scholarly journals Stress Estimation through Deep Rock Core Diametrical Deformation and Joint Roughness Assessment Using X-ray CT Imaging

Sensors ◽  
2020 ◽  
Vol 20 (23) ◽  
pp. 6802 ◽  
Author(s):  
Hanna Kim ◽  
Melvin B. Diaz ◽  
Joo Yeon Kim ◽  
Yong-Bok Jung ◽  
Kwang Yeom Kim
Keyword(s):  
Horizontal Stress ◽  
In Situ Stress ◽  
Core Sample ◽  
Deformation Analysis ◽  
Roughness Coefficient ◽  
Joint Roughness ◽  
X Ray ◽  
Deep Rock ◽  
Stress Estimation

In-situ stress estimation plays an important role on the success of an underground project. However, no method is error-free, and therefore a combination of methods is desirable. In this study, the in-situ stresses for a geothermal project have been assessed through the analysis of a deep rock core taken at 4.2 km, using the diametrical core deformation analysis (DCDA) method that relates the diametrical core expansion after stress relief with the stresses assuming elastic deformation. The extracted granodiorite core sample of 100 mm of diameter was intersected with a closed joint at a dip angle of 80.8° with respect to the vertical coring direction. The core sample was scanned using an industrial X-ray computed tomography (CT), and the diametrical deformation measurements were computed with CT slices. Results from using the DCDA method indicated an average horizontal stress difference of 13.3 MPa, similar to that reported for a nearby exploration well. Furthermore, the stress orientations were compared with the orientation of maximum roughness values. The results indicated a correlation between the orientation of the maximum horizontal stress and the orientation of the minimum joint roughness coefficient, implying a possible tracking of stress orientation using joint roughness anisotropy.

scholarly journals Evaluation of the Diametrical Core Deformation and Discing Analyses for In-Situ Stress Estimation and Application to the 4.9 km Deep Rock Core from the Basel Geothermal Borehole, Switzerland

2021 ◽  
Author(s):  
Martin Ziegler ◽  
Benoît Valley
Keyword(s):  
Elastic Anisotropy ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Deformation Analysis ◽  
Geothermal Systems ◽  
In Situ Tests ◽  
Borehole Breakout ◽  
Stress Estimation ◽  
The Impact

AbstractThe in situ state of rock mass stresses is a key design parameter, e.g., for deep engineered geothermal systems. However, knowledge of the stress state at great depths is sparse mostly because of the lack of possible in situ tests in deep boreholes. Among different options, core-based in situ stress estimation may provide valuable stress information though core-based techniques have not yet become a standard. In this study we focus on the Diametrical Core Deformation Analysis (DCDA) technique using monzogranitic to monzonitic rock drill cores from 4.9 km depth of the Basel-1 borehole in Switzerland. With DCDA the maximum and minimum horizontal stress (SHmax and Shmin) directions, and the horizontal differential stress magnitudes (∆S) can be estimated from rock cores extracted from vertical boreholes. Our study has three goals: first, to assess photogrammetric core scanning to conduct DCDA; second, to compare DCDA results with borehole breakout and stress-induced core discing fracture (CDF) data sets; and third, to investigate the impact of rock elastic anisotropy on ∆S. Our study reveals that photogrammetric scanning can be used to extract reliable core diametrical data and CDF traces. Locally aligned core pieces showed similar SHmax orientations, conform to borehole breakout results. However, the variability of core diametrical differences was large for the Basel-1 core pieces, which leads to a large spread of ∆S. Finally, we demonstrate that core elastic anisotropy must be considered, requiring robust estimates of rock elastic moduli, to receive valuable stress information from DCDA analyses.

scholarly journals In Situ Stress Prediction in Subsurface Rocks: An Overview and a New Method

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yushuai Zhang ◽  
Shangxian Yin ◽  
Jincai Zhang
Keyword(s):  
Horizontal Stress ◽  
In Situ Stress ◽  
New Method ◽  
Alternative Methods ◽  
Tensile Fracture ◽  
In Situ Stresses ◽  
Stress Estimation ◽  
Minimum Horizontal Stress ◽  
Polygon Method

Methods for determining in situ stresses are reviewed, and a new approach is proposed for a better prediction of the in situ stresses. For theoretically calculating horizontal stresses, horizontal strains are needed; however, these strains are very difficult to be obtained. Alternative methods are presented in this paper to allow an easier way for determining horizontal stresses. The uniaxial strain method is oversimplified for the minimum horizontal stress determination; however, it is the lower bound minimum horizontal stress. Based on this concept, a modified stress polygon method is proposed to obtain the minimum and maximum horizontal stresses. This new stress polygon is easier to implement and is more accurate to determine in situ stresses by narrowing the area of the conventional stress polygon when drilling-induced tensile fracture and wellbore breakout data are available. Using the generalized Hooke’s law and coupling pore pressure and in situ stresses, a new method for estimating the maximum horizontal stress is proposed. Combined it to the stress polygon method, a reliable in situ stress estimation can be obtained. The field measurement method, such as minifrac test, is also analyzed in different stress regimes to determine horizontal stress magnitudes and calibrate the proposed theoretical method. The proposed workflow combined theoretical methods to field measurements provides an integrated approach for horizontal stress estimation.

scholarly journals Orthogonal Analysis and Numerical Simulation of Rock Mechanics Parameters in Stress Field of Shaft Heading Face

