Increasing the sensitivity of controlled-source electromagnetics with synthetic aperture

Abstract

Controlled-source electromagnetics (CSEM) has been used as a derisking tool in the hydrocarbon exploration industry. We apply the concept of synthetic aperture to the lowfrequency electromagnetic field in CSEM. Synthetic aperture sources have been used in radar imaging for many years. Using the synthetic aperture concept, big synthetic sources can be constructed by adding the response to small sources (building blocks) in different ways, and consequently, big sources with different radiation patterns can be created. We show that the detectability of hydrocarbons is significantly enhanced by applying synthetic aperture to CSEM data. More challenging targets such as deep reservoirs (4 km below sea floor) can be detected. The synthetic aperture technique also increases the sensitivity of the field to subsurface targets in the towing streamer acquisition. We also show that a pseudovertical source (orthogonally distributed dipole pairs) can be constructed synthetically, and that the detection capability of this pseudovertical source is increased by applying field steering. The synthetic aperture concept opens a new line of research in CSEM, with the freedom to design suitable synthetic aperture sources for a given purpose.

An optimal synthetic aperture method for the creation of directional sensitivity and removal of the airwave effect in MCSEM data

“…The fundamental concept of the synthetic aperture method is based on an assumption that one can design a synthetic aperture source which will steer the EM energy toward the target and in this way increase the ability to detect the target (Fan et al, 2010(Fan et al, , 2012 by increasing the anomalous response from the target. This effect can be achieved automatically by selecting the synthetic aperture weights with the property that they magnify the normalized synthetic aperture data, ‫܌‬ ோ , in the anticipated area of the location of the potential target.…”

“…The synthetic aperture (SA) method is based on designing sources with specific radiation patterns, which would "steer" a generated field in the direction of an area of interest (e.g., Degraaf, 1998;Cheney, 2001;Çetin and Karl, 2001; Korobov et al, 2010;Fan et al, 2010). A similar approach was recently discussed by Fan et al (2010Fan et al ( , 2012, where the authors applied a synthetic aperture method to the marine controlled-source electromagnetic (MCSEM) survey, formed by one line of transmitters and receivers. Knaak et al (2013) applied synthetic aperture method to MCSEM surveys with multiple lines of transmitters and receivers.…”

Application of synthetic aperture concepts to Towed Streamer EM data

“…The concept of synthetic aperture processing applied to marine CSEM data was recently published by Fan et al (2012). It is a data driven approach to increase the sensitivity in the frequency response data to a deeply buried resistive anomaly.…”

“…The system facilitates data acquisition at 4 -5 knots and it can be combined with simultaneous acquisition of 2D seismic from the same vessel. Synthetic aperture processing was recently introduced by Fan et al (2012). It can be seen as a way to focus the energy on the target to increase sensitivity.…”

Rapid imaging of towed streamer EM data for reconnaissance offshore exploration using the optimal synthetic aperture method

“…It is based on the idea that a virtual source constructed from different actual sources with specific radiation patterns can steer the interfered fields in the direction of an area of interest (DeGraaf, 1998;Cheney, 2001;Cetin and Karl, 2001;Korobov et al, 2010). A similar approach has been introduced for diffusive EM fields (Fan et al, 2010(Fan et al, , 2012Knaak et al, 2013;Mattsson and Engelmark, 2013), where the authors applied the SA method for the marine controlled-source electromagnetic (MCSEM) and towed streamer EM surveys by constructing an SA source to steer the generated fields in the direction of the target.…”