bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Metal Jet Shape and Rock Damage Law near Tunnel Under Confining Pressure
Authors: Liu Xianbo , Li Jun , Liu Gonghui , He Long , Liu Wei 
Published: September 2022

ABSTRACT:
Different scholars had carried out much research on rock damage during perforation by numerical simulation or experiment, but they had not considered the influence of metal jet morphological feature on rock damage during perforation. In this paper, a numerical calculation model of perforation is established. The paper reveals the change characteristics of metal jet shape during perforation and carries out the influence law of metal jet shape on the rock near pore damage. The results show that: In the process of perforation, the shape of the metal jet changes dynamically with time, and the penetration process of the metal jet is divided into three stages. It is clear that the near channel damage of rock mainly occurs in the third stage of shape change. The paper also clarifies that the rock failure form in the perforation process is compression shear failure and reveals the influence law of confining pressure on the rock damaged area in the perforation process. The paper defines the influence law of metal jet shape and confining pressure on rock damage during perforation, which is of great guiding significance for perforation operation design.

1. INTRODUCTION
Unconventional oil and gas resources such as shale gas and shale oil often exist in low porosity and low permeability rocks. Due to the limitation of the storage environment, oil and gas exploitation is difficult (Wu et al.,2016; Lian et al.,2020; Gao et al.,2019). Aiming at the problems in the exploration and development of such oil and gas resources, the combination of perforation completion and reservoir stimulation is used to improve the oil and gas seepage conditions (Zhang et al.,2021; Albert et al.,2018; Wang et al.,2019; Behrmann et al.,1991;). However, while the perforation forms a channel for oil and gas migration, the rocks around the perforation channel will also be damaged to varying degrees. The transient nature of perforation and the complex and diverse rock damage around the perforation channel have severely restricted the stable and efficient development of unconventional and complex oil and gas reservoirs.
Determination of Continuous Kinematic Criticality in Structurally Homogeneous Zones – A New Approach
Authors: Rahman T. , Niyogi A. , Sarkar K. 
Published: September 2022

ABSTRACT:
The sectional kinematic feasibility analysis of a slope does not demonstrate the continuous kinematic criticality of a curve-faced rock slope prone to discontinuities. The geotechnical engineers and geologists need to understand the zones carefully where roads, tunnels, bridges or dams are to be constructed, which might be affected by slope failures along discontinuities. In the present study, a continuous model has been proposed considering structurally homogenous zones along a road-cut in tectonically deformed terrains. These structural zones are defined in such a way that homogeneity of discontinuity orientations are preserved, which may or may not be defined by geological boundaries such as faults, river tributaries, lithology etc. The proposed model accounts for the deviation of strikes along slopes, the dip amount in a particular section which varies from bottom to top of the slope and the criticality of slope failure. The criticality (%) depends on the number and orientation of discontinuities that are present in a particular structural zone. The variation in kinematic criticality due to deviation in slope direction and dip amount are obtained and presented in the model. This continuous criticality model for different slope failures postulates a precise and quick zonal kinematic criticality. The sections of different locations from a particular zone are plotted as an array of lines in the continuous criticality model, which are joined together (top-top and bottom-bottom) to precisely represent the potentiality of kinematic failures of the entire zone.

1. INTRODUCTION
The slope stability condition of any rock slope is controlled by the orientation of the discontinuities present in the rock mass. Therefore, to evaluate the rock slope stability, the kinematic analysis is used where the geometry of the discontinuities and the rock slope is considered, and it does not include any external force acting on the slope (Park and West, 2001).
Kinematic analysis is the most preliminary analysis for any rock slope to evaluate the potentiality of structurally controlled failure of rock slopes in various modes (such as, planar, wedge or toppling failure). The kinematic analysis used Markland’s test which was first introduced in 1972, and has been widely used in various studies (Gokceoglu et al., 2000; Smith, 2015; Niyogi et al., 2020, etc.). A number of assumptions of kinematic analysis were suggested by Markland (1972), but the assumption of a uniform slope angle and slope aspect have been addressed in the present paper. In nature, the slope angles are not found as planar or uniform rather the slopes are rugged and uneven. There is another problem related to sloping direction of the slope. Mountainous slopes are large and are sinuous in terms of sloping direction.
Upscaling of Mechanical Properties in Heterogeneous Reservoirs for Compaction Analysis
Authors: Hajiabadi M. R. , Nick H. M. 
Published: September 2022

