bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress distribution model of hard and brittle mud shale based on hydration damage
Authors: Liu Hailong , Xie Tao , Chen Zhuo , Lin Hai , Huo Hongbo 
Published: November 2020

Abstract
Hard and brittle shale developed in the middle and deep layers of the Bohai Sea cause severe challenges in drilling. During the drilling process, drilling fluid easily penetrates the rock along the microcracks, which leads to the deterioration of the mechanics and strength parameters of the rock. This consequently changes the stress distribution in the borehole wall. In addition, the fluid seepage hydrates the rock, which affects the relationship between the change in water content at any position and at any time in the rock mass is solved. The hydration equivalent of the elastic modulus is regarded as damage evolution, and a damage tensor considering hydration is introduced. A constitutive relationship of hard and brittle mud shale considering the effect of hydration damage is established, and the stress distribution around the well of the hard and brittle mudstone under non-uniform stress is solved by a semi-numerical and semi-analytical method. In addition, the influence law of hydration damage on the stress distribution around the well is analyzed. Taking an 8-1/2-inch section of an exploratory well in the Bozhong 19-6 gas field as an example, the stress distribution and collapse pressure analysis of the well bore revealed that after the section of the well was drilled for 100 h, the formation stiffness caused by hydration damage significantly decreased and borehole instability occurred inside the borehole wall. The risk of collapse was greater in the direction of the smallest in situ stress. The effect of hydration expansion on the stress distribution was limited, showing only a slight effect on the tangential stress near the well wall. The collapse of hard and brittle mud shale is mainly related to deterioration of the rock stiffness performance and strength parameters caused by hydration damage. The section incurred a short period of collapse, in which the maximum diameter expansion rate was equivalent to 5.9%, and the density of drilling fluid used on site was relatively low. Therefore, the density of the drilling fluid should be appropriately increased to enhance its sealing properties. The model reveals the hydration collapse mechanism of hard and brittle shale to a certain extent, which provides a theoretical basis for the safe and efficient drilling in similar formations.
A Modified Elastic Plate Model for the Thickness of Reinforced Soil of Shield Tunnel End
Authors: Tingshuai Sun , Kezhi Song , Teng Huang , Junhao Luo , Sukun Zhuang 
Published: November 2020

Abstract
The soil body of the shield end could be unstable and should be reinforced, and its thickness affects the stability and economy of engineering. The existing elastic thin plate model was too conservative for design. A modified elastic plate model was proposed for the calculation. Based on elastic finite element analysis data, optimal fitting was conducted for the proposed elastic model, and the coefficients of the model were obtained. A case study showed that the elastic thin plate model is too conservative when used to calculate the thickness of the reinforced soil body. The actual reinforced thickness in practice is between the values of the elastic thin plate model and the modified elastic plate model.
Real-time drilling rate prediction method of reaming while drilling based on mechanical specific energy
Authors: Ma Guoxin , Du Xu , Chen Xuyue , Hong Yuqun , Wang An , Zhang Fengxi 
Published: November 2020

Abstract
Reaming while drilling (RWD) is a drilling technique that uses a reamer and a pilot bit to expand the size of an open hole segment to be larger than the inner diameter of an upper casing string while fully drilling, especially in deep wells. This technique reduces the number of trips and is highly efficient and widely used in deep wells, ultra-deep wells, small clearance wells, and side-drilling and complex well conditions. However, in the actual operation process, the mismatching between the pilot bit and reamer often leads to slippage, string vibration, and low-quality borehole.In this paper, based on the mechanical specific energy model and the RWD weight distribution model, combined with the drilling weight, torque, and formation confined compressive strength at the interface of the pilot bit and reamer, a real-time rate of penetration (ROP) prediction model suitable for RWD is derived. Through the analysis of the downhole condition of the RWD operation, reasonable drilling parameters are determined and a set of real-time RWD performance prediction and optimization algorithm is proposed.Studies show that during the RWD operation, the size of the pilot bit and reamer and the shape of the cutter have an enormous influence on ROP. When drilling in different formations, the excellent cooperation among the pilot bit, reamer, and formation is the key to improve ROP and bottom hole assembly stability. How to optimize the bit and reamer to drill with the same ROP and predict the ROP is the focus of this paper.Field logging data test the ROP prediction model and real-time optimization method, and the results indicate that the ROP prediction model has high precision, small error, and high timeliness, which can fully meet the requirements of field engineering. This model can guide the selection of the bit, reamer, and drilling parameters in RWD, which is of considerable significance to RWD.
Estimation of micromechanical strength of brittle rocks under compression
Authors: Xiaozhao Li , Chengzhi Qi , Zhushan Shao 
Published: November 2020

