Oil field imaging on the Sarab Anticline, southwest of Iran, using magnetotelluric data

Abstract

-Sarab structure is located in the northern part of the South Dezful Embayment in the central Zagros, southwest of Iran. Asmari Formation, as the largest and youngest horizon of oil production in the southeastern Iran, is the major exploration target at the location of the Sarab Anticline lacking surface anticlinal exposure. Salt-rich evaporates of Gachsaran are the main outcrop in the region and cover the Asmari Formation as the caprock. Extension of this very high velocity top-layer leads to poor quality of reflection seismic data and magnetotelluric (MT) method is used as the alternative exploration technique in such a case. Thus, MT data have been acquired along six profiles, perpendicular; and one profile, parallel; to the general trend of Zagros. Distortion and dimensionality of the MT data are analysed and the azimuth of strike is estimated. Models obtained from magnetotelluric inversion are interpreted aiming at delineation of Asmari and possibly deeper reservoirs in terms of their electrical resistivity. A marked contrast between the evaporative and the carbonate formations of the Gachsaran and Asmari is clearly visible on the extracted resistivity models consistent with the borehole data and surface geology. The Sarab Anticline is depicted as a resistive structure due to high resistivity values of limestone related to Asmari and other potential source rocks. It can be traced consistently along the MT profiles, in their middle parts and disappears at the position of the southeasternmost line.