Parametric Diagrams Method (PDM)

Abstract

The Parametric Diagrams Method (PDM) is designed to study the variations of reflection amplitudes which characterize the reflective properties of geological boundaries, from the diagrams representing the change in time t0 parameter. These parameters are the coefficients A and B in Shuey’s equation, widely used in elastic wave field’s inversion method using Amplitude Variation versus Offset (AVO). A comparative evaluation of PDM and AVO was carried out using a representative synthetic seismic section from west of Siberia (Russian Federation). The success of PDM in obtaining the values of Parameters A and B in the previous case encouraged the authors to attempt applying the method in the geological section of North Melut Sub basin which is characterized by relatively thin layers (20-50 m). The simulation results suggest the following conclusions: PDM is technically better than AVO and has a higher accuracy. The continuous functions A(t0) and B(t0) on t0 charts, in the range of the recorded time of a separate reflected signal with apparent wavelength , which is less than the layer thickness h, have apparent frequency characteristic for the reflected signal and similar forms. The values of parameters A and B, which characterize the properties of the reflective boundary when is < h (regardless of the pulse shape), can be determined by the first extreme of the reflected signal. The continuous time t0character diagrams A(t0) and B(t0) allow the construction of the cross plot B(A) for each reflection, which, in the case of constant shape of the reflected signal with the offset, results in a straight line. Interference reflections caused by fine layering that occurs when the apparent wavelength is greater than the layer thickness, lead to difficulties in determining parameters A and B. Variation of the shape of the reflected signal with the offset caused by its distortion when applying kinematic corrections, or any other factors significantly reduces the accuracy of the dynamic analysis of PDM and AVO. Reflection plots in this case is a complicated curve shape which hampers the use of the crosplots B(A) for the prediction of hydrocarbons.