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Title: Application of the cross-hole technique for analysis of shear waves in fractured limestone reservoirs
Author: Baptie, Brian J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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In this study, I use the cross-hole method to examine the relationship between fractures in limestone reservoirs, where the presence of fractures has been determined by a priori information, and the shear-wave anisotropy of the rockmass. I process and interpret multicomponent seismic data from two producing areas: the East Fitts field Oklahoma, where a multi-azimuthal cross-hole survey is used to image the Hunton and Viola reservoir formations at depths of 3000-4000 feet; and the Iatan East Howards field, Texas, where two cross-hole azimuths are used to image the Clearfork reservoir formation at a similar depth. I apply a numerical method to measure the shear-wave splitting parameters, qS1 polarization and time delay between qS1 and qS2 arrivals, and best-fit parameters for reservoir crack strike and crack density are determined by forward modelling. The observed qS1 polarizations at three azimuths from the East Fitts site can be related to propagation through two thin layers, representing the Hunton and Viola reservoir zones, each containing distributions of micro-cracks with a best-fit strike of N35°E. The observed time delays between qS1 and qS2 arrivals can also be modelled by lower crack densities distributed throughout the layered model. Polarization measurements at one cross-hole azimuth from the Iatan site agree with a priori reservoir fracture direction of N60°E-N85°E. Results from the second azimuth fall within the expected zone of behaviour for cracks striking ±12.5° of N170°E. A measured qS1 polarization direction of N170°E from near-offset VSP data at the Iatan site also disagrees with the known reservoir fracture direction. The Iatan measurements are incompatible with hexagonal anisotropic symmetry with a horizontal axis of symmetry. No improvements in the resolution of the anisotropic parameters of fractured rocks and reservoirs was achieved by using the cross-hole method although propagation through the near-surface is avoided. Acceptable model solutions have been found for the observations, however, the problems of non-uniqueness are inherent in the forward modelling approach.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available