Ten years of marine CSEM for hydrocarbon exploration

Abstract

Marine controlled-source electromagnetic ͑CSEM͒ surveying has been in commercial use for predrill reservoir appraisal and hydrocarbon exploration for 10 years. Although a recent decrease has occurred in the number of surveys and publications associated with this technique, the method has become firmly established as an important geophysical tool in the offshore environment. This is a consequence of two important aspects associated with the physics of the method: First, it is sensitive to high electrical resistivity, which, although not an unambiguous indicator of hydrocarbons, is an important property of economically viable reservoirs. Second, although the method lacks the resolution of seismic wave propagation, it has a much better intrinsic resolution than potential-field methods such as gravity and magnetic surveying, which until now have been the primary nonseismic data sets used in offshore exploration. Although by many measures marine CSEM is still in its infancy, the reliability and noise floors of the instrument systems have improved significantly over the last decade, and interpretation methodology has progressed from simple anomaly detection to 3D anisotropic inversion of multicomponent data using some of the world's fastest supercomputers. Research directions presently include tackling the airwave problem in shallow water by applying time-domain methodology, continuous profiling tools, and the use of CSEM for reservoir monitoring during production.

Steel-cased wells in 3-D controlled source EM modelling

“…Controlled Source electromagnetic (CSEM) prospecting has become an established tool for a wide range of exploration targets, including marine (Constable 2010), airborne (Siemon et al 2009) and cross well applications (Newman & Alumbaugh 1997). Despite all improvements during the last decade, the presence of steel-cased wells in the study area remains a challenging task for EM modelling methodologies.…”

Coastal dynamics and submarine permafrost in shallow water of the central Laptev Sea, East Siberia

“…What is generally observed, by geophysical methods or direct observations, in sediment cores, is the depth of ice-bonded permafrost (IBP) below the sea floor (which is equivalent to the thickness of the overlying unfrozen sediment). Direct current resistivity and controlled source electromagnetic techniques for the investigation of submarine permafrost have been established in a number of studies (Barnes, 1963;Constable, 2010;Corwin, 1983;Sellmann et al, 1989). Laboratory measurements of the bulk electrical properties of frozen porous media show the effect of ice content and thus saline porewater on electrical resistivity .…”

Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

“…Consequently, the marine controlled-source electromagnetic (CSEM) technique (Constable et al 1998;Constable 2006;Key 2012) was modified to use higher transmitted frequencies and a fixed offset three-axis electric field receiver, to extend the CSEM capability to detect shallow and subtle resistivity anomalies with high resolution (Weitemeyer & Constable 2010). CSEM sounding is highly sensitive to volumetric changes in resistivity (Edwards 2005;Constable 2010), mainly related to pore fluid properties; therefore, it can detect robustly fluid migration pathways and quantify porosity (Harris & MacGregor 2006;MacGregor & Tomlinson 2014;Naif et al 2015).…”