this study is to determine the dominant parameters that influence the rock behavior in pulsed fracturing.
Fracturing tight reservoirs by shock waves is an extremely high strain rate problem that we studied numerically using the combined finite discrete element method (FDEM). The results show that rock of large modulus of elasticity develops longer fractures. However, Poisson’s ratio has minor effects. Multiple application of high-rate loading can be used to control the wellbore collapse issue. The presence of wellbore casing reduces the shockwave strength and minimize the wellbore integrity issue. The confining stresses have a significant impact of the developed fractures length. However, stress anisotropy does not affect the created fracture orientations.
Thermo-Poroelastic Analysis of Cold Fluid Injection in Geothermal Reservoirs for Heat Extraction Sustainability
Authors: Khalaf Mina S. , Rezaei Ali , Soliman Mohamed Y. , Farouq Ali S. M. 
Published: September 2022

ABSTRACT:
Geothermal reservoirs are usually deep and have low permeability. Hydraulic fracturing stimulation of the production and injection wells can help increase the heat extraction from these reservoirs. However, injecting cold fluid in the hot formation can cause considerable volumetric changes in reservoir rock and pore pressure distribution in the reservoir. As a result, thermal loading occurs, and local stresses change in magnitudes and directions. Such redistribution of pore pressure, stresses, and temperature may result in an unwanted propagation of the created fractures or failure of pre-existing rock discontinuities and create an unwanted closed loop circle. In this study, we investigate the effect of heat exchange between the circulating fluid and the hot rock on redistribution of local stresses.
Our approach employs the thermo-poroelasticity theory to study cold fluid injection in geothermal reservoirs. The displacement discontinuity method (DDM) is used to solve the field equations of the thermo-poroelasticity theory. The DDM is a numerical technique that belongs to the boundary element methods (BEM). This numerical technique is suitable for studying hydraulic fracture (discontinuities in displacement) simulation problems. The thermo-poroelastic theory used here accounts for three fully coupled processes (mechanical, hydraulic, and thermal) in porous media saturated with fluid.
Our results show the effect of cold fluid injection on stress magnitude and orientation. Furthermore, the evolution of fracture aperture and cold fluid injection efficiency are discussed. The results presented in this work show that the difference in temperature between the cold treatment fluid and hot reservoir help create a wider fracture in less pumping time. In addition, it can cause a 90° re-orientation of the minimum principal stress direction, which controls the propagation of fractures. Also, cold fluid injection in hot formation creates thermal (tensile) stresses that can be much higher than iso-thermal fluid injection.
Inferring Compressional Wave (P-Wave) Travel Time from Conventional Well Logs Using Supervised Machine Learning: Case Studies from Texas Basins
Authors: Kholy S. M. , Lee Hunjoo P. 
Published: September 2022

ABSTRACT:
Compressional wave (P-wave) travel time is an important sonic log that can be utilized to indirectly estimate geomechanical properties such as Young’s modulus and Poisson’s ratio. Unfortunately, sonic travel-time logs are often absent in the conventional well log suites and need to be interpreted from other well logs. Many previous studies have developed data-driven models to synthesize the sonic logs, but those models have not been thoroughly evaluated for its prediction accuracy using field cases from several depositional basins. The objective of this study is to develop supervised machine learning models to accurately predict the P-wave travel time from the conventional well logs (i.e., Gamma Ray, bulk density, and neutron porosity) for a wide range of lithologies with the incorporation of confining stress effect by including the true vertical depth as an input. A linear regression model and an artificial neural network model have been trained using conventional well logs obtained from the Volve oil field in the Norwegian North Sea then the prediction accuracy of the two models have been tested using several cases from the Eagle Ford and the Midland basins. The testing results show that the inferred P-wave travel time yields a root mean square error range of 1.5 μs/ft-6.7 μs/ft indicating a good agreement with the actual sonic log measurements. Eventually, the findings of this study are essential in optimizing the design of drilling and well completion by providing accurately estimated geomechanical properties when the actual sonic logs are unavailable.

1. INTRODUCTION
Compressional wave, P-wave, transit time (DTC) is critical in estimating rock mechanical properties when the subsurface cores are unavailable due to financial and operational constraints on core retrieval. For many subsurface engineering applications, including drilling and well stimulation, geomechanical properties are important in understanding subsurface deformations to prevent hazards and enhance the recovery of resources. Wyllie et al. (1956) measured DTC with dry core samples, saturated core samples of several fluids, and hence developed an empirical equation to estimate the formation porosity. Nielsen et al. (1979) utilized the acoustic travel times to estimate rock mechanical properties including Poisson’s ratio and dynamic shear moduli.
Furthermore, the interpreted geomechanical properties (e.g., Poisson’s ratio and Young’s modulus) of the subsurface formations from the DTC could help improve the prediction of the in-situ stress conditions. Eaton (1975) estimated pore pressure by comparing the compressional transit time well logs to its normal trend. Others have also analytically derived the in-situ stresses from the interpreted mechanical properties (Blanton et al., 1999).
Characterization of Fracture Process Zone in Short Beam Compression Tests on Barre Granite
Authors: Garg Prasoon , Hedayat Ahmadreza , Griffiths D. V. 
Published: September 2022

