Information Content in Forward 4D-Seismic Modelling and Elastic Inversion

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractElastic seismic inversion is a tool frequently used in analysis of seismic data. Elastic inversion relies on a simplified seismic model, and generally produces 3D cubes for Vp, Vs and density. By applying rock physics theory such volumes may be interpreted in terms of lithology and fluid properties. Understanding the robustness of forward and inverse techniques is important when deciding how much information seismic data really carry.This paper discusses the observed deviation between a reference and simulated reservoir, and its dependency on the seismic parameters and the reservoir characterization parameters. The ability to utilize the results from a 4D seismic survey in reservoir characterization will depend on several aspects. To investigate this, a loop that performs independent forward seismic modeling and elastic inversion at two time stages has been established.The multi-disciplinary workflow has several independent steps:1. Generation of a synthetic reference reservoir, by realistic geostatistical modeling. 2. Flow simulation of the reference reservoir to predict reservoir conditions at survey acquisition times. 3. Establishing a relationship between petrophysical and fluid properties and seismic parameters by a rock physics model. 4. Generation of seismic AVA responses corresponding to reservoir conditions at base and monitor survey times. 5. Elastic seismic inversion of both AVA response sets. 6. Simulation of lithology and fluid parameters conditioned on seismic inversion. 7. Comparison of static reservoir parameters of reference and simulated realization.8. Comparison of seismic responses at initial and monitor survey times. By working on a realistic synthetic reservoir, full knowledge of the reservoir characteristics is achieved. This makes the evaluation of the questions regarding the fundamental dependency between the seismic and petrophysical domains stronger. The theoretical limitations of the information content of the seismic data, including 4D, are investigated since the synthetic reservoir is an ideal case with accuracy never achieved in the applied situation.The production deviation between the reference and predicted reservoir was significantly decreased by using 4D seismic data in addition to the 3D inverted elastic parameters.