FAULT AND TOP SEAL INTEGRITY AT RELAYS AND INTERSECTIONS USING A 3D DISTINCT ELEMENT CODE

2004 ◽  
Vol 44 (1) ◽  
pp. 481 ◽  
Author(s):  
B.A. Camac ◽  
S.P. Hunt ◽  
P.J. Boult
Keyword(s):  
Rock Mass ◽  
Principal Stress ◽  
Fault Plane ◽  
Numerical Technique ◽  
Distinct Element ◽  
South Australia ◽  
Local Stress ◽  
Surrounding Rock ◽  
Regional Stress ◽  
Seal Integrity

It has long been known that faults and horizon boundaries can greatly affect the magnitude and orientation of the in-situ rock stress state. Significant success has been shown in the geo-engineering disciplines, whereby geomechanical models have been built to model local stress fields generated by rock mass inhomogeneities.In this work 3DEC (3D) the discrete element code has been applied to model stress perturbations around three simple fault configurations, two relay configurations (relay ramp and horst structure) and one fault intersection. The results show rotation in the principal stress orientation and stress magnitudes of the regional stress field about the faults. The degree of rotation of the principal stress direction and the stress magnitude are dependant on the fault friction angle parameter, the angle of maximum principal stress to the fault plane and the ratio of maximum to minimum principal stress. The degree of perturbation is demonstrated graphically in the surrounding rock mass along the fault strike, the perturbation generated by the fault can be up to 1.4 times the magnitude of the maximum principal regional stress and is highly dependent on friction angle.Case studies are presented where this 3D numerical technique has been used to truly integrate risking methods on the fault plane and in the surrounding rock mass. Case study examples are given for the Otway Basin, South Australia and the Bonaparte Basin, Timor Sea, where these predictors can be applied to accurately identify high-risk reservoir seals.

UNCONVENTIONAL BOREHOLE BREAKOUT ROTATION ANALYSIS PROVIDES A QC TOOL FOR STRESS MODELS

2006 ◽  
Vol 46 (1) ◽  
pp. 307
Author(s):  
B.A. Camac ◽  
S.P. Hunt ◽  
P.J. Boult ◽  
M. Dillon
Keyword(s):  
Principal Stress ◽  
Input Data ◽  
Distinct Element ◽  
Maximum Principal Stress ◽  
Principal Stresses ◽  
Stress Regime ◽  
Seal Integrity ◽  
Borehole Breakout ◽  
Stress Models ◽  
Kupe Field

In distinct element (DEM) numerical stress modelling, the principal stress magnitudes and orientations are applied to the boundary of the 3D model. Due to data restrictions and typical depths of investigation, it is possible to have much uncertainty in the conventional methodologies used to constrain the regional principal stress magnitudes and orientations.A case study from the Kupe field in the Taranaki Basin, New Zealand is presented where the uncertainty in the input data made it difficult to determine which stress regime—a transitional normal/strike-slip or reverse/thrust—is active at reservoir depth (approximately 3,000 m). The magnitudes and orientation of the principal stresses were constrained using published techniques. A sensitivity analysis was applied to account for the uncertainty in the input data. A model of the Kupe field incorporating 18 major faults was subsequently loaded under both derived stressed regimes, using the calculated magnitudes.Borehole breakout analysis was used to acquire interpreted orientations of the maximum principal stress (Shmax). The work presented herein describes a different or unconventional approach to the general petroleum geomechanics methodology. Typically, the breakout data is averaged to get one data point per well location. Here, all breakout data is retained and displayed vertically. The data is actively used and the variations with depth can be seen to show how faults can generate local perturbations of the regional stress trajectory. These data are then used to compare the observed or field indications of the breakouts along the borehole with the modelled Shmax predicted by both end point DEM stress models. This comparison has provided additional confidence in the derived stress regime and the derived stress models for the Kupe field. The stress models are used to predict areas of enhanced hydrocarbon pooling and low seal integrity.

scholarly journals Effect of Wetting-Drying Cycle on the Deformation and Seepage Behaviors of Rock Masses around a Tunnel

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Qingzhen Guo ◽  
Haijian Su ◽  
Hongwen Jing ◽  
Wenxin Zhu
Keyword(s):  
Rock Mass ◽  
Principal Stress ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water Inrush ◽  
Surrounding Rock ◽  
Tunnel Excavation ◽  
Cycle Number ◽  
Simulation Results

Water inrush caused by the wetting-drying cycle is a difficult problem in tunnel excavation. To investigate the effect of the wetting-drying cycle on the stability of the tunnel surrounding rock, physical experiments and numerical simulations regarding the process of tunnel excavation with different wetting-drying cycle numbers were performed in this study. The evolutions of stress, displacement, and pore water pressure were analyzed. With the increase in cycle number, the pore water pressure, vertical stress, and top-bottom approach of the tunnel surrounding rock increase gradually. And the increasing process could be divided into three stages: slightly increasing stage, slowly increasing stage, and sharply increasing stage, respectively. The failure process of the surrounding rock under the wetting-drying cycle gradually occurs from the roof to side wall, while the baseplate changes slightly. The simulation results showed that the maximum principal stress in the surrounding rock mass of the tunnel increases, while the minimum principal stress decreases. Furthermore, the displacement of the rock mass decreases gradually with the increasing distance from the tunnel surface. By comparing the simulation results with the experimental results, well consistency is shown. The results in this study can provide helpful references for the safe excavation and scientific design of a tunnel under the wetting-drying cycle.

