HR: 1340h
AN: MR33A-0146    [Abstracts]
TI: Seismic Signatures of Fractures in Bombay High Basement
AU: * Bandyopadhyay, K
EM: kaushikb@pangea.stanford.edu
AF: Stanford Rock Physics Laboratory, Geophysics Department, 397 Panama Mall, Mitchell Building 360, Stanford University, Stanford, CA 94305 United States
AU: Mukerji, T
EM: mukerji@pangea.stanford.edu
AF: Stanford Rock Physics Laboratory, Geophysics Department, 397 Panama Mall, Mitchell Building 360, Stanford University, Stanford, CA 94305 United States
AU: Mavko, G
EM: mavko@stanford.edu
AF: Stanford Rock Physics Laboratory, Geophysics Department, 397 Panama Mall, Mitchell Building 360, Stanford University, Stanford, CA 94305 United States
AB: Basement fractures in offshore Western coast of India are of interest as secondary reservoirs and fluid flow conduits. Fracture characterization is always uncertain due to limited resolution of seismic data, imperfect relationship between the data and fracture parameters and natural variability of target rock properties and anisotropy. The problem becomes even more complicated when we do not have data that provide fracture indicators like shear wave splitting or azimuthal variation of reflectivity. In this poster we present: 1. Rock physics studies using well and core data to explore rock properties of fractured vs. unfractured basement rock. Computation of various seismic signatures of the fractures using rock physics transforms show that fractures should have measurable anomalies in amplitude, azimuthal variation in AVO, and inverted acoustic and elastic impedance. 2. Interpretation of partially stacked (near, mid and far offset) P-wave seismic data in terms of possible fracture signatures. We explore various seismic attributes and their variations with offset. The nature of the data precludes exploring azimuthal variations. Fractured zones in the Bombay High basement are mostly associated with decreased seismic amplitude, poor continuity and poor quality of the reflectors. They show different impedance variation with offset (IVO) with respect to the un-fractured regions. Observed decrease in the spatial autocorrelation of seismic amplitudes, decreased frequency bandwidth and increased attenuation are inferred to be plausible evidence for the presence of fractures as these observations are consistent with expected fracture signatures. We also emphasize that one of the biggest difficulties of seismic fracture detection is the non-uniqueness of interpretation. While the rock physics modeling might suggest that fractures are associated with anomalies in amplitude or impedance, we must remember that other non-fracture heterogeneities in the earth might also be the source of these anomalies. Hence at best, seismic attributes can only indicate increased probability of fractures, but they cannot guarantee their presence.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5102 Acoustic properties
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 5144 Wave attenuation
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005