Fluid substitution and AVAZ analysis of fractured domains: An ultrasonic experimental study

Many regions of subsurface interest are, or will be, fractured. Seismic characterization of these zones is a complicated, but essential, task for resource development. Physical modeling, using ultrasonic sources and receivers over scaled exploration targets, can play a useful role as an analogue for reservoir characterization. The goal of this thesis is to understand and characterize fractured regions using physical models. Two physical models, with domains of aligned vertical fractures (HTI symmetry), are studied here. Through ultrasonic measurements, their elastic properties are measured and calculated. The first model is a glass block with an internal laser-etched fracture zone. Azimuthal CMP gathers are surveyed over the fracture zone with star-shooting pattern and multicomponent data are recorded with ultrasonic transducers. Using low frequency transducers, and small crack spacing relative to source frequency, target fracture zones behaves as an effective medium. Reflections from the fracture zone interfaces are carefully processed so that the true amplitudes of reflected signals are recovered. By AVO and AVAZ analysis, fracture orientation is estimated. The second model studied in this thesis is a 3D-printed model. Since the model material is porous, and we are interested in fluid effects, we saturate it with water. Significant changes after saturation are observed as P-wave velocity increase by 4.6% and S-wave velocity decrease by 1.6%. Thomsen’s parameters $ϵV$ and $\delta V$ decrease 40% in magnitude while $\gamma V$ increase over 8%. To explain these changes, a new set of equations based on linear slip theory and Gassmann's equations are derived and tested with both synthetic and experimental data.The predictions of these new equations match observations closely.