Abstract

AVO interpretation has been the most common pre- drill hydrocarbon prospect identification methods. However as a predictive tool AVO has got lithofacies and acoustic profile of rock framework affecting the amplitude, in addition to fluids. Even though gas is known to give the maximum AVO differentiation, widely different lithofacies such as mud-filled channels, distal debris flow facies, fizz water sands are known to have gas AVO in terms of brightness and geometry. PSEI in place of AVO has less of uncertainties as it is not the results of convolution and arrived at through simple deconvolution. Our work, to actually to predict PSEI from wireline logs has led us to the important finding that we can immediately recognise potential false AVO from being possible in a horizon and thus of immense value addition to risk mitigation in exploration and amenability to statistical uncertainties predictions. On a practical case, in spite of positive AVO response, there have been some surprises encountered when some of the observed bright amplitudes in the sediments of shallow as well as deep-water basins as they have been explored. The lithofacies, fluids, log responses and the total outcome of the drilling had opacity and ambiguity to a level not amenable for the required clarity for enabling decision making. The log response and seismic characters of the bright amplitude intervals agree with each other, yet are found to be non-hydrocarbon bearing. This paper presents an application of near and far offset P to S Elastic Impedance (PSEI) at 100 and 500 respectively as a better discriminator as compared to the normal methods on the log data, for economic to non-economic gas intervals or fizz water intervals. The application of PSEI property using log data gives great confidence about its discriminating capability in the seismic domain as a prediction tool. Further studies related to PSEI attributes are in progress.