Estimation of crack tensor components for the different distributions of crack orientation

2014 ◽  
pp. 411-414
Author(s):  
A Idziak
Keyword(s):  
Crack Orientation

scholarly journals Parameterization of elastic stress sensitivity in shales

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. WA147-WA155 ◽  
Author(s):  
Marina Pervukhina ◽  
Boris Gurevich ◽  
Pavel Golodoniuc ◽  
David N. Dewhurst
Keyword(s):  
Elastic Properties ◽  
Anisotropy Parameter ◽  
Transversely Isotropic ◽  
Bedding Plane ◽  
Stress Sensitivity ◽  
Crack Orientation ◽  
Fluid Identification ◽  
Orientation Anisotropy ◽  
Characteristic Pressure ◽  
Stress Dependency

Stress dependency and anisotropy of dynamic elastic properties of shales is important for a number of geophysical applications, including seismic interpretation, fluid identification, and 4D seismic monitoring. Using Sayers-Kachanov formalism, we developed a new model for transversely isotropic (TI) media that describes stress sensitivity behavior of all five elastic coefficients using four physically meaningful parameters. The model is used to parameterize elastic properties of about 20 shales obtained from laboratory measurements and the literature. The four fitting parameters, namely, specific tangential compliance of a single crack, ratio of normal to tangential compliances, characteristic pressure, and crack orientation anisotropy parameter, show moderate to good correlations with the depth from which the shale was extracted. With increasing depth, the tangential compliance exponentially decreases. The crack orientation anisotropy parameter broadly increases with depth for most of the shales, indicating that cracks are getting more aligned in the bedding plane. The ratio of normal to shear compliance and characteristic pressure decreases with depth to 2500 m and then increases below this to 3600 m. The suggested model allows us to evaluate the stress dependency of all five elastic compliances of a TI medium, even if only some of them are known. This may allow the reconstruction of the stress dependency of all five elastic compliances of a shale from log data, for example.

Numerical Simulation of Ring-Shape Rock Failure under Compressive Loading

2011 ◽  
Vol 378-379 ◽  
pp. 15-18
Author(s):  
Yong Bin Zhang ◽  
Zheng Zhao Liang ◽  
Shi Bin Tang ◽  
Jing Hui Jia
Keyword(s):  
Numerical Simulation ◽  
Fracture Process ◽  
Failure Modes ◽  
Failure Process ◽  
Compressive Loading ◽  
Orientation Angle ◽  
Crack Orientation ◽  
Ring Specimen ◽  
Ring Shape ◽  
Good Agreement

In this paper, a ring shaped numerical specimen is used to studying the failure process in brittle materials. The ring specimen is subjected to a compressive diametral load and contains two angled central cracks. Numerical modeling in this study is performed. It is shown that the obtained numerical results are in a very good agreement with the experiments. Effect of the crack orientation angle on the failure modes and loading-displace responses is discussed. In the range of 0°~40°, the fracture paths are curvilinear forms starting from the tip of pre-existing cracks and grow towards the loading points. For the crack orientation angle 90°, vertical fractures will split the specimen and the horizontal cracks do not influence the fracture process.

Three-Dimensional Study of Fatigue Crack Growth in a Rotating Disc

2013 ◽  
Vol 3 (2) ◽  
pp. 45-62
Author(s):  
Eskandari Hadi ◽  
Nami Mohammad Rahim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Crack Orientation ◽  
Rotating Disc ◽  
Mesh Density ◽  
Three Dimensional Finite Element

The problem of fatigue-crack-growth in a rotating disc at different crack orientation angles is studied by using an automated numerical technique, which calculates the stress intensity factors on the crack front through the three-dimensional finite element method. Paris law is used to develop the fatigue shape of initially semi-elliptical surface crack. Because of needs for the higher mesh density and accuracy near the crack, the sub-modeling technique is used in the analysis. The distribution of SIF’s along the crack front at each step of growth is studied and the effect of crack orientation on the rate of crack-growth is investigated. The calculated SIF’s are reasonable and could be used to predict the probable crack growth rates in fracture mechanics analysis and can help engineers to consider in their designing and to prevent any unwanted failure of such components.

