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Geomechanical Characteristics and Wellbore Instability for Nahr Umr Oil Field

PETROLEUM CHEMISTRY 2024年第7期64卷 771-780页

作者： Alhusseini, Ahmed K. Hamzah, Sarah H. Iraqi Minist Oil Petr Res & Dev Ctr Gas Technol Res Sect Baghdad 10001 Iraq Iraqi Minist Oil Upstream Dept Petr Res & Dev Ctr Baghdad 10001 Iraq

instability occurs when an open well cannot maintain its size, shape, or structural stability. It is a common issue especially in shale sections and can be caused by both mechanical factors, such as poor drilling technique or weak rock, and chemical factors, such as interactions between the rock and drilling fluid. This problem can lead to costly and dangerous complications. In this study data from three wells in Nahr Umr Oil Field (NR-10, NR-12, and NR-14) in southern Iraq were analyzed to determine pore pressure and rock strength parameters, as well as in situ horizontal stresses. The results showed an increase in pore pressure and horizontal stress in shale units, and various geomechanical parameters were also estimated. The study showed the fault regime in the area is a strike-slip fault and suggested the estimated pore pressure values while drilling hole sections to prevent problems at abnormal and subnormal formations.

关键词： wellbore instability Nahr Umr geotechnical parameter horizontal stress fault regime pore pressure

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Ground surface settlement analysis of shield tunneling under spatial variability of multiple geotechnical parameters

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HELIYON 2019年第9期5卷 e02495-e02495页

作者： Hu, Baolin Wang, Changhong Shanghai Univ Dept Civil Engn 333 Nanchen Rd Shanghai 200444 Peoples R China

This paper presents an efficient method of shield tunneling reliability analysis using spatial random fields. We introduced two stochastic methods into numerical simulation. The first one computes the maximal ground surface settlement using classical statistics, in which the response surface method is utilized to calculate the failure probability by first-order second moment. Cohesion, internal friction angle, Young's modulus and mechanical model factor are considered as random variables. The second method is the spatial random fields of aforementioned three key geotechnical parameters. Using these two methods, similar multiple soil layers are converted into a stationary random field by local regression as the first step, and then the process is followed by the spatially conditional discretization of multivariate. Failure probability of maximal ground surface settlement is calculated by a subset Monte-Carlo Algorithm. This approach is applied into the four-overlapping shield tunnels of the 5th and 6th metro lines intersecting at Huanhu W Rd station, Tianjin China. The failure analysis results indicated that classical statistics of geotechnical parameters showing higher variability than spatial random fields, which substantially support the complex shield tunneling project.

关键词： Civil engineering Structural engineering geotechnical parameter Ground surface settlement Reliability index Spatial variability Stochastic simulation Risk analysis Soil engineering Construction engineering Foundation engineering Computer-aided engineering

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Reliability Analysis of Ground Surface Settlement Given Multivariate Spatial Random Field in Shield Tunneling 4th

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4th GeoShanghai International Conference on Tunneling and Underground Construction

作者： Wang, Changhong Shanghai Univ Shanghai 200444 Peoples R China

ISBN: (纸本)9789811300172;9789811300165

It is well known that geotechnical parameters impact dramatically soil-tunneling mechanics. Random field theory has been widely used for a single geotechnical parameter, including aleatory uncertainty, spatial variability and local singularity. Current challenge is focused on analyzing the spatially correlated soil layers. Coefficient of cohesion, internal friction angle, and Young's modulus are accounted in reliability analysis of ground surface settlement due to shallow-buried shield tunneling. At first, convert multiple non-stationary soil layers into stationary field using a local detrending method, and define the geostatistical parameters. Then, assume spatial variability of geotechnical parameters into aleatory randomness, and classical response surface method is utilized into reliability analysis. Furthermore, Co-sequential Gaussian discretization is conceived for multivariate spatial random field, in which failure probability of ground surface settlement is calculated directly by subset Monte-Carlo simulation. This approach is applied into the paralleling zone of four shield tunnels of the 5th and 6th metro lines linking to HuanhuWRd station, Tianjin China. Results prove that reliability index of considering geotechnical parameters as random variables is lower than the assumption of multivariate spatial random field, which would support substantially to construction control and design optimization in complex shallow-buried shield tunneling projects.