Abstract
A unified micro-macro method is proposed to estimate short-term, long-term, and shear strength of rocks under compression. This method is formulated by combining the wing microcrack model, subcritical crack growth law, Mohr–Coulomb failure criterion, and crack–strain relation. The short-term strength is predicted by the theoretical stress–strain relationship caused by microcrack growth. The stress states for a given creep failure time and long-term strength are analyzed using the proposed theoretical three-level creep evolution relationship. Moreover, the shear strength is reviewed by the proposed predictive method for shear failure. Correlation of short-term, long-term, and shear strength is closely analyzed, and the effects of crack size, crack friction, and fracture toughness on short-term, long-term, and shear strength are discussed.
Analysis of the effect of dam impoundment at the Baihetan site using coupled fluid-mechanical elasto-plastic simulations
Authors: Hou Jin , Xu Jianrong , Meng Guotao , Chu Weijiang , Cheng Zhao , Detournay Christine , Cundall Peter 
Published: November 2020

Abstract
Contractional valley deformation is a phenomenon quite specific to high dams in the southwest of China. Numerical simulations with coupling of stress and seepage were performed to study the mechanisms of valley deformation after impoundment and to determine whether and when valley contraction could develop at the Baihetan site. The initial generic study highlighted two competing mechanisms, a “Mattress Effect” and a “Swelling Effect”, associated with dam impoundment. The comprehensive FLAC3D model incorporates detailed rock mass property values, a grout curtain, an impounding plan, and the drainage volumes. The large-scale coupled seepage-mechanical simulations show that the convergence mechanism is activated by fluid diffusion in the valley. At sites upstream and up to about 400 m downstream of the dam, the valley deformation occurs shortly after the impoundment water level is raised; this behaviour reflects the impact of the mattress effect caused by the weight change of the standing impoundment water. However, deformation also occurs during periods when the impoundment level remains the same; this behaviour is caused by the large-scale water seepage associated with pore-pressure changes under and around the dam in the valley banks. The maximum convergence along the monitoring lines does not exceed 5 cm in the simulations, where affected by the presence of faults and bedding planes.
Rock Breaking Mechanism and Drilling Performance of Harmonic Vibro-Impact Drilling
Authors: Li Siqi , Tian Shenglei , Li Wei , Huan Zhao , Ling Xin , Zhuolun Li 
Published: November 2020

Abstract
An improved model of displacement response of rock considering damping is proposed and the energy response model is further presented. Then, the rock breaking mechanism under harmonic vibro-impact is investigated based on the displacement response and energy response. Furthermore, the numerical simulations are conducted to analyze the principal stress of rock and drilling characteristics in axial and torsional directions under harmonic vibro-impact. Finally, the performance of the harmonic vibro-impact drilling technology is verified by the field application. Based on the analysis undertaken, it can be concluded that the periodic harmonic impact force makes the rock subjected to more tensile stress and continuous damage accumulation, which causes the efficient rock breakage. What’s more, the harmonic vibro-impact can also alleviate the stick-slip effect and bounce phenomenon of drill bit to a certain extent. Our investigations confirm that the harmonic vibro-impact can achieve the purpose of rate of penetration (ROP) improvement.
Experimental study on creep characteristics of anchorage rock with cracks under cable pulling condition
Authors: Sun Xiaoming , Cui Li , Hu Jiangchun , Zhang Yong 
Published: November 2020

