Feasibility of prediction of principal stress from reflection seismic data
Creators: name: Liu, Xin, 1993-
Publisher: name: The University of Texas at Austin
Year: 2021
Subjects: Principal stress estimation
Seismic modeling and inversion
VFSA

description: Orientations and magnitudes of subsurface principal stresses are crucial information for understanding the structure and tectonic processes inside the Earth. This knowledge is not only important in geotechnical applications but also vital in the petroleum industry. For example, the stress state in the Earth’s crust controls stress concentration around wellbores and, therefore, plays a critical role in wellbore instability and fluid flow in fractured reservoirs. Several efforts to obtain subsurface principal stresses have been reported in published articles. However, most of these studies are based on the analyses of well log data and core plug measurements, which only provide accurate information at some specific locations. On the other hand, seismic inversion is one popular approach that aims at predicting some of the physical properties from observed seismic data indirectly. It can provide an even greater comprehensive description of the subsurface geology but at a lower vertical resolution. Using laboratory data and theoretical modeling, several researchers have reported that subsurface stress can lead to seismic anisotropy. Noticeable anomalies in field seismic data due to anisotropy, such as non-hyperbolic move-out, AVO, and anomalous waveforms have also been reported in the literature. However, no field scale estimation of subsurface stress variation from seismic data has yet been carried out. Therefore, in my research, I attempt to examine the feasibility of predicting principal stresses from seismic inversion based on a stress-anisotropy relationship. Forward modeling is the foundation of seismic inversion. The finite-difference (FD) method is the most widely used forward modeling method in seismic waveform inversion. However, it suffers from the stair-casing problem, which introduces unwanted noise from irregular model parameter boundaries. Therefore, I develop an improved mesh-free method to accurately describe the irregular boundaries. My work entails the following three closely related steps: 1) Relate stress to anisotropy. Rock physics can be used to create models for subsurface lithologies, which describe the petrophysical and elastic behavior through a set of empirical, heuristic, and theoretical relations. In my current work, I derive stress to stiffness relationship from laboratory measurements from a mudrock sample. This analysis demonstrates that the stiffnesses are anisotropic under vertical stress. 2) Mesh-free anisotropy media forward modeling. I develop the radial basis-function generated finite-difference (RBF-FB) method for the mesh-free discretization scheme. Then I generalize this forward modeling method for anisotropic media and test it on some synthetic models. I employ this method to generate synthetic seismograms based on a realistic model derived from laboratory data and demonstrate the effect of stress on seismic data. 3) Seismic inversion sensitivity analysis. I generate synthetic seismograms for simple models for which stiffnesses are computed for different stress magnitudes and directions. These data are then inverted by a global optimization method called Very Fast Simulated Annealing (VFSA) to demonstrate the feasibility of seismic inversion for principal stress. The forward modeling procedure in the VFSA method is carried out via the mesh-free RBF-FD method. My initial work shows that the magnitudes and angles of the stress have noticeable effects on the seismic response that can be estimated by seismic inversion