Subsurface electromagnetic measurement through steel casing

Becker, Alex; Wang, B.; Lee, K. H.

doi:10.2172/6527

Cited by 3 publications

(7 citation statements)

References 4 publications

(7 reference statements)

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“…As the length is increased to 0.08 m and beyond, however, the response rapidly increases, and it reaches a maximum when the length is about 0.3 m. As the length increases, the response appears to become smaller, and at about 4 m it seems to be stabilized and becomes close to that of the infinite casing. Such behaviour was observed in the laboratory experiment conducted at the Richmond Field Station of the University of California at Berkeley (Becker et al 1998). It should be noted that there is a little deviation from the infinite casing as the vertical offset is increased, indicating that some leakage may exist through the ends of the casing segment.…”

Section: N U M E R I C a L E X A M P L E Smentioning

confidence: 53%

“…Field calculations have been made inside the cased borehole as well as in another borehole which is not cased. Although there is adequate sensitivity in the anomaly observed in a cross-borehole configuration, it is important to remember that the knowledge of casing properties is a prerequisite to the proper interpretation of the data thus obtained (Becker et al 1998;Lee et al 1998). The measurement in a single-borehole configuration (not shown here), however, turns out to be insensitive to the formation resistivity.…”

Section: O N C L U S I O N Smentioning

confidence: 81%

“…The model used was an infinitely long, uniform casing embedded in a homogeneous whole space . The results indicated that the formation * E-mail: khlee@lbl.gov signal could be accurately recovered if the casing characteristics were independently known (Becker et al 1998;Lee, Kim and Song 1998). Actual steel-cased wells are much more complex than the simple laboratory models used in work to date.…”

Section: Introductionmentioning

confidence: 99%

“…An integral equation method may be considered (Cheryauka and Sato 1999), but the numerical complexity caused by the intrinsic coupling of electric and magnetic fields renders the approach less attractive. Earlier laboratory and numerical experiments (Augustin et al 1989;Wu and Habashy 1994;Wilt et al 1996;Becker et al 1998) indicated that the casing effect is local and is related only to the casing nearest to the sensor. This conclusion is very useful because, in principle, data obtained through casing can be corrected by considering only the local conditions.…”

Section: Introductionmentioning

confidence: 99%

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Electromagnetic fields in a steel‐cased borehole

Lee

Kim

Uchida

2004

Geophysical Prospecting

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A B S T R A C TThe development of an electromagnetic numerical modelling scheme for a magnetic dipole in an arbitrary casing segment in an inhomogeneous conductivity background has been difficult, due to the very high electrical conductivity and magnetic permeability contrasts between the steel casing and the background medium. To investigate the effect of steel casing efficiently, we have developed an accurate but simple finite-element modelling scheme to simulate electromagnetic fields in a medium of cylindrically symmetric conductivity structures. In order to preserve the cylindrical symmetry in the resulting electromagnetic fields, a horizontal loop current source is used throughout. One of the main advantages of the approach is that the problem is scalar when formulated using the azimuthal electric field, even if the casing is both electrically conductive and magnetically permeable. Field calculations have been made inside the cased borehole as well as in another borehole which is not cased. Careful analyses of the numerical modelling results indicate that the anomaly observed in a cross-borehole configuration is sensitive enough to be used for tomographic imaging.

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Section: N U M E R I C a L E X A M P L E Smentioning

confidence: 53%

Section: O N C L U S I O N Smentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electromagnetic fields in a steel‐cased borehole

Lee

Kim

Uchida

2004

Geophysical Prospecting

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“…However, this subject is beyond the scope of this paper. Becker et al (1998) and downhole EM equipment manufactures are currently working on systems and data-processing techniques to remove the casing response from data prior to inversion.…”

Section: Practical Considerationsmentioning

confidence: 99%

Reservoir characterization using crosswell electromagnetic inversion: A feasibility study for the Snorre field, North Sea

et al. 2001

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The spatial resolution of a commercially available crosswell electromagnetic (EM) system is demonstrated using models derived from three time steps from a reservoir simulation of the Snorre field in the North Sea. The numerical simulation of the Snorre field waterflood shows that crosswell EM field measurements provide high sensitivity to changes in the reservoir over time. This sensitivity is achieved by combining the reservoir geometry derived from surface 3-D seismic interpretation, reservoir conductivities at well locations, and constrained EM inversion of the reservoir's electrical conductivity.Inversions of 2-D and 3-D numerical models show that the changes in electrical conductivity attributable to changes in water saturation can be quantitatively mapped as a function of time. The inversions provide smooth estimates of the spatial variation of reservoir electrical conductivity that can discriminate between the level of water saturation at different stages of the waterflood. Inversions performed on 2-D data show that for the Snorre example, 3%-5% Gaussian random noise (depending on the model) can be added without a significant degradation in the inverse models. Two-dimensional inversions of the full 3-D data in the Snorre example can map the vertical average electrical conductivity within the reservoir in the interwell region almost as well as when the model is two dimensional (constant in strike direction). The effect of 3-D structure does not seriously degrade 2-D inversion in the Snorre example-even between wells that lie in a line parallel to structure.A series of 2-D inversions where various constraints and starting models are used demonstrates the importance of incorporating a priori information in the form of starting models and restricting the inversion domain to the reservoir zone. These tests show that totally unconstrained, smooth inversions of the interwell volume provide very limited quantitative information. However, when the reservoir geometry is constrained by seismic data and starting models are provided by linear interpolation of conductivities at well locations, the reservoir's vertical average electrical conductivity can be predicted to within a few percent by 2-D inversion.The Snorre field consists of a full-scale reservoir with interwell spacings that exceed 1 km where previous work has demonstrated the applicability of crosswell EM in shallow reservoirs with well separations on the order of 100 m. The simulations show that, given current transmitter and receiver technology, the magnetic fields could be measured in the Snorre field in steel-cased wells separated from the transmitter by up to 725 m.

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Electromagnetic fields in a non‐uniform steel‐cased borehole

Kim

Lee

2006

Geophysical Prospecting

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Abstract:Since most oil wells are cased with steel pipes, electromagnetic (EM) signals undergo a severe attenuation as they diffuse across the casing. This paper presents the effect of non-uniform casing properties on EM fields measured in a steel-cased well embedded in a layered formation. We use a finite-element method to compute secondary azimuthal electric fields for a cylindrically symmetric conductivity model, while primary fields are analytically obtained for a homogeneous casing in a whole space. Although EM signals induced by a layered formation are greatly masked by the steel casing, phase responses are more pronounced than amplitude responses. The effect of casing non-uniformity is quite large but highly localized. When the conductivity rapidly varies in the casing wall, the resulting EM fields also fluctuate rapidly. These fluctuations are so similar that their cross correlation function is strongly peaked at two points, whose distance is equal to the separation between source and receiver. The high-frequency coherent noise caused by the non-uniform casing event can be largely suppressed by low-pass filtering to enhance EM signals from the formation conductivity.

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Subsurface electromagnetic measurement through steel casing

Cited by 3 publications

References 4 publications

Electromagnetic fields in a steel‐cased borehole

Electromagnetic fields in a steel‐cased borehole

Reservoir characterization using crosswell electromagnetic inversion: A feasibility study for the Snorre field, North Sea

Electromagnetic fields in a non‐uniform steel‐cased borehole

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