ABSTRACT:
Due to rock mass being commonly subjected to compressive or shear loading, the mode II fracture toughness is an important material parameter for rocks. Fracturing in rocks is governed by the behavior of a nonlinear region surrounding the crack tip called the fracture process zone (FPZ). However, the characteristics of mode II fracture are still determined based on the linear elastic fracture mechanics (LEFM), which assumes that a pure mode II loading results in a pure mode II fracture. In this study, the FPZ development in Barre granite specimens under mode II loading was investigated using the short beam compression (SBC) test. Additionally, the influence of lateral confinement on various characteristics of mode II fracture was studied. The experimental setup included the simultaneous monitoring of surface deformation using the two-dimensional digital image correlation technique (2D-DIC) to identify fracture mode and characterize the FPZ evolution in Barre granite specimens. The 2D-DIC analysis showed a dominant mixed-mode I/II fracture in the ligament between two notches, irrespective of confinement level on the SBC specimens. The influence of confinement on the SBC specimens was assessed by analyzing the evolution of crack displacement and changes in value of mode II fracture toughness. Larger levels of damage in confined specimens were observed prior to the failure than the unconfined specimens, indicating an increase in the fracture resistance and therefore mode II fracture toughness with the confining stress.

1. INTRODUCTION
The fracturing in laboratory-scale rock specimens is often characterized by the deformation of the inelastic region surrounding the crack tips, also known as the fracture process zone (FPZ) (Backers et al., 2005; Ghamgosar and Erarslan, 2016). While the influence of the FPZ on mode I fracture in rocks has been extensively investigated, there are limited studies on FPZ development in rocks under pure mode II loading (Ji et al., 2016; Lin et al., 2020; Garg et al., 2021; Li et al., 2021).
Meshfree Penetration of Projectiles into Rock
Authors: Foster C. D. , Atif M. , Chi S.-W. 
Published: September 2022

ABSTRACT:
The penetration of projectiles into soil and rock has many applications, both military and civilian. In this research we are concerned with depth of penetration of projectiles at formerly used munitions sites. We examine here a numerical framework for analyzing such penetration.
Because the penetration problem includes large deformation, fracture, fragmentation, and other phenomena, standard finite elements cannot adequately capture the interaction. In this research, we employ a semi-Lagrangian Reproducing Kernel Particle Method (RKPM) framework. This meshfree technique updates the influence functions for each particle with deformation, naturally extremely large deformation, particle rearrangement, separation, and contact. The method has recently been updated with improved nodal integration for enhanced stability and accuracy.
At this a stage a Drucker-Prager with damage model is used the capture the hardening and softening of the material. The damage function is modified to only include damage in tension.

1. INTRODUCTION
Penetration of projectiles into rock and soil is of interest in many applications. These include protection of sensitive underground structures, projectile design, nuclear waste disposal, investigate of properties of remote sites, and mining. The ultimate goal in this research is the prediction of penetration depths at formerly used munitions sites, in order to detect buried projectiles and remediate the sites.
While there are many empirical, analytical, and numerical approaches to this problem, it remains a challenging endeavor. Reasons for this include uncertainty in material properties, complicated physics of interaction between projectile and rock, and limitations of numerical methods. In the last case, challenges include large deformation inelastic behavior of the material, multiple discontinuities, and tracking of complex evolving contacts among the interacting projectile and rock mass.
Standard finite elements struggle with penetration problems, due to the basic assumption of continuous deformation. While many enhancements have been created to handle fracturing [1-6] and large deformation [7-8], the problem of multiple rapidly changing contacts of parts creates a computationally intense problem. Discrete elements [9-11] can handle separation and contact more easily but are computationally expensive.
Determining the Mechanical Property of Martian Rocks Using Accurate Grain-Based Model
Authors: Zhang Yiheng , Xu Jingjing , Tang Xuhai , Paluszny Adriana 
Published: September 2022

ABSTRACT:
In the future, the extraterrestrial human activities, such as resources exploitation and base construction on Mars needs the aid of geotechnical engineering technology. Currently, there are only two approaches to obtain the Martian rock samples: sample-return activities by spacecraft and the collection of meteorites. However, meteorites are rare, expensive, arbitrarily sized and shaped, so it is difficult to process them into standard rock samples required by the traditional macroscale rock mechanics experiments (macro-RME). In the present work, the mechanical property of small-sized Martian meteorites was obtained by Accurate Grain-Based Modelling (AGBM) based on the microscale rock mechanics experiments (micro-RME). Firstly, the mineral composition and microstructure of NWA12564 Martian meteorites are achieved by the TESCAN Integrated Mineral Analyzer (TIMA). Secondly, the micromechanical properties of rock-forming minerals in meteorites was measured using nanoindentation tests. Thirdly, with the combination of micro-RME results and AGBM, the macroscale mechanical property of Martian rocks was able to be achieved using small and any-shaped meteorites. The present methodology is potential useful to estimate the mechanical property of Martian rocks using only arbitrarily shaped samples.

1. INTRODUCTION
Mars shares many similarities with Earth: hard crust, dense cores and similar materials composition, which is also most likely to be the second home of individuals living in Earth (Horne, 2015). Study of rock samples from the Mars provides useful information for the future human activities on Mars, such as resources exploitation and base construction (Steele, 2007). Now, many countries and organizations are working on geological exploration of Mars (Changela et al., 2021). The US National Aeronautics and Space Administration (NASA)’s Perseverance rover is paving the way for the first Mars-sample return (Farley et al., 2020; Witze, 2021). The China National Space Administration’s (CNSA)’s Zhurong rover (Wan et al., 2020) also focus on investigating the geology of Mars. SpaceX has an ambitious program for human settlement on Mars (Bramson et al., 2021). The use of resources on the Mars may provide a means of reducing the cost and risk of Martian exploration (Sanders and Duke, 2005). Understanding and controlling the mechanical behavior of Martian raw material (e.g. rocks and soil) is critical for the construction and expand colonization on the Mars.