ABSTRACT:
Geo-mechanical grid of reservoir simulations often contains coarse cells (×1 m thick) compared with the sub-metre resolutions of well log data. The geomechanical properties of the coarse cells are usually assumed to be representative of well log data although a rigorous upscaling process is lacking. A few existing studies on the upscaling methods have mainly focused on elastic properties. Guidelines for the upscaling of other mechanical properties related to plasticity are still required.
This study aims to assess the upscaled material parameter including elastic and visco-plastic material in heterogeneous chalk reservoirs for compaction analysis which are optimized from history matching the surface subsidence. To this purpose, a 2D simulation case with over-burden, reservoir and under-burden is considered as a conceptual model. A random distribution of porosity field defines different mechanical properties within the reservoir based on porosity dependent functions which are collected for chalk. Our results demonstrate the shape of yield surface is the most important parameter for upscaling while other upscaled material parameters are relatively close to the values obtained from the material with mean porosity. These imply that the heterogeneity has the most effect on the shape of the yield surface.

1. INTRODUCTION
Reservoirs are geologically heterogeneous with vertical and lateral changes in petrophysical and lithological properties that are not investigated in laboratory. Standard triaxial tests such as uniaxial / hydrostatic compaction tests are commonly carried out on 1~3cm long core plugs and are designed to characterize one single lithology or reservoir rock type in the laboratory. Therefore, upscaling technics from the geo-statistical description to reservoir grid are necessary to use laboratory data acquired at the cm-scale for reservoir modeling carried out at the km-scale. Studies on the upscaling methods for geo-mechanical properties are limited to the elastic properties for multi-layer reservoirs (Fokker, 2012 and Settari et al., 2013, Zhang et al., 2020). However, the effect of heterogeneity on the upscaled material parameter is missing in literatures.
Influence of Stress Field Evolution on Refracturing of Horizontal Wells
Authors: Fen Peng , Hongtao Liu , Shiyong Qin , Longcang Huang , Zhikun Pan , Yakai Tian , Longqiao Hu , Yixuan Liu , Fujian Zhou , Ben Li , Junling Wang , Zhaokun Yuan , Haijun Gao , Yao Jiang 
Published: September 2022

ABSTRACT:
After the initial fracturing, the stress field around the wellbore will become more complex, and even stress reversal will occur. The depletion of oil and gas will lead to the reduction of reservoir pore pressure, and then increase the effective stress of the reservoir, leading to the decreases of fracture conductivity and production, thus refracturing is often needed. Most of the studies focus on the initial fracturing of the reservoir, but there are few investigations on refracturing. In this paper, based on the global Cohesive zone model, the finite element method is used to simulate the initial fracturing and oil and gas production and extract the stress field distribution. Then the stress field is introduced into the new model to simulate the initiation and extension of the fracture during refracturing. The results show that under the influence of the initial fracturing, the stress concentration problem exists in the refracturing area, and the uniform repeat reconstruction can be achieved by adjusting the perforation position or combining it with the temporary plugging process.

1. BACKGROUND
Tight oil exploration has broad prospects and has become the key object of unconventional oil and gas development, with great exploitation potential(Bing et al. 2016). The large section and multi-cluster hydraulic fracturing technology of horizontal wells is an effective means to develop low permeability oil and gas fields. With the progress of production, the production capacity is gradually reduced, and the refracturing operation needs to be carried out (Zhou et al. 2017). The implementation of refracturing technology measures can effectively expand the reservoir reconstruction volume and supplement formation energy, improve the single well production and extend the stable production period. But different from the initial fracturing, the stress field around the wellbore is disturbed by the initial fracture, and the long-term production has an impact on the formation pressure, which leads to a more complex formation environment for refracturing(Xu et al. 2020).
Experimental Study and Analysis of Proppant Conductivity Under Gas-Liquid Alternation
Authors: Zhikun Pan , Longqiao Hu , Yixuan Liu , Bin Wang , Ben Li , Dunhao Chen , Fujian Zhou , Fen Peng , Hongtao Liu , Shiyong Qin , Longcang Huang , Junling Wang , Zhaokun Yuan , Haijun Gao , Yao Jiang 
Published: September 2022

ABSTRACT:
The conductivity of the proppant filling layer is directly related to the quality of fracturing construction and stimulation effect. The existing diversion experiments are mainly pure liquid measurement diversion, but there is oil-gas mixed flow in actual oil well production, so it is necessary to carry out systematic experiments on the actual conductivity of the formation. To make the experimental results closer to the actual formation production, this paper carried out the gas measurement conductivity test, liquid measurement conductivity test, and gas-liquid alternating conductivity test of different proppants. The experimental results show that the conductivity of gas measurement is much greater than that of liquid measurement, and the former is about 12.6 times that of the latter. Related to the air permeability and water-resistance of the experimental film coating material, the conductivity of gas-liquid alternating measurement is lower than that of pure liquid measurement.

