Deep exploration using long‐offset transient electromagnetics: interpretation of field data in time and frequency domain

Mörbe, Wiebke; Yogeshwar, Pritam; Tezkan, B.; Hanstein, T.

doi:10.1111/1365-2478.12957

Cited by 24 publications

(13 citation statements)

References 21 publications

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“…After adopting seismic hardware standards, further standardization occurred and interest in the seismic community grew [72]. After hardware and data standards, the processing and interpretation became so transparent that time and frequency domain processing gave almost identical results [73]. We experienced that each target requires different adaptive workflow and because the EM signal is diffusive and its frequency content changes with depth, we must validate our workflow every time.…”

Section: Resulting Requirementsmentioning

confidence: 99%

An Array Multi-Physics Acquisition System with Focus on Reservoir Monitoring

Strack¹,

Paembonan²,

Davydycheva³

et al. 2021

Preprint

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Focusing geophysics to improve recovery factor of hydrocarbon reservoirs adds value and contributes toward ZERO carbon footprint by increasing the recovery factor by of 30-40 % and thus reducing the cost/carbon emission per produced barrel. Thus, the Enhanced Oil Recovery (EOR) market is expected to grow more than 3.5% annually. This will be even more fueled by the Green-House-Gas (GHG) reduction and subsequent CO2 injection into the reservoirs as they are being produced. Presently, geophysics only ac-counts for a small percentage of this market, thus its growth is inevitable since more deterministic observation lead higher operating efficiency. Imaging the fluids (hydro-carbon, water, and CO2) is a key component to optimized production and injection. We designed a novel electromagnetic (EM) acquisition system that combines mul-ti-physics fluid imaging and acquires surface and borehole data with high fidelity. Borehole calibration is needed to upscale reservoir data and parameters to measurement scale. Multiple electromagnetic methods are used as well as microseismics in one layout for Exploration and Production (E & P) problems. Multi-components in electromagnetics allows resolving oil and water-bearing zones equally well while achieving the best ac-curacy suitable for repeat measurements. Because sedimentary basins are intrinsically anisotropic, considering 3-dimensional anisotropy is essential from measurement and 3D modeling viewpoint. Thus, the results have the better subsurface images. Here, we combine hardware design, methodology, 3D modeling, processing, and interpretations into an integrated technology and demonstrate the success with verifiable case histories.

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Section: Resulting Requirementsmentioning

confidence: 99%

An Array Multi-Physics Acquisition System with Focus on Reservoir Monitoring

Strack¹,

Paembonan²,

Davydycheva³

et al. 2021

Preprint

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“…Transforming the measured step‐off data into step‐on data using () as shown by Mörbe et al . (2020) is feasible. However, it is worth clarifying that the data quality of such derived step‐on transient will be inferior due to error propagation.…”

Section: Discussionmentioning

confidence: 99%

“…Weitemeyer et al ., 2011; Gehrmann et al ., 2016; Goswami et al ., 2016; Schwalenberg et al ., 2017; Attias et al ., 2018), mineral exploration (e.g. Gehrmann et al ., 2019; Mörbe et al ., 2020) and environmental research such as mud volcano imaging (e.g. Haroon et al ., 2015; Hölz et al ., 2015) or offshore groundwater studies (e.g.…”

Section: Introductionmentioning

confidence: 99%

Step‐on versus step‐off signals in time‐domain controlled source electromagnetic methods using a grounded electric dipole

Haroon

Swidinsky

Hölz

et al. 2020

Geophysical Prospecting

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The time-domain controlled source electromagnetic method is a geophysical prospecting tool applied to image the subsurface resistivity distribution on land and in the marine environment. In its most general setup , a square-wave current is fed into a grounded horizontal electric dipole, and several electric and magnetic field receivers at defined offsets to the imposed current measure the electromagnetic response of the Earth. In the marine environment, the application often uses only inline electric field receivers that, for a 50% duty-cycle current waveform, include both step-on and step-off signals. Here, forward and inverse 1D modelling is used to demonstrate limited sensitivity towards shallow resistive layers in the step-off electric field when transmitter and receivers are surrounded by conductive seawater. This observation is explained by a masking effect of the direct current signal that flows through the seawater and primarily affects step-off data. During a step-off measurement, this direct current is orders of magnitude larger than the inductive response at early and intermediate times, limiting the step-off sensitivity towards shallow resistive layers in the seafloor. Step-on data measure the resistive layer at times preceding the arrival of the direct current signal leading to higher sensitivity compared to step-off data. Such dichotomous behaviour between step-on and step-off data is less obvious in onshore experiments due to the lack of a strong overlying conductive zone and corresponding masking effect from direct current flow. Supported by synthetic 1D inversion studies, we conclude that time-domain controlled source electromagnetic measurements on land should apply both step-on and step-off data in a combined inversion approach to maximize signal-to-noise ratios and utilize the sensitivity characteristics of each signal. In an isotropic marine environment, step-off electric fields have inferior sensitivity towards shallow resistive layers compared to step-on data, resulting in an increase of non-uniqueness when interpreting step-off data in a single or combined inversion.

