Application of 2D inversion of magnetotelluric in exploration of hydrocarbon in south west of Iran

Abstract

Since hydrocarbon sources have an important role in development of industry and technology, exploration of them has been lionized by human. The seismic reflection method is one of the most applicable investigative methods to identify the hydrocarbon reservoirs, but in some cases this method does not work well because of geology conditions and wave attenuation in depth. Thus, some exploration methods such as magnetotelluric can help us reach better results and lead to better interpretation of such reservoirs in compound with seismic methods. The Magnetotelluric (MT) method is suitable to map electrical resistivity in hydrocarbon explorations. This method has been widely used in exploration of conventional energy and also the renewable energy such as geothermal resources and a powerful tool to investigate different kinds of geological structures under the earth's surface. MT method usually focuses on the deeper geologic targets than the other EM methods. MT provides an excellent image of subsurface formations in the areas covered by high-velocity carbonate. The investigated area is located in southeastern part of the most prolific oil province of Iran, the Khuzestan in Dezful Embayment. Oil reservoirs of Iran have been contributed by Mesozoic and Cenozoic evaporated sediments. Multiple petroleum systems exist in the investigated area, since at least two proven source rocks exist within the area: The Kazhdumi and Pabdeh shale sediments. Tree main groups of reservoirs are recognized in the Khuzestan basin: the Khami Group, the Bangestan Group and the Asmari Formation. All the tree groups of reservoirs are recognized in investigated area with excellent fracture permeability and locally primary porosity. A formational interpretation of 2D inversion of MT data is used to demarcate hydrocarbon prospective formations underneath carbonated sediments of south west Iran. MT measurements are made in southwest Iran. The sites were distributed in two profiles of approximate SW-NE direction. Profiles are called P1 and P2, respectively. The MT experiment was carried out by deploying 63 sites with about 600 m spacing with 40 frequency values in seven decades and the period ranged 0.003-2000 (s). The dimensionality and the best geoelectrical strike estimation were carried out using tensor decomposition and phase tensor analysis. The ellipticity, phase tensor and skew angle are other measured parameters. NLCG inversion algorithm is used to inverse two MT data profiles. Both TE and TM modes with both MT polarizations were jointly inverted using the NLCG algorithm. The NLCG algorithm attempts to minimize an objective function that is the sum of the normalized data misfits and the smoothness of the model. The obtained MT sections show three anticlines underground. Seh Qanat anticline is the most important one in the investigated area. The lithological log of Seh Qanat Deep-1 (SQD-1) borehole is applied to interpret MT sections. This borehole has been drilled on Seh Qanat Anticline with total depth of 2876 meters. It could be detected a boundary of Asmari formation that is the primary shallow oil target in the investigated area. Other formations such as Sarvak, potentially are reservoir of hydrocarbon resources.