Abstract
The creep characteristics of anchorage rock mass with cracks are the basis for the stability control of anchorage rock and current research hotspots. Relying on the Muzhailing soft rock tunnel project, the anchorage segment is taken as the research object, numerical simulation as the main method is used to systematically study the instantaneous and creep mechanical properties of rock with different crack combinations under the condition of cable pulling, the results show that: 1) Under instantaneous pulling conditions, the effective anchorage range is funnel-shaped, and the maximum value of the maximum shear stress(MSS) appears at the front end of the anchorage rock, while under long-term pulling conditions, the effective anchorage range is uniform along the cable axis distribution, the maximum value of the MSS appears at the end of the cable; 2) Cracks with specific combinations can expand the anchorage range along the axial direction and slow down the shear failure at the front end of the anchorage rock, which is especially obvious for the anchorage rock under instantaneous pulling conditions 3) The optimal number of cracks and the specific area can be obtained by the "virtual intersection method". For the instantaneous MSS and the creep MSS, there is an obvious 45° crack angle effect. The research results are intended to provide a reference for further probing the creep mechanism of anchorage rock with complex crack combinations.
A simple elastoplastic dynamic constitutive model of saturated structural soft clay
Authors: Feng Shuangxi , Lei Huayang , Qi Ziyang 
Published: November 2020

Abstract
The dynamic constitutive relation of soil is widely applied to the ground design of marine structure and infrastructure in offshore geotechnical engineering. Increasing evidence from marine geotechnical design has shown that the traditional dynamic constitutive model has uncertain theories, many parameters, and complexity. Therefore, it is urgent to overcome these limitations and develop a simple and practical elastoplastic dynamic constitutive relation for the saturated structural soft clay. A simple dynamic constitutive relation with 5 parameters was proposed in this study, which can reflect the strain accumulation, hysteretic characteristics and cyclic degradation of the stress-strain for structural soft clay. First, the Drucker-Prager model was selected as the bounding surface, hardening modulus equation was established by the hardening law, interpolation function and structural strength coefficient. Then, the incremental stress-strain relationship was derived based on the incremental theory. The UMAT subroutine was compiled by FORTRAN language. Finally, the cyclic triaxial test and numerical simulation were carried out, and the stress-strain relationship was analyzed. The research results showed that the test results were in good agreement with the prediction results of the model.
Impact of reservoir heterogeneity on fluid injection-induced fault slip: insights from numerical simulation
Authors: Wang Zineng , Huang Xin , Huang Zhaoqin , Wang Xiaoguang , Lei Qinghua 
Published: November 2020

Abstract
In order to meet the growing energy demand worldwide, the technology of hydraulic fracturing for shale gas extraction has been rapidly developed and applied in recent years. However, man-made fluid injection has also caused several problems of high societal concern such as induced earthquakes. The focus of this paper is on the process of induced fault activation in shale reservoirs caused by hydraulic stimulation activities. We constructed a two-dimensional numerical model representing the horizontal cross-section of a faulted reservoir and simulated important coupled hydro-mechanical processes during fluid injection. We parameterized our model with the site investigation data of an actual shale gas project including in-situ stress, rock properties and injection protocol, etc. We represented the natural fault zone as a geological composite involving a fault core and a damage zone consisting of a set of subsidiary fractures parallel to the fault strike. We coupled the solid deformation and fault displacement with Darcy-type fluid flow based on poroelasticity principles and hydro-mechanical constitutive relationships. The heterogeneous nature of the permeability of the shale formation is mimicked by a random field model governed by a log-normal probability density function and directional correlation lengths, such that we can explore the impact of reservoir heterogeneity on the fault slip behaviour. In addition, we also studied the effects of fault length, dip angle and injection point-to-fault distance on the fault slip. Specifically, we analysed the link between fault slip and fluid flow field, permitting the capture of fluid movement in the heterogeneous faulted reservoir, the temporal and spatial evolution of preferential flow channels and their consequences on induced fault slip. The results of this research have important implications for understanding the triggering processes and mechanisms of fault slip during shale gas exploitation as well as many other injection-related engineering activities.
Numerical simulation on post-earthquake debris flows: A case study of the Chutou gully in Wenchuan, China
Authors: Liu Bo , Hu Xiewen , He Kun , Wu Mingyang , Huang Tao 
Published: November 2020

