Reservoir Characterization Through AVO Inversion And Geostatistical Techniques

One of the most complex topics in reservoir characterization is the estimation of pore-fluid content away from well locations.The unconventional reservoirs in Sulige gas field(Ordos Basin,North China)face this problem of having high heterogeneity,low pressure,low permeability,and low gas richness features.Sand bodies are widely distributed and most of them are adjacent to each other,but the hydrocarbon presence is scattered.Thus,the challenge in the Lower Permian Shihezi Formation(LPSF),which is the Sulige tight field's most prolific formation,is pore-fluid content description rather than lithological description.Accordingly,the fluid discrimination of the Lower Permian Shihezi Formation is successfully accomplished and a resistivity volume is generated by combining two non-standard fluid attributes(direct Russell fluid factor and modified version of Poisson impedance-fluid impedance)with conventional seismic attributes in a geostatistical inversion using linear as well as non-linear approaches.As a first step,this thesis involves two different seismic inversion techniques:a direct stochastic inversion for Russell fluid factor based on a Bayesian framework and on the Russell approximation theory,as well as a deterministic pre-stack inversion for Poisson impedance computation based on the Fatti's modification to the Aki and Richards approximation.Subsequently,multi-attributes analysis is performed by combining the two 3D fluid identifying volumes of Russell fluid factor and fluid impedance,with traditional post-stack seismic attributes.Finally,the multi-linear transforms is used to construct a radial basis function neural network and apply it throughout the entire 3D seismic dataset Additionally,a brittleness volume is derived based on the elastic rock-physics properties of the reservoir rocks obtained through pre-stack seismic inversion.The objective of the fracability volume is to have an initial idea on the geomechanical behavior of the field,so it helps to identify fracture-prone areas that can be effectively hydraulic stimulated for the hydrocarbon flow.A comprehensive analysis of results allows to pinpoint potential hydrocarbon-bearing zones,based on reservoir fluid-related anomalies.