A method for coal structure division based on AVO simultaneous inversion
Wu, H., Dong, S., Huang, Y., Chen, G. and Wang, H., 2015. A method for coal structure division based on AVO simultaneous inversion.Journal of Seismic Exploration, 24: 365-378. Prospecting for enriched areas must be the primary goal of seismic exploration of coal-bed methane (CBM) reservoirs, and coal structure is the principal factor controlling CBM enrichment within a mining field that has relatively uniform geological characteristics such as reservoir thickness, cap rock, and coal quality. Based on reservoir rock physics and coal structure theory, this study found that development areas of mylonitized coal, which correspond to CBM-enriched areas, show abnormally low values of P-wave and S-wave impedance (Ip and Ix). It was also established that I, and I, act as valid parameters for coal structure division. Before adopting a pre-stack inversion for I, and Is, the applicability of the AVO approximation equation (expressed by lp and I,) with small incidence angles (< 30°) was tested and verified. Thereafter, the AVO inversion equation based on Bayes’ theorem could be derived by adopting the modified Cauchy distribution as the prior distribution. A test using a model typical of a CBM reservoir containing Gaussian white noise illustrated the stability of this inversion method and provided accurate inversion values for I, and I,. Moreover, the seismic profile of a CBM reservoir ina field in Qinshui Basin, as an inversion case study, revealed an area of abnormally low values of I, and I,. This demonstrated that the method is capable of the effective division of coal structure types in a CBM reservoir and of the delineation of areas of mylonitized coal development.
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