A radiomagnetotelluric survey on an oil‐contaminated area near the Brazi Refinery, Romania

Abstract

A B S T R A C TScalar radiomagnetotelluric measurements were carried out on a contaminated test area close to the Brazi Refinery in Romania in order to detect and to monitor a 1 m thick oil layer expected at 5 m depth. Radio transmitters broadcasting in a frequency range from 10 kHz to 300 kHz were selected to observe the apparent resistivity and the phase data associated with the E-and B-polarizations. They were located parallel and perpendicular to the assumed strike direction of the contamination plume. The data were interpreted by a 2D inversion technique from which the conductivity structure of the area was derived. The 2D inversion models of all profiles on the contaminated area show a poor-conductivity zone above the groundwater table which could be associated with the oil contamination.A first attempt was also made to monitor the contaminated layer: the radiomagnetotelluric measurements were repeated on the same profiles a year later, but this time in a dry period, not in a rainy one. The 2D inversion results of the measurements in the dry period indicate that the high-resistivity layer moved closer to the surface. Additional reference measurements were then carried out on a non-contaminated area situated at a distance from the refinery, in the opposite direction to the flow of the groundwater. These reference measurements were used for the derivation of the unperturbed geology and they were also compared with the measurements of the contaminated test area. There is a significant difference in the frequency dependences of the apparent resistivities of the reference and contaminated areas, which could indicate a contamination at shallow depth. The 2D inversion results show the increase of resistivity at a depth of about 5 m beneath the contaminated area where the oil contamination is expected according to the information from the boreholes.

Geophysical Signatures of Microbial Activity at Hydrocarbon Contaminated Sites: A Review

“…Another EM technique that has been applied to hydrocarbon plume mapping and for exploration of the shallow subsurface is the radiomagnetotelluric method (RMT). An explanation of the principles of this technique can be found in Tezkan et al (2005) and much of their discussion on the RMT method is excerpted here. The RMT-method is a relatively new EM technique that uses EM waves produced by high powered civilian and military transmitters operating at frequencies between 10 and 300 kHz.…”

“…8). Any anomalous conductivity body in the Earth will modify the measured magnetic and electric fields (Tezkan et al 2005). The ratio of the orthogonal electric and magnetic horizontal components for the observed frequencies is related to the apparent resistivity of the subsurface.…”

“…Tezkan et al (2005) investigated an ''aged'' hydrocarbon contaminated site at a refinery 60 km North of Bucharest in Romania. The first reports of hydrocarbon contamination occurred in 1974 when oil contamination was documented from domestic wells in nearby villages.…”

“…Over the past two decades, geophysical techniques have been employed at several LNAPL contaminated sites to characterize both the spatial (e.g., Benson and Stubben 1995;Bermejo et al 1997;Sauck et al 1998;Atekwana et al 2000;2004a;Osella et al 2002;Werkema et al 2003;Tezkan et al 2005;Abdel Aal et al 2006;Sogade et al 2006;Bradford 2007;Cassidy 2007) and temporal (e.g., Lopes de Castro and Branco 2003;Che-Alota et al 2009) extent to understand the evolution of the contamination in the subsurface. Many of these geophysical studies have provided valuable insights into the behavior of LNAPL contamination; however, the results remain mixed.…”

Magnetotelluric modeling considering vertical transversely isotropic electrical anisotropy

“…MT 탐사는 0.001 Hz에서 수십 kHz 범위의 낮은 진동수 소 스를 이용하기 때문에 탐사심도가 매우 깊어 심부 전기비저항 구조를 규명하는 데 유용하여, 탄화수소 탐사 (Orange, 1989;Berdichevsky and Dmitriev, 2002;Zhdanov et al, 2004)뿐만 아니라 지구 지각 구조나 상부 맨틀에 대한 연구를 위한 심부 지질구조 탐사 (Pham et al, 1986;Slolon et al, 2005), 광물 탐사 (Tuncer, 2006), 환경 분야 탐사 (Tezkan, 2005;Unsworth et al, 2007) 등에도 활용되고 있다. MT 탐사는 특히 지열 에 너지 분야에서 그 중요성이 매우 높은데 (Goldstein, 1988;Bedrosian et al, 2004;Mendrinos et al, 2010), 최근에는 단 순히 심부 지열에너지원의 탐사에 그치지 않고 인공 지열 저 류층(engineered geothermal system; EGS)에 대한 모니터링 등 에도 널리 이용되고 있다(e.g., Peacock et al, 2013;Nam and Song, 2014 …”