Induced polarization signal manifestation in multi-spacing installations in offshore areas up to 100 m deep

The purpose of the work is to show the manifestation of an induced polarization signal in the transient electromagnetic signal for multi-spacing axial electrical installations depending on the spacing and sizes of the source at different depths of installation for the offshore conditions of sea depth of up to 100 m. The study uses the solution of the direct problem of a transient electromagnetic field for conducting polarizable media with a description of electrical resistivity dispersion by the Cole – Cole formula. Analysis is given to the change in the transient signal ΔU(t), final difference of the transient signal Δ2U(t) and transform P1(t) (ratio of Δ2U(t) to ΔU(t)) depending on multi-spacing installation size. The study involves installations with a source length (a source is a horizontal grounded electrical line AB) from 50 to 500 m, receiver length (receiver is represented by three-electrode electrical lines) from 50 to 500 m, and distance between the centers of the source and receiver (spacing) multiple of the source length: (3/2)·AB, 2·AB, (5/2)·AB, 3·AB, (7/2)·AB, 4·AB, (9/2)·AB, 5·AB. Comparison is given to the signals from conductive model and conductive polarizing model. A multi-spacing installation was placed inside a conductive medium with a conductive polarizing base. The conductive medium was associated with the layer of sea water in offshore areas with sea depths of up to 100 m. The conductive polarizing base was represented by a geological formation (ground) covered by a layer of water. Calculations performed as a result of conducted research works show the manifestation of various components of the transient process associated with electromagnetic field formation and manifestation of low-frequency dispersion of the electromagnetic properties of the earth caused by both galvanic and eddy currents. These components manifest themselves in different ways on multi-spacing installations at different depths. Therefore, it could be argued that the components of the transient process associated with the transient electromagnetic field, galvanically induced polarization and inductive induced polarization manifest themselves in different ways in multi-spaced installations of different sizes immersed at different depths. Induced polarization manifests itself in two ways for water area conditions as it is associated with both galvanic and eddy currents. Previously, when performing practical measurements, the manifestation of inductive induced polarization was considered as interference manifestation. But being simulated this signal can be considered as information about induced polarization. The factor influencing the manifestation character of induced polarization signal in the transient signal is the installation height above the bottom Δh and the spacing r. Δh is the distance between the installation and the seafloor, which is a polarizing base of the model. r is the distance between the centers of the source and the meter represented by a three-electrode measuring line. Depending on the installation height and spacing the induced polarization signal in the transform P1(t) can appear as an ascending branch at later times, as well as in the form of a descending branch that turns into negative values of P1.

1. Kontorovich A. E., Epov M. I., Burshtein L. M., Kaminskii V. D., Kurchikov A. R., Malyshev N. A., et al. Geology and hydrocarbon resources of the continental shelf in Russian Arctic seas and the prospects of their development. Geologiya i geofizika. 2010;51(1):7-17. (In Russ.).

2. Kaminskii V. D., Suprunenko O. I., Suslova V. V. The continental shelf of the Russian Arctic region: the state of the art in the study and exploration of oil and gas resources. Geologiya i geofizika. 2011;52(8):977-985. (In Russ.).

3. Wait J. R. Geo-electromagmetism. 1982. 235 p. (Russ. ed.: Geoelektromagnetizm. Moscow: Nedra; 1987. 235 p.).

4. Legeido P. Yu., Mandel'baum M. M., Rykhlinskii N. I. Differential-normalized electrical survey in direct HC exploration. Geofizika = Russian Geophysics. 1995;4:42-45. (In Russ.)

5. Legeido P. Yu., Mandel'baum M. M., Rykhlinskii N. I. Self-descriptiveness of differential methods of electrical survey in the exploration of polarizable media. Geofizika = Russian Geophysics. 1997;3:49-56. (In Russ.).

6. Ageenkov E. V., Davydenko Yu. A., Fomitskii V. A. Influence of the off-axis position of the transmitter and receiver circuits on the results of differentially normalized electromagnetic sounding. Russian Geology and Geophysics. 2012;53(1):116-121. https://doi.org/10.1016/j.rgg.2011.12.009.

7. Bogdanov A. G., Kobzarev G. Yu., Deliya S. V., Zelentsov V. V., Ivanov S. A., Legeido P. Yu., et al. Application experience and geological results of using the differential normalized method of electrical survey in the Russian aquatory of the Caspian Sea. Geofizika = Russian Geophysics. 2004;5:38-41. (In Russ.).

8. Kolesov V. V., Vovk V. S., Dzyublo A. D., Kudryavtseva E. O. Exploration and development of deposits in the Ob Bay coastal zone. Gazovaya promyshlennost' = Gas Industry. 2008;12:66-68. (In Russ.).

9. Veeken P., Legeydo P., Pesterev I., Davidenko Y., Kudryavceva E., Ivanov S. Geoelectric modelling with separation between electromagnetic and induced polarization field components. First Break. 2009;27(12):53-64. https://doi.org/10.3997/1365-2397.2009020.

10. Veeken P., Legeydo P., Davidenko Y., Kudryavceva E., Ivanov S., Chuvaev A. Benefits of the induced polarization geoelectric method to hydrocarbon exploration. Geophysics. 2009;74(2):47-59. https://doi.org/10.1190/1.3076607.

11. Markov S. Yu., Gorbachev S. V., Ivanov S. A., Myatchin O. M., Nurmukhamedov T. V., Smilevets N. P., et al. Improving the reliability of the forecast of hydrocarbons on the Pechora Sea shelf based on the results of reinterpretation of electrical exploration works in combination with seismic data. Geofizika = Russian Geophysics. 2021;3:25- 33. (In Russ.).

12. Sitnikov A. A., Ageenkov E. V., Ivanov S. A., Zhugan P. P., Mal'tsev S. Kh. Equipment, devices and surveying systems to solve the problems of oil and gas exploration and engineering geology in water areas with application of DNME and NDEMS electrical prospecting methods. Pribory i sistemy razvedochnoi geofiziki. 2017;60(2):42-49. (In Russ.).

13. Ageenkov E. V., Sitnikov A. A., Pesterev I. Yu., Popkov A. V. Manifestation of induction and induced polarization in the case of axial and symmetrical electrical arrays. Russian Geology and Geophysics. 2020;61(7):795- 808. https://doi.org/10.15372/RGG2019151.

14. Moiseev V. S. Induced polarization method for oilbearing areas prospecting. Novosibirsk: Nauka; 2002. 136 p. (In Russ.).

15. Kozhevnikov N. O. Fast-decaying inductive IP in frozen ground. Russian Geology and Geophysics. 2012; 53(4):406-415. https://doi.org/10.1016/j.rgg.2012.02.013.

16. Kamenetsky F. M., Trigubovich G. M., Chernyshev A. V. Three lectures on geological medium induced polarization. Munich: Vela Verlag; 2014. 58 p.

17. Lee T. Transient electromagnetic response of a polarizable ground. Geophysics. 1981;46(7):1037-1041. https://doi.org/10.1190/1.1441241.

18. Pelton W. H., Ward S. H., Hallof P. G., Sill W. R., Nelson P. H. Mineral discrimination and removal of inductive coupling with multi-frequency IP. Geophysics. 1978;43(3):588-609. https://doi.org/10.1190/1.1440839.

19. Gubatenko V. P. Maxwell – Wagner effect in electrical prospecting. Fizika Zemli. 1991;4:88-98. (In Russ.).

20. Petrov A. A. Potential of the electrical transient method in hydrocarbon prospecting in the shelf zones. Geofizika = Russian Geophysics. 2000;5:21-26. (In Russ.)