TY  - JOUR
A1  - Gaci, Said
A1  - Zaourar, Naima
A1  - Briqueu, Louis
A1  - Holschneider, Matthias
T1  - Regularity analysis applied to sonic logs data a case study from KTB borehole site
JF  - Arabian journal of geosciences
N2  - Borehole logs provide in situ information about the fluctuations of petrophysical properties with depth and thus allow the characterization of the crustal heterogeneities. A detailed investigation of these measurements may lead to extract features of the geological media. In this study, we suggest a regularity analysis based on the continuous wavelet transform to examine sonic logs data. The description of the local behavior of the logs at each depth is carried out using the local Hurst exponent estimated by two (02) approaches: the local wavelet approach and the average-local wavelet approach. Firstly, a synthetic log, generated using the random midpoints displacement algorithm, is processed by the regularity analysis. The obtained Hurst curves allowed the discernment of the different layers composing the simulated geological model. Next, this analysis is extended to real sonic logs data recorded at the Kontinentales Tiefbohrprogramm (KTB) pilot borehole (Continental Deep Drilling Program, Germany). The results show a significant correlation between the estimated Hurst exponents and the lithological discontinuities crossed by the well. Hence, the Hurst exponent can be used as a tool to characterize underground heterogeneities.
KW  - Regularity analysis
KW  - Wavelet transform
KW  - Well log
KW  - Fractal
KW  - Lithology
Y1  - 2011
U6  - https://doi.org/10.1007/s12517-010-0129-y
SN  - 1866-7511
VL  - 4
IS  - 1-2
SP  - 221
EP  - 227
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Fernandez, Ricardo
A1  - Bruno, Giovanni
A1  - Garces, Gerardo
A1  - Nieto-Luis, H.
A1  - Gonzalez-Doncel, Gaspar
T1  - Fractional brownian motion of dislocations during creep deformation of metals
JF  - Materials science & engineering. A, Structural materials
N2  - The present work offers an explanation on how the long-range interaction of dislocations influences their movement, and therefore the strain, during creep of metals. It is proposed that collective motion of dislocations can be described as a fractional Brownian motion. This explains the noisy appearance of the creep strain signal as a function of time. Such signal is split into a deterministic and a stochastic part. These terms can be related to two kinds of dislocation motions: individual and collective, respectively. The description is consistent with the fractal nature of strain-induced dislocation structures predicated in previous works. Moreover, it encompasses the evolution of the strain rate during all stages of creep, including the tertiary one. Creep data from Al99.8% and Al3.85%Mg tested at different temperatures and stresses are used to validate the proposed ideas: it is found that different creep stages present different diffusion characters, and therefore different dislocation motion character.
KW  - Creep
KW  - Aluminum alloys
KW  - Dislocation motion
KW  - Diffusion
KW  - Fractal
KW  - structures
Y1  - 2020
U6  - https://doi.org/10.1016/j.msea.2020.140013
SN  - 0921-5093
SN  - 1873-4936
VL  - 796
PB  - Elsevier
CY  - Lausanne
ER  -