Controlled-source marine electromagnetic 2-D modeling gas hydrate studies
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ORIGINAL RESEARCH PAPER
Controlled-source marine electromagnetic 2-D modeling gas hydrate studies T. Harinarayana • Bob Hardage • Arnold Orange
Received: 4 May 2011 / Accepted: 10 July 2012 Ó Springer Science+Business Media B.V. 2012
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 seabottom receivers helps us delineate the subsurface structure more clearly and may help reduce drilling costs. Our models
T. Harinarayana (&) GERMI, Gandhinagar, Gujarat, India e-mail: [email protected] T. Harinarayana Earlier at CSIR-NGRI, Hyderabad, India B. Hardage Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, USA e-mail: [email protected] A. Orange Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, San Diego, CA, USA e-mail: [email protected]
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. Keywords CSEM Marine environment Gas hydrates 2D modeling
Introduction Controlled source electromagnetics (CSEM) is increasingly being accepted as a powerful geophysical tool in hydrocarbon exploration, especially in the deep-water marine environment, where the risk of high drilling costs is involved. In recent years, many areas have been successfully investigated using CSEM surveys (e.g., Edwards 1988, 1997; Sinha et al. 1990; Ellingsrud et al. 2002; McGregor et al. 2006; Weitemeyer et al. 2006; Srnka et al. 2006; Scholl and Edwards 2007; Chen et al. 2007; Constable and Srnka 2007; Scholl and Edwards 2007; Ellis et al. 2008; Chave 2009) that have helped to identify thin, resistive layers. Although the seismic method for a gas hydrate search provides more reliable structural features (Hardage et al. 2006), CSEM adds value to the information by identifying the electrical resistivity property of units within the structures. In the absence of anomalous geological formations in the se
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