Electromagnetic Fields Due to a Thin Resistive Layer*

Passalacqua, Herminio

doi:10.1111/j.1365-2478.1983.tb01099.x

Cited by 23 publications

(14 citation statements)

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“…Keller (1968), Kaufmann & Keller (1983) and Passalacqua (1983) showed theoretically that a thin resistive hydrocarbon zone could be sensed using a low-frequency EM source on land, and there were several attempts to exploit the method (e.g. Keller et al 1990).…”

Section: Introductionmentioning

confidence: 99%

On the physics of frequency-domain controlled source electromagnetics in shallow water. 1: isotropic conductivity

Chave¹,

Everett

Mattsson³

et al. 2016

Geophys. J. Int.

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S U M M A R YIn recent years, marine controlled source electromagnetics (CSEM) has found increasing use in hydrocarbon exploration due to its ability to detect thin resistive zones beneath the seafloor. It is the purpose of this paper to evaluate the physics of CSEM for an ocean whose electrical thickness is comparable to or much thinner than that of the overburden using the in-line configuration through examination of the elliptically polarized seafloor electric field, the time-averaged energy flow depicted by the real part of the complex Poynting vector, energy dissipation through Joule heating and the Fréchet derivatives of the seafloor field with respect to the subseafloor conductivity that is assumed to be isotropic. The deep water (ocean layer electrically much thicker than the overburden) seafloor EM response for a model containing a resistive reservoir layer has a greater amplitude and reduced phase as a function of offset compared to that for a half-space, or a stronger and faster response. For an ocean whose electrical thickness is comparable to or much smaller than that of the overburden, the electric field displays a greater amplitude and reduced phase at small offsets, shifting to a stronger amplitude and increased phase at intermediate offsets and a weaker amplitude and enhanced phase at long offsets, or a stronger and faster response that first changes to stronger and slower, and then transitions to weaker and slower. These transitions can be understood by visualizing the energy flow throughout the structure caused by the competing influences of the dipole source and guided energy flow in the reservoir layer, and the air interaction caused by coupling of the entire subseafloor resistivity structure with the sea surface. A stronger and faster response occurs when guided energy flow is dominant, while a weaker and slower response occurs when the air interaction is dominant. However, at intermediate offsets for some models, the air interaction can partially or fully reverse the direction of energy flux in the reservoir layer toward rather than away from the source, resulting in a stronger and slower response. The Fréchet derivatives are dominated by preferential sensitivity to the reservoir layer conductivity for all water depths except at high frequencies, but also display a shift with offset from the galvanic to the inductive mode in the underburden and overburden due to the interplay of guided energy flow and the air interaction. This means that the sensitivity to the horizontal conductivity is almost as strong as to the vertical component in the shallow parts of the subsurface, and in fact is stronger than the vertical sensitivity deeper down. However, the sensitivity to horizontal conductivity is still weak compared to the vertical component within thin resistive regions. The horizontal sensitivity is gradually decreased when the water becomes deep. These observations in part explain the success of shallow towed CSEM using only measurements of the in-line component of the electric field.

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Section: Introductionmentioning

confidence: 99%

On the physics of frequency-domain controlled source electromagnetics in shallow water. 1: isotropic conductivity

Chave¹,

Everett

Mattsson³

et al. 2016

Geophys. J. Int.

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“…Passalaqua (1983) showed theoretically that a thin resistive hydrocarbon zone could be sensed using CSEM and several groups attempted to exploit this property on land through the 1990s (e.g. Keller et al 1995; Strack & Vozoff 1996).…”

Section: Introductionmentioning

confidence: 99%

On the electromagnetic fields produced by marine frequency domain controlled sources