AN ENHANCED METHOD FOR CRACK EVALUATION UTILIZING NEUTRON GAMMA TRACER IMAGING LOGGING TECHNOLOGY IN CARBONATE RESERVOIR

2021 ◽  
Author(s):  
Qian Chen ◽  
◽  
Feng Zhang ◽  
Lili Tian ◽  
Xiaoyang Zhang ◽  
...  
Keyword(s):  
Cross Section ◽  
Quantitative Evaluation ◽  
Pore Fluid ◽  
Absorption Cross ◽  
Crack Orientation ◽  
Carbonate Formation ◽  
Tracer Imaging ◽  
The Difference ◽  
Pulsed Neutron ◽  
High Absorption

The evaluation of carbonate rocks with fractures, caves, and pores is of great significance in the search for reservoir sweet spots and the prediction of reservoir productivity. With the advancement of exploration and development technology, the targets of oil and gas exploration move to deep high temperature, high pressure (HPHT) formations drilled with oil-based mud systems. The existing fracture evaluation methods often rely on dipole acoustic logging, electrical or acoustic formation micro-imaging, which utilize the difference of rock and pore fluid petrophysical properties for fracture detection, but the adverse HPHT conditions are a huge challenge to evaluate reservoir structure by such means. The tracer imaging technology (TIT) which utilizes pulsed neutron technology and tagged proppant containing high absorption cross-section element has been proposed for crack evaluation after hydraulic fracturing, but a quantitative evaluation of crack parameters, due to their low sensitivity caused by neutron self-shielding, has not been feasible. In this paper, the combination of the new pulsed neutron tool with multi-detector array design and oil-based mud with high absorption cross-section element is used to achieve the crack parameter evaluation in carbonate reservoirs under oil-based mud invasion condition via tracer element imaging. The special oil-based mud is injected into the carbonate formation through the borehole to enhance the difference of the nuclear properties between crack and rock. A multi-detector array tool that contains four gamma detectors arranged in a ring with 90 degrees between detectors is adopted to acquire capture the gamma spectrum in different orientations. Here, a new crack inversion method adopting a joint of the multi-element characteristic peak is used to eliminate the influence of neutron self-shielding to improve the response sensitivity of crack and calculation accuracy. The new method is suitable for all pore fluid types. Meanwhile, the effect of formation backgrounds which consist of formation matrix, pore fluid, and borehole fluid on the quantitative evaluation is analyzed and discussed for limitations of this method. To improve the recognition accuracy of the parameters in the image, the digital imaging recognition method based on artificial intelligence is applied in crack imaging for the information extraction of crack orientation. The effect of formation background on the quantitative evaluation of crack parameters is analyzed and discussed. Quantitative evaluation of carbonate with fractures, caves, and cavities can be realized with the new tracer imaging technology, which eliminates the saturation effect caused by neutron self-shielding to improve the calculation precision of fracture width. Finally, an example of carbonate formation with multiple cracks and formation background is simulated utilizing a Monte Carlo N-Particle transport model (MCNP). The calculation results of the crack density and crack width are presented and the crack orientation is determined from crack imaging, which is consistent with the model set. The result verifies the feasibility of the method.

Influence of crack orientation on the ductile–brittle behavior in Fe–3 wt.% Si single crystals

2007 ◽  
Vol 58 (10) ◽  
pp. 892-900 ◽  
Author(s):  
Alena Spielmannová ◽  
Michal Landa ◽  
Anna Machová ◽  
Petr Haušild ◽  
Pavel Lejček
Keyword(s):  
Single Crystals ◽  
Crack Orientation ◽  
Brittle Behavior

Two time domain models for fatigue life prediction under multiaxial random vibrations

2019 ◽  
Vol 233 (13) ◽  
pp. 4707-4718 ◽  
Author(s):  
Zhengbo Luo ◽  
Huaihai Chen ◽  
Xudong He ◽  
Ronghui Zheng
Keyword(s):  
Fatigue Life ◽  
Time Domain ◽  
Life Prediction ◽  
Random Vibration ◽  
Notch Root ◽  
Critical Plane ◽  
Crack Orientation ◽  
Spectral Density Matrix ◽  
Power Spectral ◽  
Domain Models

Two time domain models for fatigue life prediction under multiaxial random vibrations are developed on the basis of the critical plane approach. Firstly, the stress power spectral density matrix of each node at the notch root of the test specimen is obtained by the random vibration analysis with finite element method, and the stress time-histories are generated from the stress power spectral density matrix by the time domain randomization approach. Then, the fatigue life of each node is predicted based on the damage on the critical plane, where the cumulative damage value is the greatest. The minimum fatigue life of all nodes at the notch root is considered as the fatigue life of the test specimen. Finally, the proposed models are validated by the multiaxial random vibration fatigue test with the 6061-T4 aluminum alloy. The results show that the predicted fatigue lives and predicted crack orientation angles are in good agreement with the experimental fatigue lives and experimentally observed crack orientation angles, respectively.

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