Dynamic Analysis of the Seismic Section of North Melut Sub-basin, South Sudan, Using Parametric Diagrams Method (PDM)
[1]
Gamal Abdalla A. M. Et Toam, Department of Geophysics, Faculty of Petroleum and Minerals, Al Neelain University, Khartoum, Sudan.
[2]
Adam Konstantinovich Urubov, Department of Geophysics and Computer Systems, Russian State University for Oil and Gas named after I. M. Gubkin, Moscow, Russian Federation.
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 λ, 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 λis < h (regardless of the pulse shape), can be determined by the first extreme of the reflected signal. The continuous time t0 character 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.
Parametric, PDM, AVO, Seismic, Dynamic, Sudan
[1]
Aki, K., and Richards, P. G., Quantitative seismology: Theory and methods: W. H. Freeman and Co. 1980.
[2]
Ali Mohamed, Gamal Abdalla, (2004), Forecasting of oil and gas bearing objects and their analysis using seismic and wireline logs data in Melut Basin (Sudan). Unpublished Ph. D. thesis in geological-mineralogical sciences, Russian State University of Oil and Gas named after I. M. Gubkin, (In Russian).
[3]
Castagna, J. P. and Smith, S. W. Comparison of AVO indicators: A modeling study. - Geophysics, 1994, Vol. 59, p.p. 1849-1855.
[4]
Castagna, J. P. and Swan, H. W. Principles of AVO crossplotting, The Leading Edge, 1997, 16, pp 337–342.
[5]
Castagna, J. P. AVO analysis - Tutorial and review, in Castagna, J. P. and Backus, M.M., Eds., Offset-dependent reflectivity - Theory and practice of AVO analysis. – Tulsa, SEG, 1993, Investigations in Geophysics No. 8, pp. 3-36.
[6]
Castagna, J. P., Bazle M. L. and Eastwood, R. L. Relationships between compressional-wave and shear-wave velocities in clastic silicate rocks. - Geophysics, 1985, V. 50, pp. 571-581.
[7]
Castagna, J. P., Bazle M. L., Kan, Т. К., (1993), Rock physics - The link between rock properties and AVO response, in Castagna J.P. and Backus M.M., Eds., Offset-dependent reflectivity - Theory and practice of AVO analysis. Tulsa, SEG, 1993, Investigations in Geophysics No. 8, pp. 135-171.
[8]
Castagna, J. P., Swan, H. W. and Foster, D. J. Framework for AVO gradient and intercept interpretation. - Geophysics, 1998, V. 63, N 3, p.p. 948-956.
[9]
Knott, C. G., Reflexion and refraction of elastic waves with seismological applications: Phil. Mag., 1899, 48, 64-97.
[10]
Mahdi H. Almutlaq and Gary F. Margrave, Tutorial: AVO inversion, CREWES Research Report — 2010, V. 22, pp 1-23
[11]
Parkhomenko, O. M. (2004), Evaluation of the accuracy of determination of the dynamic parameters based on modeling by PDM and AVO methods, Unpublished M. Sc. thesis, Department of Exploration Geophysics and Computer Systems, Russian State University for Oil and Gas, named after I. M. Gubkin (In Russian).
[12]
Rob Simm and Mike Bacon. Seismic Amplitude: An Interpreter’s Handbook, Cambridge University Press, New York 2014.
[13]
Shuey, R. T. A simplification of the Zoeppritz equations, Geophysics, 1985, Vol.50, pp 609-614.
[14]
Urupov, A. K, and Kivokurtsev, V. I. A method of interpretation of the observations by the method of reflected waves by means of parametric diagrams (process of parametric diagrams). Exploration Geophysics, 1964, Vol. 1 Core. M., pp 27-31, (In Russian).
[15]
Urupov, A. K. Some results of the application of Parametric diagram from checking up multiple waves and investigating Quasinnisotropy., Geophysic and Geologia, 315, Leipzig, 1968, p.720-745 (In German).
[16]
Urupov, A. K. Parkhomenko, O. M. and Ali Mohamed, G. Parametric Diagrams Method - a worthy alternative method for AVO, Abstracts of the XVII Gubkin’s Conference "The geological sciences of oil and gas - XXI Century", Russian State University of Oil and Gas, named after I. M. Gubkin, 9-10 December 2004 (In Russian).
[17]
Urupov, A. K., Characteristics of Parametric Diagrams when registering the reflections from a plane boundary. Scientific notes of the Perm University, Part 102, Perm, 1963, pp 9-19 (In Russian)
[18]
Voskresenskiy, U. N. The study of changes in the amplitude of seismic reflections for prospecting and exploration of hydrocarbon deposits. Textbook for high schools. - M., Russian State University of Oil and Gas, 2001 (In Russian).
[19]
Zoeppritz, K. Erdbebenwellen VIIIB. Über Reflexion und Durchgang seismischer Wellen durch Unstetigkeitsflächen. Göttinger Nachrichten, 1919, V. I, 66–84.