1. BACKGROUND
Since the advent of hydraulic fracturing technology in the 1940s(Raghavan et al. 1972), due to the remarkable stimulation effect, the process technology has been widely valued, the research has been deepened and the application scope has been expanded(Mckay et al. 1993). Especially in recent years, with the large-scale development and utilization of unconventional oil and gas resources such as tight oil and gas and shale oil and gas, oil and gas wells combined with hydraulic fracturing has become one of the key technologies for the efficient development of unconventional reservoir stimulation and transformation(Zheng et al. 2013). The key of hydraulic fracturing technology is to form artificial fractures with a certain length and width and keep the fractures open by pumping proppant(Gao et al. 2006). Therefore, the performance of proppant is related to whether it can play an effective supporting role in fractures, and will also directly determine the fracturing construction effect and the productivity of oil and gas wells after stimulation(Yang et al. 2016).
Strength of Utah Coal Evaluated Using Laboratory Tests with an Unloading Path
Authors: Walton G. , Kim B. H. , Larson M. K. 
Published: September 2022

ABSTRACT:
Conventional triaxial tests evaluate rock strength using a load path where the minimum principal stress is held constant and the maximum principal stress is increased monotonically until the peak strength is achieved. Although brittle rock mechanical behavior is relatively well-understood under this loading path, in many practical rock mechanics applications, damage and failure develop as a result of loss of confinement (decreasing minimum principal stress). Since the inelastic behavior associated with damage that develops prior to rock failure is not path-independent, it is possible that rock damage and strength characteristics may differ depending on the loading path considered. To investigate this potential path-dependence, a series of tests were performed on Utah Coal where, following attainment of a target confining stress and deviatoric stress, the confining stress was decreased at a constant rate until failure while maintaining the deviatoric stress. These results were then compared to previously published data for Utah Coal obtained using conventional laboratory testing procedures. The previously published data for Utah Coal showed highly confinement-dependent strength behavior, where the peak strength increased by as much as up to 50% of the mean unconfined compressive strength (UCS) with confining stresses as low as 1% of the UCS applied. The peak strength and crack damage (CD) envelopes were found to be highly anisotropic, but the crack initiation (CI) envelope was relatively insensitive to the angle between the loading direction and the primary cleat orientation. In this study, although the CI stress, CD stress, and peak strength envelopes are all generally similar for both the loading and unloading tests, some of the test results for samples with cleating inclined at 30° to the loading direction suggest the CD stress envelope may be slightly lower under unloading conditions than under loading conditions.
Hydraulic ‘Fracturing’ Mechanisms of Unconsolidated Sands from Novel Laboratory Experiments and Modelling
Authors: De Borst K. , Tan C. P. , Mat Piah F. , Groenenboom J. 
Published: September 2022

ABSTRACT:
"Fracturing" mechanisms and associated injectivity impairment were investigated by means of large-scale laboratory experiments on sand packs built from synthetic sands and highly unconsolidated downhole core materials. Various fines were mixed into the sands around the perforations to mimic effects of plugging, formation damage and fines migration. Generation, closure and re-opening of "fractures" were monitored through in-situ CT-scanning. The water injection resulted in the opening of cavities rather than the formation of sharp fractures. The cavities opened at injection pressures exceeding the confining stress and enlarged against very low cohesive strength of the sands. This suggests material fluidization rather than shear failure as the immediate cavity initiation mechanism. A significant influence of the laminar and turbulent flow regimes on cavity shape and cavity closure characteristics was observed. It was found that injectivity was controlled by the interplay of fines transport away from the injection region, resulting in injectivity increase, and the permanent compaction of the sand around the cavity, resulting in injectivity decrease. The first-time insights highlight the role of sand fluidization and cavity formation in matrix vs "fractured" injection in unconsolidated sand reservoirs. The knowledge of the sand destabilization and mobilization processes enable design and operation optimization of water injectors with implications on sand control strategies and remediation measures.

1. INTRODUCTION
Rapid injectivity decline has frequently been observed during injection into unconsolidated sand formations. The rapid decline usually happens in "fractured mode", where the injection pressure surpasses a critical limit at which the flow localizes, and a dynamic propagating "fracture" is created. This mode is contrary to the matrix mode, during which water enters the formation through infiltration into the pore space without (significant) damage to the formation. The creation of void space i.e., "fracture" in the sand is a consequence of grain displacements, for which shear failure and fluidization have been considered as potential mechanisms. The injection rate can be increased without further increase in injection pressure, which indicates the creation of additional space, i.e., "fractures", to accommodate the injected water. However, it remains unclear under what condition the mechanisms prevail, and how the leak-off from the void space into the highly permeable sand affects the local stress state and, thus, propagation of the "fractures". The "fractures" adversely affect the performance of injector well and either the injectivity rapidly declined or the injector failed prematurely soon after initiating the ‘fractures’ (Dambani et al., 2014, Khodaverdian et al., 2010 and Sharma et al., 2000).
Integrated Experimental and Numerical Study on Debonding of Cement-Casing Interface
Authors: Wang Yangang , Feng Yongcun , Deng Jingen , Cai Wenjun , Wang Kongyang , Ma Chengyun , Wanyan Qiqi , Li Kang , Bai Song , Li Haitao 
Published: September 2022