Chave¹

2009

Geophysical Journal International

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S U M M A R YIn recent years, marine controlled source electromagnetics (CSEM) has found increasing use in hydrocarbon exploration due to its ability to detect thin resistive zones beneath the seafloor. Although it must be recognized that the quantitative interpretation of marine CSEM data over petroleum-bearing formations will typically require 2-D surveys and 2-D or 3-D modelling, the use of the 1-D approximation is useful under some circumstances and provides considerable insight into the physics of marine CSEM. It is the purpose of this paper to thoroughly explore the 1-D solutions for all four fundamental source types-vertical and horizontal, electric and magnetic dipole (VED, HED, VMD and HMD)-using a set of canonical reservoir models that encompass brine to weak to strong hydrocarbon types. The paper introduces the formalism to solve the Maxwell equations for a 1-D structure in terms of independent and unique toroidal and poloidal magnetic modes that circumscribe the salient diffusion physics. Green's functions for the two modes from which solutions for arbitrary source current distributions can be constructed are derived and used to obtain the electromagnetic (EM) fields produced by finite VED, HED, VMD and HMD sources overlying an arbitrary 1-D electrical structure. Field behaviour is analysed using the Poynting vector that represents the time-averaged flow of energy through the structure and a polarization ellipse decomposition of the triaxial seafloor EM field that is a complete field description. The behaviour of the two EM modes using unimodal VED and VMD sources is presented. The paper closes by extending these results to the bimodal HED and HMD sources.

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“…We concluded in several cases (US, Middle East and Asia) that magnetic and Focused Source versus CSEM electrical tensor measurements are required. Normally, we assume hydrocarbon reservoirs are mostly resistive and give an anomalous EM response known as Direct Hydrocarbon Indicator (DHI) [8,9]. When you add steam flood to such a reservoir, one gets a more conductive anomaly which requires 3-component magnetic data.…”

Section: Proposed Methodologymentioning

confidence: 99%

“…This means we are trying to map reservoir boundaries at top and bottom as well as the heavy oil zone. For electromagnetics, this means we need to use high frequency and low frequency sensors for the conductive water saturated zones and electric sensor for the resistive oil zone [8,9] show that resistive hydrocarbon bearing layers are mapped with controlled source electromagnetics and electric field measurements). Since reservoir leakage in the upper layer is possible, we should use also microseismic sensors [1].…”

Section: Introductionmentioning

confidence: 99%

A new array system for multiphysics (MT, LOTEM, and microseismics) with focus on reservoir monitoring

Strack¹,

Davydycheva²,

Hanstein³

et al. 2017

AIP Conference Proceedings

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Over the last 6 years we developed an array system for electromagnetic acquisition (magnetotelluric & long offset transient electromagnetics [LOTEM]) that includes microseismic acquisition. While the system is being used in many countries for magnetotellurics, we focus here on the autonomous operation as reservoir monitoring system including a shallow borehole receiver and 100/150 KVA transmitter. Marine extension is also under development. For Enhanced Oil recovery, in addition to reservoir flood front movements, reservoir seal integrity has become an issue [1]. Seal integrity is best addressed with microseismics while the water flood front is best addressed with electromagnetics. Since the flooded reservoir is conductive and the hydrocarbon saturated part is resistive, you need both magnetic and electric fields. The fluid imaging is addressed using electromagnetics, and after careful 3D feasibility and noise tests, we selected Controlled Source Electromagnetics (CSEM) in the time domain as the most sensitive method [2,3]. From the 3D modeling, we derived a key requirement that borehole and surface data needed to be integrated by measuring between surface to borehole and calibrated using conventional logs including anisotropy. This would significantly reduce the risk [4,5,6]. To overcome the volume-focus inherent to electromagnetics we added a new methodology to focus the sensitivity under the receiver. The same can be achieved using a shallow borehole system that includes microseismic, 3C magnetics and 3C electrical measurements. Field data and 3D modeling confirm this and as results this could increase the efficiency of applying LOTEM to exploration and reservoir monitoring problems.

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Electromagnetic Fields Due to a Thin Resistive Layer*

Cited by 23 publications

References 0 publications

On the physics of frequency-domain controlled source electromagnetics in shallow water. 1: isotropic conductivity

On the physics of frequency-domain controlled source electromagnetics in shallow water. 1: isotropic conductivity

On the electromagnetic fields produced by marine frequency domain controlled sources

A new array system for multiphysics (MT, LOTEM, and microseismics) with focus on reservoir monitoring

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