Elasto-static and -dynamic Analysis of Subsurface Fracture Phenomena

David Cho

ABSTRACT

In this thesis, we investigate fracture phenomena as it pertains to unconventional resource exploration and development, specifically in tight oil and gas. We present methods for the inference of natural fracture systems and evaluate the hydraulic fracture response, especially in the vicinity of fault related features that pose a greater risk for development.

To infer the presence of natural fractures, we develop an inversion algorithm to estimate anisotropic fracture parameters from reflection seismic data. The inversion results address several shortcomings associated with conventional techniques, including a relaxed constraint on fracture orientations and the resolution of a 90 degree azimuthal ambiguity, providing an improved estimate of subsurface fracture parameters. In addition, we present a case study that investigates the use of isotropic analysis to infer the presence of fractures, including the use of structural attributes and elastic properties. The combined interpretation of these results revealed the lateral extent of fractures related to a structural feature that was not possible from conventional attribute analysis alone.

Furthermore, we present two case studies to evaluate the hydraulic fracture response in the vicinity of fault related features. In the first case study, we investigate the large variations observed in the hydraulic fracture response of a tight gas reservoir. The variability was hypothesized to be the result of tectonic loading that alters the mechanical properties of the rock mass prior to brittle failure, representing a pre-rupture fault. The reflectivity response of such media was discussed to infer their presence from seismic data. In addition, an effective stress model was presented to explain the changes in the stress field experienced by the rock mass. This allows us to anticipate the stimulation response and mitigate the associated risks in the vicinity of these features. In the second case study, we present a methodology to infer fluid mobility in the stimulated zone through analysis of the attenuation response of a time-lapse seismic survey. The results obtained from the analysis were in qualitative agreement with microseismic observations and time-lapse seismic amplitude and traveltime anomalies, suggesting fluid mobility and confirming the extent of the stimulated rock volume.

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