关键词： geotechnical parameter Spatial variability Stochastic simulation Multivariate Reliability index

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Determination of monitoring systems and installation location to prevent debris flow through web-based database and AHP

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MARINE GEORESOURCES & GEOTECHNOLOGY 2017年第8期35卷 1049-1057页

作者： Jun, Hwandon Min, Dae-Hong Yoon, Hyung-Koo Seoul Natl Univ Sci & Technol Dept Civil Engn Seoul South Korea Daejeon Univ Dept Construct & Disaster Prevent Engn Daejeon 300716 South Korea

Various monitoring systems have been applied to warn regarding debris flow;however, the information regarding the selection sensors and determination of the installation area is deficient. The objective of this paper is to propose an appropriate monitoring system to prevent debris flow and a method for determining the installation location. A web-based database is used to find the applied frequency of sensors, and the sensors are grouped into eight parts with consideration of the performance, including rainfall, debris flow velocity, displacement, fluid pore pressure, ground vibration, image processing, impact force, and peak flow depth. Through the statistical technique, the rain gage and geophone sensors are revealed as hugely selected sensors among various systems to provide an alarm. The analytic hierarchical process (AHP) is also used to analyze experts' opinion through pairwise comparison with consideration of eight geotechnical parameters, including the fine content, void ratio, shear strength, elastic modulus, hydraulic conductivity, saturation, soil thickness, and water content. The weighting factors of every parameter are deduced through AHP and the installation area is chosen with calculated values using the weighting factor. The suggested analyses are helpful to select appropriate sensors and determine the installation location of a monitoring system.

关键词： Analytic hierarchical process debris flow geotechnical parameter monitoring system weighting factor

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Identifiability of geotechnical Site-Specific Trend Functions

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ASCE-ASME JOURNAL OF RISK AND UNCERTAINTY IN ENGINEERING SYSTEMS PART A-CIVIL ENGINEERING 2017年第4期3卷

作者： Ching, Jianye Phoon, Kok-Kwang Beck, James L. Huang, Yong Natl Taiwan Univ Dept Civil Engn 1 Roosevelt RdSect 4 Taipei 10617 Taiwan Natl Univ Singapore Dept Civil & Environm Engn Blk E1A07-031 Engn Dr 2 Singapore 117576 Singapore CALTECH Div Engn & Appl Sci 206 355 S HollistonMC 9-94 Pasadena CA 91125 USA Harbin Inst Technol Minist Educ Sch Civil Engn Key Lab Struct Dynam Behav & Control Harbin 150090 Heilongjiang Peoples R China

This paper investigates the possibility of consistently identifying a site-specific geotechnical trend function t(z) in the presence of spatial variability epsilon(z), where z denotes depth. The trend function t(z) is represented as the linear combination of prescribed basis functions (BFs), whereas epsilon(z) is modeled as a zero-mean stationary Gaussian stochastic process with unknown standard deviation and scale of fluctuation. It is found that t(z) can be unidentifiable if the single exponential (SExp) autocorrelation model is adopted for epsilon(z). Two mechanisms, overfit and poor fit, that cause unidentifiability are explored. The overfit happens when part of epsilon(z) is falsely fitted by the BFs, whereas the poor fit happens when part of t(z) is erroneously interpreted as spatial variability. Nonetheless, identifiability is also affected by the sounding depth (or data record length) and the number of (statistically independent) soundings. An important feature for the SExp autocorrelation model is that it produces rough realizations with local jitters. If an autocorrelation model that produces smooth realizations is adopted, the trend function can become identifiable. The reason the identifiability for t(z) is related to the smoothness of the realizations is explored. Finally, it is found that the sparse Bayesian learning framework can effectively alleviate overfit but cannot alleviate poor fit. (c) 2017 American Society of Civil Engineers.

关键词： geotechnical parameter Depth trend Site characterization Spatial variability

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Numerical simulation of seepage-induced behavior of tunnel for analyzing deformation characteristic and estimating geotechnical parameters

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KSCE JOURNAL OF CIVIL ENGINEERING 2014年第2期18卷 659-671页

作者： Shin, Young-Jin Kim, Do-Hoon Lee, In-Mo Samsung C&T DTS Project T 01 Abu Dhabi U Arab Emirates Hyundai Engn & Construct Co Ltd Dept Civil Seoul 110920 South Korea Hyundai Engn & Construct Co Ltd Environm Div Seoul 110920 South Korea Korea Univ Sch Civil Environm & Architectural Engn Seoul 136713 South Korea