scholarly journals Influence of Three-Dimensional Stress Field Variation on Fracture Evolution Characteristics of a Roof

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Xuyang Shi ◽  
Zhaolin Li ◽  
Qingxiang Cai ◽  
Wei Zhou ◽  
Wenshuai Li
Keyword(s):  
Rock Mass ◽  
Stress Field ◽  
Principal Stress ◽  
Three Dimensional ◽  
Surrounding Rock ◽  
Fracture Characteristics ◽  
Principal Stress Direction ◽  
True Triaxial ◽  
Fracture Evolution ◽  
Macroscopic Fracture

Excavation disturbance on the dynamic variation of the three-dimensional stress field is the main cause for the dynamic disasters of the surrounding rock mass of the roof. The stress condition in the surrounding rock mass of the roof during entry excavation and its impact on entry stability are systemically studied in this study. It is found that the surrounding rock mass of the roof is mainly influenced by the combined effect of the stress unloading and stress transference induced by entry excavation. A servo-controlled true triaxial material testing system is used to conduct the true triaxial loading and unloading experiments of rocks under different stress paths. The influence of different stress paths, especially the variation of the principal stress direction, on the mechanical characteristics and fracture characteristics of rocks is investigated. The results indicate that the variation of the principal stress direction has a significant impact on the macroscopic fracture characteristics of the rock. The main macroscopic fracture plane of the rock highly depends on the intermediate principal stress. The fracture evolution of the roof rock mass during entry excavation is analyzed. The results show that the change of the three-dimensional stress field induces the formation of complex fracture networks in the surrounding rock mass of the roof. The roof is likely to dislocate horizontally and collapse. The corners of the entry are seriously damaged. Based on the above findings, a support scheme is proposed to maintain the stability of a gob-side entry. The field experience suggests that the support scheme can achieve good results.

scholarly journals The Mechanism of Rock Mass Crack Propagation of Principal Stress Rotation in the Process of Tunnel Excavation

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Guanfeng Chang ◽  
Xinzhu Hua ◽  
Jie Zhang ◽  
Peng Li
Keyword(s):  
Rock Mass ◽  
Crack Propagation ◽  
Principal Stress ◽  
Maximum Principal Stress ◽  
Surrounding Rock ◽  
Shear Load ◽  
Principal Stress Rotation ◽  
Principal Stress Direction ◽  
Stress Rotation ◽  
Crack Angle

Rock excavation has experienced complex stress paths. The development of the original crack under the path of principal stress magnitude and principal stress direction is a key scientific problem that needs to be solved in rock underground engineering. The principal stress magnitude dominates the initiation and propagation of the crack and increases rock damage under the action of principal stress rotation. In this study, the theoretical calculation and numerical analysis method have been combined with the crack propagation conditions to study the stress-driven mechanism of brittle rock crack propagation under principal stress rotation. The results show that the “relative initial angle” of crack angle is being updated in time during the principal stress rotation process; once the stress is rotated, it will become the next initial crack angle; the crack propagation direction is deviated under the applied shear load, and it is always in the direction of minimum shear load, leading to a certain degree of inhibition of crack propagation depth in the initial direction. According to the results of numerical simulation, the effect of principal stress rotation caused by mining excavation is obvious and has a certain range of influence depth, the stress of surrounding rock of roadway is the highest within the depth range of 1∼2 m, and the maximum principal stress is as high as 26.89 MPa. The rotation of principal stress direction on the roadway surrounding rock surface is the strongest, which makes the surrounding rock more fragmented, and the middle principal stress and the maximum principal stress rotate about 90° counterclockwise along the Ox axis. Studying the action mechanism of principal stress rotation on fractured rock masses can provide scientific basis for geotechnical engineering design and rock mass surrounding support.

Influence exerted by underground excavation shape and by effective stresses on the formation of a tensile strain zone at a depth greater than 1 km

2020 ◽  
pp. 67-75
Author(s):  
Van Min Nguyen ◽  
V. A. Eremenko ◽  
M. A. Sukhorukova ◽  
S. S. Shermatova
Keyword(s):  
Rock Mass ◽  
Cross Sections ◽  
Tensile Strain ◽  
Rock Fracture ◽  
Strain Analysis ◽  
Surrounding Rock ◽  
Underground Excavation ◽  
Secondary Stress ◽  
Principal Stresses ◽  
Mining Depth

The article presents the studies into the secondary stress field formed in surrounding rock mass around underground excavations of different cross-sections and the variants of principal stresses at a mining depth greater than 1 km. The stress-strain analysis of surrounding rock mass around development headings was performed in Map3D environment. The obtained results of the quantitative analysis are currently used in adjustment of the model over the whole period of heading and support of operating mine openings. The estimates of the assumed parameters of excavations, as well as the calculations of micro-strains in surrounding rock mass by three scenarios are given. During heading in the test area in granite, dense fracturing and formation of tensile strain zone proceeds from the boundary of e ≥ 350me and is used to determine rough distances from the roof ( H roof) and sidewalls ( H side) of an underground excavation to the 3 boundary e = 350me (probable rock fracture zone). The modeling has determined the structure of secondary stress and strain fields in the conditions of heading operations at great depths.

