TY - THES

T1 - Elastic wave velocity measurements during uniaxial loading - Petrophysical and geomechanical aspects

AU - Schifko, Thomas

N1 - embargoed until null

PY - 2016

Y1 - 2016

N2 - This thesis investigates the elastic wave velocities during uniaxial loading. Therefore rocks are prepared according to ISRM guidance and velocities are determined during various loading and unloading cycles until the sample reaches the UCS. Different cycles are carried out to observe phenomena like elastic hysteresis, different stages of compaction and closure of present micro cracks, furthermore the phase of new fracture inducement got visible. The determination of dynamic elastic properties is linked to the velocity measurements. Furthermore thin section analyses and detailed petrophysical measurements were performed in order to get a better understanding of stress dependent velocity influencing factors like effective porosity, grain size or fractures. Applications like borehole stability issues are described in detail and further possibilities to enhance the power of this technique are presented additionally. This measurement technique is a powerful tool to determine rock failure geophysically. Interesting is the velocity ratio of compressional- and shear waves, which can indicate fracture formation or compaction processes. Moreover it got clear that the dynamic shear- and Young’s modulus depend on shear wave velocity, and bulk modulus is more related to a variation in velocity ratio rather than highest values. Due to the possibility of estimating in situ stresses of boreholes, velocities determined in the laboratory can be measured at similar stress levels. This way of measurement allows achieving real conditions thus geomechanical properties can be determined in the most accurate way. However, according to the strong lithology dependency of geomechanical parameters, this technique cannot replace static measurements.

AB - This thesis investigates the elastic wave velocities during uniaxial loading. Therefore rocks are prepared according to ISRM guidance and velocities are determined during various loading and unloading cycles until the sample reaches the UCS. Different cycles are carried out to observe phenomena like elastic hysteresis, different stages of compaction and closure of present micro cracks, furthermore the phase of new fracture inducement got visible. The determination of dynamic elastic properties is linked to the velocity measurements. Furthermore thin section analyses and detailed petrophysical measurements were performed in order to get a better understanding of stress dependent velocity influencing factors like effective porosity, grain size or fractures. Applications like borehole stability issues are described in detail and further possibilities to enhance the power of this technique are presented additionally. This measurement technique is a powerful tool to determine rock failure geophysically. Interesting is the velocity ratio of compressional- and shear waves, which can indicate fracture formation or compaction processes. Moreover it got clear that the dynamic shear- and Young’s modulus depend on shear wave velocity, and bulk modulus is more related to a variation in velocity ratio rather than highest values. Due to the possibility of estimating in situ stresses of boreholes, velocities determined in the laboratory can be measured at similar stress levels. This way of measurement allows achieving real conditions thus geomechanical properties can be determined in the most accurate way. However, according to the strong lithology dependency of geomechanical parameters, this technique cannot replace static measurements.

KW - elastic wave velocity

KW - uniaxial compressive test

KW - stress dependency of elastic waves

KW - borehole stability

KW - dynamic geomechanical properties

KW - elastische Wellengeschwindigkeit

KW - einaxialer Druckversuch

KW - Druckabhängigkeit elastischer Wellen

KW - Bohrlochstabilität

KW - dynamische geomechanische Eigenschaften

M3 - Master's Thesis

ER -