Frequency-Dependent AVO Forward Modelling and Inversion for Seismic Detection of Reservoir Units – An Example from Marrat Reservoir in Mutriba Field, NW Kuwait

Abstract In seismic interpretation and reservoir characterization, seismic resolution and detectability of reservoir units play an important role for successful identification of sweet spots from seismic data. Often due to the seismic frequency bandwidth limit, we cannot fully resolve the reservoir units from seismic data. However, it is possible to detect and identify the reservoir units and their distribution, if the data is processed properly and enhanced to a desired frequency bandwidth. This study focusses on finding the desired seismic frequency bandwidth, for the purpose of proper detection and identification of the reservoir units from seismic data. Seismic detectability is influenced predominantly by seismic frequency bandwidth, thickness of the reservoir units and the impedance contrast of the reservoir units from the background, i.e., the reflection strength of the reservoir units, apart from S/N ratio being the other factor. A workflow has been devised to understand the seismic detectability vis-à-vis frequency bandwidth; the other factors and their ranges being known from well data. In this study, a workflow has been devised by integrating frequency-dependent AVO forward modelling and pre-stack inversion. With this integrated approach, a set of elastic attributes were generated from synthetic gathers with varying frequency content. For this purpose, elastic attribute volumes at different frequency bandwidths are visualized and examined for the detection of the desired reservoir units, as observed from petrophysical interpretations in the available wells. Through this analysis, seismic frequency content threshold is identified, so that the reservoir units and sweet spots are detected properly from seismic data. The analysis of the results from the integrated workflow will be useful in understanding the detection limit of the reservoir units from seismic data, which is very important in validating the results from seismic reservoir characterization and understanding the uncertainty while using the results from the reservoir characterization study. Moreover, by knowing the seismic detection threshold of the reservoir units aprior, it will help in setting the expectation from a seismic processing / re-processing study on the desired frequency for performing proper seismic reservoir characterization study for successful identification of the sweet spots from seismic data.