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Liyun Yang ◽  
Siyu Chen ◽  
Pengxiang Dong ◽  
Qingcheng Wang ◽  
Chen Huang
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Vertical Direction ◽  
Peak Stress ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Orthogonal Analysis ◽  
Deep Rock ◽  
Different Depths

This paper focuses on improving the blasting effect of the drilling and blasting method in the deep rock mass and solves the problems of blasthole collapse and misfire accident in the process of drilling and blasting construction of heading face. FEM software, ABAQUS, is used to simulate the stress distribution around the blasthole by extending a certain depth in the vertical direction of the shaft heading face. The sensitivity of different depths, different heading face sizes, and different lithologies on the horizontal stress distribution is analyzed by using a six-factor four-level orthogonal analysis method. The results show that the change of the radius of the heading face has the most considerable influence on the distance of the distressed zone and the stress concentration zone, followed by the lithology and the excavation depth. Also, the excavation depth has the most significant influence on the peak stress value. Through the industrial field experiment, the in situ stress of the shaft heading face is tested, and the numerical simulation results are consistent with the field monitoring results. The results reveal the law of stress distribution near the heading face, which can provide some reference for the design of blasthole depth in the drilling and blasting construction scheme.

Analysis of Casing Strength after Casing Wear in Ultra-Deep Rock Salt Formation

2012 ◽  
Vol 616-618 ◽  
pp. 538-542 ◽  
Author(s):  
Fu Xiang Zhang ◽  
Wei Feng Ge ◽  
Xiang Tong Yang ◽  
Wei Zhang ◽  
Jian Xin Peng
Keyword(s):  
Rock Salt ◽  
Coupling Effect ◽  
Equivalent Stress ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Attrition Rate ◽  
Salt Formation ◽  
Salt Creep ◽  
Casing Wear

To alleviate the problems of casing collapse induced by the coupling effect of rock salt creep and casing wear, the effects of salt creep, attrition rate and casing abrasive position on the equivalent stress on casings in non-uniform in-situ stress field is analyzed by finite-difference model with worn casing, cement and salt formation. It indicates that, creep reduces the yield strength of worn casing to a certain extent; Equivalent stress on casings is bigger and more non-uniform when the abrasion is more serious; Wear position obviously changes the distribution of equivalent stress on casing, and when the wear located along the direction of the minimum in-situ stress, equivalent stress on casing could be the largest that leads to the casing being failed more easily. Equivalent stress on casings increases gradually with creep time increasing and will get to balance in one year or so; In addition, new conclusions are obtained which are different from before: the maximum equivalent stress on casings is in the direction of the minimum horizontal stress, only when the attrition rate of the casing is little; otherwise, it is not. This method could help to improve the wear prediction and design of casings.

scholarly journals Exploring Deep-Rock Mechanics through Mechanical Analysis of Hard-Rock In Situ Coring System

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jianan Li ◽  
Heping Xie ◽  
Ling Chen ◽  
Cong Li ◽  
Zhiqiang He
Keyword(s):  
Rock Mechanics ◽  
Hard Rock ◽  
Design Method ◽  
Drill Pipe ◽  
In Situ Stress ◽  
Drilling Depth ◽  
Innovative Design ◽  
The Core ◽  
Deep Rock

Exploration of deep-rock mechanics has a significant influence on the techniques of mining and rock mechanics. Rock coring technique is the basic method for all rock mechanics study. With the increase of the drilling depth and increasing strength of the hard rock, how to obtain high-quality rock core through various coring techniques is an eternal work. Here an innovative method is applied to design the new coring system to maximize the efficiency of operation. The stress conditions or parameters of rock core in the coring are analyzed, and the mechanism of the core with in situ stress is shown in this paper. The conflict of the core and coring tool chamber is proposed for the innovative design. The innovative design method is fulfilled by the theory of inventive problem solving (TRIZ). An improved coring system for the full-length core with in situ stress was obtained with the solutions of improved coring mechanism, cutting mechanism, and spiral drill pipe.

In Situ Stress Measurement and Surrounding Rock Stability Analysis of the Gaoligong Mountain Tunnel

2014 ◽  
Vol 501-504 ◽  
pp. 1766-1773
Author(s):  
Lin Hai Bao
Keyword(s):  
Large Deformation ◽  
Principal Stress ◽  
Stress Measurement ◽  
Pressure Coefficient ◽  
Horizontal Stress ◽  
Wall Rock ◽  
In Situ Stress ◽  
Rock Stability ◽  
Mountain Tunnel

Gaoligong Mountain tunnel is the key project in the Dali-Ruili Railway. In order to optimize the design and guide construction, In-situ stress has been conducted in five boreholes using hydraulic fracturing method, the current shallow crustal in-situ stress state at the project area are obtained according to the measurements results, and deep in-situ stress is predicted using lateral pressure coefficient. The test results show that at depths ranging from 299-979m, the maximum horizontal principal stress is 5.33-30.12Mpa, the minimum horizontal principal stress is 4.94-23.11Mpa, the horizontal principal stress reach 30Mpa at maximum the depth of burial, indicating that the engineering stress filed is dominated by horizontal stress. Based on the In-situ stress data and different distinguish methods, rockburst and large deformation are predicted. The results show that In-situ stress magnitude in this area is classified as high level, and the direction of the maximum horizontal stress is NEE, In-situ stress orientation is conductive to stable of the tunnel. When the tunnel passes through the deep-burial and hard rock, the wall rock may happen rockburst; and the large deformation may happen when the tunnel pass through the weak rock. In order to avoid the disadvantage conditions, reasonable excavation method and safety support method should be adopted during tunnel excavating.

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