Abstract
Since the 2008 Wenchuan earthquake, post-earthquake debris flows have severely threatened people’s lives and the safety of public transit facilities, making particularly crucial to understand their formation mechanism. We focused on the Chutou gully debris flow and analyzed its formation mechanism based on field investigations and satellite images. The main inducing factor of this debris flow was a continuous heavy rainfall that exceeded the threshold of the study area: this, combined with the large amount of loose material created by the earthquake, dramatically promoted the volume and hazard degree of the debris flow. The three-dimensional debris flow simulation software RAMMS, based on an improved Voellmy–Salm fluid model, was used to simulate the movement process of the Chutou gully debris flow. The calibrated Coulomb friction (μ) and viscous turbulent friction (ξ) coefficients in the study area were 0.225 and 180 m/s2, respectively. The simulation results revealed the post-earthquake debris flow mechanism in terms of flow height, velocity, flow rate, and deposition area. The results of the numerical simulation were in good agreement with those of the field investigations. In particular, it was found that the peak flow of debris flow upstream of the Chutou gully was shorter in duration than the one upstream; however, due to the convergence of the branch gully, the downstream peak flow of debris flow increased significantly, while a large amount of solid material stranded downstream of the channel. Notably, this process is prone to occur again. This study proposes a new post-earthquake debris flow evaluation method, and its results are of reference value for the design of debris flow prevention engineering in meizoseismal areas.
Numerical simulation analysis of the shear tests on cemented surface between bedrock and concrete
Authors: Wu C J , Lai Y J , Yu J 
Published: November 2020

Abstract
Based on anchorage foundation of Ganjiang Highway Bridge situated on weakly weathered argillaceous siltstone, numerical simulation analysis of shear tests were carried out to investigate the shear strength of cemented surface, which is between anchorage foundation concrete and bedrock surface. In order to evaluate the effect on shear strength effectively due to the cemented surface roughness, random distribution of parameters is firstly introduced to quantify the roughness and the Monte-Carlo method is employed to simulate the morphology of cemented surface. Secondly, numerical simulation analysis on shear tests is implemented to study the effect of different cemented surface roughness on shear strength. At last, a new evaluation method of cemented surface shear strength is put forward based on the numerical simulation with random contact interface. In addition, the results from numerical simulation method are compared with the field direct shear test, and it is validated that the results are highly consistent.
Numerical simulation study of the support system by gob-side entry retaining by roof cutting
Authors: Li Wei Tao , Guo Zhi Biao 
Published: November 2020

Abstract
Gob-side entry retaining by roof cutting (GERRC) is an innovative, long-wall mining method that has been widely used in China as a new mining revolution. However, current research on the influence of this technology on the support system remains limited. To understand the response of each supporting structure after cutting the roof, this study uses the cable element and beam element built in the finite difference software FLAC3D to simulate the bolt, anchor cable, steel beam, and single hydraulic props based on the engineering geological conditions of the Lvtang Coal Mine in Guizhou Province, China. Then, the force and displacement changes of each supporting structure between the GERRC and traditional coal pillar mining are compared and analyzed. Simulation results reveal that during the process of conventional mining, the force and deformation of anchor cable behind the working face is relatively large; furthermore, even yield and breaking of the cable occurs. Meanwhile, the serious deformation of a single hydraulic prop occurs, which affects the normal use of the roadway. When the GERRC is adopted, the force of each supporting structure is reduced by 17.6% on average and the deformation is not obvious. Moreover, using the GERRC decreases the stress of the supporting and reduces the displacement of solid coal in the roadway by 33.3%. Finally, the concentration degree of stress becomes lower, and the environment of retaining roadway is more optimized.
Influence of rainfall on transient seepage field of deep landslides: A case study of area II of Jinpingzi landslide
Authors: Jing Fu , Ling Huang Shu , Xiuli Ding , Jinlong Wang 
Published: November 2020

