Sensitivity of the near-surface vertical electric field in land controlled-source electromagnetic monitoring

Schaller, Andreas; Hunziker, Jürg; Streich, Rita; Drijkoningen, G.G.

doi:10.1190/segam2014-1460.1

Cited by 8 publications

(15 citation statements)

References 13 publications

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“…Since the only difference between initial and true model is the reservoir structure, we conclude that vertical electric field data are more influenced by the resistive reservoir and hence provide higher sensitivity towards this structure. This confirms simulation studies of Wirianto et al (2010), Schaller et al (2014) and Tietze et al (2015) among others who suggested that the vertical electric field is particularly useful to model resistive sub-horizontal layers at depth.…”

Section: O N T R O L L E D S O U R C E E L E C T R O M a G N E T I supporting

confidence: 87%

“…(), Schaller et al . () and Tietze et al . () among others who suggested that the vertical electric field is particularly useful to model resistive sub‐horizontal layers at depth.…”

Section: Controlled Source Electromagnetic Inversionmentioning

confidence: 99%

“…Measurements of the vertical electric field became of interest over the last years, mainly for monitoring hydrocarbon reservoirs (e.g. Schaller et al 2014;Tietze, Ritter and Veeken 2015) and more recently due to the abundance of existing boreholes in mining environments for mineral exploration (Kalscheuer, Juhojuntti and Vaittinen 2018b). Modelling studies shown by Tietze et al (2015) and Wirianto, Mulder and Slob (2010) indicate that the vertical electric field is one to two orders of magnitudes smaller than the horizontal field at surface, which means it can only be measured with dipole-lengths on the order of 100 m. Since measurements are in boreholes, it is likely that the dipoles span a number of sedimentary layers with varying resistivity, across which the (vertical) electric field is discontinuous.…”

Section: Introductionmentioning

confidence: 99%

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Elongated horizontal and vertical receivers in three‐dimensional electromagnetic modelling and inversion

Patzer

Tietze

Ritter

2019

Geophysical Prospecting

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Electromagnetic geophysical methods often rely on measurements of naturally occurring or artificially impressed electric fields. It is technically impossible, however, to measure the electric field directly. Instead, the electric field is approximated by recording the voltage difference between two electrodes and dividing the obtained voltage by the distance between the electrodes. Typically, modelling and inversion algorithms assume that the electric fields are obtained over infinitely short point‐dipoles and thus measured fields are assigned to a single point between the electrodes. Such procedures imply several assumptions: (1) The electric field between the two electrodes is regarded as constant or being a potential field and (2) the receiver dimensions are negligible compared to the dimensions of the underlying modelling grid. While these conditions are often fulfilled for horizontal electric fields, borehole sensors for recordings of the vertical electric field have dimensions in the order of ≈100 m and span several modelling grid cells. Observations from such elongated borehole sensors can therefore only be interpreted properly if true receiver dimensions and variations of electrical conductivity along the receiver are considered. Here, we introduce a numerical solution to include the true receiver geometry into electromagnetic modelling schemes, which does not rely on such simplifying assumptions. The algorithm is flexible, independent of the chosen numerical method to solve Maxwell's equations and can easily be implemented in other electromagnetic modelling and inversion codes. We present conceptual modelling results for land‐based controlled source electromagnetic scenarios and discuss consideration of true receiver geometries for a series of examples of horizontal and vertical electric field measurements. Comparison with Ez data measured in an observation borehole in a producing oil field shows the importance of both considering the true length of the receiver and also its orientation. We show that misalignment from the vertical axis as small as 0.1° may seriously distort the measured signal, as horizontal electric field components are mapped into the desired vertical component. Adequate inclusion of elongated receivers in modelling and inversion can also help reducing effects of static shift when interpreting (natural source) magnetotelluric data.

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Section: O N T R O L L E D S O U R C E E L E C T R O M a G N E T I supporting

confidence: 87%

“…(), Schaller et al . () and Tietze et al . () among others who suggested that the vertical electric field is particularly useful to model resistive sub‐horizontal layers at depth.…”

Section: Controlled Source Electromagnetic Inversionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Elongated horizontal and vertical receivers in three‐dimensional electromagnetic modelling and inversion

Patzer

Tietze

Ritter

2019

Geophysical Prospecting

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“…Those latter components are of another order of magnitude and may obscure the E z behaviour rather easily. The influence of direct energy is more pronounced on the E z data (Schaller et al 2014).…”

Section: Borehole E Z Vertical Component Sensormentioning

confidence: 90%

“…The behaviour of the vertical E z component is measured in dedicated shallow drillholes. The project is run in collaboration with researchers from Delft University (Schaller et al 2014). The vertical receiver data adds anisotropic information for the properties of the subsurface, which helps to reduce the solution space in the inversion of the CSEM data (Hunziker et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Borehole Controlled Source Electromagnetic (CSEM) Surveying for Monitoring HC-Saturation in the Bockstedt Oilfield (NW Germany)

Tietze

Ritter

Patzer

et al. 2015

Day 2 Tue, November 10, 2015

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Main objective is to support reservoir monitoring in an EOR production scheme. Enhanced oil recovery calls for efficient monitoring of hydrocarbon saturation changes. In the onshore Bockstedt oil field there exists a substantial difference in resistivity at reservoir level: for initial oil saturation it exceeds 100 Ohmm reducing to 0.6 Ohmm once fully displaced by formation brine. Applicability of the controlled-source electromagnetic method to monitor such resistivity changes is investigated. Targets are Lower Cretaceous shallow marine clastics at approximately 1200 m depth.Finite difference forward modelling shows CSEM is sensitive to expected resistivity changes, but the effect is difficult to resolve with surface measurements only. Resolution increases significantly if sensors or transmitters are placed in observation wells closer to the reservoir. Behaviour of the vertical electric component (E z ) in shallow boreholes and/or use of complex source configrations look rather promising.In 2014, a borehole-to-surface CSEM configuration was deployed successfully across the Bockstedt oil field, whereby the current was injected via the metal casing of an abandoned production well. The set-up also allowed conventional magnetotelluric (MT) data acquisition when the transmitter is turned off at night. CSEM response functions are of good quality with high repeatability. Recordings from conventional and new borehole transmitters indicate different current distributions in the subsurface. Results of the tested source configuration are in agreement with predictions by numerical simulations. Preliminary 3D inversion is consistent with previous numeric simulations.A timelapse CSEM survey is scheduled for 2015, inclusive drilling of a shallow observation well for E z component monitoring with a new borehole sensor. In parallel, a timelapse workflow for 3D CSEM inversion is developed. Figure 1-Paleo-geographic map of northern Germany at Valanginian age and location of Bockstedt oil field, 60 km SW of Bremen (after Leonhardt et al. 2011).

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Controlled-Source Electromagnetic Approaches for Hydrocarbon Exploration and Monitoring on Land

Streich

2015

Surv Geophys

150

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Sensitivity of the near-surface vertical electric field in land controlled-source electromagnetic monitoring

Cited by 8 publications

References 13 publications

Elongated horizontal and vertical receivers in three‐dimensional electromagnetic modelling and inversion

Elongated horizontal and vertical receivers in three‐dimensional electromagnetic modelling and inversion

Borehole Controlled Source Electromagnetic (CSEM) Surveying for Monitoring HC-Saturation in the Bockstedt Oilfield (NW Germany)

Controlled-Source Electromagnetic Approaches for Hydrocarbon Exploration and Monitoring on Land

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