The Longitudinal Deformation Profile (LDP) represents the tunnel wall displacements along the axis of the tunnel, which can be used to estimate support loads and final tunnel deformations. This paper presents the effects of groundwater flow on the radial and axial LDPs of deep circular tunnels in an elasto-plastic and homogeneous ground and the usage of a back-analysis method in order to estimate geotechnical parameters using LDP under groundwater flow. A deep tunnel was chosen to remove the surface effect of shallow one, so that the analysis was concentrated on the ground response by tunnel excavation. The elasto-plastic ground was considered to sufficiently reflect how the ground behave but it may vary depending on the failure criteria and the flow rule. A number of parametric studies have been conducted, which cover a wide range of tunnel and ground conditions, liner installation, unsupported ground length and drainage conditions at the tunnel wall (fully drained and partially drained cases). The seepage forces are developed in the fully drained case, resulting in the increase of effective stresses in the radial and axial directions. The pore pressure developed in the partially drained case squeezes the tunnel wall radially, not axially. The liner installation and the unsupported ground length also affect tunnel wall deformations. Results from the numerical simulations show that the groundwater flow at the tunnel wall influences deformations both radially and axially. For the application of these results, a back-analysis which uses a relative convergence curve determined from LDP is performed to estimate geotechnical properties. Several numerical studies have been conducted in order to test this back-analysis method. The results show that estimated parameters match well with the real parameters.

关键词： longitudinal deformation profile groundwater drainage elasto-plasitc behavior back-analysis geotechnical parameter

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A modified method to fit probability distributions of geotechnical parameters using stochastic weighted entropy principle

A modified method to fit probability distributions of geotec...

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4th International Conference on Civil Engineering, Architecture and Building Materials (CEABM)

作者： Zhang Shu-jun Xu Zhi-jun Zhong Luo Xiao Zhaoran Wuhan Univ Technol Sch Civil Engn & Architecture Wuhan 430070 Peoples R China Nanyang Technol Univ Sch Civil Engn Nanyang 473004 Peoples R China Henan Univ Technol Sch Civil Engn & Architecture Zhengzhou 450001 Peoples R China

ISBN: (纸本)9783038351658

Due to various uncertainties, most of geotechnical parameters are small samples, which causes much trouble when the probability distribution of geotechnical parameter is fitted using traditional distributions. This paper uses stochastic weighted method to improve the small samples of geotechnical parameters into big samples, thus solving the problems caused by the small samples. Meanwhile, the probability density function of geotechnical parameter is derived based on maximum entropy principle, the advantage of presented method is verified through Kolmogorov-Smirnov Test. Case study shows that the proposed method not only overcomes the dependence of conventional fitting methods on classical probability distributions, but also the fitting more close to the fact because the data come from the big sample improved by geotechnical parameters, which has important engineering significance.

关键词： geotechnical parameter entropy principle small samples stochastic weighted probability distribution

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geotechnical parameters of reclaimed sandfill from the cone penetration test

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CANADIAN geotechnical JOURNAL 2005年第1期42卷 91-109页

作者： Na, YM Choa, V Teh, CI Chang, MF Hyundai Engn & Construct Co Ltd Yongin 449716 Gyounggi Do South Korea Nanyang Technol Univ Student Serv Ctr Singapore 639815 Singapore Nanyang Technol Univ Sch Civil & Environm Engn Singapore 639798 Singapore

Sandfill at reclaimed sites is usually formed by more than one placement method. Reclaimed sandfill is often highly variable, and the cone penetration test is most commonly used for site characterization. Correlations among the cone resistance and geotechnical parameters for sand are influenced by the in situ stress level, and it is important to incorporate the stress-level effect. In this study, cone penetration tests were performed at several levels from the top of a 10 m high surcharge, which was later removed step by step, and in situ density was determined layer by layer at the Changi East reclamation site in Singapore. Different ways of normalizing the cone resistance by the corresponding in situ stress were investigated. Specialized in situ tests including the self-boring pressuremeter test, the cone pressure meter test, the seismic cone penetration test, and the plate load test were conducted to provide the reference deformation characteristics of sandfill. Results of the in situ tests indicate that the sand density and the cone resistance profiles vary between areas formed by different sand placement methods. Site-specific correlations developed based on comparison of normalized cone resistance with the reference data obtained from laboratory tests and other in situ tests are found to be suitable for the evaluation of relevant soil parameters.

关键词： stress normalization cone resistance correlations geotechnical parameter in situ characterization granular soil

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