A technique is presented for recognizing different types of fractured zones within the internal subsurface structure, including zones of extended fractures with dimensions larger than the signal wavelength, and zones of small differently oriented fractures with dimensions smaller than the signal wavelength. The technique is based on dynamic analysis, using prospecting indicators for fractures and faults of different classes, determined from the dynamic parameters of P-P reflections. These prospecting indicators are determined from the results of seismic modeling, as well as physical modeling with samples of natural rock and field seismic surveys on known fractured objects with fracture parameters in different lithologic rock types. We have studied the quality, stability and statistical significance of the indicators, and on the basis of the dynamic analysis we determine the probability of the presence of fractured objects of a particular type. The resulting technique has been applied to a fractured hydrocarbon reservoir under the North Sea, where it has been possible to better determine the particular features of its geologic structure. Fractured zones in a gas-saturated unstratified subsurface have been mapped; possible large tectonic faults and block structure have been revealed; results show the likely presence of diffracting objects within the rock matrix, determine their type, and improve the imaging of reflecting horizons with weak intensity and fragmented correlation.
Reservoir geophysics, parameter estimation, modelling, wave interpretation
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