Numerical solutions for strain-softening surrounding rock under three-dimensional principal stress condition

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sheng Yu-ming ◽  
Li Chao ◽  
Xia Ming-yao ◽  
Zou Jin-feng
Keyword(s):  
Finite Element ◽  
Principal Stress ◽  
Stress Condition ◽  
Strain Softening ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Strength Criterion ◽  
Surrounding Rock ◽  
Flow Rule ◽  
Finite Element Software

Abstract In this study, elastoplastic model for the surrounding rock of axisymmetric circular tunnel is investigated under three-dimensional (3D) principal stress states. Novel numerical solutions for strain-softening surrounding rock were first proposed based on the modified 3D Hoek–Brown criterion and the associated flow rule. Under a 3D axisymmetric coordinate system, the distributions for stresses and displacement can be effectively determined on the basis of the redeveloped stress increment approach. The modified 3D Hoek–Brown strength criterion is also embedded into finite element software to characterize the yielding state of surrounding rock based on the modified yield surface and stress renewal algorithm. The Euler implicit constitutive integral algorithm and the consistent tangent stiffness matrix are reconstructed in terms of the 3D Hoek–Brown strength criterion. Therefore, the numerical solutions and finite element method (FEM) models for the deep buried tunnel under 3D principal stress condition are presented, so that the stability analysis of surrounding rock can be conducted in a direct and convenient way. The reliability of the proposed solutions was verified by comparison of the principal stresses obtained by the developed numerical approach and FEM model. From a practical point of view, the proposed approach can also be applied for the determination of ground response curve of the tunnel, which shows a satisfying accuracy compared with the measuring data.

Hydro-Mechanical Coupled Analysis of the Stability of Surrounding Rock Mass of Underground Water-Sealed Oil Storage

2013 ◽  
Vol 405-408 ◽  
pp. 402-405 ◽  
Author(s):  
Yun Jie Zhang ◽  
Tao Xu ◽  
Qiang Xu ◽  
Lin Bu
Keyword(s):  
Rock Mass ◽  
Underground Water ◽  
Surrounding Rock ◽  
Comsol Multiphysics ◽  
Coupled Analysis ◽  
Coupling Theory ◽  
Oil Storage ◽  
Stability Of Surrounding Rock ◽  
Straight Wall ◽  
The Stability

Based on the fluid-solid coupling theory, we study the stability of surrounding rock mass around underground oil storage in Huangdao, Shandong province, analyze the stress of the surrounding rock mass around three chambers and the displacement change of several key monitoring points after excavation and evaluate the stability of surrounding rock mass using COMSOL Multiphysics software. Research results show that the stress at both sides of the straight wall of cavern increases, especially obvious stress concentration forms at the corners of the cavern, and the surrounding rock mass moves towards the cavern after excavation. The stress and displacement of the surrounding rock mass will increase accordingly after setting the water curtains, but the change does not have a substantive impact on the stability of surrounding rock mass.

Application of ABAQUS in Surrounding Rock Stability Analysis of Shallow Large Cross-Section Tunnel

2015 ◽  
Vol 777 ◽  
pp. 8-12 ◽  
Author(s):  
Lin Zhen Cai ◽  
Cheng Liang Zhang
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Strong Support ◽  
Surrounding Rock ◽  
Tunnel Engineering ◽  
Tunnel Excavation ◽  
Rock Stability ◽  
Rock Bolting ◽  
Excavation Support ◽  
The Stability

HuJiaDi tunnel construction of Dai Gong highway is troublesome, the surrounding-rock mass give priority to full to strong weathering basalt, surrounding rock integrity is poor, weak self-stability of surrounding rock, and tunnel is prone to collapse. In order to reduce disturbance, taking advantage of the ability of rock mass, excavation adopt the method of "more steps, short footage and strong support". The excavation method using three steps excavation, The excavation footage is about 1.2 ~ 1.5 m; The surrounding rock bolting system still produce a large deformation after completion of the first support construction, it shows that the adopted support intensity cannot guarantee the stability of the tunnel engineering. Using ABAQUS to simulate tunnel excavation support, optimizing the support parameters of the tunnel, conducting comparative analysis with Monitoring and Measuring and numerical simulation results, it shows that the displacement - time curves have a certain consistency in numerical simulation of ABAQUS and Monitoring and Measuring.

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