Numerical modeling analysis of short-offset electric-field measurements with a vertical electric dipole source in complex offshore environments

The possibility of a time‐domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated. The method operates on source–receiver offsets, which are several times less than the depth of the reservoir. Geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field. The basics of the method, as well as its sensitivity, resolution, and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths, are analyzed. For the analysis, 1D and 3D geoelectric models of hydrocarbon reservoirs are used. It is shown that under existing technologies of excitation and measurement of vertical electric fields, the highest accessible depth of soundings can be up to 4 km. Technology for the inversion and interpretation of transient responses is demonstrated on experimental data.

Section: O C a L I T Y O F S O U N D I N G Smentioning

confidence: 93%

Section: T I L T S O F T H E E L E C T R I C L I N E S I N T H E Veb mentioning

confidence: 99%

Marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs: principles, methodologies and limitations

Barsukov

Fainberg

2016

“…Their feasibility was discussed in a number of earlier (Goldman and Mogilatov ) and recent (Um et al . ; Singer and Artamonova ; Goldman et al . ; Barsukov and Fainberg ) publications.…”

Section: Unimodal Marine Transverse Magnetic Field Methods As An Altementioning

confidence: 99%

Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results

Mogilatov

Zlobinskiy

Balashov

2016

The theory behind transient electromagnetic surveys can be well described in terms of transverse magnetic and transverse electric modes. Soundings using transverse magnetic and transverse electric modes require different source configurations. In this study, we consider an alternating transverse magnetic field excitation by a circular electric dipole. The circular electric dipole transmitter is a horizontal analogue of the vertical electric dipole. Offshore surveys using circular electric dipole might represent an alternative to the conventional marine controlled‐source electromagnetic method at shallow sea and/or for exploring relatively small targets. Field acquisition is carried out by recording either electric or magnetic responses. Electric responses bear information on the 1D structure of a layered earth and successfully resolve high‐resistivity targets in marine surveys. Land‐based circular electric dipole soundings are affected by induced polarisation. On the contrary, magnetic responses are absent on the surface of a 1D earth, and as a result, they are very sensitive to any and even very small 3D conductivity perturbations. In addition, they are sensitive to induced polarisation or some other polarisation effects in the subsurface. At present, circular electric dipole transmitters and magnetic receivers are successfully used in on‐land mineral and petroleum exploration.

“…This value differs for diverse measuring systems and different data types in a marine environment between 10 −9 and 10 −15 V/m (Um et al . ; Hölz et al . ; Haroon ).…”

Section: Effects Of a 2d Sea Floor Topography In Deep Watermentioning

confidence: 99%

“…Using a 3D FE time‐domain modelling algorithm, Um et al . () analysed effects of a subtle multidimensional seafloor topography on short offset electric‐field measurements near a vertical electric dipole (VED). However, effects of seabed topography on the identification of resistive targets in the time‐domain using 1D inversion are rarely reported in literatures.…”

Section: Introductionmentioning

confidence: 99%

Effects of the sea floor topography on the 1D inversion of time‐domain marine controlled source electromagnetic data

Cai

Tezkan

2018

Time‐domain marine controlled source electromagnetic methods have been used successfully for the detection of resistive targets such as hydrocarbons, gas hydrate, or marine groundwater aquifers. As the application of time‐domain marine controlled source electromagnetic methods increases, surveys in areas with a strong seabed topography are inevitable. In these cases, an important question is whether bathymetry information should be included in the interpretation of the measured electromagnetic field or not. Since multi‐dimensional inversion is still not common in time‐domain marine controlled source electromagnetic methods, bathymetry effects on the 1D inversion of single‐offset and multi‐offset joint inversions of time‐domain controlled source electromagnetic methods data are investigated. We firstly used an adaptive finite element algorithm to calculate the time‐domain controlled source electromagnetic methods responses of 2D resistivity models with seafloor topography. Then, 1D inversions are applied on the synthetic data derived from marine resistivity models, including the topography in order to study the possible topography effects on the 1D interpretation. To evaluate the effects of topography with various steepness, the slope angle of the seabed topography is varied in the synthetic modelling studies for deep water (air interaction is absent or very weak) and shallow water (air interaction is dominant), respectively. Several different patterns of measuring configurations are considered, such as the systems adopting nodal receivers and the bottom‐towed system. According to the modelling results for deep water when air interaction is absent, the 2D topography can distort the measured electric field. The distortion of the data increases gradually with the enlarging of the topography's slope angle. In our test, depending on the configuration, the seabed topography does not affect the 1D interpretation significantly if the slope angle is less or around 10°. However, if the slope angle increases to 30° or more, it is possible that significant artificial layers occur in inversion results and lead to a wrong interpretation. In a shallow water environment with seabed topography, where the air interaction dominates, it is possible to uncover the true subsurface resistivity structure if the water depth for the 1D inversion is properly chosen. In our synthetic modelling, this scheme can always present a satisfactory data fit in the 1D inversion if only one offset is used in the inversion process. However, the determination of the optimal water depth for a multi‐offset joint inversion is challenging due to the various air interaction for different offsets.