Comparison of marine controlled-source electromagnetic data acquisition systems by a reservoir sensitivity index: analyz
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Comparison of marine controlled-source electromagnetic data acquisition systems by a reservoir sensitivity index: analyzing the effect of water depths GUO Zhenwei1*, DONG Hefeng1, LIU Jianxin2 1 Norwegian University of Science and Technology, Trondheim 7491, Norway 2 Central South University, Changsha 410083, China
Received 8 October 2015; accepted 9 May 2016 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016
Abstract
During the past ten years, a marine controlled source electromagnetic (CSEM) method has been developed rapidly as a technology for hydrocarbon exploration. For shallow water environments, two CSEM data acquisition systems: Seabed Logging (SBL) and towed streamer electromagnetics (TSEM) have been developed in recent years. The purpose is to compare the performance of the SBL and TSEM systems at different water depths. Three different methods for the comparison are presented. The first method is a quick one dimensional sensitivity modelling. As a result, the sensitivity of marine CSEM data increases with water depth for the SBL system. Further, the sensitivity decreases with the increasing water depth for the TSEM system. The two other methods use two dimensional synthetic data from a simple 2-D isotropic model. The second method is a reservoir sensitivity index (RSI) method which has been developed to provide a quick comparison of the two systems. The RSI is calculated as the amplitude of the scattered field dividing by data uncertainty. From the calculations, it is found that with the increasing water depth RSI increases for the SBL system, while it decreases for the TSEM system. The third method uses Occam’s inversion, and applies an anomaly transverse resistance (ATR) ratio for evaluating the resulting resistivity image. In shallow water environments, the resolution of the CSEM inversion results is good for both the SBL and TSEM systems. In deep water environments, the resolution of the CSEM inversion is better for the SBL system than for the TSEM system. The ATR ratios of the resistivity images show the similar conclusion. The SBL data acquisition system has an advantage in deep water environments. The TSEM system, on the other hand, is preferable for the shallow water environments. Key words: controlled-source electromagnetic, reservoir sensitivity index, seabed logging, towed streamer electromagnetic Citation: Guo Zhenwei, Dong Hefeng, Liu Jianxin. 2016. Comparison of marine controlled-source electromagnetic data acquisition systems by a reservoir sensitivity index: analyzing the effect of water depths. Acta Oceanologica Sinica, 35(11): 113–119, doi: 10.1007/s13131-016-0954-2
1 Introduction The marine controlled-source electromagnetic (CSEM) method uses the high electrical resistivity of hydrocarbon-saturated rocks to discover subsurface rocks that are filled with, such as gas and oil. The EM field propagates through the water layer into the subsurface, and the measurements at the receivers can be used to determine the resistivity at different locations and depths
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