Feasibility of electromagnetic methods for sub-basalt exploration

Herredsvela, J.; Colpaert, Arnout; Foss, S. K.; Nguyen, Anh Kiet; Hokstad, Ketil; Morten, Jan Petter; Twarz, Claudia; Fanavoll, S.; Mrope, Frida

doi:10.1190/segam2012-0590.1

Cited by 6 publications

(5 citation statements)

References 7 publications

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“…The resistivity of the sub basalt sediments is 6 ⍀m and the deep basement structure has a resistivity of 100 ⍀m. Herredsvela et al (2012) show that for the basalt case in shallow water, inline CSEM data is equally sensitive to both thick and thin basalt. A 2.5D CSEM inversion algorithm (Hansen and Mittet, 2009) and a Occam 2D MT inversion algorithm (Constable et al, 1987) was used to invert the synthetic datasets.…”

Section: Introductionmentioning

confidence: 80%

“…That makes EM methods well suited for imaging of the thickness of the basalt layer and the structures underneath. In this paper, we discuss two studies, (1) a synthetic data study based on a realistic model (Herredsvela et al, 2012) and (2) a field data example from the Faroe-Shetland Basin. Figure 1 shows the model which was used for the synthetic modelling and inversion study.…”

Section: Introductionmentioning

confidence: 99%

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Offshore Sub-Basalt Exploration Using CSEM and MT

Panzner¹,

Kumar²,

Mrope³

2014

International Petroleum Technology Conference

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Seismic sub-basalt imaging is challenging and often leaves remaining uncertainties about the sub-basalt structures. This paper considers how the marine controlled source electromagnetic (CSEM) and the magnetotelluric (MT) method can reduce the interpretation uncertainty by providing structural and quantitative resistivity information about the thickness and extent of the basalt sequence and the sediments below. In order to demonstrate the capability of these technologies, we will present two recent studies: (1) a synthetic inversion test from a realistic model based on well-log and seismic data and (2) inversion of field data acquired over the Faroe-Shetland Escarpment. We will show that this information can also be used to improve the velocity models for seismic depth imaging.

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Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Offshore Sub-Basalt Exploration Using CSEM and MT

Panzner¹,

Kumar²,

Mrope³

2014

International Petroleum Technology Conference

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“…The feasibility of using marine CSEM data for imaging of a basalt layer is suggested by MacGregor and Sinha (2000). Herredsvela et al (2012) and Alumbaugh et al (2013) confirm in synthetic modeling and inversion studies that a combination of CSEM and MT data can significantly increase the sensitivity to the subbasalt resistivity structure. It is also shown that the marine MT data alone typically do not have sufficiently high-frequency content to resolve the basalt layer due to the water column acting as a low-pass filter.…”

Section: Introductionmentioning

confidence: 83%

Integrated seismic and electromagnetic model building applied to improve subbasalt depth imaging in the Faroe-Shetland Basin

et al. 2016

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Subbasalt imaging has gained significant interest in the last two decades, driven by the urge to better understand the geologic structures beneath volcanic layers, which can be up to several kilometers thick. This understanding is crucial for the development and risking of hydrocarbon play models in these areas. However, imaging based on the reflection seismic data alone suffers from severe amplitude transmission losses and interbed multiples in the volcanic sequence, as well as from poor definition of the subbasalt velocity structure. We have considered a sequential imaging workflow, in which the resistivity model from joint controlled-source electromagnetic and magnetotelluric data inversion was used to update the velocity model and to improve the structural definition in the migrated seismic image. The quantitative link between resistivity and velocity was derived from well data. The workflow used standard procedures for seismic velocity analysis, electromagnetic data inversion, and well analysis, and thereby allowed detail control and input based on additional geophysical knowledge and experience in each domain. Using real data sets from the Faroe-Shetland Basin, we can demonstrate that the integration of seismic and electromagnetic data significantly improved the imaging of geologic structures covered by up to several-kilometer-thick extended volcanic sequences. The improved results might alter the interpretation compared with the imaging results from seismic data alone.

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“…Li and Dai (2011) studied the possible effect of TTI conductivity anisotropy on CSEM data, but only in 2D cases. Despite the fact that a 3D TTI model is a more practical approximation of resistivity anisotropy of sedimentary formations than a 3D VTI model is, publications show that commercial marine CSEM applications do not use 3D TTI resistivity anisotropy models for sensitivity analysis and 3D inversion (e.g., Herredsvela et al, 2012;Zach and Frenkel, 2012;Colombo et al, 2013).…”

Section: Introductionmentioning

confidence: 95%

The impact of 3D tilted resistivity anisotropy on marine CSEM measurements

Davydycheva

Frenkel

2013

The Leading Edge

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O f f s h o r e a n d o n s h o r e b r o a d b a n d s e i s m o l o g y 1374 The Leading Edge November 2013 SPECIAL SECTION: Offshore and onshore broadband seismologyThe impact of 3D tilted resistivity anisotropy on marine CSEM measurements M arine CSEM modeling and data-interpretation algorithms currently used by the E&P industry are based on application of vertical transverse isotropic (VTI) resistivity models, which in many practical cases cannot adequately describe complex tilted anisotropic geologic structures typical for accumulation of hydrocarbons (e.g., syncline or anticline types). Use of VTI models is a serious limitation of CSEM technology and might be one of the core reasons for some false-positive and false-negative outcomes of marine CSEM surveys. To investigate this phenomenon in more detail and assess the impact of arbitrary tilted resistivity anisotropy on CSEM data, we performed simulations for a set of 3D tilted transverse isotropic (TTI) and VTI benchmark models. The 3D modeling results show that ignoring the TTI effect, if it is present, might lead to incorrect assessment of the feasibility of a potential CSEM survey as well as erroneous assessments and /or mispositioning of hydrocarbon targets during interpretation of field data and, in turn, might compromise the reliability of marine CSEM technology. Therefore, there is a strong practical need to start using TTI models, which provide more accurate descriptions of complex anisotropic resistivity structures than VTI models do. Application of 3D TTI modeling will improve the reliability of CSEM technology and its derisking potential.

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Feasibility of electromagnetic methods for sub-basalt exploration

Cited by 6 publications

References 7 publications

Offshore Sub-Basalt Exploration Using CSEM and MT

Offshore Sub-Basalt Exploration Using CSEM and MT

Integrated seismic and electromagnetic model building applied to improve subbasalt depth imaging in the Faroe-Shetland Basin

The impact of 3D tilted resistivity anisotropy on marine CSEM measurements

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