TY  - JOUR
A1  - Farkas, Márton Pál
A1  - Yoon, Jeoung Seok
A1  - Zang, Arno
A1  - Zimmermann, Günter
A1  - Stephansson, Ove
A1  - Lemon, Michael
A1  - Danko, Gyula
T1  - Effect of foliation and fluid viscosity on hydraulic fracturing tests in mica schists investigated using distinct element modeling and field data
JF  - Rock Mechanics and Rock Engineering
N2  - Several hydraulic fracturing tests were performed in boreholes located in central Hungary in order to determine the in-situ stress for a geological site investigation. At a depth of about 540m, the observed pressure versus time curves in mica schist with low dip angle foliation shows atypical pressure versus time results. After each pressurization cycle, the fracture breakdown pressure in the first fracturing cycle is lower than the refracturing or reopening pressure in the subsequent pressurizations. It is assumed that the viscosity of the drilling mud and observed foliation of the mica schist have a significant influence on the pressure values. In order to study this problem, numerical modeling was performed using the distinct element code particle flow code, which has been proven to be a valuable tool to investigate rock engineering problems such as hydraulic fracturing. The two-dimensional version of the code applied in this study can simulate hydro-mechanically coupled fluid flow in crystalline rock with low porosity and pre-existing fractures. In this study, the effect of foliation angle and fluid viscosity on the peak pressure is tested. The atypical characteristics of the pressure behaviour are interpreted so that mud with higher viscosity penetrates the sub-horizontal foliation plane, blocks the plane of weakness and makes the partly opened fracture tight and increase the pore pressure which decreases slowly with time. We see this viscous blocking effect as one explanation for the observed increase in fracture reopening pressure in subsequent pressurization cycles.
KW  - Hydraulic fracturing
KW  - Stress measurement
KW  - Particle flow code
KW  - Hydro-mechanical coupling
KW  - Microcrack
KW  - Viscous blocking
Y1  - 2019
U6  - https://doi.org/10.1007/s00603-018-1598-7
SN  - 0723-2632
SN  - 1434-453X
VL  - 52
IS  - 2
SP  - 555
EP  - 574
PB  - Springer
CY  - Wien
ER  - 
TY  - BOOK
A1  - Zang, Arno
A1  - Stephansson, Ove
T1  - Stress field of the earth's crust
Y1  - 2010
SN  - 978-1-402-08443-0
U6  - https://doi.org/10.1007/978-1-4020-8444-7
PB  - Springer Science+Business Media B.V
CY  - Dordrecht
ER  -