ABSTRACT:
During the hydraulic fracturing process, the cement-casing interface may debond to be a severe leakage pathway for fluids. It is of significant interest to understand how stresses cause the debonding of cement-casing interface. A casing-cement interface normal bond parameters test device was fabricated to test normal bond parameters of the interface, including normal bond strength, normal stiffness and normal fracture energy. And a casing-cement interface shear bond parameters test device was fabricated to obtain the shear bond strength, shear stiffness and shear fracture energy of the interface. A 3D finite element numerical model of casing-cement-formation assembly was established to study the casing-cement interface debonding during hydraulic fracturing process, cohesive elements were employed to model the debonding of casing-cement interface, and the parameters obtained from our experiments were assigned to the cohesive elements. The simulation results demonstrate that the debonding of casing-cement interface is highly influenced by the normal bond parameters, shear bond parameters, situ stresses and internal casing pressure. The possibility and degree of casing-cement interface debonding and plastic deformation of cement increases with the increase of internal pressure.

1. INTRODUCTION
Well integrity plays an important role in conventional and unconventional oil and gas development. With the development of unconventional resource the application of hydraulic fracturing is becoming more and more widespread (Vengosh et al.,2014). During the hydraulic fracturing process, the casing will be subjected to significant internal pressure fluctuations, the casing-cement and cement-formation interfaces may debond to be a severe leakage pathway for fluids (Xi et al.,2020; Li et al.,2020).
Debonding between casing-cement and cement-formation interfaces can be decomposed into normal failure and shear failure. Debonding will occur once the normal and/or shear stress exceed the normal and/or shear bonding strength of the interface. It is of significant interest to understand how stresses cause the debonding of cement-casing and cement-formation interfaces. Since the difference of mechanical properties between cement and formation is higher than that between cement and casing, the casing-cement interface is more inclined to debond than the cement-formation interface. This paper focus only on the casing-cement interface debonding.
Analysis of Strain Responses in Vertical Monitoring Wells for Low-Frequency Distributed Acoustic Sensing
Authors: Srinivasan Aishwarya , Liu Yongzan , Wu Kan , Jin Ge , Moridis George J. 
Published: September 2022

ABSTRACT:
Fiber-Optic sensing has become invaluable for analyzing stimulation effectiveness and fracture geometries in unconventional reservoirs. Distributed Acoustic Sensing (DAS) is a Fiber Optic-based technique that provides dynamic strain variations along the length of the fiber during well stimulation. The strain measurements can provide critical information about the fracture characteristics. Most of the studies on Low-Frequency DAS (LF-DAS) focus on interpreting data measurements from horizontal monitoring wells. The LF-DAS measurements from vertical monitoring wells can provide valuable information about fracture propagation. However, strain responses from vertical monitoring wells are not fully understood. Therefore, it is necessary to model LF-DAS signals from vertical offset wells to understand the mechanisms and fracture characteristics. In this paper, we use a complex hydraulic fracture simulator to generate dynamic fracture geometries and obtain strain variations during fracture propagation at vertical monitoring wells located at different offsets. The mechanism of various strain-rate patterns with different fiber-to-fracture distances is illustrated using the spatial distribution of induced stresses during stimulation. A 1D feature, the sum of absolute strain rate along the fiber length is developed to determine the fracture passing time. This study provides valuable insights into the LF-DAS signals obtained from vertical monitoring wells and helps to better interpret the field LF-DAS measurements.

1. INTRODUCTION
Multi-stage hydraulic fracturing with horizontal drilling has made the development of unconventional reservoirs economically feasible. However, the questions about the exact hydraulic fracture geometry are still one of the most argued topics in the industry (Singh et al., 2020). A better understanding of the fracture geometry is vital for optimizing completion designs and improving well production. Various fracture diagnostic tools are available with their own limitations, such as, microseismic (Maxwell, 2014; Zhang et al., 2018), tiltmeters, tracers, pressure gauges, and time-lapse seismic (Byerley et al., 2018; Hull et al., 2019). Distributed fiber optic technique is recently being used for fracture diagnostics due to its capacity to provide continuous, real-time measurements along the length of the fiber optic cable (Sherman et al., 2019).