Abstract
Rainfall is one of the primary factors that induce landslides. Rainfall infiltration forms a transient seepage field in slopes, thereby leading to an increase in water content, a decrease in matric suction, and an increase in the volume weight of slopes. The increase in water content in rock and soil leads to the degradation of the mechanical properties of the slope medium and reduces the shear strength, thus causing slope instability. In this study, a large-scale accumulation landslide is taken as the research object. The front edge of the landslide is high and is not eroded by river water. Hence, rainfall is regarded as the main external factor that changes the groundwater and seepage field of the landslide. According to the landslide’s topography, geological data, local rainfall, and hydrological monitoring results, the saturated–unsaturated seepage theory of rock and soil and the finite difference method are used to analyze the impact of rainfall on the landslide’s seepage field and groundwater. The evolution law of the transient seepage field of the landslide under the condition of rainfall duration is studied. The results provide a basis for the analysis of landslide deformation and stability.
Casing Deformation Caused by Hydraulic Fracturing-Induced Fault Slip in Sichuan Basin and Optimization of Treatment Parameters
Authors: Huang Rui , Chen Zhaowei , Zeng Bo , Song Yi , Zhou Xiaojin 
Published: November 2020

Abstract
Casing deformation is a key issue that restricts the efficient development of shale gas in the Sichuan Basin. In this study, the H pad of shale gas wells in this area is used to determine correlations among the casing deformation and ant-tracking faults, microseismic events, and treatment pressure. The results show that the deformation might have been caused by fault slip induced by hydraulic fracturing. Moreover, three-dimensional seismic and well log data are used to establish fracture and in situ stress models based on discrete fracture network and finite element methods, respectively. The relationship between treatment parameters and fault activation is established by hydraulic fracturing simulation, from which the parameter sensitivity is evaluated. The results show that when the fluid volume is reduced by 20%, the length of the activated fault and the number of activated fractures decrease by 9% and 23%, respectively. In contrast, when the pumping rate is reduced by 20%, these parameters decrease by 25% and 38%, respectively. These results indicate that reducing the pumping rate is more effective than reducing the fluid volume for mitigating fault activation. In summary, arranging the fracture stages adjacent to the fracture zones should reduce the pumping rate to some extent. This method can be used to mitigate fault activation during hydraulic fracturing, which in turn can prevent casing deformation.
Dynamic Stress Field Evolution of the Shale Oil Reservoirs: Development and Optimization of Well Patterns
Authors: Wang Shiguo , Jin Yan , Wei Shiming , Xia Yang 
Published: November 2020

Abstract
Research on shale oil has gained considerable attention with regard to global unconventional oil exploration, which is of the strategic significance in the field of energy. Considering the characteristics of continental shale reservoirs, a three-dimensional fluid–solid coupling model of a multistage fracturing horizontal well was established based on the poroelasticity theory. The difference in stress sensitivity among different layers was also considered in this model. The evolution of pore pressure and stress field during the production process was analyzed through numerical simulation. A comparison of the planar well pattern and stereo well pattern revealed that the latter has less interwell-flow interference and smaller alteration angle of the minimum principal stress; thus, in the latter pattern, intersection with existing hydrofractures during refracturing can be avoided. It is more advantageous to refracturing in the middle of the outside horizontal section, but with increase in production time, the optimal fracturing section shrinks. Considering the maximum recovery factor and interwell interference, well-spacing optimization is recommended from 200 m to 300 m.