Near Surface Characterization Using TDEM Over Marmul Area, South Oman

A. Al-Shukeili¹, H.M. El-Kaliouby¹, S. Mahrooqi², and A.S. Al-Ismaily ²

¹Sultan Qaboos University

²Petroleum Development Oman

Abstract

Time Domain Electromagnetic (TDEM) method has been used to map the near surface electrical properties in Marmul oil field (South Oman) in order to characterize the near surface lithological formations and variations both laterally and vertically.

The principle of TDEM method is based on faraday's law. The flow of the AC in the transmitter will produce primary magnetic field. This primary magnetic field will propagate down and generate eddy current within any conductive buried body and consequently it will produce secondary magnetic field. A receiver coil is placed at the center of the transmitter on the ground surface to measure the decay of the secondary magnetic field in time domain. Secondary magnetic field will provide a lot of information about the electrical conductivity and the geometry of the conductive body (McNeill, 1994). In the study area, the transmitter square loops (20x20; 100x100 and 200x200 m) are employed to transmit current to different depths. The measured voltage is converted to resistivity through least squares ridge regression and Occam inversion processes to estimate the resistivity distribution in the subsurface in a 2D geoelectrical cross section (Constable et al., 1987 and Inman, 1975). Correlation of these sections with available lithologic and resistivity logs measured at the wells along the TDEM profiles help in interpreting the subsurface geology and hydrogeology more reliably.