| Description |
Marine electromagnetic (EM) surveys have been extensively used for offshore hydrocarbon exploration over the last decade. One can consider two major types of marine EM surveys. One is aimed at conducting a reconnaissance study of the large survey area with the purpose of locating the prospective zones of hydrocarbons accumulation. Another type of the EM surveys is used for a detailed study of these prospective zones with the goal to determine a specific position of the potential HC reservoirs. In this dissertation, I introduce two new techniques for solving these two important problems â€" optimal synthetic aperture method for analysis of the reconnaissance surveys and a hybrid finite difference and integral equation method for rigorous 3D inversion of the EM data collected by exploration surveys. The optimal synthetic aperture method is a technique to find the optimal parameters of the synthetic aperture of the EM data acquisition system, which can steer the generated EM field toward the area of interest by combining the responses from multiple sources, so that it can enhance the anomaly from the potential HC target. With the application of the optimal synthetic aperture method to the conventional MCSEM data and the towed streamer EM data, I demonstrate that the method can be used for not only increasing the EM anomaly from the target, but also reducing the distorting airwave effect in the shallow marine environment. I also demonstrate that the method can be used for mapping the electric anomalies over the true locations of the targets, which is important for the reconnaissance surveys. The second technique that I have developed is the hybrid finite-difference and integral equation (FD-IE) method for 3D modeling and inversion of the EM data, which combines the advantages of conventional FD and IE methods. The hybrid FD-IE method makes it possible to provide a more accurate and efficient forward modeling solution than the conventional FD or IE methods for multisource data. The developed new approaches to analysis and interpretation of the marine EM data have been carefully tested on a number of realistic synthetic models and a case study. |
