Controlled-source marine electromagnetic 2-D modeling gas hydrate studies

Abstract

Research on gas hydrate has increased recently as an alternative to fossil fuel. This study of marine controlled source electromagnetics (CSEM) is motivated by this increase, particularly in deep waters, and examines representative models. We present 2D models and test their efficacy in detection and characterization of gas hydrates. Earlier modeling studies used a horizontal transmitter to study the CSEM response—two electrical and one magnetic component—for resistive subsurface layers. Here we use six components—three electrical and three magnetic—and show that the proposed method reduces ambiguity in interpretation. Additionally, we show results utilizing the transmitter dipole in a borehole and receivers at the sea bottom. We found that CSEM response from a vertical transmitter helps us characterize resistive layers more confidently than from a transmitter moving horizontally at sea bottom. We conclude that in a complex environment, combining horizontal and vertical movements of the transmitter with sea-bottom receivers helps us delineate the subsurface structure more clearly and may help reduce drilling costs. Our models closely match the gas hydrate region in the Gulf of Mexico—Walker Ridge Block-313. Although this study examines gas hydrate, the methodology is applicable to other areas—for example, in monitoring gas diffusion at subsurface depths, which may help in CO2 sequestration.