Magnetotelluric Data Modeling for Imaging of Hydrocarbon Reservoir

Abstract

A huge and high resolution magnetotelluric investigation was conducted in the Sehqanat oil field, SW of Iran, in 2013 to map geoelectrical structure of the region from surface down to several kilometers. The Sehqanat oil field is located in sedimentary Zagros zone comprising ranges of the biggest oil fields in Iran. The most interesting target in this survey was geological contact between Gachsaran (Cap Rock) and Asmari (Reservoir) formation. According to the electrical logs information, large resistivity contrast exists at the boundary of two mentioned formations. The Gachsaran formation is formed by tens to hundreds meter of evaporites which is highly conductive (ca. 1-10 ohm-m) and the Asmari formation, in contrary, comprising of dense carbonates with more electrical resistivity range (more than 100 ohm-m). The broadband magnetotelluric data were collected in a 3-D pattern at more than 500 stations along five parallel southwest-northeast profiles crossing the main geological trend of the study area. In order to image a comprehensive subsurface resistivity map throughout the Sehqanat oil field, three-dimensional inversion was performed on the magnetotelluric data as well as two-dimensional routine. The 2-D inversion results depicted the main resistivity structures while the 3-D inverted model shows significantly more details and consistency.