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“…They are efficient tools for resource explorations, e.g. mineral detection (e.g., Mörbe et al, 2020), ground water investigation (e.g., Haroon et al, 2018b), hydrocarbon (e.g., Schwalenberg et al, 2017) and geothermal prospection (e.g., Commer et al, 2005). Recently, a novel semi-airborne controlled source electromagnetic (semi-AEM) system operating in frequency-domain has been developed and tested in the frame of the DESMEX (Deep Electromagnetic Sounding for Mineral Exploration) project (Becken et al, 2020;Smirnova et al, 2019).…”

mentioning

confidence: 99%

“…Based on extracting the different resolution characteristics of semi-AEM and LOTEM data, we intend to optimize mineral exploration surveys via the joint inversion of these two EM methods. In a large-scale mineral exploration survey conducted in the DESMEX frame in eastern Thuringia, Germany (Liu et al, 2020;Mörbe et al, 2020;Steuer et al, 2020;Smirnova et al, 2019), one 8.5 km long LOTEM profile was measured along one of the semi-AEM flight lines. Many other geophysical experiments were also conducted during the DESMEX survey.…”

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confidence: 99%

2-D joint inversion of semi-airborne CSEM and LOTEM data in eastern Thuringia, Germany

Cai

Yogeshwar

Mörbe

et al. 2022

Geophysical Journal International

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Summary Various electromagnetic (EM) techniques have been developed for exploring natural resources. The novel frequency-domain semi-airborne controlled source electromagnetic (semi-AEM) method takes advantages of both ground and airborne techniques. It combines ground-based high-power electrical dipole sources with large scale and spatially densely covered magnetic fields measured via airborne receivers. The method can survey the subsurface down to approximately 1000 m and is particularly sensitive towards conductive bodies (e.g. mineralized bodies) in a more resistive host environment. However, the signal-to-noise ratio of semi-AEM is lower than that of ground-based methods such as long-offset transient electromagnetics (LOTEM), mainly due to the limited stacking time and motion induced noise. As a result, the semi-AEM often has reduced depth of investigation in comparison to LOTEM. One solution to overcome these flaws is to analyse and interpret semi-AEM data together with information from other EM methods using a joint inversion. Since our study shows that LOTEM and semi-AEM data have complementary subsurface resolution capabilities, we present a 2-D joint inversion algorithm to simultaneously interpret frequency-domain semi-AEM data and transient electric fields using extended dipole sources. The algorithm has been applied to the field data acquired in a former mining area in eastern Thuringia, Germany. The 2-D joint inversion combines the complementary information and provides a meaningful 2-D resistivity model. Nevertheless, obvious discrepancies appear between the individual and joint inversion results. Consequent synthetic modelling studies illustrate that the discrepancies occur because of i) differences in lateral and depth resolution between the semi-AEM and LOTEM data caused by different measuring configurations, ii) different measured EM components, and iii) differences in the error weighting of the individual datasets. Additionally, our synthetic study suggests that more flexible land-based configurations with sparse receiver locations are possible in combination with semi-AEM without a significant loss of target resolution, which is promising for accelerating data acquisition and for survey planning and logistics, particularly when measuring in inaccessible areas.

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Deep exploration using long‐offset transient electromagnetics: interpretation of field data in time and frequency domain

Cited by 24 publications

References 21 publications

An Array Multi-Physics Acquisition System with Focus on Reservoir Monitoring

An Array Multi-Physics Acquisition System with Focus on Reservoir Monitoring

Step‐on versus step‐off signals in time‐domain controlled source electromagnetic methods using a grounded electric dipole

2-D joint inversion of semi-airborne CSEM and LOTEM data in eastern Thuringia, Germany

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